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Experimental and numerical studies of ballistic resistance of hybrid sandwich composite body armor

  • Waad Adnan Khalaf EMAIL logo and Mohsin Noori Hamzah
Published/Copyright: March 14, 2024
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Open Engineering
From the journal Open Engineering Volume 14 Issue 1

Abstract

Defense mechanisms remain important and indispensable due to the different types of pistols and ordnance besides many guns. Hybrid composite sandwich panels are an attractive focus because of their ingrained characteristics, such as high stuffiness and high energy absorption. Hybrid composite sandwich panels are among the most important in armoring various structures. Despite the high density of these panels, they have significant qualities that qualify them to be the first selection for use in armored vehicles or body armor. Recently, there have been several types of structures, and selecting the appropriate structure as armor against the projectiles is very important. The study subjected three samples to the ballistic impact test using a 7.62 × 39 mm bullet. The first sample, S1, consists of ultra high molecular weight polyethylene (UHMWPE)/epoxy, unfilled honeycomb core, Kevlar/epoxy, unfilled honeycomb core, Kevlar/epoxy, and UHMWPE/epoxy; the second sample, S2, comprises Kevlar/epoxy, unfilled honeycomb core, Kevlar/epoxy, unfilled honeycomb core, and UHMWPE/epoxy, and the third sample, S3, comprises Al2O3, Kevlar/epoxy, unfilled honeycomb core, carbon/epoxy, unfilled honeycomb core, and carbon/epoxy. ABAQUS software was used to evaluate the ballistic impact numerically, and after that, the study examined the same armor samples experimentally. The results manifested that only the armor S3 succeeded in stopping the bullet. This is attributed to the structure of the cores, which helps compress and accumulate the cells under the projectile. The speeds of the bullet after penetration (residual velocity; VR) were 748.5 and 715.3 m/s for S1 and S2 armors, respectively, where the back face signature for S3 was 1.5 mm, which is optimum and within the allowed range. The total energy absorption of these armors S1, S2, and S3 is 344.65, 539.04, and 2585.66 J. Furthermore, the highest deviation between numerical and experimental approaches is about 2.04% in the VR.

Keywords: ballistic impact; 7.62 × 39 mm bullet; hybrid sandwich armor; energy absorption; back face signature

1 Introduction

One of the primary issues for engineers and researchers in ballistic armor against bullets and shrapnel is the requirement for high-level ballistics for military and defense sectors. In recent years, terrorist attacks and wars have increased. This is because donning body armor has prevented armies and warriors from losing countless lives while waging wars and conducting counterterrorism operations. According to the research conducted during the Iraq warfare in 2003, 58% of the wounds were medium, while 9% were in the eyes, legs, or hands, and several of the wounds infected the trunk [1].

Furthermore, body armor is spaciously employed in peacekeeping and public security missions. According to statistics, ballistic-resistant body armor supplied by international police enforcement forces has recently kept over 3,000 cops on the beat. Personnel armor is designed to withstand bullets, fragments, and small 2-caliber projectiles [2]. The degree to which a person is protected from a ballistic attack provided by these armaments is determined by the kinetic energy that bullets deliver, which can be sealed with the armor. The National Institute of Justice (NIJ) has issued a report detailing defamatory threats. The whole plane of safeguard and bomb gender has its requirements [3]. Several armor solutions for effective ballistic protection use advanced alloys, ceramics, and composite materials. One of these important solutions is the sandwich structure together with composite materials [4].

The concepts of science underlying the construction of sandwich armor structures must be understood to satisfy the armor industry’s demands better. The industry still needs to overcome significant hurdles, such as mobility and protection, despite the enormous effort to grasp these concepts, particularly concerning armor textiles and composite. Mobility and protection are the two main requirements of the users of armor materials. The lightest armor materials are required for ballistic armors to improve mobility. On the other hand, defensive qualities improve as the armor material weight increases, which restricts movement. Research into armor materials now primarily focuses on weight reduction and strength development to improve mobility and conserve user energy. As a result, the field was attracted to a lightweight, flexible, and highly energy-absorbent material. Sandwich composites changed the game thanks to their high-rigidity and lightweight structure. Composite materials that enable large-scale manufacture are gaining interest due to various reinforcing elements’ availability and novel processing techniques’ development [5]. Numerous studies are now looking into ways to enhance the performance of composite structures. To enhance the energy-absorbing qualities of the structures without losing sight of the overall weight, researchers are examining alternative settings for sandwich composite materials. Other parameters that can be changed to enhance the performance of sandwich composite structures include material qualities, thickness, and core characteristics. The ballistic armor performance has been improved thanks to the use of cutting-edge materials in producing armor systems [6].

Several studies have examined the ballistic resistance of sandwich structures and hybrid composites to understand the characteristics of the materials and their effectiveness when subjected to impact loads. Stanislawek et al. [7] modeled a pyramidal ceramic (Al2O3) in the front face of armor with a ductile aluminum alloy (AA2024) in the back face besides different arrangements of ceramic structure and AA2024 in other models, and this structure was impacted by armor piercing (AP) projectiles. The experimental and numerical studies proved that pyramidal ceramic armor could resist a projectile threat due to the change in its trajectory [7]. Liu et al. (2016) simulated the fish skin to produce a protection system collected between effective resistances to external loads with superior flexibility. The scales comprise silicon carbide ceramic and aluminum (Al6061-T6) materials in the outer and inner faces, respectively. FEM has been used to simulate the ballistic impact of steel bullets on the scaled armor. The numerical results displayed that the depth of penetration (DOP) and the residual velocity (VR) of the scales decreased with the increase in the thickness of composite scales; furthermore, the inclination of the scale led to eroding and a slip of the projectile, and this is very important to absorb the kinetic energy of the projectile [8].

Mullaoğlu et al. investigated how polycarbonate (PC) projectile dynamically impacts at varied speeds. The numerical test of a PC plate under impact was examined using LS-DYNA. The findings demonstrated that the PC materials are significantly more impact-resistant than other materials [9]. Hu et al. used three types of a mosaic of silicon carbide (SiC) with a ultra high molecular weight polyethylene (UHMWPE) plate to resist the impact of an AP bullet. The geometry of mosaic was square, cylindrical, and hexagonal in the front face. The test results offered a significant enhancement in the ballistic resistance of armor and proved the effect of geometry on the ballistic performance of the armor [10]. Oliveira Braga et al. evaluated the multilayered armor system that was impacted by a projectile; the front face of the system consists of the hexagonal convex or flat ceramic tile, and the aramid fabric and aluminum plate arrangement are in the middle and last layer, respectively. The test presents satisfactory results regarding the back face signature (BFS) and the superior performance of convex ceramic tile [11].

Liu et al. exhibited the high-strength material (UHMWPE) with a high-energy absorption material and structure (EAMS) to construct a new type of armor. The hybrid panel was used against the high speed of spherical bullets. The UHMWPE was used in the front of the panel, and the hollow cylinders of EAMS were utilized in the back. The experimental and numerical results of the study exhibited an increase in the ballistic performance of the panel compared with the pure UHMWPE [12]. Eventually, Yang et al. [13] designed sandwich panels made from the carbon fiber composite in the front face, then the aluminum alloy and the core of this structure made from the pyramidal truss. For these sandwich panels, an experimental and numerical test was done to evaluate this structure, and the result elucidated the considerable amount of energy absorption [13]. According to the literature reviews above, research was conducted on how well the sandwich structures can survive the bullets.

It was also concluded that the various sandwich structure reviews are mostly directed at the test of metallic sandwich structures. Only a few works have been carried out using composite sandwich structures that consist of metallic honeycomb core and composite skins. This study presented a hybrid sandwich structure with an aluminum honeycomb as the core, ceramic tiles, steel plates, and Kevlar fibers reinforced polymers as the skins. Finally, the hybrid sandwich panels were fabricated from Kevlar fibers, SiC ceramic tiles, steel plate, and aluminum honeycomb in this work. Two hybrid sandwich specimens were fabricated utilizing the hand lay-up method for sheets and the water jet machine cutting for the aluminum honeycomb core.

2 Experimental work

2.1 Materials used

The first step in the experimental work is to choose the right materials. The materials used in the manufacturing process for the present work are listed below and shown in Figure 1.

  1. Aluminum honeycomb

  2. Aluminum oxide tiles (Al2O3)

  3. Composite material (UHMWPE, Kevlar and carbon fibers, and epoxy resin)

  4. MS hybrid polymer silicon

Figure 1 The main materials used in the armor. (a) aluminum honeycomb, (b) aluminum oxide (Al2O3) tiles, (c) Kevlar fibers, (d) carbon fibers, (e) UHMWPE fibers, (f) epoxy resin, and (g) MS hybrid polymer silicon.
Figure 1

The main materials used in the armor. (a) aluminum honeycomb, (b) aluminum oxide (Al2O3) tiles, (c) Kevlar fibers, (d) carbon fibers, (e) UHMWPE fibers, (f) epoxy resin, and (g) MS hybrid polymer silicon.

The aluminum honeycomb was purchased from “Huarui Honeycomb Technology Co., Ltd, China.” The aluminum oxide ceramic tiles (Al2O3) were bought from “Ningxia Northern Hi-Tech Industry Co., Ltd., China.” The woven Kevlar, woven carbon and unidirectional UHMWPE fibers were purchased from “Wuxi GDE Technology Co., Ltd. China.” Epoxy resin type (Sikadur 52LB) was purchased from Sikadur Company. MS hybrid polymer silicon was bought from SOUDAL Company. Mechanical properties of Kevlar, carbon and UHMWPE fibers, and epoxy [14], aluminum alloy (AL3003) [15] and aluminum oxide ceramic are defined in previous literature [16].

2.2 Composite fabrication process

The composite material was prepared using the hand lay-up technique, which is the open molding technique to fabricate the composite materials. This study used this method to fabricate high-performance composites consisting of a matrix material (epoxy) reinforced by the layers of Kevlar, carbon, and UHMWPE fibers. After that, the mold (glass sheet) was prepared for brushing by covering the inner surface via a layer of wax to guarantee no adhesion between the woven fabric and the mold to facilitate the laminate removal. Then, the base material of epoxy was manually mixed with the hardener, taking into account that the weight percent between hardener and epoxy is 3:1. At room temperature, the fabric was manually placed in the mold and then the resin matrix was brushed on the laminates of reinforcing material until it covered all the layers. Another glass sheet was laid on top of the laminated fibers, and the excess resin was allowed to escape from the sides. An appropriate load was used to press the fiber and epoxy mixture. Finally, after completing the hand lay-up process, the sample was left for 24 h at room temperature before opening the mold. Figure 2 shows the mold and fabrication process, and Figure 3 depicts the final shape of the composite.

Figure 2 The mold and the fabrication process.
Figure 2

The mold and the fabrication process.

Figure 3 The final shape of composite layers; (a) UHMWPE/epoxy, (b) Kevlar/epoxy, and (c) carbon/epoxy.
Figure 3

The final shape of composite layers; (a) UHMWPE/epoxy, (b) Kevlar/epoxy, and (c) carbon/epoxy.

2.3 Preparation of aluminum honeycomb

Using a water jet cutter machine, the aluminum honeycomb structure was cut to the required dimension (150 × 150 mm). This machine works depending on the principle of micro erosion, which occurs due to the large volume of the water jet through a very small-diameter bore of the nozzle (0.2–0.3 mm) with a very high jet speed, about 869 m/s with huge kinetic energy. Figure 4 reveals the photo of this machine with the nozzle. The water jet cutting machine owns main sub-systems, such as the water and abrasive tank, a high-pressure pump used to compress water up to 3,000 bar to generate sufficient kinetic energy for cutting, high-pressure valves, and a hydraulic unit. Figure 5 illustrates the final shape of aluminum honeycomb after cutting. To control the cutting process, this machine uses computer-aided manufacturing and design systems [17].

Figure 4 Water jet cutter.
Figure 4

Water jet cutter.

Figure 5 The final shape of aluminum honeycomb after cutting.
Figure 5

The final shape of aluminum honeycomb after cutting.

2.4 Layers assembly and fabrication of hybrid sandwich body armor

After completing the composite layers, the layers of hybrid sandwich composite structure body armor to be fabricated were prepared. The honeycomb core was assembled (glued) with the front and back sheets using the modified-silane hybrid polymer silicon. It remained until the full silicon curing of sandwich structure body armor samples. After completing the adhesion process, the sample was left for 24 h at room temperature before using the sample in a ballistic test [18,19]. The MS hybrid polymer adhesive is excellent [20]. Figures 6–8 describe the hybrid sandwich composite body armor after assembly and fabrication for the first, second, and third samples. The three samples of hybrid sandwich body armor (150 mm × 150 mm) were made. The first sample, S1, consists of UHMWPE/epoxy, unfilled honeycomb core (6.4 mm cell size), Kevlar/epoxy, unfilled honeycomb core (12.7 mm cell size), Kevlar/epoxy (EPX), and UHMWPE/epoxy, the second sample, S2, comprises Kevlar/epoxy, unfilled honeycomb core (6.4 mm cell size), Kevlar/epoxy, unfilled honeycomb core (12.7 mm cell size), and UHMWPE/epoxy, and the third sample, S3, comprises Al2O3, Kevlar/epoxy, unfilled honeycomb core (6.4 mm cell size), carbon/epoxy, unfilled honeycomb core (6.4 mm cell size), and carbon/epoxy. Table 1 provides the measurements and details of the hybrid sandwich body armor’s various parts.

Figure 6 Hybrid sandwich body armor of first sample S1 after assembly and fabrication. (a) Schematic of arrangement of layers, (b) schematic of isometric view, and (c) photograph of side view.
Figure 6

Hybrid sandwich body armor of first sample S1 after assembly and fabrication. (a) Schematic of arrangement of layers, (b) schematic of isometric view, and (c) photograph of side view.

Figure 7 Hybrid sandwich body armor of second sample S2 after assembly and fabrication. (a) Schematic of arrangement of layers, (b) schematic of isometric view, and (c) photograph of side view.
Figure 7

Hybrid sandwich body armor of second sample S2 after assembly and fabrication. (a) Schematic of arrangement of layers, (b) schematic of isometric view, and (c) photograph of side view.

Figure 8 Hybrid sandwich body armor of third sample S3 after assembly and fabrication. (a) Schematic of arrangement of layers, (b) schematic of isometric view, and (c) photograph of side view.
Figure 8

Hybrid sandwich body armor of third sample S3 after assembly and fabrication. (a) Schematic of arrangement of layers, (b) schematic of isometric view, and (c) photograph of side view.

Table 1

Details of the hybrid sandwich body armor components of three samples

Number of samples Face skin material Core material Back skin material Thickness (mm) Core cell size (mm) Armor weight (g) Armor thickness (mm) Notes
Face skin Core Back skin
1 UHMWPE Aluminum UHMWPE 10 10 2 6.4 1,380 30.8 Double core with intermediate Kevlar 2 mm
honeycomb 2 15 6.4
2
2 Kevlar Aluminum Kevlar 10 10 2 6.4 1,331 28.9 Double core with intermediate Kevlar 2 mm
honeycomb UHMWPE 2 10 12.7
2
3 Al2O3 Aluminum Carbon 10 10 2 6.4 37.5 Double core with intermediate carbon 2 mm
Kevlar honeycomb 2 10 12.7
2

2.5 Ballistic test: chronograph apparatus and test procedures

The chronograph refers to an apparatus used to measure the speed of a projectile that is launched from any weapon or can be defined as a shooting speed tester. Consequently, this apparatus is one of the substantial tools used to characterize and assess any panel subject to the ballistic test [21]. Figure 9(a) manifests the beta model chronograph used in this investigation. However, before implementing the ballistic test, the armor panel must be clamped using the backing material fixture. This equipment comprises several parts, such as a square frame, rigid plates, a hollow shaft, and the ground base [22]. Figure 9(b) reveals the equipment for the ballistic test.

Figure 9 Schematics of (a) the chronograph device and (b) the backing material fixture.
Figure 9

Schematics of (a) the chronograph device and (b) the backing material fixture.

To obtain a suitable ballistic response for an armor panel, it is necessary to acquire reliable data about the shots. Consequently, according to the NIJ ballistic standard, a particular number of shots are required for each round of tests [23]. In effect, the complete and partial penetrations are the only two types of penetrations for any impact test. Undoubtedly, the benefit from complete penetration is to calculate the energy absorption by the armor panel, and experimentally that occurs when two devices of speed measurement are placed between the tested panels to measure the bullet speed before and after penetration. The initial or strike velocity and the residual velocity represent the velocities of the bullet before and after penetration, respectively. Hence, these velocities were used to calculate the lost energy of the bullet [24].

Set up the distance between the muzzle and the backing material fixture; this distance equals (5.0 m ± 1.0 m). Set up the distance between the chronograph and the backing material fixture; this distance equals (2.5 m ± 25 mm). Figure 10 shows the equipment of the ballistic test, and the whole equipment has been set up according to the standard of NIJ.

Figure 10 Photographs of the ballistic test equipment used in this study.
Figure 10

Photographs of the ballistic test equipment used in this study.

2.6 Details of projectile

The bullet 7.62 × 39 mm is the projectile adopted in all tests of the study. This type of caliber is so familiar in this domain, and many handguns shoot this ammo. All specifications of the bullet are listed in Table 2.

Table 2

Specifications of 7.62 × 39 mm bullet

Caliber Cartridge weight (g) Bullet weight (g) Bullet length (mm) Bullet diameter (mm) Cartridge length (mm)
7.62 × 39 mm 18 8 17.3 7.62 56

3 Numerical work

It is recommended to use the software LS-DYNA, ABAQUS, and ANSYS (AUTODYN) to simulate the impact of armor; this software represents the most useful and reliable tools, according to most of the cited articles [25]. This study used the commercial program ABAQUS to use the finite element approach on the hybrid sandwich composite armor. The armor model for the analysis was developed in a step-by-step manner. In the part module, geometric pieces were first constructed, after which the material properties were assigned to the parts. These components were put together in the assembly module after the creation of boundary conditions, interactions, steps, mesh, and ballistic loading with a velocity of 804 m/s. The goals of this research were then accomplished by varying the model parameters using various design matrices. Below is a discussion of the key steps in the finite element analysis.

3.1 Bullet

The bullet has a hemispherical top and a cylindrical base. This refers to a typical ballistic with a diameter of 7.62 mm and a length of 17.3 mm. It has a steel property given to it, resulting in an overall mass of 8 g [26]. The penetrator employed in the finite element study is displayed in Figure 11.

Figure 11 Steel bullet.
Figure 11

Steel bullet.

3.2 Armor skin layer

Kevlar and epoxy, UHMWPE and epoxy, and carbon and epoxy composites were used to design the armor’s top and bottom layers. The composites were built as a 3D deformable shell 150 mm by 150 mm rectangular laminates. It was extruded to a thickness of 2 mm to evaluate the performance of the armor. These laminates have four plies, each of which is 0.5 mm thick. In weaved orientation, the plies are piled. The layers of the armor composites made of Kevlar and epoxy, UHMWPE and epoxy, and carbon and epoxy are manifested in Figure 12.

Figure 12 Armor skin layer of composites.
Figure 12

Armor skin layer of composites.

3.3 Armor honeycomb core

A honeycomb structure built of the aluminum alloy Al3003 makes up the core. A 3D deformable solid with dimensions of 150 × 150 mm and heights of 10 and 15 mm was used in its construction. The cells have a thickness of 0.1 mm and a size of 6.4 and 12.7 mm. The software ABAQUS depicts the honeycomb core structure in Figure 13.

Figure 13 Aluminum honeycomb core.
Figure 13

Aluminum honeycomb core.

3.4 Armor ceramic tiles

The tile is a ceramic structure made of Al2O3, the first top layer of the armor. It was built with a 3D deformable solid with dimensions of 150 × 150 mm and a height of 10 mm. The number of tiles is nine. The software ABAQUS portrays the ceramic tiles structure in Figure 14.

Figure 14 Al2O3 ceramic tiles.
Figure 14

Al2O3 ceramic tiles.

3.5 Armor assembly

The geometric components are all put together, as illustrated in Figure 15. To enable the initiation of the steel bullet, a 1 mm gap was designated between the projectile and the top skin.

Figure 15 Armor assembly.
Figure 15

Armor assembly.

3.6 Armor meshing

The assembly meshing is shown in Figure 16; the total number of elements and nodes of the assembly mesh are 203,513 and 330,463, respectively.

Figure 16 Assembly meshing.
Figure 16

Assembly meshing.

3.7 Armor step, interaction, and load

The final body armor model was built with 150 mm × 150 mm dimensions. The ABAQUS software widely depends on the steps in working; indeed, after constructing and assembling the geometries, generating the appropriate meshes of the model, selecting the appropriate mathematical model for materials that play a vital role in the accuracy of results, and inserting the properties of materials, the next step is how to utilize these steps to obtain a more realistic simulation. Hence, the use of these steps is different from one model to another, so the software consists of many categories, and these categories can be divided into the following main groups:

  • Step: Include defining the time to conduct the simulation where the step time is 0.005 s.

  • Interaction: Includes the contact between the layers and the contact between the armor and the bullet where the coefficient of friction is 0.3.

  • Load: Include the boundaries, initial conditions, clamped, and the applied loads where the bullet’s velocity is 840 m/s. Figure 17 Shows the armor clamping.

Figure 17 Armor clamping.
Figure 17

Armor clamping.

3.8 Armor material properties

The material properties of all geometric components that make up the armor have material properties defined. All fundamental properties of Kevlar/epoxy [27], UHMWPE/epoxy [28], carbon/epoxy [29], Aluminum alloy (AL3003) [15,30] and ceramics Al2O3 [16], and AISI 4140 steel alloy [31] were used in the model. Table 3 lists the mechanical properties of the bullet (AISI 4140 steel alloy).

Table 3

Results of the experimental test of the hybrid sandwich composite armor samples

Samples Initial velocity (m/s) VR (m/s) Ballistic limit velocity (m/s) Areal density (kg/ m 2 ) Energy absorption (J) Specific energy absorption (J/kg) DOP (mm) BFS (mm)
S1 804 748.5 293.5366 9.688 344.65 1580.986 27.8 —
S2 804 715.3 367.0993 13.55 539.047 1767.369 — —
S3 804 0 804 58.84 2585.66 1952.918 — 1.5

3.9 Mesh and mesh convergence

Meshing is a crucial step required to build a model simulation for ABAQUS, so getting the appropriate meshing is required to give accurate results through several attempts to divide the total area of each part into an ideal number of elements. The output results may differ slightly depending on the mesh size selection. The number of element-level calculations may grow, as may the computing cost, but the accuracy of the results may increase with a finer mesh. It is a well-known fact that mesh refining improves the outcomes of most simulations. Prior to doing finite element analysis on the built-in hybrid sandwich armor models in this research, a mesh convergence check was performed. The goal is to produce correct findings for these models’ finite element analysis. This was accomplished by employing the hybrid sandwich armor to plot the VR against the mesh sizes of 0.4, 0.6, 0.8, and 1.0 mm. The outcome confirmed the convergence, which indicated a difference of about 3% between the 0.8 and 1 mm mesh. In this investigation, a fine mesh of 0.6 mm was chosen in the hybrid sandwich structure armors’ center and a coarse mesh of 3 mm at the edges. Because of the complexity of these structures, different mesh sizes were chosen. The skins’ fine and coarse meshes were combined to cut down on computing time.

3.10 Materials constitutive models

The significant enhancement of computer technology and numerical analyses affected the beneficial utilization of constitutive models; indeed, selecting an appropriate constitutive model is crucial and entirely locates the insight into the actual problem and the method of analysis [32]. Hence, the study focused on understanding the constitutive material models and offered a group of essential models available in the simulation programs and used in many engineering applications. Accordingly, these models can be used as a guide for researchers in this domain of study.

3.10.1 Drucker–Prager model

To determine whether a material has failed or suffered plastic yielding, Drucker and Prager proposed the Drucker–Prager material model in 1952, which is a pressure-dependent model. The model was developed to transact soil plastic deformation. It has been used with various cohesive geological materials, including ceramic, concrete, rock, polymers, foams, and other pressure-dependent materials [33]. In this work, it has been used for ceramic tiles (SiC and Al2O3).

(1) J 2 = λ I 1 ′ + κ ,

where λ and κ are Drucker–Prager material constants, J 2 is the second invariant of the stress deviator tensor, and I 1 ′ is the first invariant of the stress tensor, and are defined as follows:

(2) I 1 ′ = σ 1 ′ + σ 2 ′ + σ 3 ′ ,

(3) J 2 = 1 6 [ ( σ 1 ′ − σ 2 ′ ) 2 + ( σ 1 ′ − σ 3 ′ ) 2 + ( σ 3 ′ − σ 1 ′ ) 2 ] .

σ 1 ′ , σ 2 ′ , and σ 3 ′ are the major, intermediate, and minor principal effective stresses.

3.10.2 Johnson–Cook (JC) model

The JC has been suggested in 1983. Despite being empirical and having a simple form, it is the most common model used today. However, two factors, namely, strain rate and temperature significantly impact how most materials behave, particularly alloys and metals. According to this concept, the influence of temperature and speed of strain on flow stress are alternately independent, so it is crucial to research a wide range of deformation and temperatures before designing any structure or component. In this work, this model has been used for an aluminum honeycomb core. The model can be expressed as follows [34,35]:

(4) σ y = ( A + B ε ‾ p n ) ( 1 + C ln ⁡ ε * ) ( 1 − T * m ) ,

where A, B, C, n, and m are material coefficients for the JC equation. The expression in the first series of this equation gives strain hardening term. The second series of this equation expresses the effect of strain rate, and the third series expresses the thermal effects. ε −p is the equivalent plastic strain constant. ε * is the dimensionless strain rate. A is the material’s yield stress under reference deformation conditions, B is the strain hardening constant, C is the strain rate strengthening coefficient, and T * is the homologous temperature.

(5) ε * = ε − p ε o ,

where ε o is reference strain rate.

(6) T * = T − T room T melt − T room ,

where T is the deformation temperature, T room is the reference deformation temperature, and T melt is the material’s melting temperature.

The fracture occurs when the value of D equals one, the formula for calculating D is as follows:

(7) D = ∑ Δ ε − p ε f ,

where D is the damage parameter and ε f is the strain at fracture.

3.10.3 Hashin failure model

In the numerical analysis of composite materials, the damage initiation and modes can be judged using Hashin damage failure criteria. This model was proposed in 1980 and is considered the most popular in this field. However, this model has four failure modes, i.e., tensile failure of fiber, compression failure of fiber, tensile failure of matrix, and compression failure of matrix [36,37]. In this work, it has been used for composite materials (Kevlar, carbon, and UHMWPE).

Fiber tension ( σ ˆ 11 ≥ 0 ) :

(8) F f t = σ ˆ 11 X T 2 + α τ ˆ 12 S L 2 .

Fiber compression ( σ ˆ 11 < 0 ) :

(9) F f c = σ ˆ 11 X C 2 .

Matrix tension ( σ ˆ 22 ≥ 0 ) .

(10) F m t = σ ˆ 22 Y T 2 + τ ˆ 12 S L 2 .

Matrix compression ( σ ˆ 22 < 0 ) :

(11) F m c = σ ˆ 22 2 S T 2 + Y C 2 S T 2 − 1 σ ˆ 22 Y C + τ ˆ 12 S L 2 ,

where X T denotes the tensile strength in the fiber direction, X C denotes the compressive strength in the fiber direction, Y T represents the tensile strength in the direction perpendicular to the fibers, Y C represents the compressive strength in the direction perpendicular to the fibers, S L indicates the longitudinal shear strength, and S T indicates the transverse shear strength; and α is a coefficient that determines the contribution of the shear stress to the fiber tensile initiation criterion; and σ ˆ 11 , σ ˆ 22 , and τ ˆ 12 are the components of effective stress tensor, σ ˆ that is used to evaluate the initiation criteria is computed as follows:

(12) σ ˆ = M σ ,

where σ is the nominal stress and M is the damage operator.

(13) M = 1 ( 1 − d f ) 0 0 0 1 ( 1 − d m ) 0 0 0 1 ( 1 − d s ) ,

where d f , d m , and d s are internal (damage) variables that characterize fiber, matrix, and shear damage, which are derived from damage variables d f t , d f c , d m t , and d m c corresponding to the four modes previously discussed, and expressed as follows:

(14) d f = d f t if σ ˆ 11 ≥ 0 , d f c if σ ˆ 11 < 0 ,

(15) d m = d m t if σ ˆ 22 ≥ 0 , d m c if σ ˆ 22 < 0 ,

(16) d s = 1 − ( 1 − d f t ) ( 1 − d f c ) ( 1 − d m t ) ( 1 − d m c ) .

4 Results and discussion

This section presents the experimental and numerical results of the ballistics tests performed on the manufactured hybrid sandwich composite armor samples, and these samples have been classified based on the protection, deformation, and order of the layers. Different materials were selected to fabricate the ballistic hybrid sandwich composite body armors, including aluminum oxide ceramic tiles (Al2O3) having 10 mm thickness, aluminum honeycomb (6.4 and 12.7 mm cell size) possessing 10 and 15 mm thickness, carbon/epoxy composite, UHMWPE/epoxy composite, and Kevlar/epoxy composite, and all composites were of 2 mm thickness. Six parameters were used to analyze all samples after the ballistic impact of hybrid sandwich composite armor samples by the 7.62 × 39 mm bullet with an average impact velocity of 804 m/s. These parameters are the ability to withstand this projectile, method of layers (sheets) order, Vr, BFS, the mode of deformation, and the energy dissipation and absorption.

Figures 18–23 demonstrate the deformation behavior of the hybrid sandwich composite body armor samples (S1, S2, and S3) in real ballistic and numerical tests. These samples include the first sample (UHMWPE/epoxy, unfilled honeycomb, Kevlar/epoxy, unfilled honeycomb, Kevlar/EPX, and UHMWPE/epoxy), the second sample (Kevlar/epoxy, unfilled honeycomb, Kevlar/epoxy, unfilled honeycomb and UHMWPE/epoxy), and the third sample (Al2O3, Kevlar/epoxy, unfilled honeycomb, carbon/epoxy, unfilled honeycomb, and carbon/epoxy). Under the ballistic velocity impact, the hybrid sandwich composite body armors (S1 and S2) failed to stop the bullet, while the armor S3 succeeded in stopping the bullet. From these figures, it can be seen that the failures of the S1 and S2 samples include the rupture of front face sheets, compression of the cells of the double honeycomb core, and rupture of the intermediate layer and back face sheet. The armors S1 and S2 failed to stop the bullet because of the absence of the ceramic tiles material in these samples, where these samples can be strengthened by adding the ceramic tiles to them to prevent penetration. The hybrid sandwich composite armor S3 system formed by the combination of the ceramic strike, Kevlar/epoxy facing sheet, double aluminum honeycomb core, carbon/epoxy intermediate layer, and carbon/epoxy backing sheet exhibited superior ballistic performance against the Type III threat, completely stopping the projectile. This is attributed to the geometry of doubled honeycomb cores, where the compressibility of double honeycomb cores preserves the ceramic faceplates from excessive damage, and the structure of the cores helps crush and accumulate the cells under the projectile. The speeds of the bullet after penetration (VR) were 748.5, 715.3, and 0 m/s, respectively. The BFS for S3 was (1.5) mm, which is optimum and within the allowed range [38]. The DOP through this armor S3 was 27.8 mm. Figure 24 illustrates the initial and VR after the impact for these samples.

Figure 18 Photographs of the deformation of first sample (S1) after the ballistic impact (Experimental). (a) Front face, (b) back face, and (c) isometric.
Figure 18

Photographs of the deformation of first sample (S1) after the ballistic impact (Experimental). (a) Front face, (b) back face, and (c) isometric.

Figure 19 Photographs of the deformation of first sample (S1) after the ballistic impact (Numerical). (a) Front face, (b) back face, and (c) isometric.
Figure 19

Photographs of the deformation of first sample (S1) after the ballistic impact (Numerical). (a) Front face, (b) back face, and (c) isometric.

Figure 20 Photographs of the deformation of second sample (S2) after the ballistic impact (Experimental). (a) Front face, (b) back face, and (c) isometric.
Figure 20

Photographs of the deformation of second sample (S2) after the ballistic impact (Experimental). (a) Front face, (b) back face, and (c) isometric.

Figure 21 Photographs of the deformation of second sample (S2) after the ballistic impact (Numerical). (a) Front face, (b) back face, and (c) isometric.
Figure 21

Photographs of the deformation of second sample (S2) after the ballistic impact (Numerical). (a) Front face, (b) back face, and (c) isometric.

Figure 22 Photographs of the deformation of third sample (S3) after the ballistic impact (Experimental). (a) Front face, (b) back face, and (c) isometric.
Figure 22

Photographs of the deformation of third sample (S3) after the ballistic impact (Experimental). (a) Front face, (b) back face, and (c) isometric.

Figure 23 Photographs of the deformation of third sample (S3) after the ballistic impact (Numerical). (a) Front face, (b) back face, and (c) isometric.
Figure 23

Photographs of the deformation of third sample (S3) after the ballistic impact (Numerical). (a) Front face, (b) back face, and (c) isometric.

Figure 24 Initial and VR after the impact of the samples.
Figure 24

Initial and VR after the impact of the samples.

The brittle crack in Kevlar/epoxy, carbon/epoxy, and UHMWPE/epoxy composites layers with perforation in (S1, S2, and S3) at the failure includes delamination, matrix spalling and pullout, and breaking and shearing failure of fibers in the layers of the composite, while in S3, the bullet can shatter the ceramic. The aluminum honeycomb’s deformation appeared ductile with a large plastic deformation after the ballistic impact [39]. In S3, upon impact, the hard ceramic face plate shatters while deforming and eroding the tip of the projectile [40], where the projectile can cause ceramic failure in a ring, radial cracks form, and the resulting damage pattern in the ceramic is conical in shape and serves to spread out the impact area; however, just one tile in the impact zone was damaged. The projectile may destroy the whole ceramic plate, while smaller tiles will only receive localized damage that only has an impact on the nearby tiles, so that it is able to survive multiple impacts; benefits of using numerous tiles over a single ceramic faceplate is to limit the spread of damage, and being more durable [41]. If the ceramic is utilized with no support layers, under heavy impact force, it will break quickly due to extreme little toughness. The ceramic layer cracked and fractured, absorbing the majority of the kinetic energy of the projectile [40]. The face sheets contain a more significant number of layers than the back sheet, making the front sheets and aluminum honeycomb core absorb the projectile’s remaining kinetic energy through plastic deformation and damage, supporting the damaged ceramic layer [42]. The back sheet was responsible for withstanding the compression of the front and intermediate layers and honeycomb cores and catching the fragments. The ceramics are brittle on the surface that faces the projectile, where the reduced localized pressure on the backing plate is the primary goal of the ceramic’s capability to warp and degrade the projectile. Little projectile fragments stay inside the Kevlar/Epoxy and honeycomb core layers, or no fragments of this projectile could be found after the ballistics tests of armors, which suggests a complete disintegration of the 7.62 × 39 bullet. The kinetic energy of the bullet represents the magnitude of the energy which the structure of armor should absorb. Therefore, the kinetic energy undergoes a severe descent after the impact, so the speed of the bullet after penetrating the armor is inversely proportional to the amount of absorbed energy. The initial or strike velocity and the residual velocity represent the velocities of the bullet before and after penetration, respectively. Hence, these velocities have been used to calculate the absorbed energy via the following equation [43,44].

(17) ∆ E = 1 2 m ( v i 2 − v r 2 ) .

v i , v r , and m represent the initial and residual velocities and the mass of the bullet, respectively, as well as ∆E is the energy absorption by the sample after the ballistic impact. After calculating the initial and VR beyond the impact of the hybrid sandwich composite armors samples (S1, S2, and S3), the values of energy absorbed and specific energy absorbed were calculated. Therefore, the total energy absorption of these armors is (344.65, 539.04, and 2585.66 J) for S1, S2, and S3, respectively. Furthermore, the specific energy absorption of these armors is (1580.98, 1767.36, and 1952.91 J/kg) for S1, S2, and S3, respectively, where the specific energy absorption is the energy absorption per unit mass. Figures 25 and 26 evince the energy absorption and specific energy absorption for each sample, respectively. To provide a consistent way of comparing the weights of armor, the term areal density was used. This is defined as the mass of armor per unit surface area and is usually stated in kg/m2. The areal density of these armor samples (S1, S2 and S3) were (9.68, 13.55 and 58.84) kg/m2, respectively. The ballistic limit velocity of the bullet represents the magnitude of the velocity required for a particular bullet to penetrate a particular piece of material reliably (at least 50% of the time). In other words, a given bullet will generally not pierce a given target when the bullet velocity is lower than the ballistic limit, and when the VR is zero, the ballistic limit velocity is equal to the initial impact velocity [45]. The initial and residual velocities were used to calculate the ballistic limit velocity of the bullet via the following equation [46]:

(18) v b = v i 2 − v r 2 ,

Figure 25 Energy absorption by each sample.
Figure 25

Energy absorption by each sample.

Figure 26 Specific energy absorption by each sample.
Figure 26

Specific energy absorption by each sample.

where v b represents the ballistic limit velocity. The ballistic limit velocities of these armors were 293.53, 367.09, and 804 m/s, respectively. Figure 27 plots the ballistic limit velocity as a function of the areal density of the hybrid sandwich composite armor samples. The results of this figure show that the complete penetration of S1 and S2 can be attributed to the low areal density of the armor and the early failure of each layer. The results also revealed that using the ceramic tiles in the face sheet in S3 results in a moderate percentage increase and improved ballistic limit velocity. However, this increase in ballistic limit velocity is accompanied by an increase in sample areal density. These results indicate that the ceramic tiles’ ballistic resistance of the samples can be significantly enhanced, with a moderate increase in their areal density. The relation between the specific energy absorption and the areal density of the hybrid sandwich composite armor samples is shown in Figure 28. From this figure, the results demonstrate that adding ceramic tiles to the S3 face sheet improves the specific energy absorption by a significant percentage. However, the sample areal density increase coincides with this increase in specific energy absorption. These results manifest that, with a moderate increase in areal density, the sample’s ability to absorb energy can be significantly improved by employing ceramic tiles. Table 3 lists the resulting values of the ballistic test of initial velocity, VR, ballistic velocity, areal density, energy absorption, specific energy absorption, DOP, and BFS of the hybrid sandwich composite armor samples experimentally. Table 4 depicts the resulting values of the ballistic test of initial velocity, VR, and BFS of the hybrid sandwich composite armor samples numerically.

Figure 27 The ballistic limit velocity-areal density behavior of all samples.
Figure 27

The ballistic limit velocity-areal density behavior of all samples.

Figure 28 The specific energy absorption-areal density behavior for all samples.
Figure 28

The specific energy absorption-areal density behavior for all samples.

Table 4

Results of the numerical test of the hybrid sandwich composite armor samples

Samples Initial velocity (m/s) VR (m/s) BFS (mm)
S1 804 755 —
S2 804 719 —
S3 804 0 1.7

The validation of numerical simulations is essential, especially in modeling the protective structures, due to the high rate of the kinetic energy of this event. In general, to validate the BFS of modeling, the following relation was used to calculate the deviation of the numerical results to the exact values recorded in the ballistic test:

(19) Deviation % = ( Experimental results − Numerical results ) Experimental results .

After using this equation to calculate the deviation of numerical results, the results elucidated a good agreement between the experimental and numerical results of the BFS. Table 5 shows the deviation of VR results. If the comparison is made among the S1, S2, and S3, S3 is the best and strongest, and it was able to stop the bullet due to the presence of ceramic tiles and the structure of the cores, which helps compress and accumulate the cells under the projectile. In the double core, the compressing and accumulating of the cells is increased, whereas it cushions the bullet and begins to compress and densify in a localized region.

Table 5

Results deviation of the VR

Sample VR (m/s) Deviation %
Experimental Numerical
S1 748.5 756.8 1.10
S2 715.3 729.9 2.04

5 Conclusion

In this work, hybrid composite sandwich structures were manufactured and tested experimentally and numerically. After analyzing the experimental results of the work, this work presents the fundamental conclusion and highlights the essential results that contributed to the evaluation of the hybrid sandwich armors performance. However, the ballistic impact of using a 7.62 × 39 mm bullet offered crucial points that explain the importance of this structure. The analysis of the ballistic behavior of the S3 armor elucidated the ability of this armor to absorb all the energy of impact except S1 and S2, which were penetrated by the bullet. The BFS of the S3 armor was 1.5 mm, which is optimum and within the allowed range. The DOP through the armor S3 was 27.8 mm. Also, the energy absorption according to the velocity of the initial impact of the S1, S2, and S3 were 344.65, 539.04, and 2585.66 J, respectively. Furthermore, the ballistic limit velocity of these armors was 293.53, 367.09, and 804 m/s, respectively. On comparing the samples S1, S2, and S3, S3 was found to be the best and strongest, and it was able to stop the bullet due to the structure of cores, which helps compress and accumulate the cells under the projectile, as it cushions the bullet and begins to compress and densify in a localized region.

The results of the experimental and numerical work comparison elucidated a good agreement between these approaches, with a significant matching in the failure pattern. The deviation of the VR result of numerical modeling from the experimental work is acceptable and limited between 1.10 and 2.04% for S1 and S2, respectively. Finally, the software of ABAQUS is one of the most reliable software; hence, this study highly recommends using this software in the ballistic field, and it also recommends evaluating the performance of this armors under ballistic impacts by using the last type of ammunitions 30 caliber M2 AP after the pre-last type used in this study is 7.62 × 39 mm bullet.

6 Recommendations and future works

The number of observations might serve as a reflection of a particular insight, and these points of view serve as a crucial road map for enhancing this unique form of body armors; therefore, several recommendations can be made for future work in this field of study, some of these recommendations are:

  • Create new hybrid sandwich composite structure designs of body armors via a selection of new hybrid sandwich systems.

  • Change the core’s geometry to another geometry, such as an auxetic, corrugated, and chiral shape.

  • Evaluate the performance of these armors under ballistic impacts by using ammunition such as a 30 caliber M2 AP (IV level).

  • Use new ballistic materials for the core, front and back sheets of these designs of body armors.

  • Change the thickness and cell size of the core and the thickness of the front and back sheets.

  • Use advanced materials such as nanotubes, nanomaterials, or natural fibers in the armor’s structures.

  • It is recommended to use functionally graded materials in the armor’s structures.

  1. Funding information: Authors declare that this manuscript was done depending on the personal effort of the author, and there is no funding effort from any side or organization.

  2. Conflict of interest: The authors state no conflict of interest with anyone related to the subject of the manuscript or any competing interest.

  3. Data availability statement: Most datasets generated and analyzed in this study are comprised in this submitted manuscript. The other datasets are available on reasonable request from the corresponding author with the attached information.

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Received: 2023-09-03
Revised: 2023-10-09
Accepted: 2023-10-16
Published Online: 2024-03-14

© 2024 the author(s), published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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  66. A study of the vibrations of a rotor bearing suspended by a hybrid spring system of shape memory alloys
  67. Stability analysis of Hub dam under rapid drawdown
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  69. Numerical and experimental comparison study of piled raft foundation
  70. Effect of asphalt modified with waste engine oil on the durability properties of hot asphalt mixtures with reclaimed asphalt pavement
  71. Hydraulic model for flood inundation in Diyala River Basin using HEC-RAS, PMP, and neural network
  72. Numerical study on discharge capacity of piano key side weir with various ratios of the crest length to the width
  73. The optimal allocation of thyristor-controlled series compensators for enhancement HVAC transmission lines Iraqi super grid by using seeker optimization algorithm
  74. Numerical and experimental study of the impact on aerodynamic characteristics of the NACA0012 airfoil
  75. Effect of nano-TiO2 on physical and rheological properties of asphalt cement
  76. Performance evolution of novel palm leaf powder used for enhancing hot mix asphalt
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  78. Flexural behavior of RC beams externally reinforced with CFRP composites using various strategies
  79. Influence of fiber types on the properties of the artificial cold-bonded lightweight aggregates
  80. Experimental investigation of RC beams strengthened with externally bonded BFRP composites
  81. Generalized RKM methods for solving fifth-order quasi-linear fractional partial differential equation
  82. An experimental and numerical study investigating sediment transport position in the bed of sewer pipes in Karbala
  83. Role of individual component failure in the performance of a 1-out-of-3 cold standby system: A Markov model approach
  84. Implementation for the cases (5, 4) and (5, 4)/(2, 0)
  85. Center group actions and related concepts
  86. Experimental investigation of the effect of horizontal construction joints on the behavior of deep beams
  87. Deletion of a vertex in even sum domination
  88. Deep learning techniques in concrete powder mix designing
  89. Effect of loading type in concrete deep beam with strut reinforcement
  90. Studying the effect of using CFRP warping on strength of husk rice concrete columns
  91. Parametric analysis of the influence of climatic factors on the formation of traditional buildings in the city of Al Najaf
  92. Suitability location for landfill using a fuzzy-GIS model: A case study in Hillah, Iraq
  93. Hybrid approach for cost estimation of sustainable building projects using artificial neural networks
  94. Assessment of indirect tensile stress and tensile–strength ratio and creep compliance in HMA mixes with micro-silica and PMB
  95. Density functional theory to study stopping power of proton in water, lung, bladder, and intestine
  96. A review of single flow, flow boiling, and coating microchannel studies
  97. Effect of GFRP bar length on the flexural behavior of hybrid concrete beams strengthened with NSM bars
  98. Exploring the impact of parameters on flow boiling heat transfer in microchannels and coated microtubes: A comprehensive review
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  103. Optimization and characterization of sustainable geopolymer mortars based on palygorskite clay, water glass, and sodium hydroxide
  104. Sediment transport modelling upstream of Al Kufa Barrage
  105. Study of energy loss, range, and stopping time for proton in germanium and copper materials
  106. Effect of internal and external recycle ratios on the nutrient removal efficiency of anaerobic/anoxic/oxic (VIP) wastewater treatment plant
  107. Enhancing structural behaviour of polypropylene fibre concrete columns longitudinally reinforced with fibreglass bars
  108. Sustainable road paving: Enhancing concrete paver blocks with zeolite-enhanced cement
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  111. Optimization and design of a new column sequencing for crude oil distillation at Basrah refinery
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  115. Effect of surface roughness on the interface behavior of clayey soils
  116. Investigated of the optical properties for SiO2 by using Lorentz model
  117. Measurements of induced vibrations due to steel pipe pile driving in Al-Fao soil: Effect of partial end closure
  118. Experimental and numerical studies of ballistic resistance of hybrid sandwich composite body armor
  119. Evaluation of clay layer presence on shallow foundation settlement in dry sand under an earthquake
  120. Optimal design of mechanical performances of asphalt mixtures comprising nano-clay additives
  121. Advancing seismic performance: Isolators, TMDs, and multi-level strategies in reinforced concrete buildings
  122. Predicted evaporation in Basrah using artificial neural networks
  123. Energy management system for a small town to enhance quality of life
  124. Numerical study on entropy minimization in pipes with helical airfoil and CuO nanoparticle integration
  125. Equations and methodologies of inlet drainage system discharge coefficients: A review
  126. Thermal buckling analysis for hybrid and composite laminated plate by using new displacement function
  127. Investigation into the mechanical and thermal properties of lightweight mortar using commercial beads or recycled expanded polystyrene
  128. Experimental and theoretical analysis of single-jet column and concrete column using double-jet grouting technique applied at Al-Rashdia site
  129. The impact of incorporating waste materials on the mechanical and physical characteristics of tile adhesive materials
  130. Seismic resilience: Innovations in structural engineering for earthquake-prone areas
  131. Automatic human identification using fingerprint images based on Gabor filter and SIFT features fusion
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  133. Visible light-boosted photodegradation activity of Ag–AgVO3/Zn0.5Mn0.5Fe2O4 supported heterojunctions for effective degradation of organic contaminates
  134. Production of sustainable concrete with treated cement kiln dust and iron slag waste aggregate
  135. Key effects on the structural behavior of fiber-reinforced lightweight concrete-ribbed slabs: A review
  136. A comparative analysis of the energy dissipation efficiency of various piano key weir types
  137. Special Issue: Transport 2022 - Part II
  138. Variability in road surface temperature in urban road network – A case study making use of mobile measurements
  139. Special Issue: BCEE5-2023
  140. Evaluation of reclaimed asphalt mixtures rejuvenated with waste engine oil to resist rutting deformation
  141. Assessment of potential resistance to moisture damage and fatigue cracks of asphalt mixture modified with ground granulated blast furnace slag
  142. Investigating seismic response in adjacent structures: A study on the impact of buildings’ orientation and distance considering soil–structure interaction
  143. Improvement of porosity of mortar using polyethylene glycol pre-polymer-impregnated mortar
  144. Three-dimensional analysis of steel beam-column bolted connections
  145. Assessment of agricultural drought in Iraq employing Landsat and MODIS imagery
  146. Performance evaluation of grouted porous asphalt concrete
  147. Optimization of local modified metakaolin-based geopolymer concrete by Taguchi method
  148. Effect of waste tire products on some characteristics of roller-compacted concrete
  149. Studying the lateral displacement of retaining wall supporting sandy soil under dynamic loads
  150. Seismic performance evaluation of concrete buttress dram (Dynamic linear analysis)
  151. Behavior of soil reinforced with micropiles
  152. Possibility of production high strength lightweight concrete containing organic waste aggregate and recycled steel fibers
  153. An investigation of self-sensing and mechanical properties of smart engineered cementitious composites reinforced with functional materials
  154. Forecasting changes in precipitation and temperatures of a regional watershed in Northern Iraq using LARS-WG model
  155. Experimental investigation of dynamic soil properties for modeling energy-absorbing layers
  156. Numerical investigation of the effect of longitudinal steel reinforcement ratio on the ductility of concrete beams
  157. An experimental study on the tensile properties of reinforced asphalt pavement
  158. Self-sensing behavior of hot asphalt mixture with steel fiber-based additive
  159. Behavior of ultra-high-performance concrete deep beams reinforced by basalt fibers
  160. Optimizing asphalt binder performance with various PET types
  161. Investigation of the hydraulic characteristics and homogeneity of the microstructure of the air voids in the sustainable rigid pavement
  162. Enhanced biogas production from municipal solid waste via digestion with cow manure: A case study
  163. Special Issue: AESMT-7 - Part I
  164. Preparation and investigation of cobalt nanoparticles by laser ablation: Structure, linear, and nonlinear optical properties
  165. Seismic analysis of RC building with plan irregularity in Baghdad/Iraq to obtain the optimal behavior
  166. The effect of urban environment on large-scale path loss model’s main parameters for mmWave 5G mobile network in Iraq
  167. Formatting a questionnaire for the quality control of river bank roads
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  170. In-depth analysis of critical factors affecting Iraqi construction projects performance
  171. Behavior of container berth structure under the influence of environmental and operational loads
  172. Energy absorption and impact response of ballistic resistance laminate
  173. Effect of water-absorbent polymer balls in internal curing on punching shear behavior of bubble slabs
  174. Effect of surface roughness on interface shear strength parameters of sandy soils
  175. Evaluating the interaction for embedded H-steel section in normal concrete under monotonic and repeated loads
  176. Estimation of the settlement of pile head using ANN and multivariate linear regression based on the results of load transfer method
  177. Enhancing communication: Deep learning for Arabic sign language translation
  178. A review of recent studies of both heat pipe and evaporative cooling in passive heat recovery
  179. Effect of nano-silica on the mechanical properties of LWC
  180. An experimental study of some mechanical properties and absorption for polymer-modified cement mortar modified with superplasticizer
  181. Digital beamforming enhancement with LSTM-based deep learning for millimeter wave transmission
  182. Developing an efficient planning process for heritage buildings maintenance in Iraq
  183. Design and optimization of two-stage controller for three-phase multi-converter/multi-machine electric vehicle
  184. Evaluation of microstructure and mechanical properties of Al1050/Al2O3/Gr composite processed by forming operation ECAP
  185. Calculations of mass stopping power and range of protons in organic compounds (CH3OH, CH2O, and CO2) at energy range of 0.01–1,000 MeV
  186. Investigation of in vitro behavior of composite coating hydroxyapatite-nano silver on 316L stainless steel substrate by electrophoretic technic for biomedical tools
  187. A review: Enhancing tribological properties of journal bearings composite materials
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  189. Design a new scheme for image security using a deep learning technique of hierarchical parameters
  190. Special Issue: ICES 2023
  191. Comparative geotechnical analysis for ultimate bearing capacity of precast concrete piles using cone resistance measurements
  192. Visualizing sustainable rainwater harvesting: A case study of Karbala Province
  193. Geogrid reinforcement for improving bearing capacity and stability of square foundations
  194. Evaluation of the effluent concentrations of Karbala wastewater treatment plant using reliability analysis
  195. Adsorbent made with inexpensive, local resources
  196. Effect of drain pipes on seepage and slope stability through a zoned earth dam
  197. Sediment accumulation in an 8 inch sewer pipe for a sample of various particles obtained from the streets of Karbala city, Iraq
  198. Special Issue: IETAS 2024 - Part I
  199. Analyzing the impact of transfer learning on explanation accuracy in deep learning-based ECG recognition systems
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  201. Improving multi-object detection and tracking with deep learning, DeepSORT, and frame cancellation techniques
  202. The impact of using prestressed CFRP bars on the development of flexural strength
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  204. A data augmentation approach to enhance breast cancer detection using generative adversarial and artificial neural networks
  205. Modification of the 5D Lorenz chaotic map with fuzzy numbers for video encryption in cloud computing
  206. Special Issue: 51st KKBN - Part I
  207. Evaluation of static bending caused damage of glass-fiber composite structure using terahertz inspection
https://doi.org/10.1515/eng-2022-0543
Keywords for this article
ballistic impact; 7.62 × 39 mm bullet; hybrid sandwich armor; energy absorption; back face signature
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BY 4.0

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  2. Methodology of automated quality management
  3. Influence of vibratory conveyor design parameters on the trough motion and the self-synchronization of inertial vibrators
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  18. Improved correlation of soil modulus with SPT N values
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  20. Assessing the need for the adoption of digitalization in Indian small and medium enterprises
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  29. Experimental and numerical investigation on composite beam–column joint connection behavior using different types of connection schemes
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  37. Applications of nanotechnology and nanoproduction techniques
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  39. Communication
  40. Techniques to mitigate the admission of radon inside buildings
  41. Erratum
  42. Erratum to “Effect of short heat treatment on mechanical properties and shape memory properties of Cu–Al–Ni shape memory alloy”
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  53. Special Issue: AESMT-5 - Part II
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  56. Restrained captive domination number
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  58. Asphalt binder modified with recycled tyre rubber
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  62. Evaluation of mechanically stabilized earth retaining walls for different soil–structure interaction methods: A review
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  64. Sulfate removal from wastewater by using waste material as an adsorbent
  65. Experimental investigation on strengthening lap joints subjected to bending in glulam timber beams using CFRP sheets
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  73. The optimal allocation of thyristor-controlled series compensators for enhancement HVAC transmission lines Iraqi super grid by using seeker optimization algorithm
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  76. Performance evolution of novel palm leaf powder used for enhancing hot mix asphalt
  77. Performance analysis, evaluation, and improvement of selected unsignalized intersection using SIDRA software – Case study
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  79. Influence of fiber types on the properties of the artificial cold-bonded lightweight aggregates
  80. Experimental investigation of RC beams strengthened with externally bonded BFRP composites
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  82. An experimental and numerical study investigating sediment transport position in the bed of sewer pipes in Karbala
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  88. Deep learning techniques in concrete powder mix designing
  89. Effect of loading type in concrete deep beam with strut reinforcement
  90. Studying the effect of using CFRP warping on strength of husk rice concrete columns
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  95. Density functional theory to study stopping power of proton in water, lung, bladder, and intestine
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  103. Optimization and characterization of sustainable geopolymer mortars based on palygorskite clay, water glass, and sodium hydroxide
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  105. Study of energy loss, range, and stopping time for proton in germanium and copper materials
  106. Effect of internal and external recycle ratios on the nutrient removal efficiency of anaerobic/anoxic/oxic (VIP) wastewater treatment plant
  107. Enhancing structural behaviour of polypropylene fibre concrete columns longitudinally reinforced with fibreglass bars
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  118. Experimental and numerical studies of ballistic resistance of hybrid sandwich composite body armor
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  121. Advancing seismic performance: Isolators, TMDs, and multi-level strategies in reinforced concrete buildings
  122. Predicted evaporation in Basrah using artificial neural networks
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  125. Equations and methodologies of inlet drainage system discharge coefficients: A review
  126. Thermal buckling analysis for hybrid and composite laminated plate by using new displacement function
  127. Investigation into the mechanical and thermal properties of lightweight mortar using commercial beads or recycled expanded polystyrene
  128. Experimental and theoretical analysis of single-jet column and concrete column using double-jet grouting technique applied at Al-Rashdia site
  129. The impact of incorporating waste materials on the mechanical and physical characteristics of tile adhesive materials
  130. Seismic resilience: Innovations in structural engineering for earthquake-prone areas
  131. Automatic human identification using fingerprint images based on Gabor filter and SIFT features fusion
  132. Performance of GRKM-method for solving classes of ordinary and partial differential equations of sixth-orders
  133. Visible light-boosted photodegradation activity of Ag–AgVO3/Zn0.5Mn0.5Fe2O4 supported heterojunctions for effective degradation of organic contaminates
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  135. Key effects on the structural behavior of fiber-reinforced lightweight concrete-ribbed slabs: A review
  136. A comparative analysis of the energy dissipation efficiency of various piano key weir types
  137. Special Issue: Transport 2022 - Part II
  138. Variability in road surface temperature in urban road network – A case study making use of mobile measurements
  139. Special Issue: BCEE5-2023
  140. Evaluation of reclaimed asphalt mixtures rejuvenated with waste engine oil to resist rutting deformation
  141. Assessment of potential resistance to moisture damage and fatigue cracks of asphalt mixture modified with ground granulated blast furnace slag
  142. Investigating seismic response in adjacent structures: A study on the impact of buildings’ orientation and distance considering soil–structure interaction
  143. Improvement of porosity of mortar using polyethylene glycol pre-polymer-impregnated mortar
  144. Three-dimensional analysis of steel beam-column bolted connections
  145. Assessment of agricultural drought in Iraq employing Landsat and MODIS imagery
  146. Performance evaluation of grouted porous asphalt concrete
  147. Optimization of local modified metakaolin-based geopolymer concrete by Taguchi method
  148. Effect of waste tire products on some characteristics of roller-compacted concrete
  149. Studying the lateral displacement of retaining wall supporting sandy soil under dynamic loads
  150. Seismic performance evaluation of concrete buttress dram (Dynamic linear analysis)
  151. Behavior of soil reinforced with micropiles
  152. Possibility of production high strength lightweight concrete containing organic waste aggregate and recycled steel fibers
  153. An investigation of self-sensing and mechanical properties of smart engineered cementitious composites reinforced with functional materials
  154. Forecasting changes in precipitation and temperatures of a regional watershed in Northern Iraq using LARS-WG model
  155. Experimental investigation of dynamic soil properties for modeling energy-absorbing layers
  156. Numerical investigation of the effect of longitudinal steel reinforcement ratio on the ductility of concrete beams
  157. An experimental study on the tensile properties of reinforced asphalt pavement
  158. Self-sensing behavior of hot asphalt mixture with steel fiber-based additive
  159. Behavior of ultra-high-performance concrete deep beams reinforced by basalt fibers
  160. Optimizing asphalt binder performance with various PET types
  161. Investigation of the hydraulic characteristics and homogeneity of the microstructure of the air voids in the sustainable rigid pavement
  162. Enhanced biogas production from municipal solid waste via digestion with cow manure: A case study
  163. Special Issue: AESMT-7 - Part I
  164. Preparation and investigation of cobalt nanoparticles by laser ablation: Structure, linear, and nonlinear optical properties
  165. Seismic analysis of RC building with plan irregularity in Baghdad/Iraq to obtain the optimal behavior
  166. The effect of urban environment on large-scale path loss model’s main parameters for mmWave 5G mobile network in Iraq
  167. Formatting a questionnaire for the quality control of river bank roads
  168. Vibration suppression of smart composite beam using model predictive controller
  169. Machine learning-based compressive strength estimation in nanomaterial-modified lightweight concrete
  170. In-depth analysis of critical factors affecting Iraqi construction projects performance
  171. Behavior of container berth structure under the influence of environmental and operational loads
  172. Energy absorption and impact response of ballistic resistance laminate
  173. Effect of water-absorbent polymer balls in internal curing on punching shear behavior of bubble slabs
  174. Effect of surface roughness on interface shear strength parameters of sandy soils
  175. Evaluating the interaction for embedded H-steel section in normal concrete under monotonic and repeated loads
  176. Estimation of the settlement of pile head using ANN and multivariate linear regression based on the results of load transfer method
  177. Enhancing communication: Deep learning for Arabic sign language translation
  178. A review of recent studies of both heat pipe and evaporative cooling in passive heat recovery
  179. Effect of nano-silica on the mechanical properties of LWC
  180. An experimental study of some mechanical properties and absorption for polymer-modified cement mortar modified with superplasticizer
  181. Digital beamforming enhancement with LSTM-based deep learning for millimeter wave transmission
  182. Developing an efficient planning process for heritage buildings maintenance in Iraq
  183. Design and optimization of two-stage controller for three-phase multi-converter/multi-machine electric vehicle
  184. Evaluation of microstructure and mechanical properties of Al1050/Al2O3/Gr composite processed by forming operation ECAP
  185. Calculations of mass stopping power and range of protons in organic compounds (CH3OH, CH2O, and CO2) at energy range of 0.01–1,000 MeV
  186. Investigation of in vitro behavior of composite coating hydroxyapatite-nano silver on 316L stainless steel substrate by electrophoretic technic for biomedical tools
  187. A review: Enhancing tribological properties of journal bearings composite materials
  188. Improvements in the randomness and security of digital currency using the photon sponge hash function through Maiorana–McFarland S-box replacement
  189. Design a new scheme for image security using a deep learning technique of hierarchical parameters
  190. Special Issue: ICES 2023
  191. Comparative geotechnical analysis for ultimate bearing capacity of precast concrete piles using cone resistance measurements
  192. Visualizing sustainable rainwater harvesting: A case study of Karbala Province
  193. Geogrid reinforcement for improving bearing capacity and stability of square foundations
  194. Evaluation of the effluent concentrations of Karbala wastewater treatment plant using reliability analysis
  195. Adsorbent made with inexpensive, local resources
  196. Effect of drain pipes on seepage and slope stability through a zoned earth dam
  197. Sediment accumulation in an 8 inch sewer pipe for a sample of various particles obtained from the streets of Karbala city, Iraq
  198. Special Issue: IETAS 2024 - Part I
  199. Analyzing the impact of transfer learning on explanation accuracy in deep learning-based ECG recognition systems
  200. Effect of scale factor on the dynamic response of frame foundations
  201. Improving multi-object detection and tracking with deep learning, DeepSORT, and frame cancellation techniques
  202. The impact of using prestressed CFRP bars on the development of flexural strength
  203. Assessment of surface hardness and impact strength of denture base resins reinforced with silver–titanium dioxide and silver–zirconium dioxide nanoparticles: In vitro study
  204. A data augmentation approach to enhance breast cancer detection using generative adversarial and artificial neural networks
  205. Modification of the 5D Lorenz chaotic map with fuzzy numbers for video encryption in cloud computing
  206. Special Issue: 51st KKBN - Part I
  207. Evaluation of static bending caused damage of glass-fiber composite structure using terahertz inspection
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