Sandwich structures with carbon fiber-epoxy face sheets and polyvinyl chloride foam core material are known for their high strength and flexural stiffness despite their low weight. However, the structural response, in terms of crush strength, of the particles added sandwich structures are not very well known under impact loading conditions. In this study, the impact resistance and damage characteristics of particle added low weight composite sandwich structures were investigated with a low-velocity drop weight impact test device. Boron carbide (B 4 C) particles, which had excellent hardness, thermoelectric, and radiation absorbing characteristics, were used as an additive for the epoxy matrix. For this purpose, 2%, 5%, and 10% by weight additives were mixed into the epoxy matrix and sandwich structures were produced with hand lay-up followed by vacuum bagging method. All configurations were subjected to low-velocity drop weight impact test at three different energy levels (10, 17.50, and 25 J). The results obtained from the experiments and the images of the post-impact damage of the sandwich structures were presented comparatively. According to the test results, configurations containing 10% boron carbide (B 4 C) additive has shown the best performance in terms of resistance to impact load. K E Y W O R D S boron carbide (B 4 C) particles, carbon fiber reinforced polymer (CFRP), epoxy matrix modifying, low-density PVC foam core sandwich structures, low-velocity impact properties, radiation shielding barriers
In this study, flexural characteristics of low-density polyvinylchloride foam core sandwich structures consist of carbon fibre/epoxy facings hybridised with very thin stainless-steel wire mesh sheets were investigated. A comprehensive work was conducted considering the following design parameters: core thicknesses, wire mesh sizes, stacking sequences of wire mesh sheets and support span lengths for flexural tests. During the evaluation of flexural characteristics, experimental ASTM standards (C393, D3039, D7249 and D7250) were utilised. In addition, experimental flexural stiffness values were compared to analytically obtained results. By hybridisation of carbon fibre/epoxy facings with wire mesh sheets, significant improvements in flexural characteristics of sandwich structures were obtained. Besides improving bending behaviour and the larger amount of load-carrying capacity even at the same deflection values, the sandwiches with wire mesh sheets also prevented catastrophic sudden failure, which is the common case for carbon/epoxy/polymer foam core sandwiches. Response surface methodology was applied to evaluate the effects of the design variables on the load capacity of the sandwiches, and optimal solutions were revealed. The developed sandwiches can be good candidates in applications where both high stiffness-to-weight ratio and resistance to sudden failure are desired.
Composite materials are the combination of two or more materials to achieve certain improved or desired properties. And construction of the composite material can be performed by using a continuously distributed medium called as matrix. Metals, ceramic, glass and polymer materials are commonly used as matrix. The reinforcing material can be a metal, ceramic, glass, textile, polymer, or organic material in the form of lamina, fiber (short and long), particle, whisker, etc. Composite materials have emerged as a major class of structural elements due to their benefits such as lightweight, flexible, good impact strength, improved fatigue strength, high corrosion resistance, etc. Because of these advantages, composite materials are considered as a replacement of traditional materials which are used in the fields of aerospace, automotive, and other industries [1,2].
Sandwich structures offer innovative alternative solutions to many weight-critical industrial fields due to their lightweight and very high flexural rigidity compared to conventional materials. A vast number of sandwich configurations can be produced from a variety of materials for use as face sheets and core as well as matrix. Although there are many sandwich structures available in the literature to obtain the desired mechanical and physical properties, the usage of very low-density core materials is very limited. In this study, carbon and glass fiber fabrics having woven plain and ±45 ° fiber orientations and industrial PVC foam core having extremely low density of 40 kg × m−3 and 48 kg × m−3 were used for manufacturing the sandwich panels. Eight different configurations were constructed by hand lay-up followed by vacuum bagging. According to ASTM C393/C393M standard, the sandwiches were subjected to three-point bending (TPB) tests. After performing the TPB tests, the composite sandwich specimens were examined under a stereomicroscope to determine failure modes. The primary failure modes under quasi-static bending loading were found to be top face sheet failures due to fiber and matrix cracks and delamination, and core shear failures due to core crushing just below the top facing and core fractures. In addition, the consistency of the test results were verified and the effects of parameters were investigated by using statistical variance (ANOVA) and regression analysis. The study provides a valuable contribution to the literature regarding sandwich structures having extremely low-density foam core materials and may contribute to the material universe by introducing strong, stiff and lightweight sandwich composites. It provides a comprehensive comparison by considering the effect of different fiber types, fabric fiber orientations and core densities.
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