Microscopic damage of quasi-isotropic carbon/epoxy laminates at various temperatures

Quasi-isotropic Carbon/Epoxy laminates under tensile loading are investigated to understand the effects of temperature on stress-strain response and damage progress including the interlaminar delamination growth behavior. The material system used is T800H/3631 and the stacking sequence is quasi-isotropic [0°/45°/-45°/90°]_s. The transverse crack behavior is microscopically observed and its density is quantitatively measured by using an optical microscope under various loads at different temperatures, i.e., low (-100°), room (25°) and high (150°) temperatures. The interlaminar delamination growth behavior is non-destructively examined by a scanning acoustic microscope (SAM). It is found that nonlinearity observed in the stress-strain response is caused by the large scale interlaminar delamination throughout the length of the specimen. The transverse crack propagation and interlaminar delamination growth behavior are obviously affected by the temperature environments. Characteristic transverse crack formation at the edge of -45° layer under -100°C is pointed out and its mechanism is discussed with the use of shear coupling of an off-axis lamina.