Band 21, Heft 3

Formation mechanism of ledeburites in laser alloying composite coating on a titanium alloy was investigated. The amorphous reinforced composite coatings were fabricated on the TA2 alloys by laser alloying of Co-Al-Fe-TiC/C mixed powders. Through the X-ray diffraction and high resolution transmission electron microscope test, it was confirmed that the amorphous phases were produced in such a coating. Scanning electron microscope results indicated that the ledeburites were produced in the Co-Al-Fe-C laser alloying coating, and the content of the ceramics played an important role in the formation mechanism of ledeburites. This research provides essential experimental basis to promote the application of laser alloying technique in the surface modifications of the titanium alloys.

In order to produce a rubber sealing material with decent physical and mechanical properties, heat resistance, and flame retardance, a nano MH/GF/NBR composite material was made by using nitrile butadiene rubber (NBR), glass fiber (GF), and nano magnesium hydroxide (MH). The physical and mechanical performances, heat resistance, and flame retardance of the composite material were investigated for different fractions of nano MH and GF. The results showed that nano MH reinforces the internal structure of the composite material. The bond strength between GF and the rubber matrix decreases with the increase in the amount of GF in the composite. The proportion of nano MH and GF can improve the physical and mechanical performances of NBR. The tensile strength, tear strength, permanent compression deformation, and hardness also increase. The nano MH/GF composite has good flame retardance, which improves the thermal stability of NBR. Additionally, the total smoke production of the composite material is reduced and the lifetime of the material is extended. The results established a foundation for further applications using the nano MH/GF/NBR composite material as a sealant.

The aim of this study is to investigate the effect of surface modification through sodium hydroxide (NaOH) treatment and fiber length on the tensile strength of coir fiber of reinforced epoxy composites. The coir fibers were treated with 2%, 4%, 6%, 8%, and 10% concentration of NaOH separately for 10 days. The tensile strength of untreated and alkali-treated fiber was measured. For each group of the coir fiber, experiments were conducted on different fiber lengths, namely, 10, 20, and 30 mm. The experimental results showed that increasing the NaOH concentration leads to a decrease in fiber diameter in a linear fashion. This reduction in diameter naturally ends up with reduced tensile strength. The treated coir fiber was used as a reinforcement and epoxy as a matrix to fabricate the composites. The tensile strength of different samples of composites was measured. Increased NaOH concentration (up to 4%) in fiber treatment was found to increase the tensile strength, and further increase in NaOH concentration reduces the tensile strength; also, increased fiber length was found to increase in tensile strength. The maximum tensile strength of the composite was observed at 4% NaOH-treated samples. On the basis of the nonlinear regression analysis, the tensile strength equation was proposed for coir fiber-reinforced epoxy composites.

In this study, the effect of addition of Rockforce mineral and glass fiber fillers on the mechanical properties and morphological characteristics of polyamide-6 composites were evaluated and compared. Reinforcements, single and mixed compounds by various weight ratios between 10 and 30 wt%, were added to polyamide-6 polymer. Uniaxial tensile, Izod impact, and flexural tests were carried out. Tensile strength, elongation at break, tensile modulus, flexural strength, flexural modulus, and impact strength were obtained. The results showed that the tensile strength, tensile modulus, flexural strength, and flexural modulus of polyamide-6 composite increased with the increase in the glass fiber ratio and are slightly influenced by the addition of Rockforce mineral fibers. Moreover, the impact strength follows an increasing and decreasing profile, whereas elongation at break values decreased with the increase in reinforcement ratio. Finally, scanning electron microscopy was used for comparison and evaluation of the fracture surface of the polyamide-6 composite.

In this article, a kind of superabsorbent resin (SAR) was synthesized by copolymerizing acrylic acid (AA) partly neutralized, acrylamide (AM), and polyvinyl alcohol (PVA) with ammonium persulfate/sodium hydrogen sulfite (APS/SHS) as radical initiating system and N , N -dimethylene bisacrylamide as crosslinking agent in aqueous polymerization system at 60°C. This kind of SAR exhibited excellent properties of temperature tolerant, salt tolerant, and water absorbency (WA) deferred. The experiment results showed that the WA at 90°C was about two times than that at 25°C when SAR modified with PVA was immersed in water for 24 h. The absorbency of 0.9% NaCl solution increased from 5 to 60 ml/g when AM was introduced into the SAR networks.

Tribological properties of a series of aluminum matrix composites reinforced with AlB 2 particles developed for lightweight machinery parts intended for aerospace and automotive applications were evaluated. In this study, the worn surfaces of aluminum matrix composites containing copper and magnesium with different amounts of reinforcing AlB 2 dispersoids were examined by scanning electron microscopy to determine the effects of a pin-on-disk wear test. These observations also allowed identification of the probable wear mechanisms involved upon wearing against a martensitic stainless steel ball. The effect of chemical composition on the wear volume and wear coefficient was measured to establish the relationship between the reinforcing diboride content and matrix conditions and the corresponding wear response.

The microstructure of TiAl 3 composites with addition of different weight contents of solid lubricant (LiF, NaF, CaF 2 , and 38% CaF 2 -62% BaF 2 ) were observed by scanning electron microscopy. Hardness, bend strength, and fracture toughness tests were carried out on an electron omnipotence testing machine. The friction and wear tests were performed using a high-temperature pin-on-disc tribometer at different friction conditions such as different loads, different sliding speeds, and different working temperatures. The results show that TiAl 3 composites with 38% CaF 2 -62% BaF 2 solid lubricant exhibit higher bending strength and fracture toughness than composites with other solid lubricants. In addition, the wear rate of TiAl 3 composites with 38% CaF 2 -62% BaF 2 solid lubricant is lowest in all composites. It is attributed to 38% CaF 2 -62% BaF 2 solid lubricant forming a compact film on the wear surface of TiAl 3 composites. The compact-film-forming mechanism is attributed to fluoride particles forced out of the reservoirs due to its high thermal expansion coefficient.

This article primarily focuses on investigating the feasibility of enhancing the mechanical properties of Al 2 O 3 coatings on AISI 304 stainless steel specimen. Taguchi’s L 27 orthogonal array was used to optimize the microhardness of Ni-nano-Al 2 O 3 composite coatings over AISI 304 stainless steel specimen by pulsed electrodeposition method. Pulse frequency 10 Hz, duty cycle 20%, and peak current density 0.6 A/cm 2 are found to be optimal values. Moreover, the influences of the optimized pulse parameters over the microstructure, energy-dispersive X-ray spectroscopy (EDX), corrosion resistance, X-ray diffraction (XRD), and coating thickness of Ni-nano-Al 2 O 3 composite coatings were also investigated. The microhardness, microstructure, and texture of the composite coatings were significantly influenced by pulse frequency. The EDX results confirmed that the composites were fairly dispersed over the specimen. The hardness as well the corrosion resistance of the specimen was greatly improved.

In this study, the effects of fly ash on Khorasan mortar composed of brick or tile powder and lime were investigated to improve its mechanical properties. In the mixtures, fly ash was used instead of 0- to 4-mm crushed tile or 0- to 1-mm tile powder as aggregate. In addition, slaked lime was used as a binder, and 0–10–20–30–40% fly ash was replaced with crushed tile or tile powder. The consistency, hardened unit weight, ultrasonic pulse velocity, compressive strength and flexural strength before and after exposure to freeze-thaw, and the microstructure and chemical composition of specimens were examined. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and thermogravimetric analysis were conducted on specimens. On the basis of the results, notable improvements were observed in the mechanical properties of specimens with addition of fly ash.

In this study, effect of silica fume (SF) waste colemanite on properties of cement mortar was investigated. The parameters studied were initial and final setting times, specific gravity, specific surface, water demand, flow ability, volume expansion, compressive strength, and freeze-thaw durability. A number of mixtures were prepared by the replacement of Portland cement with SF and waste colemanite. The results showed that the initial and final setting times of cement pastes were generally retarded when the SF and waste colemanite replaced part of the cement. It was observed that the inclusion of SF increases compressive strength of the specimens in 28 days compared with that of the control concrete. However, those of the specimens with colemanite decrease both early and later days. Up to 10% and 12% colemanite content in the mixture, strength loss of specimens after freeze-thaw cycles is below the limit permitted.

In emerging countries, the driving elements for sustainable development are greenhouse and global warming concerns and the need for the development of low-CO 2 cements as replacement for Portland cement. Pumice is an aluminosilicate-type material that can be condensed with NaOH and Na 2 SiO 3 solution and can be used for green building with reduction in CO 2 footprint. The present paper highlights the effect of curing temperature on Hasankale pumice activation. Four curing temperatures have been investigated in this paper, 25°C, 45°C, 65°C, and 85°C, and 65°C has been confirmed as the best temperature for ground pumice activation. Furthermore, the aging effect has been studied at different curing temperatures. The aging of the samples before 28 days has a remarkable effect on compressive strength gain, but after 28 days this effect is inconsiderable for all heat treatment temperatures.

Carbon nanotube (CNT) is considered as a new generation of material possessing superior mechanical, thermal, and electrical properties. In this research, a multiscale finite element analysis is proposed to study the interaction between nanotubes and matrix at the nanoscale near a crack tip. The influence of the chirality and length of single-walled CNT (SWCNTs) on the stress intensity factor of epoxy/SWCNT were studied. It was found that the chirality, length, and radius of CNT have significant effects on the stress intensity factor of nanocomposites. Multiscale simulations from macro to nano or the reverse improved specification of toughness mechanisms.

The purpose of this paper was to investigate the stress distribution of adhesive single-lap joint loaded in the elastic and elastoplastic range. The stress variation across the adhesive length was achieved both analytically and numerically. A two-dimensional finite element solution presented a detailed picture of the stress behavior in a single-lap joint loaded in the elastic and elastoplastic range. After the finite element results matched very well with results obtained from analytic solution in the elastic range, it was decided that adhesive plasticity needed to be added to the finite element models in order to make them as accurate as possible. The residual stresses after elastic-plastic loading were calculated. The results obtained from numerical analysis showed that the residual stress was important as the joint strength can be increased by residual stresses. In addition, the effect of the adhesive length, thickness of adhesive, and thickness of adherends on the shear distribution of the adhesive was examined numerically by using elastoplastic finite element method. The target was to change the geometry of the joint and study its effects on the stress distribution in the adhesive.

In this paper, we combine a new higher-order layerwise formulation and collocation with radial basis functions for predicting the static deformations and free vibration behavior of three-layer composite plates. The skins are modeled via a first-order theory, while the core is modeled by a cubic expansion with the thickness coordinate. Through numerical experiments, the numerical accuracy of this strong-form technique for static and vibration problems is discussed.

A ceramic-polytetrafluoroethylene high-permittivity dielectric material-based split-ring patch antenna of dimensions 12 mm×16 mm is presented in this paper. The measured operating bandwidths (reflection coefficient <-10 dB) range from 5.0 to 6.5 GHz (1.5 GHz), 9.1 to 9.6 GHz (500 MHz), and 10.7 to 11 GHz (300 MHz) as observed from the proposed antennas. Average gains of 0.69, 3.52, and 3.48 dBi were measured at the first, second, and third band, respectively. Radiation efficiencies of 87.3%, 88.5%, and 93.1% were achieved at three resonant frequencies 5.6, 9.5, and 10.9 GHz, respectively. The measured symmetric and nearly consistent radiation pattern makes the proposed antenna suitable for C band and X band applications. In this paper, the effects of the dielectric properties of substrate material and design parameters have been studied.

In this study, an artificial neural network approach was employed to predict the effect of B 4 C size, B 4 C content, and milling time on the particle size and particle hardness of Al2024-B 4 C composite powders. Al2024-B 4 C powder mixtures with various reinforcement weight percentages (5%, 10%, and 20% B 4 C), reinforcement size (49 and 5 μm), and milling times (0–10 h) were prepared by mechanical alloying process. The properties of the composite powders were analyzed using a laser particle size analyzer for the particle size and a microhardness tester for the powder microhardness. The three input parameters in the proposed artificial neural network (ANN) were the reinforcement size, reinforcement ratio, and milling time. Particle size and particle hardness of the composite powders were the outputs obtained from the proposed ANN. The mean absolute percentage error for the predicted values did not exceed 4.289% for the best prediction model. This model can be used for predicting properties of Al2024-B 4 C composite powders produced with different reinforcement size, reinforcement ratio, and milling times.

One of the disadvantages of shear thickening fluid (STF) is high concentration. For better immersion of fibers, at first STF is diluted in ethanol, and then the fibers are left therein for a specified period in order to impregnate all fibers with the fluid. After this stage, to eliminate the ethanol in the sample, it is heated at a temperature range of 60–80°C. The composite’s sensitivity to the impact will be reduced through ethanol combining with the fluid and its elimination. Furthermore, by means of vacuum infusion processing method, without use of ethanol (or reducing its portion) and heating, lighter composite could be obtained. The fluid is distributed to the required extent among the fibers and the additional fluid that causes weight increase is discharged through vacuum. In addition, the bubbles among the fibers and fluid are removed by vacuum. Specimens with 3 and 5 layers have been tested. By comparing the nanocomposites and neat specimens, experimental results show higher ballistic limit in all of the nanocomposite specimens. Results show that the ballistic limit is highest in the VIP method.

One of the important concerns about the quality of the thermoplastic composite in automated fiber placement (AFP) process is the degradation of thermoplastic resin, resulting from the overheating or the lack of proper heating by the heating system used in the AFP machine head. Heat transfer between the heating system and incoming pre-impregnated tow is not easy to control and can result in energy loss or nonconsistent heating of pre-impregnated tow. Advanced control systems are used to control the key processing parameters of the nip point temperature of the heating system. In this study, two advanced control systems are designed by using the dynamic thermal model of the fiber placement process. One is linear quadratic regulator controller, which is implemented to achieve optimal results for quality performance. The other is model predictive controller, which is proved more efficient as the physical capacity, safety, and performance constraints of the heating system are explicitly addressed in the controller design. Polyether ether ketone reinforced with carbon fiber (APC-2) is used as the tow material in this study. The results of this study are presented including a comparison of the performance of the two control strategies through simulation study.

Milling glass fiber reinforced plastic (GFRP) composite materials are problematic, owing to, e.g., nonhomogeneous and anisotropic properties and effects of plastic deformation. To reduce these problems, the effects of cutting speed, feed rate, and the number of flutes on surface roughness and of thrust forces occurring during the milling of GFRP composite materials were investigated by both experimental and fuzzy logic models. Experiments were performed at 30 m/min, 60 m/min, and 90 m/min cutting speeds, at 0.1 mm/rev, 0.15 mm/rev, and 0.2 mm/rev feed rates and 10 mm diameters in a cemented carbide end mill, which has two, three, and four flutes without cutting fluids. The values obtained from experiments were defined by a fuzzy logic model. A fuzzy logic model was employed to estimate the surface roughness and thrust forces for different cutting parameters. As a result of both the experimental study and the fuzzy logic model, while the minimum thrust force was obtained at low cutting speeds, and feed rates and a high number of flutes end mill, the best surface quality was obtained at low feed rates, high cutting speed, and number of flutes end mill.

Aluminum-based composite reinforced materials produced in situ with titanium boride (TiB 2 ) particulates have higher potential for advanced structural applications where high specific strength modulus as well as superior temperature resistance is imperative. In the present work, aluminum alloy-titanium boride composites were developed using a new combination of in situ techniques. Electrical discharge machining studies were conducted on aluminum alloy-TiB 2 composite workpieces using a brass electrode. From the results, it is clear that the material removal rate and surface cracks of the workpiece increase with an increase in current and decreases with increase in the composition of titanium boride.

In this study, the free vibration behavior of an annular disc made of functionally graded material (FGM) with variable geometry is investigated. The elasticity modulus, density, and thickness of the disc are assumed to vary through the radial direction according to the power law so that the effects of their indexes on the natural frequency of the disc are investigated. The Poisson’s ratio is assumed as a constant. The natural frequencies of the disc are calculated for various boundary conditions by using classical plate theory, and the various types of mode shapes, which are described by the number of nodal diameters and nodal circles, are also discussed. Moreover, the effects of the ratio of the inner radius to the outer radius on the natural frequency are also considered. It is found that in order to increase the natural frequency, the elasticity modulus and thickness should be increased at the inner surface, whereas density should be increased at the outer surface. The natural frequency can also be increased by increasing the ratio of inner radius to outer radius. The results obtained are compared with the results of a finite-element-based commercial program, ANSYS ® , and found to be consistent with each other.

The aim of this experimental study is to investigate the buckling behaviors after impact of the composite plates. The increasing impact energies, which ranged from approximately 3–15 J, are performed at three different impact points of the composite plates having three different thicknesses until vicinity of the penetration threshold of specimens. After the impact tests, the effects of the different impact points, energy levels, and thickness on the buckling behaviors of the impacted specimens are investigated. Also, compared with nonimpacted specimens, the buckling loads are presented nondimensionally. As expected, the lowest critical buckling load occurs in thin plates impacted at the center point. The critical buckling loads become more stable both by increasing number of layers and in the impact points that are away from the center.