Volume 64, Issue 6

In this study, a low-alloy steel component was manufactured using specially produced E70C-6M class of metal-cored welding wire according to AWS A5.18 standard for the WAAM process. The manufactured low-alloy steel component was first subjected to radiographic examination to detect any weld defect. Uniaxial tensile tests were conducted for the bottom, middle and upper regions. The micro-hardness tests were performed parallel to the deposition direction. The results show that microstructures varied from base metal to the face region of the WAAM component, including the bottom, middle and top sections. The bottom region showed lamellar structures; the middle and upper region presented equiaxed ferrite structure with a small amount of grain boundary pearlites and the face region displayed a mix of equiaxed and lamellar structures of ferrites. The yield and ultimate tensile strengths of the top, middle, and bottom regions exhibited similar results varying between 370 MPa and 490 MPa, respectively. In contrast, the top region showed an elongation value about 15% higher than other regions. Moreover, the yield and ultimate tensile strength for WAAM-produced component were found to be 14% and 24% lower than the multiple-pass all-weld metal of E70C-6M class of metal-cored wire.

Within the study’s scope, impact analyses of homogeneous bumper beam-crash box systems designed from AA6063-O, AA6063-T5, and AA6063-T6 materials and hybrid systems designed from combinations of these materials were made and compared in terms of energy absorption values. In designs where failure does not occur, the highest energy absorption value was obtained using the AA6063-T5 bumper beam and AA6063-O crash box system, and single and multi-objective optimization studies were conducted using this design. The optimal bumper system improved the crash performance of the structure. Accordingly, this bumper system can be used in vehicles to improve crashworthiness.

Owing to their specific advantages like thermal insulation, being lightweight and strong, laminated composites were designed by using natural fiber (female or male palm fiber) between two layers of glass stitched [0°/90°] to improve the impact properties of glass/epoxy composite. Natural fiber is cheap and plentiful in Iraq. The composite material was manufactured by vacuum assisted resin infusion molding (VARIM) at 80 °C for a duration of 8 h. The low velocity impact response of laminated composite was investigated experimentally. Impact tests were conducted on the composite specimens by Ceast Fractovis Plus impact test machine with constant mass of 5.03 kg at room temperature for the impact energies of 20 J, 30 J and 40 J. After impact tests, maximum contact forces versus impact energy, contact force versus deflection and absorbed energy-impact energy curves are drawn. The obtained results showed that the addition of palm fibers to glass/epoxy composite materials made significant contributions in absorbing energy and delaying the damage mode.

In engineering applications, cylindrical bars of 20 carbon steel are often subjected to a combination of tensile loading and torsional loading during the service, thereby causing premature failure or an accident. In order to explore the influence of loading sequence of tension and torsion on the mechanical properties of 20 carbon steel, tests of combined tension-torsion loading and combined torsion-tension loading are employed in this work. During experiments, a microscope is used for the in situ characterization of micro-damage evolution on the surface of specimens. At the same time, to analyze the influence of loading sequence on the stress distribution, ABAQUS software is utilized to conduct the relevant finite element simulation, where the results of finite element analysis are consistent with the experiments. Evidently, the torsional strength of 20 carbon steel is decreased with an increase in the pre-tensile stress, under the combined tension-torsion. However, the tensile strength of 20 carbon steel is enhanced with the increasing pre-torsional angles, under the combined torsion-tension. Moreover, the in situ images characterized the micro-damage evolution of 20 carbon steel under pure tension, pure torsion, combined tension-torsion and combined torsion-tension. It is concluded that the deference in loading sequence changes the failure mechanism of 20 carbon steel is different.

Steel pipe piles are used to reinforce the grounds. Due to high hardness of the rocky materials, in some cases, the tip surface should be developed with new designs in terms of geometry, material and heat treatment. In this study, a hardfacing welding, which reinforces the application point of the tip surface, was applied on the steel pipe pile shoe tip which was manufactured from S355J2 steel. Wear tests were applied and hardness measurements were made to explain wear behavior. According to the results, the hardened surface of the 3rd layer which was welded with FCH-360 flux cored wire showed higher hardness than other layers. Similarly, the highest wear resistance was obtained in this layer. Martensitic and bainitic structures with ferrite islets were observed from the first layer to the second layer. The bainite and ferrite isles were gradually transformed to martensite and maintained itself from first to third layer. The martensitic structure mainly controlled the hardness and wear resistance. The sizes of the martensite highly affected the hardness and wear resistance of the layer itself.

The purpose of this study was to investigate the performance of different lubricated and protective conditions of wire ropes. The failure behaviors of wire ropes under different surface conditions were evaluated by using salt spray, wear, and tensile testing. The four surface conditions of the test wire ropes included naked wire and wires coated with wire rope oil, 85W/140 gear oil, and grease, respectively. The potentiodynamic polarization curves revealed that the naked wire was more easily corroded in 3.5% aqueous NaCl solution than in 5%. The results indicated that only the specimen coated with wire rope oil showed no corrosion in the 5% aqueous solution after nine days of the salt spray, and likewise this specimen was not characterized by long distance scratches in a starvation lubrication condition, causing the wire’s tensile strength underwent almost no degradation. Furthermore, the uncertain performance of grease restricted the applications of wire ropes in corrosive environment.

Impact is defined as an instantaneous external force applied to a material or structure at low, medium, and high speeds over a very short period of time. In this study, we investigate the impact behavior of glass-epoxy composite (GFRP), carbon-epoxy composite (CFRP), and glass/carbon-epoxy hybrid composite (GCFRP) samples subjected to low-velocity impact testing with varying impact energy levels. Composite plates of 330 × 330 mm 2 consisting of eight layers were prepared using the VARTM method for impact experiments. Each composite type was tested with impact energy values of 10, 20, 30, and 40 J and their impact behaviors were examined. It was observed that as impact energy increased, the maximum force and the collapse values increased as well. The GFRP composite samples had the highest impact strength, while the GCFRP hybrid composite samples had poorer impact resistance compared to the GFRP composites and better impact resistance compared to the CFRP composites.

The AISI 4140 and AISI 4340 tempered steels are widely used in industry. This study investigated the effects of the tempering temperature on the mechanical properties of these steels. The steels were kept at 850 °C for 30 min, left in an oil environment, and then subjected to hardening. The samples were then tempered for 1 h at four different temperatures (300, 450, 550, and 650 °C). Hardness measurements were performed to determine the mechanical properties of the materials. In addition, the samples were subjected to tensile, notch impact, and wear tests. The samples were also examined microstructurally. The results revealed that the hardness, impact energy, and wear rates of samples of both steels decreased when tempering was applied after quenching. As the tempering temperature was increased, these values tended to decrease. However, the impact value increased in parallel with the tempering heat treatment and tempering temperature.

Fiber-reinforced composite materials may contain open holes according to the needs of service conditions. This research aims to determine the effect of the shape and size of the open-holes on the compressive strength of the carbon fiber/epoxy laminated composite material. The mechanical properties and the open-hole compressive failure of the laminate were introduced first. The experimental study was simulated with Finite element analysis and the difference between the experimental and numerical methods used to determine the compressive strength were compared. The results showed that the failure starts with matrix shear failure at the interface between the consecutive plies that have the greatest angle difference in fiber directions. The angle difference between the load and the reinforcement fibers is also important in determining the interface where the damage occurs. In terms of compressive strength, the shape and orientation of the holes are at least as important as the size of the holes.

Sandwich panels are frequently used in transportation, automotive, aerospace and marine sectors due to their high rigidity, strength and ability to absorb energy. In this study, finite element analyses investigated the bending behaviour of aluminium sandwich panels fixed at both ends with different geometrical tubular core structures. The sandwich panels consist of 6063-T5 Aluminium core and 7075-T6 Aluminium skin. The core structure used square, circle, triangle, honeycomb, vertical ellipse and horizontal ellipse tube geometries. The square tube-core sandwich panel has the highest specific load-carrying capacity (SLCC) among the different tube-core geometries. In the square tube-core sandwich panel, where the number of tubes varies, the seven-tube-core panel showed the highest SLCC .

Fracture is the most common damage form of concrete buildings. Due to the opaqueness of concrete, the internal structure can be hardly observed so that it is difficult to predict the occurrence and development of cracks. Therefore, an image-based modeling method using digital image correlation (DIC) is proposed in this work. The realistic distribution of each phase in a concrete structure is captured by a camera, and the corresponding concrete models are then established for further simulation. With the image-based models, a series of three-point and four-point bending experiments are carried out experimentally and numerically, and their fracture processes are compared. It is revealed that the simulation analysis is in good agreement with the experimental result on crack propagation and the trend of strain in three-point bending tests. It should also be remarked that the image-based model needs to be optimized for simulating crack development in four-point bending tests because of the randomness of crack position, although the strain field of simulation is close to one of the experiments.

Manufacturers often employ the extrusion process to form an object with any cross-section. An experiment was carried out to examine the effect of die angle on the quality of the extruded product. The four types of extrusion dies were designed for finding the desirable quality of aluminium composite extruded billet. The five percentages of the Silicon carbide have been chosen as reinforcement with aluminium alloys. Further, the various extrusion dies configurations were considered as 12:8, 12:2, 12:4, and 8:4 for producing the extruded billets. In addition, the die angles that correspond to the required minimum extrusion load were determined. According to the findings, 12:8 extrusion configurations with a 30° die angle produced the desired quality billet and fine grain structure of extruded product with reduced extrusion load. The extruded billet surface quality was analyzed by scanning electron microscopy.

One of the most hazardous accidents in jet engine is striking of bird into the engine blades during flight. The collision of bird leads to high deformation of blades and other elements which leads to malfunction of jet engine. In recent times, the analysis of bird strike was performed using numerical calculations and software simulations. These tests have to be implemented in the design stage of jet engine. The present research focuses on developing W–Cr (tungsten–chromium) coated jet engine blades as alternate for existing Ti–Ni (titanium–nickel) coated blades. The surface morphology and microstructure of W–Cr were studied using HRTEM. The hardness test was performed to predict material properties such as wear, strength and ductility. The microstructure of W–Cr was analysed using FESEM. In the bird strike analysis, the contact between blade and bird was considered as the important phenomenon.

In this paper, the tensile damage mechanism of carbon fiber composites at high temperatures is analyzed. The acoustic emission technique was employed to monitor the tensile process of specimens. The acoustic emission signals at high and room temperatures were classified based on k -means and the wavelet packet energy spectrum. The results show that the damage mechanisms at high temperatures and room temperature differ. At high temperatures, there is more stress release, the material instability appears earlier, and redistribution occurs in the specimen. The damage mechanisms include matrix cracking, fiber/matrix debonding, and fiber breakage. For damage mechanism identification, the acoustic emission characteristics were used under room temperature and high-temperature conditions in the fully connected neural network, with an accuracy rate of 97.5%. The results indicate that the network is suited for both high temperatures and room temperature and can better identify various damage mechanisms.