The fracture toughness and strength of materials are adversely affected by the cracks in the materials, which can be induced during manufacturing, assembly, and usage. In this study, the effect of crack length and crack location on the fracture toughness of woven glass and carbon reinforced hybrid and non-hybrid composite plates were investigated experimentally and numerically. For this purpose, glass/epoxy (G 8 ), and carbon/epoxy (C 8 ) non-hybrid composite plates and glass-carbon/epoxy (G 2 C 4 G 2 ), and carbon-glass/epoxy (C 2 G 4 C 2 ) hybrid composite plates were produced by using hand lay-up method. The fracture toughness of hybrid and non-hybrid composite plates having three different crack locations as single edge crack (SEC), center crack (CC), and double edge crack (DEC) with different crack lengths were obtained by determining failure loads under tensile loading. The ANSYS finite element package program was used in order to determine the fracture toughness of hybrid and non-hybrid composites by means of J-Integral methods. The results showed that the highest and the lowest fracture toughness values were obtained in the specimens with SEC and CC, respectively. POLYM. COMPOS., 00:000-000,

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Recently, for making the low-cost engineering materials the use of natural fibers as reinforcement in polymers composites has brought forth a lot of interest. The use of natural products instead of synthetic materials reduces the amount of carbon released into the atmosphere. Nevertheless, reuse of used materials by recycled is important both for the environment and for economic reasons. In this study, flexural behaviors of sandwich composites manufactured by using natural and recycled material were investigated. In this context, 9 different core materials, which were made by using 3 different granules size (1 mm, 2 mm and 4 mm) and 3 different core thickness (4 mm, 8 mm and 12 mm), were manufactured from waste vehicle tires. After, sandwich composites were produced by combining the core materials with natural jute fabric reinforced laminated composites. In order to test the usability of the produced sandwich composite materials as building material, the flexural behaviors of the sandwich composite were investigated under three-point bending load. Test results show that flexural behavior of the material varies according to the granular size and thickness of the core material.

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Cracks can occur in the composite structures during production, assembly, or usage. Environment temperature, deformation rate, and crack geometry have a direct influence on the fracture behavior of laminated composites. In this study, the fracture behavior of S-2 glass/epoxy composites having different crack geometry at different temperatures and deformation rates was investigated experimentally and numerically. Within the scope of the study, the fracture toughness (K) and strain energy release rate (G) values of samples with 5 mm crack geometry were calculated for the crack tip opening conditions in Mode I and Mode I/II. Fracture tests at different environmental temperatures were performed to investigate the effects of temperature on fracture behavior. Fracture tests were achieved at three different deformation rates, to exhibit the relationship between crack initiation and deformation rate. Also, the fracture behavior of S-2 glass/epoxy laminated composites was analyzed by using the finite element method (FEM). S-2 glass fabric reinforced composite is used as a new alternative to traditional building materials, especially in the aviation, space and military industries. The results obtained from the experimental and FEM studies of this composite structure showed that different environmental and loading conditions were effective on the fracture behavior of the composite structure.

Decreasing natural resources and increasing environmental destructions dispatch researchers to find more ecological solutions in material industry. Natural fibers have recently become an interesting topic as an alternative reinforcement material for fiber reinforced polymer composites for researchers. In this study; the effect of knitting density, natural fiber type, crack length, and fabric direction (wale or course) on the fracture strength and fracture toughness of laminated composites reinforced with natural fiber knitted fabric were investigated. For this aim, plain fabrics made of 50/50 bamboo/cotton, 50/50 viscose/cotton, and 50/50 modal/cotton blended yarns were knitted with three different knitting density. After that; bamboo/epoxy, viscose/epoxy, and modal/epoxy laminated composites were produced by using hand lay‐up method. Quasi‐static three‐point bending tests have been carried out on the single‐edge notched bending composite specimens, which have a crack in wale or course directions. Fractured surfaces investigated through the Scanning Electron Microscopy describing different failure mechanisms are also reported. Test results showed that fabric which knitted in cellulosic fibers, reinforced composites, had higher flexural strength and fracture toughness in the wale direction. It has also been observed that the knitting density and crack geometry affect the crack propagation behavior. POLYM. COMPOS., 40:217–228, 2019. © 2017 Society of Plastics Engineers

Mechanical joining and adhesive bonding provide convenience for manufacturing of complex structures, which made of composite materials. Failure load is directly related with process parameters of mechanical joining or adhesive bonding. In this study, the effects of bonding angle, patching type (single side and double side) and patching structure on the failure load were investigated in the pultruded composite specimens. For this aim, the pultruded composite specimens, which bonded with five different bonding angles (45°, 51°, 59°, 68° and 90°) and five different bonding types as unpatched, single-side woven patch, single-side knitting patch, double-side woven patch and double-side knitting patch were exposed to tensile loads at room temperature. In the view of experimental results, the failure loads of bonded pultruded composite specimens were predicted by training six different artificial neural network algorithms. The only three best prediction results of Bayesian regularization, Levenberg–Marquardt and scaled conjugate gradient were given in the figures for better understanding.