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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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