Band 21, Heft 2

A series of poly(imide-ether)-clay nanocomposite materials-based 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and 1,3-bis(4-aminophenoxy)propane and layered sodium montmorillonite (MMT/Na + ) clay were successfully prepared by in situ reaction through thermal imidization up to 200°C. Poly(amic acid) ( 6 ) was prepared through the reaction of 1,3-bis(4-aminophenoxy)propane ( 4 ) and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride ( 5 ), and then a thermal plan of imidization was used for the synthesis of nanocomposite materials. The resulting nanocomposite films containing 0.5, 1, 3, and 5 wt.% of organoclay were characterized by Fourier transform infrared spectroscopy, wide-angle powder X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis, respectively. The introduction of organoclay in the polymer resulted in improved thermal stability.

This work is based on the dry sliding wear and cyclic oxidation of composites deposited on a TA1 substrate using laser melting deposition (LMD) technique, the parameters of which are such as to provide almost crack-free composites with minimum dilution and very low porosity. To our knowledge, it is the first time that Stellite SF12-Al-FeSi-B 4 C mixed powders are deposited as hard composites by LMD technique. Scanning electron microscopy results indicate that such composites with metallurgical joint to a TA1 substrate were formed. It is noted that many nanocrystalline/amorphous phases are also produced, which improve the surface performance of such composites. Compared with the TA1 substrate, improvement of cyclic oxidation and wear resistance are obtained for such composites.

In this paper, carbon nanotubes (CNTs) were added to activated carbon to enhance the mesopores. At first, different amounts of CNTs were added to phenolic resin and composite spheres were synthesized by suspension polymerization. Then, by carbonizing these spheres at 600°C followed by steam activation at 850°C for more than 90 min, we prepared highly developed porous CNTs/activated carbon composite spheres. The composite spheres were characterized by a laser particle size analyzer, scanning electron microscopy, Raman spectrum, and nitrogen adsorption-desorption isotherms. Results showed that the composite spheres had good sphericity even with high proportion of CNTs (45 wt.%). Analysis also showed that the pore size distribution of the composite spheres containing CNTs was “multi-peak”, especially with 20–100-nm pores. The improved 20–100-nm porous structures in the composite spheres can be ascribed to aggregated pores of CNT bundles. The amount of vitamin B12 adsorbed on the 45 wt.% CNT composite spheres was as high as 32.38 mg/g. The spheres could be used as adsorbents for middle-molecular-weight toxins or large molecules in hemoperfusion.

Pseudoelastic fiber-reinforced metal matrix composite with enhanced ductility and energy absorption capacity was developed. This composite system relies on the distributed nature of large pseudoelastic strains to mitigate localization of inelastic deformation and failure, and thus mobilizes a major fraction of volume for effective energy absorption. The pseudoelastic fibers were made of Ni-Ti-Cr alloy used in conjunction with two different matrices, aluminum and copper. Tension and pull-out tests were performed to evaluate the ductility and energy absorption capacity of control and pseudoelastic fiber-reinforced composites. Experimental results confirmed the ability of pseudoelastic fibers to induce distributed inelastic deformation within metal matrix composites for realizing major gains in ductility and energy absorption capacity.

The present work aimed to study the tensile and impact behaviour of fly ash particle reinforced aluminium matrix composites. Fly ash particles reinforced aluminium (Al/3Cu/8.5Si) matrix composites were fabricated by the stir casting technique. Three different size ranges of fly ash particles (50–75, 75–103 and 103–150 μm) were used. The composites were subjected to tensile and impact tests. The tensile and impact fracture surfaces of the aluminium alloy and composites were investigated using a scanning electron microscope to characterise the fracture mechanism of the composites. The tensile strength of composites increased, while the ductility and impact strength of composites decreased with an increase in fly ash particle content. The fracture surface of the unreinforced material was characterised by uneven distribution of a large number of dimples resulting in ductile failure. In the case of composites, the presence of hard and brittle reinforcement particles in the ductile aluminium matrix places constraints on the plastic flow of the matrix leading to brittle failure with an increase in fly ash particles.

The main objective of this study was to investigate the effect of paraffin application technique on the quality properties of particleboard. The paraffin was applied to the wood particles in three different techniques: (1) before resination, (2) after resination, and (3) with resin. The modulus of rupture, modulus of elasticity, internal bond strength, thickness swelling, surface roughness parameters, contact angle, and formaldehyde emission of the boards were determined. Statistical analysis showed that paraffin application technique had a significant influence on all properties of particleboards. The boards made using technique (1) had the highest mechanical properties and lowest surface roughness, formaldehyde emission and contact angle values. The worst properties were obtained from the board made using technique (2).

The thermal conductivity of wood flour (WF) filled high-density polyethylene composites (wood plastic composite, WPC) is investigated experimentally as a function of filler content and temperature. Samples are prepared by compression molding process of previously blended and extruded WPC pellets, up to 50% weight content of WF. The thermal conductivity is measured by the heat flow meter technique in a temperature range from -15°C to 80°C. Experimental results show that the WPC thermal conductivity decreases with temperature and WF content, with the last effect due to the increase in porosity with the filler content, as confirmed by density measurements. Using the thermal conductivity of bare WF, the thermal conductivity of the wood material in WPC is estimated. This value successfully predicts the upper and lower bounds of the WPC thermal conductivity by means of the parallel and series conduction model of a multiphase composite material.

This study represents an in situ polymerization by preparation of tetrafunction polyester acrylate mixed with 1,6-hexanediol diacrylate/clay nanocomposite by digital light processor rapid prototyping. The morphology of nano-clay fillers and the dispersing agent in the photopolymer matrix are investigated by scanning electron microscopy (SEM). Degradation temperature, tensile strength, impact strength, and hardness are characterized by using thermogravimetric analysis, universal tensile machine, Izod impact tester, and hardness shore A tester, respectively. Results show that the effect of clay loading with an appropriate amount of dispersant tends to significantly increase not only the tensile strength and hardness but also the degradation temperature of photopolymer/clay nanocomposite; however, the impact strength is not affected. In the same conditions, as visualized on SEM images, the nanocomposite tends to form the exfoliated structure with agglomeration of clay, which is caused by uneven distribution of nano-clay in the photopolymer matrix.

This paper investigated the effect of the incorporation of basalt fibers on the tensile properties of carbon fiber-reinforced epoxy laminates manufactured by vacuum-assisted resin transfer molding. The purpose of this research was to design a carbon-basalt/epoxy hybrid composite material that is of low cost in production, is lightweight, and has good strength and stiffness. The tensile strength and stiffness of the hybrid laminates demonstrated a steady, linear decrease with an increase in basalt fiber content, but the fracture strain gradually increased together with the increase in the basalt layer content. In this study, the incorporation of basalt fibers into the carbon fiber-reinforced polymer (CFRP) showed lower tensile strength than CFRP but has higher tensile strain. Furthermore, we found that the arrangement and enhancement of basalt fiber into the CFRP significantly influence the mechanical properties of interply hybrid composites.

In this study, the boundary element method is presented for the prediction of longitudinal modulus of aligned discontinuous fiber-reinforced composites. The details of the boundary element formulation model covering infinite friction (stick) contact conditions are given. Both fiber and matrix materials are assumed to display linear elastic material behavior. The formulation is applied to boron/epoxy discontinuous fiber-reinforced composites. The computed results show a very good agreement with the modified Cox model and the finite element analysis with experimental data.

Simulation of fracture by using numerical methods is important to treat geometries that change in time. In this study, both numerical and experimental investigations are presented for the delamination under mode II loading, detailing the derivation of the formulations in numerical simulations of fracture. The simulation of the delamination under mode II loading based on the cohesive segments model was investigated by using a meshfree method. Then, an experimental investigation was used to verify the meshfree method’s results. For tests under mode II loading, three-point end-notched flexure specimens, which are made of carbon/epoxy laminate (AS4/3501-6) which consists of 10 plies in [0] 10 and [0/90/0/90/0] s lay-up with delamination inserted in the middle of the laminate, were used for the interlaminar fracture toughness tests. The problem was solved for [0] 10 , [0/45/-45/90/0] s , [0/90/0/90/0] s , [0/90/0/90/30] s , [0/90/0/90/45] s and [0/90/0/90/60] s laminates with mid-plane delaminations, and the results were verified for different composite materials. The critical fracture force, which can be experimentally measured, was used to calculate the mode II delamination fracture toughness of the carbon/epoxy laminate. In addition, values of the integral for 209 (11×19) and 253 (11×23) background meshes with equivalent interval sizes were compared. For a relatively fine background mesh, the critical load was converged. Results obtained from the meshfree element-free Galerkin method showed very good agreement with experimental data for single-mode delamination under mode II loading. The results presented will help in the implementation of mesh design techniques that protect numerical accuracy while minimizing computational expense.

In this study, the efficiency of artificial neural networks (ANN) in predicting the shear strength of reinforced concrete (RC) beams, strengthened by means of externally bonded fiber-reinforced polymers (FRP), is explored. Experimental data of 96 rectangular RC beams from an existing database in the literature were used to develop the ANN model. Eight different input parameters affecting the shear strength were selected for creating the ANN structure. Each parameter was arranged in an input vector and a corresponding output vector that includes the shear strength of the RC beam. For all outputs, the ANN model was trained and tested using a three-layered back-propagation method. The initial performance of back-propagation was evaluated and discussed. In addition, the accuracy of well-known building codes in predicting the shear strength of FRP-strengthened RC beams was also examined, in a comparable way, using same test data. The study shows that the ANN model gives reasonable predictions of the ultimate shear strength of RC beams (R 2 ≈0.93). Moreover, the study concludes that the ANN model predicts the shear strength of FRP-strengthened RC beams better than existing building code approaches.

Free vibration analyses of angle-ply laminated composite beams were investigated by the Gâteaux differential method in the present paper. With the use of the Gâteaux differential method, the functionals were obtained and the natural frequencies of the composite beams were computed using the mixed finite element formulation on the basis of the Euler-Bernoulli beam theory and Timoshenko beam theory. By using these functionals in the mixed-type finite element method, two beam elements, CLBT4 and FSDT8, were derived for the Euler-Bernoulli and Timoshenko beam theories, respectively. The CLBT4 element has 4 degrees of freedom (DOFs) containing the vertical displacement and bending moment as the unknowns at the nodes, whereas the FSDT8 element has 8 DOFs containing the vertical displacement, bending moment, shear force and rotation as unknowns. A computer program was developed to execute the analyses for the present study. The numerical results of free vibration analyses obtained for different boundary conditions were presented and compared with the results available in the literature, which indicates the reliability of the present approach.

In this paper, the nonlinear dynamic behavior of a long hollow cylinder consisting of temperature-dependent functionally graded material (FGM) subjected to thermal shocking is investigated. Material parameters of the FGM hollow cylinder, except the Poisson’s ratio, are assumed to be graded continuously through the thickness according to the power law expressions, and they are assumed to be temperature dependent. The governing equation of the motion of the FGM hollow cylinder is obtained based on the plane-stain theory and together with the governing equation of the transient heat transfer problem is solved by the finite difference method, Newmark method, and iterative method. Numerical examples are carried out in which the Si 3 N 4 -SUS304 FGM hollow cylinders are considered, and some valuable dynamic thermoelastic characteristics of the FGM hollow cylinder subjected to symmetric or asymmetric thermal shocking are revealed.

The fracture behavior of quasi-brittle material exhibits commonly brittle behavior with some ductility in the fracture processing zone. Therefore, a matrix of experimental works is performed to investigate the failure behaviors based on a parameter known as brittleness number, which is a measure of brittle behaviors. Glass fiber-reinforced epoxy laminates of three stacking sequences, cross-ply [0/90] 2s and two quasi-isotropic [0/45/90] 2s and [0/45/90/-45] s , are manufactured using hand lay-up technique. A matrix of different specimen geometric scaling with open hole of the same material is used. The fracture energy G IC and nominal strength of these composite laminates are measured experimentally using compact tension test, center crack specimen, and tension test, respectively. The results showed that the increase of homogeneity of composite laminates, which is introduced by inserting a certain angle ply for the laminate structure, enhanced the material ductility as the brittle number increased. The larger size of specimen leads to the increase of brittleness for the same stacking sequences due to the increase of stress concentration factor.

Hemp fiber-reinforced green composites with organoclay-filled poly(butylene succinate) (PBS) matrix were fabricated by pultrusion process. Morphological studies revealed that the clay particles were intercalated/partially exfoliated when the clay content was lower than 6 wt%. The tensile modulus and strength of PBS/25% hemp composites were 15 and 2.9 times of the neat PBS. By adding organoclay to the PBS/hemp composites, the tensile properties of the hybrid composites generally reflected the similar change with the organoclay modified PBS matrix. Upon certain duration of environmental exposure, the degradation of tensile properties of hemp/organoclay/PBS hybrid composites was retarded compared with hemp/PBS composites.

Efforts have been made to improve the line speed and consequently the economy of the pultrusion in last few years, but most of the reported work focuses on the kinematics of the curing reaction and different resin systems. Pultrusion is a fast cure process where heat is supplied through heaters to start and complete the curing process inside the die to get quality product at relatively high speeds. This work has extended the previous studies and quantifies for the first time the duty cycle of the heaters of a typical process to establish a relationship between the duty cycle and the specific energy consumption (SEC) of the process. It is shown experimentally and analytically that preheating the precursor would result in higher line speeds and shorter duty cycle, thus contributing to the reduction in SEC by up to 30%.