Experimental and numerical investigation of macro and micro damage behavior in composite structures

This thesis aims to reveal the micro and macro damage behavior of composite structures encountered in engineering applications and to improve them with innovative approaches. For this purpose, firstly, damage (erosion) behavior under solid particle impact of plain-woven glass fiber reinforced polymer (GFRP) composite, carbon fiber reinforced polymer (CFRP) composite, commercial 3M-8663 polyurethane (PU) tape, 304 stainless steel and pure nickel materials was characterized experimentally and numerically. Also, the solid particle erosion performances of the aforementioned materials were numerically determined for 0º angle of attack and different impact velocities (110, 150, 190 and 230 m/s) in wear shield of a helicopter rotor blade. Secondly, composite sandwich panels were manufactured by combining CFRP composite face sheets and in-plane and out-of-plane oriented thermoplastic core structures fabricated using 3D printers. Energy absorption and damage behavior of the composite sandwich panels under low-energy (20, 40 ve 70 J) impact were experimentally and numerically investigated. Lastly, the crushing characteristics and damage mechanisms under static compression load of the composite crash boxes with hollow and cellular (square, hexagonal) filled square, hexagonal and cylindrical outer surface, produced by vacuum bagging method using CFRP fabrics, were determined experimentally and numerically. As a result, the average erosion rate on the wear shield of the GFRP composite material was 10 times higher than that of the polyurethane material at high impact velocities (190 and 230 m/s). In terms of in-plane oriented cell pattern design, auxetic core based composite sandwich panel showed better impact resistance and energy dissipation ability than honeycomb core based composite sandwich panel. It was found that the addition of hexagonal cell filler to the hollow square type composite crash box increased the specific energy absorption ability by approximately 140%.