Effect of specimen size on the buckling behavior of laminated composites subjected to low-velocity impact

An experimental investigation was conducted to study the effect of specimen size on the buckling strains of composite laminates subjected to low-velocity projectile impact. The specimens were fabricated from a T300/5208 graphite/epoxy material with laminate configurations (+ or - 45,0,90)2s and (+ or - 45,0,90)4s. These 16- and 32-ply quasi-isotropic laminates were side-supported during testing. Specimens of three different length-to-width aspect ratios of 1, 1.5, and 2 were studied. The low-velocity projectile impact was provided by an air gun. The preload and impact energy combination necessary to cause catastrophic buckling failure was determined. The residual strength of specimens that survived the impact damage was also measured. The results were compared with those of a 48-ply laminate tested elsewhere. The present experimental results show that (1) specimen length does not seem to have any significant influence on the buckling strains at failure caused by projectile impact and (2) the influence of specimen thickness on strain at failure decreases as the velocity of the projectile increases.