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To better understand mechanisms of fracture under impact loading in cellulose-reinforced polypropylene, dynamic fracture analysis was performed based on linear elastic fracture mechanics. Dynamic critical energy release rates and ...
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To better understand mechanisms of fracture under impact loading in cellulose-reinforced polypropylene, dynamic fracture analysis was performed based on linear elastic fracture mechanics. Dynamic critical energy release rates and dynamic critical stress intensity factors were deduced from instrumented Charpy impact test measurements. Dynamic fracture toughness increased with cellulose content. However, the assumption of linear elasticity began to break down for cellulose fiber contents exceeding 40% by weight. Scanning electron microscopy showed considerable fiber curl in the composites, especially at low fiber contents; at high fiber contents, composites developed a three-layer structure.
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the studies have been carried out on the damage initiation behavior of polymer matrix woven fabric composite plates subjected to a transverse central low velocity point impact load. Specifically, the effect of incident impact velo...
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the studies have been carried out on the damage initiation behavior of polymer matrix woven fabric composite plates subjected to a transverse central low velocity point impact load. Specifically, the effect of incident impact velocity and impactor mass for the same incident impact energy on the impact behavior has been investigated with a square plate of 150 mm X 150 mm X 6 mm. The material systems considered are: E-glass/epoxy and T300/5208 carbon/epoxy woven fabric composites. Inplane failure of the layers in the form of matrix cracking/ lamina splitting and delaminations were the primary objectives of the study. The studies have been carried out using an inhouse Finite Element Analysis code. The inplane failure functions and the interalminar failure functions have been predicted using quadratic failure creiteria. It is observed that the use of incident impact energy alone as a parameter to characterize the impact behavior is inadequate. Instead, the effect of both incident impact velocity and impactor mass should be considered separately.
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In this study, an appropriate fabric weight content controlled by the density of the warp and weft fibers is determined for biaxial warp-knitted composites referring to mechanical test results. Six different types of composite pan...
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In this study, an appropriate fabric weight content controlled by the density of the warp and weft fibers is determined for biaxial warp-knitted composites referring to mechanical test results. Six different types of composite panel with two different fabric weights (813 and 1187 gr/m(2)) and with three different stacking sequences [90(we)/0(wa)/90(we)/0(wa)](s), [90(wa)/ 0(we)/90(wa)/0(we)](s), and [90(wa)/0(we)/90(we)/0(wa)](s) are fabricated by using Resin Transfer Molding method. Having produced composite panels, drop weight impact tests are conducted on specimens. Microstructural characterization of impact tested materials is performed using optical microscope. The results of this study reveal that composites with biaxial warp-knitted preforms with lower weft and warp fiber densities (thin-ply) could absorb higher impact energies compared to those with higher weft and warp fiber densities (thick-ply).
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To improve the anti-blast ability of sheet molding compound (SMC) protective structure, basalt fiber reinforced polymers (BFRPs) are applied to strengthen SMC and improve its stiffness and strength. To simultaneously guarantee the...
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To improve the anti-blast ability of sheet molding compound (SMC) protective structure, basalt fiber reinforced polymers (BFRPs) are applied to strengthen SMC and improve its stiffness and strength. To simultaneously guarantee the overall and local rigidities, the panel adopts hierarchical orthogrid-stiffened structure. Explosion experiments were carried out to reveal the blast resistance of the BFRP reinforced SMC door. With much lighter mass, the BFRP-SMC protective door exhibits excellent anti-balst ability and would be an ideal substitute for metallic or concrete protective doors. Equivalent method based on identical volume and mode superposition was adopted to build dynamic theory of blast-loaded hierarchical stiffened panels. Equivalent static load method was adopted to predict the maximum displacement of the blast-loaded panel. These two methods are reliable and provide simple ways to design hierarchical stiffened composite protective structures.
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Present work intends to study the improvement of impact performance on sandwich composites by the addition of nanoclays. For this purpose, nanoclays Cloisite 30B were previously subjected to a silane treatment in order to improve ...
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Present work intends to study the improvement of impact performance on sandwich composites by the addition of nanoclays. For this purpose, nanoclays Cloisite 30B were previously subjected to a silane treatment in order to improve their dispersion and interface adhesion. Different incident impact energy levels were used and, for both sandwiches, the maximum load, displacement or elastic recuperation shows to be very dependent of the impact energy. Mathematical relationships are proposed to estimate the maximum impact force and displacement, based on the total impact energy and impact bending stiffness. Finally, sandwiches enhanced by nanoclays presented higher maximum impact loads, lower displacements, the best performance in terms of elastic recuperation and maximum residual flexural strength.
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This study has been designed to experimentally assess the changes of buckling loads of the E-glass fiber/epoxy composite laminates impacted at different impact energy levels. With the experiments conducted, the effects of the geom...
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This study has been designed to experimentally assess the changes of buckling loads of the E-glass fiber/epoxy composite laminates impacted at different impact energy levels. With the experiments conducted, the effects of the geometry parameters such as the ratio of impact point to the length of buckling (G = y/L) have been examined. According to the results of the experiments made, when the ratio of impact position is 0.2, buckling behaviors of the impacted specimens made at the energy levels of and under 10J have been determined to be almost the same as the buckling behaviors of the non-impacted specimens. Generally, it has been found out that buckling behaviors of the impacted specimens made at the energies under such levels of energy as 15J increase with the impact point ratio, and when the ratio is 0.2, buckling behaviors have been observed to be maximum.
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In this research, the experimental method of Taguchi design has been used in order to establish a relationship between the penetrating impacts with different parameters used in developing Kevlar-epoxy composites. Therefore, differ...
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In this research, the experimental method of Taguchi design has been used in order to establish a relationship between the penetrating impacts with different parameters used in developing Kevlar-epoxy composites. Therefore, different parameters like the fiber type, the sedimentation ratio, amount of filling materials and sample thickness have been studied. The effective parameters on material resistance in the ballistic test have been optimized using Taguchi test design method (Minitab15 software). The obtained results show that the best property combination between penetrating impact and impact resistance have been obtained by the layering ratio of 0.6, filling materials weight percentage of 50 % and thickness of 6 mm, respectively, for the composite of Kevlar 49 fibers in epoxy matrix.
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The compression fatigue behaviors of CFRP laminates with impacted or quasi-static indented damage for two material systems, CCF300/QY9511 and CCF300/5428, were compared in this paper. The same surface damages, characterized by den...
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The compression fatigue behaviors of CFRP laminates with impacted or quasi-static indented damage for two material systems, CCF300/QY9511 and CCF300/5428, were compared in this paper. The same surface damages, characterized by dent depth, were induced by low velocity impact (LVI) or quasi-static indentation (QSI) tests for the CFRP laminates. Using visual observation, C-Scan and thermal de-ply experimental measure methods, the surface damage and internal delamination of the specimens are described in detail to provide more information to understand the mechanical behaviors of impacted or quasi-static indented CFRP laminates. Static tests and staircase fatigue tests were performed to obtain the static compressive strength and compressive fatigue strength. The experimental outcomes show that the compressive fatigue strength of the quasi-static indented specimens is obviously greater than that of impacted specimens, while the specimens with quasi-static indented damages have a similar static compressive strength as those with impacted damages, for both material systems. Using QSI-induced damage to replace LVI-induced damage provides a roughly equivalent strength evaluation in static compression tests but exaggerates fatigue strength estimation in compression fatigue tests. (C) 2015 Elsevier Ltd. All rights reserved.
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The high velocity impact performance in hybrid woven carbon and S2 and E glass fabric laminates manufactured by resin transfer molding (RTM) was studied. Specimens with different thicknesses and glass-fiber content were tested aga...
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The high velocity impact performance in hybrid woven carbon and S2 and E glass fabric laminates manufactured by resin transfer molding (RTM) was studied. Specimens with different thicknesses and glass-fiber content were tested against 5.5 mm spherical projectiles with impact velocities ranging from 300 to 700 m/s to obtain the ballistic limit. The resulting deformation and fracture micromechanisms were studied. Several impacts were performed on the same specimens to identify the multihit behavior of such laminates. The results of the fracture analysis, in conjunction with those of the impact tests, were used to describe the role played by glass-fiber hybridization on the fracture micromechanisms and on the overall laminate performance under high velocity impact.
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PTFE/Al/W granular composite is a kind of impact-initiated energetic material and may well enhance damage to the impacted targets. To gain insight into response behavior of PTFE/Al/W granular composite under different loadings, th...
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PTFE/Al/W granular composite is a kind of impact-initiated energetic material and may well enhance damage to the impacted targets. To gain insight into response behavior of PTFE/Al/W granular composite under different loadings, the combined approach of experiments and theoretical analyses is used in this paper. More specifically, the combinations of quasi-static compression, dynamic tests, and ballistic impact experiments are conducted. Cylindrical PTFE/Al/W granular composite specimens, with a density of 7.7 g/cm(3) and a diameter of 10mm, are fabricated by cold press molding, sintering, and cooling. Moreover, a high-speed imaging technique is used to record response process of the specimens in ballistic impact experiments. The experimental and analytical results show that the response behavior of PTFE/Al/W granular composite is significantly influenced by the loading strain rate. When the strain rate is less than 3.6x10(3) s(-1), only mechanical response is observed in the quasi-static compression and dynamic tests. However, when the strain rate is higher than 4x10(4) s(-1), the chemical reaction is found in the ballistic impact experiments. Furthermore, chemical response shows an enhanced trend with increasing of the loading strain rate.
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