Journal of Science and Technology of Composites
Year:2018 | Volume:5 | Issue:2 |Papers Count:16

According to the increase in using of polymer composite materials in industry, exact characterization of the material properties in different loading conditions, including high velocity impact is very important. In this article, the high velocity impact on non-hybrid and hybrid polymer composite panel has been investigated. After introducing the impact load types and theories used for damage evaluation and comparison of them, the matzenmiler theory has been employed to predict damage. In this theory, in order to predict more accurate damage evaluation, the shear stress is considered nonlinear in elastic region. Afterwards, in order to use the theory in the finite element modeling, a VUMAT subroutine is implementated in the Abaqus software. Finally, the obtained results from the present modeling and analysis, are compared with available experimental data for non-hybrid and hybrid composite panels. The good agreement between the theoretical results and experimental data, introduces the ability of the applied model and provided subroutine.

this study, mechanical and thermal properties of a two-phase polymeric matrix composite including polypropylene and EPDM, reinforced with glass fibers and graphene nanoplates is investigated. Compounds were containing 0, 1 and 2 wt. % of graphene nanoplates and 10, 20 and 30 wt. % of glass fibers and 10 and 15 wt. %EPDM, which were prepared by an internal mixer. Samples for mechanical testing were obtained by a hot press machine. Mechanical and thermal tests were performed to determine the impact strength, tensile strength, modulus of elasticity and melting and crystallization temperature of compounds. It was observed that by using of glass fibers, impact strength was increased 46% and tensile strength and elastic modulus were increased slightly compared to the basic ingredients PP / EPDM. By using of up to 1 wt% of graphene nanoplates, impact strength was increased 16%. The more graphene nanoplates used resulted in a decrease in intensile strength. Adding geraghene nanoplates generally increased elastic modulus up to 13%. Also by adding of EPDM, impact strength of the samples was increased 18% but theirother mechanical peorperties were decreased. Graphene nanoplates also slightly increased the crystallization temperature of samples but their melting temperature have not been affected.

The structures realized using sandwich technologies combine low weight with high energy absorbing capacity, so they are suitable for applications in the transport industry (automotive, aerospace, ship building industry) where the “ lightweight design” philosophy and the safety of vehicles are very important aspects. While sandwich structures with polymeric foams have been applied for many years, currently there is a considerable and growing interest in the use of sandwiches with aluminum foam (AFS) core. The aim of this paper was the analysis of low-velocity impact response of aluminum foam sandwich panels in two different types (integral skins and bonded skins) and the investigation of their collapse modes using computed tomography (CT). A theoretical approach, based on the energy balance model, has been applied to investigate their impact behavior and the model parameters were obtained directly from the measurements carried out on CT images of the impacted sandwiches. The AFS structures are relatively intact compared to the more catastrophic and localized fracture of the polymeric sandwiches, so the mechanical properties and their performance after imact will be better than polymeric sandwiches.

Nowadays, fiber-metal laminates (FMLs) have gained many applications in aviation, marine and automotive industries. These structures include thin metallic face sheets bonded to the composite prepregs. Internal damages in FMLs are difficult to detect and repair by conventional methods. To overcome this, in the present study a self-healing polymeric system based on chopped hollow glass tubes has been introduced and employed to recover the flexural strength of Al-2024/E-glass-epoxy/Al-2024 specimens after damage. The micro-tubes were located next to each other in pairs and filled with restorative agents (epoxy resin + amine hardener). The aim of this study was to find a suitable volume fraction and also the optimum time to achieve the maximum healing efficiency. Various volume fractions of filled tubes containing 5, 8 and 11 vol. % healing agent together with different time passing period of 3 and 5 days after primary damage were employed. The results demonstrated that the maximum healing efficiency for flexural strength (89%) was observed for the specimen with 8 vol. % healing agent after passing 5 days from the time of damage creation.

Fibre reinforced composite (FRC) structures require reliable and economical design. Under monotonic or cyclic loads the stiffness of FRC laminates is reduced. The corresponding analysis is called as the ‘ ‘ progressive failure analysis” . Which includes determining damage initiation and evolution up to structural failures. Several failures criteria of composite laminates have been developed. These criteria have a significant effect on the analytical response of FRC laminates. In this paper a comprehensive review on the general methodologies of the damage constitutive modeling is presented. For the first time, the invariant-based failure criteria for multi-layer materials together with Hashin two and three-dimensional criteria are implemented and investigated. The analysis is performed by using a constitutive material model (UMAT) developed and implemented in the finite element software ABAQUS. Twelve samples in two groups are used to evaluate failure criteria. The accuracy of numerical results is compared by experimental data taken from literature. The modeling results obtained by using invariant-based failure criteria can predict the experimental data with a maximum error of 5%.

Thermal stability characteristics of functionally graded material (FGM) cylindrical shells surrounded by elastic medium under axial load are investigated in this paper. Firstly, governing equations based on the first-order shear deformation theory of Sanders-Koiter for the cylindrical shell resting on elastic foundation are derived by using Hamilton’ s principle. The governing partial differential equations are converted to algebraic ones by using the Galerkin’ s method and thermal buckling load is obtained. The material properties of functionally graded materials are assumed to be graded in the thickness direction according to the power law. The elastic medium is assumed as two-parameter Pasternak elastic foundation that consists of Winkler and shear terms. Temperature distribution across the shell thickness is considered in three types: uniform temperature rise, linear and nonlinear temperature change. Two solution methods are used in case of nonlinear temperature distribution as series and exact analytical solutions and their effects on critical temperature of the shell are investigated. It is shown that series solution method yields different results with respect to exact analytical solution. Critical temperatures of isotropic cylindrical shell with simply supported boundary condition under uniform temperature rise and linear temperature distribution cases are obtained and compared with results in the literature. Based on the validated theory, the effects of temperature distribution, FGM configuration, elastic foundation and axial load on thermal stability of the shell are investigated.

In this paper, the process of manufacture of mold for lattice cylindrical composite is studied and lattice composite samples has been manufactured by the filament winding process. Also, the structural behavior of lattice semi-cylindrical composite made by glass/Epoxy with has been studied under high velocity impact by experimental and numerical analysis. A gas gun testing machine has been used for high velocity impact test that recorded the input and output velocities. Also, for this test, suitable fixture has been designed. The cylindrical projectile with hemispherical head has been used as impactor. Numerical simulation of impact tests has been conducted by ABAQUS commercial finite element code and the results have been verified by experimental results. Output velocity, surface damage, the separation between the shell and the rib are compared experimentally and numerically. Finally, numerical investigation of the shape of the projectile and the layup orientation has been done. Results show that45 degrees angle of layup has minimum output velocity and maximum energy absorption. Also, the projectile with flat head has been created maximum area damage, because of theless area contact with shell relative to another projectiles, therefore has less output velocity and more energy absorption.

In this paper, a numerical method is developed in order to predict the crack growth in multi-layerd composites. Reddy's layerwise theory is em employed to truly calculate the the interlaminar stresses and afterward the accuracy of results are satisfied by Abaqus finite element software. Then the capability of solving problems in the presence of delamination, as the most important cause of composites failure, is added to the elaborated model. In fallows, the J-integral method, which the integral is independent of the path around a crack, is introduced and by using the this method, the initially layerwised model is improved. Also, failure in structure is controlled by strain energy release rate; This means that firstly the process of computing total stiffness matrix of structure using layerwise element is described and nodal displacements and stress-strain fields in elements are extracted. Subsequently the possibility of predicting the crack growth is achieved by calculating the 3D J-integral using the criterion of strain energy release rate at crack front. Finally, the developed numerical model is validated by comparing the its results with the results of available analytical models and it is perceived that the model, despite being unique, is more similar to some of the analytical solutions.

Nowadays, piezoelectric transducers are widely applied because of their capability to convert environmental energies (e. g. mechanical vibrations) into the electrical energy. In an energy harvester structure, not only piezoelectric characteristics but also properties of the non-piezoelectric part of the energy harvesting structure are highly important. Therefore, in the present research, electrical energy generation from forced vibrations of a composite beam with the piezoelectric layer is considered. For this purpose, firstly, the governing equations of the system are obtained using Euler-Bernoulli beam theory. Then, Kantorovich method was used to calculate the output voltage for a composite beam with the piezoelectric layer. To verify the analytical method, the results were compared to the finite-element modeling results. Furthermore, the effects of fiber orientation angle and layup arrangement in the composite beam with piezoelectric layer on the amount of harvested energy were investigated. According to the obtained results, by increasing the elastic modulus of the composite beam and its effect on the damping ratio of the structure, considerably higher energy is harvested. Then, the effects of composite beam dimensions, the ratio of composite beam thickness to the piezoelectric layer thickness, the concentrated mass, and the damping ratio on the amount of harvested energy were studied. The results show that using the composite materials and by proper design of layup and fiber orientation angle in each layer, it is possible to get different equivalent elastic modulus in the composite beam, and consequently alter natural frequency of the system and output voltage amplitude of the circuit.

Hydroxyapatite has been studied intensively for bone repairing and replacement applications due to its biocompatibility, bioactivity and the ability of bonding to bone. Despite the poor mechanical properties of hydroxyapatite, its unique biological properties leads to study improvements of its properties rather than completely replacing it with other biomaterials. One of the ways to improve the properties of Hydroxyapatite as a bioceramic, is preparing composite based hydroxyapatite. In this study, Nitinol was used as a reinforcer phase in order to improve the mechanical properties of hydroxyapatite. Pure hydroxyapatite (HA) was obtained by the calcination of calf femoral bone. Then the hydroxyapatite composite reinforced with 5, 10 and 15 wt% Nitinol was successfully produced by powder metallurgy. In order to examine the changes that occurred in the composite phases after sintering and fracture surface, XRD, FTIR and SEM were used, respectively. Also, the compressive strength was measured to compare the bone properties. The results showed that hydroxyapatite composite with 10% Nitinol has the sutable conditions. It also optimized the mechanical properties compared to other compounds considered.

In present investigation, hard claddings treatment was performed on st37 steel using two cored wires containing Fe-B and Fe-B-C powder-based by FCAW (Flux Cored Arc Welding) method during three stages of single pass, two-pass and three-pass welding process. Results indicated that the increasing of welding pass numbers for both welding wire, boron percentage was improved from 2. 3 to 3. 18 wt. % at weld metal due to more presence of boron in welding melt which caused volume increase of welding wire at each welding pass. Microstructure observation and phase analysis using optical and scanning electron microscopes and X-ray diffraction (XRD) results also expressed that the using of Fe-B electrode for single pass welding process caused to create a ferrite matrix and α-Fe2B eutectic; for two-pass welding process compared to single pass ferrite islands have been decreased, while the amount of α-Fe2B eutectic have been increased. Third pass of welding process caused to form α-Fe2B eutectic and primary particles of Fe2B which had columnar shape. Presence of carbon in Fe-B-C electrode will form pearlite islands beside primary Fe2B. Also, at third pass of welding process by both electrodes, very low amount of FeB phase would be formed around the Fe2B primary phase. Formation of FeB compound related to segregation of boron element during welding and non-equilibrium solidification. The increase in hardness can also be attributed to an increase in the amount of boron due to the increasing number of welding passes.

In the present study, the effect of particle size in micro and nano scale on curing reaction kinetic of Styrene Butadiene Rubber (SBR)/Zinc oxide (ZnO) composite was investigated using non-isothermal differential scanning calorimetry (DSC) at four heating rate. The experimental results were analyzed by both “ model free” and “ model fitting” approaches and curing kinetic triplet, i. e., Pre-exponantioal factor [A], activation energy [Ea] and reaction orders [n, m] were determined. The results of Ozawa, Kissinger, Borchard and Daniel modified methods revealed that activation energy and pre-exponantioal factor of the curing reaction of SBR/ZnO decrease in the presence of nano particles. Meanwhile, these results indicated to more decrease in activation energy with increasing of nano-ZnO percent. Similarly, the results of isoconversional method confirmed the activation energy reduction in presesence of ZnO too. This reduction can be attributed to activation properties and catalytic effect of ZnO in presence of a saturation acid by forming a complex that exhibited more efficiency with increasing the surface by decreasing the particle size of zinc oxide. Additionally, a good agreement between experimental data and auto-catalytic model is found for all heating rates and the models can predict the behaviour of curing reaction of this composite.

Nowadays, composites are being widely used in automotive, aerospace and military industrials. Woven composites are considered as a one of textile composites. In present study, tensile behavior of carbon and Kevlar woven composites were investigated by finite element method. Weave pattern of woven fabric was twill 2×2. In the first step, a unit-cell of composite was created in TexGen software in meso scale. After that, unit-cell was imported in ABAQUS software to finite element (FE) analysis. After FE analysis, a python code was applied in meso model to calculate mechanical coefficient of composite. The mechanical coefficients of composite were assigned in macro model. Then tensile test was done on macro model and results of FE analysis were compared with experiment results. The results showed that, tensile properties of model propose good agreement with experimental results. Therefore, meso model can be used to calculate mechanical properties of composite. Using multiscale method also leads to increase precision and solving reduction.

In this study the behavior of a novel 3D integrated weft knitted sandwich composite (3DIWKSCs) were investigated. The weft knitted spacer fabrics produced by E-glass fibers on a flat knitted machine with tow cross-sectional shapes (rectangular and triangular). The 3DIWKSCs manufactured by use of the vacuum assisted resin transfer molding (VARTM). The results of the 3DIWKSCs with tow cross-sectional shapes under drop-weight impact tests in three energy levels showed that the triangular-shape of 3DIWKSC has the higher strength in all energy levels of impact than the rectangular-shape of 3DIWKSC. Furthermore the contact force of 3DIWKSCs was increased by increasing of the energy level of impacts. The main damage modes of 3DIWKSCs under impacts were the transverse cracks on the upper face-sheets and the cracks on the connecting layers of the core. Also, by increasing the energy level, cracks occurred in the lower face-sheets as the curved area and the local indentation were created underneath the impactor. There is no any de-bonding between the core-face of the 3DIWKSCs under drop-weight impact tests.

In recent years, different SPD methods have been attention of researchers to produce metal matrix multi-layered composite and to achieve good mechanical properties and microstructure. Among SPD methods, CARB process is inspired by ARB which has the ability to produce metal composites with better mechanical and microstructural properties. In this investigation, for the first time, aluminum composite matrix consisting of 5% pure nickel powder was produced by CARB in eight pass. Microstructure and mechanical properties of produced composite were evaluated in the different cycles of CARB process by optic and scanning electron microscopy, elemental analysis, uni-axial tensile test, microhardness, respectively. Results of microstructure showed that the bonding between the layers in the first passes is weak and there is a porosity in structure but by increasing the passes and after 8 pass, in produced composite, distribution of nickel powders and oxide layers has better than previous cycles, and porosity reduced. By increasing the number of CARB passes, tensile strength and microhardness increased continuously. The reason for this increase is due to the governing mechanisms in the process of SPD, and the nickel powder did not contribute much to this increase. Also, the amount of elongation after a severe drop in the initial sandwich, increased by increasing the pass until the end of the eighth cycle, continuously with a low increase rate. The tensile strength and microhardness increased 3. 88 and 2. 5 times, respectively, compared to the annealed sample.

In this study the foaming dynamics and cell microstructure of polystyrene (PS) and polystyrene/nanosilica nanocomposites containing n-pentane foaming agent were investigated. In order to evaluate the nucleation and growth of bubbles in samples, in-situ microscopic observation method was used, and their foaming process in a discontinuous system was investigated. Nanocomposites were prepared by solution mixing method and their rheological properties were determined by rheological test. The contact angle method was used surface tension measurements. Incorporating of nanosilica into PS matrix decreased the contact angle and increased the surface tension of the samples. In order to investigate the foaming dynamics of samples, sheets with thickness of 200 μ m were saturated in a high temperature and pressure chamber. Foaming dynamics was studied by the designed system. The temperature effect on the foaming dynamics was investigated in the samples containing of 3 %wt. n-pentane. Although the nucleation and growth rate of bubbles with temperature increasing from 140 to 160 º C has almost been doubled, but broader cell size distribution was observed. In nanocomposite samples the nucleation has been increased compared to polystyrene, and the onset of nucleation has been dropped. By increasing n-pentane content to 5 %wt., the nucleation in nanocomposite samples was significantly increased compared to polystyrene. For further investigation of the final microstructure of foams, scanning electron microscopy (SEM) images were prepared and the results showed that silica nanoparticles have generated more uniform cells in the final microstructure.