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In this article, the behavior of wood, plywood, and oriented strand board (OSB) under high- and low-velocity impact loadings was investigated experimentally. For the high-velocity impact test, limit velocity (Vbl) and impact energy absorbed (Eab) were determined by subjecting the material to different impact loading by conical nose projectile. For the low-velocity impact test, the materials were subjected to four levels of energy—10, 39, 78, and 98 J—and the time history responses of velocity, energy, load, and displacement were obtained. Additionally, quantitative data for damage size are presented. The results show that in comparison with OSB and solid wood plates, plywood presents better characteristics in response to both high- and low-velocity impact loadings.

Metallic bone fixations, due to their high rigidity, can cause long-term complications. To alleviate metallic biomaterials’ drawbacks, in this research new Glass Fiber/Polypropylene (GF/PP) composite internal fixations were developed, and an investigation of their mechanical behavior was performed through in vitro biomechanical experiments. Short randomly oriented, long unidirectional prepreg, and long unidirectional fiber yarn were considered as reinforcements, and the effects on their mechanical properties of different manufacturing processes, that is, 3D printing and heat-compressing, were investigated. The constructed fixation plates were tested in the transversely fractured diaphysis of bovine tibia under axial compression loading. The overall stiffness and the Von Mises strain field of the fixation plates were obtained within stable and unstable fracture conditions. The samples were loaded until failure to determine their failure loads, strains, and mechanisms. Based on the results, the GF/PP composite fixation plates can provide adequate interfragmentary movement to amplify bone ossification, so they can provide proper support for bone healing. Moreover, their potential for stress shielding reduction and their load-bearing capacity suggest their merits in replacing traditional metallic plates.

The current study investigated the influence of incorporation of graphene nanoplatelets (GNPs) on quasi-static behavior of composite and fiber metal laminate (FML) panels. The unmodified and modified composite specimens and FML panels with 2/1 configuration were fabricated using a hand lay-up method and investigated through a quasi-static punch and indentation testing. The two sets of tests were conducted with a flat-ended indenter and the loading conditions were the same for all samples, except support spans which were varied. Following experimental testing, possible damages at the punch region were closely investigated and localized and global damages were observed. The results revealed that adding 0.2 wt% GNPs improved the strength and fracture toughness of specimens by delaying the failure modes. On the contrary, GNPs made the bonding between the aluminum and composite interface to weaken.

The human being has always been looking for optimal use of his surrounding materials and over the years, has managed to invent various structures with special properties. Lattice structures are widely used in various applications due to their lower weight and desirable compressive strength. An example of these structures is the honeycomb that is very popular and many studies have been done about it. A new type of lattice structures is auxetic structure that has negative Poisson’s ratio due to its geometry. This characteristic has caused auxetic structures to have unique properties such as high shear strength, indentation resistance and energy absorption. Investigation of energy absorption of auxetic structures is a subject that has not been studied in researches. In this study, the ability of some auxetic structure for absorbing energy is investigated at quasi-static and low velocity impact transverse loading. Specimens with three types of geometries (re-entrant, arrowhead and anti-tetra chiral) are fabricated using additive manufacturing method (3D printing). Discussion about energy absorption and failure mechanisms of all three structures were carried out and compared in both types of loading.

Mechanical properties and manufacturing processes of Glass Fiber/Polypropylene (GF/PP) composites for application of flexible internal long bone fracture fixation plates have been investigated. PP/Short Chopped Glass Fiber (PPSCGF), PP/Long Glass Fiber (PPLGF) and PP/Long Glass Fiber Yarn (PPLGFY) were used in fabrication of the fixation plates. The PPSCGF and PPLGF plates were made by the heat-compressing process and Three-dimensional (3D) printing method was used to make the PPLGFY ones. The values of Young’s modulus, tensile strength, flexural modulus and strength, and impact strength of the PPSCGF in the fiber longitudinal direction were found to be [Formula: see text]GPa, [Formula: see text]MPa, [Formula: see text]GPa, [Formula: see text]MPa and [Formula: see text]kJ/m2, respectively. Where, these values for the PPLGF were to [Formula: see text]GPa, [Formula: see text]MPa, [Formula: see text]GPa, [Formula: see text]MPa, and [Formula: see text]kJ/m2 and for the PPLGFY were to [Formula: see text]GPa, [Formula: see text]MPa, [Formula: see text]GPa, [Formula: see text]MPa and [Formula: see text]kJ/m2. These have been found to be in close agreement with the human bone properties. Furthermore, the strength and modulus values of the plates were reasonable to be used as a bone implant applicable for bone fracture reconstructions. Hence, the study concluded that the GF/PP composites are useful for load-bearing during daily activities and would be recommended as a choice in orthopedic fixation plate applications. It will help the researchers for development of new fixation designs and the clinicians for better patient’s therapy in future.

The employment of lightweight structures is one of the most important goals in various industries. The lightweight sandwich panel is an excellent energy absorber and also a perfect way for decreasing the risk of impact. In this paper, a numerical study of high-velocity impact on honeycomb sandwich panels reinforced with polymer foam was performed. The results of numerical simulation are compared with the experimental findings. The numerical modeling of high-velocity penetration process was carried out using nonlinear explicit finite-element code, LS-DYNA. The aluminum honeycomb structure, unfilled honeycomb sandwich panel, and the sandwich panels filled with three types of polyurethane foam (foam 1: 56.94, foam 2: 108.65, and foam 3: 137.13 kg/m3) were investigated to demonstrate damage modes, ballistic limit velocity, absorbed energy, and specific energy absorption (SEA) capacity. The numerical ballistic limit velocity of sandwich panels, filled with three types of foam, was more than that of a bare honeycomb core and unfilled sandwich panel. In addition, the numerical results showed that the sandwich panel filled with the highest density foam could increase the strength of sandwich panel and the numerical specific energy absorption of this structure was 23% more than that of unfilled. Finally, the numerical results were in good agreement with experimental findings.

The paper investigates the addition of Nano-Al2O3 powder (alumina, Average Particle Size: 20 nm) on the characteristics of the Medium Density Fibreboards (MDF) made by the forest fibers. Some impor...

This study proposes a new theoretical model for high-velocity impact in two kinds of targets, Kevlar/elastomer and Kevlar/epoxy composites, and comprehensively discusses and compares these. In this analysis, with the aid of hyperelasticity theory, energy absorption equations are derived based on the linear and nonlinear behavior of constituents to assess the dependence of the ballistic limit on the interaction of the first, second, third, and fourth layers of the laminate on each other. Furthermore, to investigate the matrix effect on the in-plane shear, tensile tests were performed at [Formula: see text] direction for both Kevlar/elastomer and Kevlar/epoxy composite laminates. The results indicate that the adhesion of Kevlar fibers to the rubber matrix is more substantial than their adhesion to the epoxy matrix, increasing the failure shear strain of elastomeric composites and reducing the debonding between the fiber and the matrix which led to greater ballistic velocity. The results of the experimental tests verified the proposed model and confirmed its precision. With this verified model, the thickness effect on the ballistic behavior of the targets was investigated.

Gradient distribution of vascular structure made the bamboo wall structure so effective which improved the load-bearing capacity of such bio-mimicked energy absorption structures and modify the crush behavior of thin-walled composite tubes. In this research, the influence of the layering design and stacking sequence on the crush behavior, failure mechanism and absorbed energy of bamboo-inspired GFRP composite tubes is assessed experimentally and numerically. Quasi-static compression tests were conducted to explore seven permutations of Coarse Woven (CW), Fine Woven (FW), and Unidirectional (UD) E/glass fiber sheets, taking into account the longitudinal vascular bundles strengthened by organic matrix. Samples were fabricated employing a modified hand laying up method by using mechanical pressure to obtain better surface finishing and interlaminar adhesion compared to conventional hand layering up methods. To evaluate the corresponding crashworthiness parameters and characterize the crushing behavior of composite tubes, quasi-static axial compressive loading was done. The numerical simulations were validated versus experiments by a commercial finite element (FE) LS-DYNA integrating material model 54. The predicted load-displacement curves and failure mechanisms of FE analysis demonstrate acceptable correlations with visual observations during experimentation. Furthermore, the parametric numerical was performed to examine the effect of different distributions of vascular bundles. The FE analysis results revealed that the crushing behavior of bio-inspired composite tubes depended substantially on layering configuration and the stacking sequence design. The outcomes showed that the combination of woven and unidirectional fibers, respectively, located in the inner layer and hoop direction provide the optimal layering configuration design in terms of crush length efficiency, crush load efficiency, Specific energy absorption, stable progressive crushing, and better manufacturing quality.

This paper presents an analytical model for the high-velocity impact behavior of autoclaved aerated concrete (AAC) blocks under flat-ended cylindrical projectile. This model employs an energy balance approach to derive the governing differential equations related to the process. The model considers four energy absorbing mechanisms including crushing, tensile fracture, plug kinetic, and friction loss. A closed-form solution was presented to the derived governing differential equations using singularity functions. Singularity functions were used to incorporate discontinuities due to various energy absorbing mechanisms. Results of the present model are reasonably in good agreement with presented experimental results. The effects of various impact parameters on the residual velocity and energy absorption were studied and the results are reported, discussed and commented upon.

This paper presents a comparison of behavior and energy absorption of neat Kevlar fabric and polymer matrix composites under high velocity impact loading . Two types of matrices including rubber and thermoset (epoxy) matrices were used in order to study the effect of a hard and brittle matrix compared with the soft and flexible matrix on energy absorption of the composite. Moreover, two types of rubber matrix with high hardness (HH) and low hardness (LH) were used in this study to investigate the effect of rubber matrix formulation on impact resistance of composites. Ballistic impact tests were performed by firing a 10 mm hemispherical projectile onto neat fabric and composites in a velocity range of 30–150 m/s for two- and four-layer samples. Results show that the matrix affects the ballistic performance of composites significantly. Rubber matrix enhances the energy absorption of the fabric by keeping composite flexibility. Increase the number of layers for Kevlar/rubber composite results in better ballistic performance. On the contrary, the thermoset matrix leads to an inflexible composite that restricts the fabric deformation and has a negative effect on the fabric’s ballistic performance. Finally, damage mechanisms were discussed in detail for each sample.

This study aims to investigate the quasi-static and high strain rate deformation of an aluminum-based metal matrix composite reinforced with Al2O3 nanoparticles. The addition of Al2O3 nanoparticles with an optimal weight percentage increased the strength and energy absorption capacity of the composite material. The deformation characteristics of the material were found to be strain rate sensitive. It was concluded that the usage of an optimal weight percentage of nanoparticles results in a markedly higher energy absorption capacity in a variety of strain rates of deformation. Moreover, the energy absorption capacity of the present metal matrix composites increased significantly at the higher strain rates of deformation. It was found that the excessive addition of nanoparticles to the metal matrix decreases the energy absorption capacity as well as strain rate sensitivity of the composite material.

One of the best nondestructive techniques to evaluate the buckling behavior of imperfection-sensitive structures is the vibration correlation technique (VCT). This paper presents an analytical formulation for the free vibration of axially loaded composite lattice sandwich cylinders (CLSC) and numerical and experimental validations of the VCT applied to such structures. From an analytical point of view, the equations are obtained through the Rayleigh-Ritz method considering first-order shear deformation theory (FSDT). For the numerical verification of the VCT, three types of linear and nonlinear finite element analyses are performed. At first, numerical results for the critical buckling load and the first natural frequency at different load levels are compared with the corresponding analytical ones, validating the numerical models. Then, the numerical models are extended considering geometric nonlinearities and imperfection to simulate the variation of the first natural frequency of vibration with the applied load. As well, a nonlinear buckling analysis is also performed using the Riks method for a better comparison of the VCT results. In the last section, four specimens are fabricated using a new rubber mold and a filament winding machine. Additionally, the experimental buckling test is carried out, verifying the results of the VCT approach. The results demonstrate that the maximum difference between the estimated buckling load using the VCT approach and the corresponding nonlinear and experimental buckling loads is less than 5%, being the VCT result more accurate than the numerical one. Moreover, the proposed VCT provided a good estimation of the buckling load of the CLSC, considering a maximum load level of at least 62.1% of the experimental buckling load.

This paper aims to investigate the performance of an aluminum–rubber composite plate under impact loading. The impact resistance of the plate has been evaluated using both experimental and numerical methods. The experimental tests were carried out using gas gun at velocities of 75, 101, 144 and 168 m/s. The energy absorption of composite plates has been closely examined for all samples. The effect of rubber layer positioning either on front face or on back face of the aluminum plate was also evaluated. It was found that the composite plate with rubber on front face provides higher performance to absorb the energy. In parallel to the experiment, a finite element model was created using the finite element software LS-DYNA to simulate the response of the aluminum–rubber composite plate under a high energy rate loading condition. The data obtained from finite element modeling shown a close agreement with the experimental results in terms of failure mechanism and energy absorption. In addition, a parametric study was carried out incorporating different impact velocities, rubber formulation, rubber layer thickness, interface bonding strength between rubber and aluminum layers and ballistic performance of aluminum-rubber sandwich panel. It was concluded that by increasing the rubber layer's thickness the energy absorption of the composite plate will be increased, especially when rubber layer placed in front face of the aluminum plate. Although at high interface bonding of rubber and aluminum layer, the composite with rubber layer in front face has better performance, but low bonding of interface lead to higher energy absorption in back face configuration.

This study presents the response of rubber panels subjected to high-velocity impact loading. The mechanical properties and impact performance of rubber panels are altered by the variation in compound ingredients. To investigate the effect of compound ingredients, two types of rubber panels with high (SHA70) and low hardnesses (SHA45) were prepared, and mechanical properties and impact resistance of the panels were measured by high-velocity impact tests in a velocity range of 70–160 m/s. Ballistic limits of about 80 and 94 m/s were obtained for the low- and high-hardness rubbers, respectively, which show that the energy absorption of rubber panels increases as filler loading content increases. In this respect, the finite-element simulation has been performed to investigate the ballistic performance of rubber panels numerically. Rubber panel has been modeled using the LS-DYNA software and employing the experimental results of tensile test to characterize the behavior of panel. The findings show a good agreement between the numerical and experimental data. To study the effect of projectile’s shape, impact resistance of the rubber panels against hemispherical projectiles with different length-to-diameter (L/D) ratios (projectiles with diameters of 8, 10, and 12 mm) was measured and the model was also used. The results demonstrate that energy absorption of the panel increases as the diameter of projectile increases. The energy absorbed by the rubber panels appears in the form of damages that lead to increase their damage zone.

In this article, the quasistatic penetration tests were investigated on unfilled and polyurethane foam filled honeycomb sandwich panels. Failure mechanisms, specific energy absorption, interaction ...

This paper investigates the eccentric low-velocity impact of Fiber metal laminates (FMLs) subjected to spherical projectile using a unified Zig-Zag plate theory. The presented zig-zag plate theory enforces transverse shear stress continuity through the thickness and can be reduced to conventional plate theories using appropriate shape function. The governing equations and suitable boundary conditions are obtained using the principle of minimum total potenital energy . Runge-Kutta method is employed to solve initial value problem resulted by the method of Ritz. The present model is validated by comparison and good agreement between its results and those of reports in open literature. Influence of various specifications of impact phenomenon such as laminate thickness , projectile radius, projectile velocity , in-plane load and eccentricity parameter is examined on deflection and contact force time history. The obtained results indicate that continuity of transverse shear stress is required to achieve accurate contact force even for moderately thin FMLs.

In this study, two computationally efficient and accurate solution methods for heat transfer analysis in composite metal cylindrical vessel subjected to internal thermal load are presented. In order to accurately account for the thickness effects, the layerwise theory is employed to approximate the temperature field. In the first solution method, differential quadrature method (DQM) is implemented to discretize the resulting equations in the both spatial and time domains. In the second approach, DQM is applied to discretize equations in the axial direction while Newmark's time integration scheme is used to solve the problem in the time domain. The fast convergence rate of the methods is demonstrated and their accuracy is verified by comparing the results with those obtained using ABAQUS software and also with the exact solutions. Less computational efforts of the proposed approaches with respect to the finite element method is observed. Furthermore, comparative studies are performed and it is found that layerwise theory provides the capability of precise modeling of laminated composite shells.

In the present study, static behavior of short hybrid laminate beams was investigated using a unified zig-zag theory (ZZT) containing various beam theories as special cases. This theory satisfies transverse shear stresses continuity in the interface of layers via piece-wise continuous arbitrary shape functions. The principle of virtual work was employed to derive unified equilibrium equations and suitable boundary conditions. The present theory obviates the need for stress recovery for continuous transverse stresses. A general solution was presented to analyse high transversely anisotropic laminates under several kinds of transverse loads (general lateral, sinusoidal and point load) and non-linear thermal loads. The validity of this model is demonstrated by comparison of its predictions and good agreement with published results in literature. Numerical examples were given to investigate the impact of the transverse anisotropy on displacement, strain and stress fields through the thickness. The results show that the piece-wise continuous exponential and sinusoidal shape functions provide more accurate transverse stress distribution in comparison with other shape functions. In addition, the results show that the continuity of transverse shear stress through the thickness plays an important role in analysing transversely anisotropic laminated beams. A comparison of present ZZT and existing exact elasticity solutions shows that the current theory is simple and efficient.

Sandwich tube structures bio-mimicking horsetail and human tendons offered significant improvement over traditional single and multi-cell tubular energy absorbers. The present research aims to investigate three manufactured hybrid multi-cell aluminum and GFRP sandwich tubes subjected to quasi-static and low-velocity axial compression . The crashworthiness characteristics and axial crushing failure mechanisms of sandwich tubes are discussed and compared with the quasi-static axial behavior of single Al and GFRP tubes. Further investigations, based on the validation of an FE model versus experimental results, using the commercial finite element code LS-DYNA, on the effects of material permutation and inner tubes diameter are perceived through the full-factorial approach of FE parametric study . The quasi-static results revealed that, packing the Al and GFRP tubes in the form of multi-cell sandwich tube generally improves the crushing patterns of individual hollow tubes. Moreover, the low-velocity response of the hybrid multi-cell sandwich tubes showed that the crushing response of the GFRP components despite AL ones depends significantly on the strain rate , where Al tubes undergo irregular diamond deformation. Eventually the results of bio-inspired hybrid multi-cell sandwich tubes indicate that incorporating more GFRP tubes provided an optimal crashworthy design and conduce to a broad range of applications within aerospace, transportation.

The main focus of this review is on soft composites, relatively new to the literature. The ballistic fabrics, mechanism of ballistic energy absorption and parameters affect the ballistic performance of fabrics are reviewed. Adding shear thickening fluid (STF) and natural rubber (NR) to fabric and their potential to enhance the impact performance of woven fabrics are considered. Shear thickening mechanism, parameters influence the Shear thickening and impact response of fabric/STF composite are explored. Numerical modelling techniques for the estimation of impact resistance of fabric/STF are outlined. Also the role of shear thickening fluid in energy absorption of fabric/STF composite was investigated. Moreover mechanical and impact characteristics of elastomeric composites which contain one rubbery part as either matrix or completely separate media are explored as well, which have not been considered within previous review papers so far.

In this paper, experimental studies on the ballistic impact behaviour of nanomodified glass fibre-reinforced polymer (GFRP) are reported. The epoxy matrix of the GFRP was modified by the addition of graphene platelets (GNPs), carbon nanotubes (CNTs), combined hybrid hexagonal boron nitride nanosheets (BNNS)/CNT, and combined boron nitride nanotubes (BNNTs)/GNPs nanoparticles. Ballistic impact tests were carried out on GFRP laminates at two projectile velocities of 76 ± 1 m s−1 for full-field deformation measurements and 134.3 ± 1.7 m s−1 for perforation tests. The behaviour of the plates during impact was recorded using digital image correlation (DIC), in order to monitor strain and out-of-plane deformation in panels with nanoreinforced matrices. Following penetrative impact tests, pulse thermography was used to characterise the delamination of impacted plates. The results of full-field deformation, exit velocity and energy absorption measurements from the ballistic tests show significant improvements in impact resistance for the panels made from nanomodified epoxies relative to laminates with the unmodified epoxy matrix. The highest absolute absorbed energy was observed for the GFRP panels fabricated using the epoxy matrix loaded with BNNT/GNP at 255.7 J, 16.8% higher than the unmodified epoxy matrix.

Little is known about the impact behavior of composite fixation plate used in the fracture healing of long bones diaphysis. Hence, this study examined polypropylene composite fixation plates using different glass fibers and measured their biomechanical responses under axial impact loading experimentally and numerically. Short randomly oriented, long unidirectional prepregs and fiber yarn of glass were considered as reinforcements, and fixation plates were fabricated through two different heat-compressing and 3D printing processes. Furthermore, assessing the fixation plate structures impact behavior was carried out using in vitro impact test and finite element analysis (FEA). Impact damping behavior, damage mechanisms, and stress and strain pattern of the composite fixation plate structures were obtained under various bone fractures and impact energies. The impact load-time responses and the failure mechanisms demonstrated that fixation plate structures with more plastic behavior and lower stiffness could act as an initial shock absorber and dampen the transmission of axial impact load by distributing the impact energy over time. Therefore, considering the ability of stress shielding and adequate interfragmentary movement which amplifies bone ossification, the proposed Glass Fiber/PP (GF/PP) composite fixation plates could serve as a proper alternative in orthopedics.

In this paper, an analytical model has been developed for modeling high-velocity impact on ceramic/nanocomposite targets. In this model, the penetration resistance of the ceramic is determined based on the cavity expansion analysis. Also semi-angle of the ceramic conoid is modified. For modeling the back-up composite laminate, the kinetic and strain energy of yarns and shear plugging have been determined. Also the effect of nano-zirconia particles dispersed in the matrix of back-up composite, based on the ballistic performance of the ceramic/nanocomposite target, is investigated. Ballistic impact tests were performed to validate analytical predictions. Experimental results revealed an improvement in the ballistic performance of samples with nano-zirconia particles. The analytical predictions of ballistic limit velocity and residual velocity of projectile are found to be in good agreement with the experimental results.

In this paper, two different types of unstiffened and lozenge grid-stiffened E-glass/epoxy composite cylindrical shells are experimentally investigated under lateral compression. The composite shells are compressed in two different loading conditions; between two rigid flat platens and between a rigid flat platen and a rigid cylindrical indenter which is aligned perpendicular to the shell axis. The effects of the grid stiffeners on the stiffness, contact force and energy absorption capacity of the composite cylindrical shells are investigated in the two mentioned loading conditions. Incorporation of grid stiffeners in the composite cylindrical shells leads to an increase in the structural stiffness, contact force and energy absorbing capacity in both loading conditions. Furthermore, it is observed that the effect of the stiffeners on the structural stiffness is dominant in the elastic deformation stage of the compression processes. The results show that stiffening the composite cylindrical shells with lozenge grid stiffeners can increase the specific energy absorption almost twice in comparison with the unstiffened composite shells; and among all of the specimens, the grid-stiffened structures compressed between two rigid flat platens have the highest specific energy absorption, while the unstiffened structures compressed by the cylindrical indenter have the least capacity to absorb energy.

In addition to fiber properties, the fabric structure plays an important role in determining ballistic performance of composite body armor textile. Textile structures used in ballistic protection are woven fabrics, unidirectional (UD) fabric structures, and nonwoven fabrics. In this article, an analytical model based on wave propagation and energy balance between the projectile and the target is developed to analyze hybrid fabric panels for ballistic protection. The hybrid panel consists of two types of structure: woven fabrics as the front layers and UD material as the rear layers. The model considers different cross sections of surface of the target in the woven and UD fabric of the hybrid panel. Also the model takes into account possible shear failure by using shear strength together with maximum tensile strain as the failure criteria. Reflections of deformation waves at interface between the layers and also the crimp of the yarn are modeled in the woven part of the hybrid panel. The results show greater efficiency of woven fibers in front layers (more shear resistance) and UD yarns in the rear layers (more tensile resistance), leading to better ballistic performance. Also modeling the yarn crimp results in more trauma at the backface of the panel producing data closer to the experimental results. It was found that there is an optimum ratio of woven to UD materials in the hybrid ballistic panel.

Today composite structures are widely used in different industries. Since these structures are sometimes experienced impacts of low-velocity objects, evaluating the intensity of the damage due to the impact in these structures seems important and necessary. In this article, the effectiveness of the thermography method with three different thermal excitation sources, including the ultrasonic vibrothermography, infrared thermography with the heating element, and infrared thermography with hot airflow, for damage evaluation in CFRP and GFRP composite plates subjected to low-velocity impacts are investigated. The ultrasonic vibrothermography method is introduced as the most promising technique for damage evaluation in CFRP and GFRP composite plates subjected to low-velocity impacts, and the effect of the excitation power and excitation frequency on the effectiveness of this method is studied. To find the damage location in the thermography images in which the damage is not clear enough to be identified, the wavelet transform is applied while it is not suitable for calculating the damaged area. Finally, finite element (FE) simulations are carried out for the case of an internal defect. The results show the acceptable accuracy of the FE simulation in comparison with the experimental results.

This paper experimentally investigates the behavior of sandwich beam with auxetic core subjected to low-velocity impact loading. Two types of sandwich beams with different topologies of auxetic cellular cores were produced. Furthermore, a test procedure involving a cylindrical impactor was developed, and a parametric study was designed and performed. The results revealed that, at the same level of impact energy, the peak load decreased by increasing the re-entrant angle would make the auxetic sample with the highest re-entrant angle an ideal candidate for protective applications. However, in other applications where the structure needs to be protected from damage at a higher level of impact energy, the auxetic sample with the lowest re-entrant angle exhibited the best performance due to the highest amount of failure energy. Finally, the results showed that once the core structure changed from the conventional to auxetic, the energy level leading to damage to the structure increased so that it was escalated by a factor of 2 in the auxetic sample compared to the conventional sample. This is due to the negative Poisson’s ratio effect of structure that makes unit cells be drawn into the projectile impact area and, in turn, the structure is strengthened.

In this work, an experimental investigation of the high velocity impact resistance of syntactic foam core composite sandwich panel has been undertaken. The syntactic foams filled with ceramic microballoons of three different sizes and three different volume fractions. Also, to enhance the matrix strength of the foam core, some specimens reinforced with nano particles. The high velocity impact tests have been carried out using a light gas-gun and a 10 mm blunt-head steel projectile and the ballistic limit was measured. The Impact behavior and the failure mechanisms are thoroughly investigated and also the absorbed energy during projectile perforation was correlated to the damaged area of specimens. The test results show that the ballistic resistance decreases with increasing the volume fraction of microballoons and the panel with 40% volume fraction of microballoons has the highest specific perforation energy. Moreover, nano-reinforcing the syntactic foam core increased the ballistic limit velocity up to 10%.

In this paper, the experimental behavior of grid cylindrical composite structures, which are used widely in engineering structures, under ballistic impact is investigated. For this purpose, some grid cylindrical composite specimens were manufactured by the filament winding process and perforated by projectile using the ballistic gas gun. Incident impact velocity and exit velocities of projectile were recorded in each test. The results show that the presence of the ribs prevents pervading of damaged area of one cell to its adjacent cells. The structure behaves differently against projectile with velocity near ballistic limit and higher velocities. The results demonstrated that, by getting close to the ribs location, ballistic limit velocity was increased. However, due to reduction in energy absorption mechanisms in grid composite structures which are impacted in higher velocity than ballistic limit, projectile was exited of grid samples at higher velocity than unstiffened composite shells. Also, investigation of delamination in composite shell and ribs, debonding between ribs and shell (or separation of ribs and shell), residual velocity of projectile, damaged area of the grid specimens and the effects of curvature in two different velocities are presented and the results are discussed. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

This study aims to investigate the impact performance of composite panels consisting of plain-woven Kevlar fabric and rubber matrix. A finite element (FE) model in conjunction with experimental tests was developed to simulate the response of neat fabric and composite under impact loading. Each warp and weft yarn of fabric was individually modeled and combined with rubber matrix network to form the composite. To understand the effect of natural rubber on impact resistance of Kevlar/rubber composites, two types of rubber with different formulation were considered and their mechanical properties were obtained by split Hopkinson pressure bar tests and assigned to the model. Numerical results showed good agreement with the experimental data for both neat fabric and composite. It was shown that rubber matrix improves the ballistic performance of Kevlar fabric by keeping composite flexibility. High hardness rubber matrix composite has higher energy absorption capacity compared to the low hardness rubber matrix composite, due to presence of stronger intermolecular chains. Additionally, deformation and damage mechanism of fabric and composite were investigated under impact loading. The results were presented, discussed and commented upon.

This paper presents a closed-form model for the analysis of symmetric planar W-type shaped charges (WSCs) with two V-sections, which produce two primary cores and two primary jets. If these two V-sections have proper asymmetry, these primary cores will force two primary jets into a secondary core formed on the axis of symmetry of a planar symmetric WSC. For the analysis of such a planar WSC, a complete generalized model for an asymmetric planar V-shaped charge (VSC) with any desired order of asymmetry is mandatory. In this paper, the model is applied to describe the secondary jet formation in the WSC. By presenting a closed-form analysis of the WSC, the secondary jet specifications can be easily evaluated and, thus, can be compared with respect to the jet quantities in symmetric or asymmetric VSCs. Finally, for the primary and secondary jets, the coherency conditions are investigated, and the critical parameters responsible for these conditions are determined.

In this paper, analytical solutions of low velocity transverse impact of a nanoparticle (mass) on a nanobeam are presented using the nonlocal theories to bring out the effect of the nonlocal behavior on dynamic deflections. Impact of a mass on simply supported and clamped nanobeams are investigated by using nonlocal Timoshenko beam theory. In order to obtain an analytical result for this problem, an approximate method has been developed wherein the applied impulse is replaced by a suitable boundary condition. The dynamic deflections predicted by the classical theory are always smaller than those predicted by the nonlocal theory due to the nonlocal effects. Based on molecular mechanics, an improved 3D finite element (FE) model for armchair and zigzag single-walled carbon nanotubes (SWNTs) has been developed. Numerical examples for estimating Young's modulus of nanotubes are presented to illustrate the accuracy of this simulation technique. Based on this model, the maximum dynamic deflections of single-walled carbon nanotubes with different boundary conditions, geometries as well as chiralities are obtained and then compared with theory investigation. The simulation results demonstrated good agreement with analytical results. Furthermore, the mass and the velocity of the nanoparticle (striker) have significant effects on the dynamic behavior of nanobeams.

This paper presents a model that has less constraints than similar models and explains the collapse phenomenon in any desired order of geometrical asymmetries and in the presence of symmetric and asymmetric general-form wave fronts. It seems that, in this model, a complete generalized form of the classical jet formation theory has been developed. Available models that describe the symmetric jet and slug formation phenomenon are very good in such conditions. But the liner and confinement asymmetries, detonation wave front asymmetries, and other specifications, such as manufacturing tolerances, can affect the collapse and the behavior of the jet and slug. Some proposed models that describe asymmetric cases are not closed-form models or are only applicable for limited conditions, such as small asymmetries and a planar wave front. With the presented model, effects of concave, plane, and convex wave fronts on the off-axis velocity of the jet, other parameters of the jet and slug, and effects of an asymmetric wave front on jet formation for a completely symmetric liner and confinement geometry can be evaluated.

This article derives some theoretical relations to predict diagrams of absorbed energy and axial force versus axial displacement during the folding process in square and rectangular columns. By considering the folding wavelength as a constant parameter during the folds creation and using balance of internal and external energy and minimum principle in plasticity, final relations are calculated. Also, two different relations are introduced to predict the maximum folding force of the empty and polyurethane foam-filled columns with square and rectangular cross sections, by considering the interaction effects between column wall and foam-filler. Furthermore, some experiments were carried out on the empty and foam-filled metal columns and the experimental measurements were compared with predictions of the theoretical formulas that showed good correlation.

Bi-metallic corrosion resistant steel pipes were produced through explosive welding process. The weldability window of the stainless steel pipe (inner pipe) and the carbon steel pipe (outer pipe) was determined by the use of available semi-empirical relations. The impact velocity of the pipes as the most important collision parameter was calculated by the finite element simulation. Direct effect of the explosive mass reduction on the bonding interface of the pipes was studied. Optical microscopy study showed that a transition from a wavy interface to a smooth one occurs with decrease in explosive load.

GLARE is a fiber metal laminate that is a novel hybrid composite, consisting of thin aluminum and glass/epoxy layers. The main advantage of GLARE is its high fatigue and impact loading resistance. Also its areal density is lower than metals or composites when they are used alone. In fact, it has benefits of metals and composites simultaneously. In this paper some 2/1 GLARE laminates are manufactured and impacted by 8.7mm diameter blunt cylinder projectiles at energies up to that required to achieve complete perforation of the target using a helium gas gun. Aluminum and composite layers in these laminates have different thicknesses so the effect of changing thickness of aluminum or composite layers on the ballistic performance of GLARE, ie. Ballistic limit velocity and specific perforation energy, can be investigated. The efficient thickness ratio to maximize the specific perforation energy is obtained, too. The same tests are analyzed numerically by LS-DYNA and the results show good agreement with experimental data. The results are discussed and commented upon.

In this paper, forming parameters of tube hydroforming (THF) process are investigated and optimized using Simulated Annealing optimization algorithm linked with a finite element commercial code. The goal of this research is to obtain the maximum formability of two dimensional (2D) axisymmetric tubes under a failure criteria based on material's forming limit diagram (FLD). The initial approximated pressure loading path is determined by proved theoretical equations. Then the Simulated Annealing algorithm written in Matlab software is combined with a nonlinear structural finite element code ANSYS/ LS-DYNA in order to optimize internal hydraulic pressure. The results are compared by experimental observations and a good agreement was observed between them.