Fracture characterization of knitting fabric reinforced laminated composites

Features such as strength and lightness come into prominence in the engineering application with the development of technology. This situation obligates the use of composite materials, which are as strong as metallic materials but lighter than the metallic materials, instead. Polymeric composites have been used in many engineering applications due to their high strength in proportion to their weight, high stability, rigidity, superior corrosion, and fatigue resistance. For this aim, glass and carbon fibers used as reinforcement materials in the polymeric composites must be improved in order to constitute more strength in the structures. Composite materials used as a structure material can be damaged during manufacturing, assembly, and usage of them. These damages can cause breaking of the construction under environmental effects and external loadings in some period of times. One of these damages is creating crack and fracture, which depends on crack propagation. Fracture, which is dangerous for composite structures, can cause loss of life and property. To improve safety level of the structures, strength value of materials for crack propagation named fracture toughness must be known. In this study, fracture characterizations of laminated composites reinforcing with hybrid and non-hybrid knitting fabric were investigated under different loading conditions. For this purposes, hybrid and non-hybrid fabrics were knitted in 1x1 rib knitting structure by using glass and carbon fibers. Non-hybrid fabrics were knitted with pure glass fibers (100%) and pure carbon fibers (100%) and hybrid fabrics were knitted with equal as weight glass-carbon fibers (50%-50%). Also, hybrid fabrics were knitted in 3 different pattern widths in order to investigate the effect of knitting pattern width on the fracture toughness. Laminated composites, which reinforced with knitted fabrics, were manufactured by hand lay-up method and Arcan test specimens having desired sizes were obtained from manufactured laminated composites. After that crack having 4mm length was created on the each manufactured Arcan test specimens. Fracture toughness of cracked Arcan test specimens were determined under mode I (0o), mode I-II (30o, 45o, and 60o), and mode II (90o) loading conditions. After Arcan tests, morphology of fracture surfaces was examined by using scanning electron microscope (SEM). Another study in this thesis is determination of fracture toughness of laminated composites, which reinforced with hybrid and non-hybrid glass and carbon fabrics by using J-integral method in ANSYS package program, numerically. Mechanical properties of each composite structure, which is needed for numerical study, were also determined experimentally.