Predicting the upper-bound of interlaminar impact damage in structural composites through a combined nanoindentation and computational mechanics technique

Low-energy/speed impact damage of composite laminates is still challenging to simulate due to difficulties in measuring some key material properties. The present study develops an integrated numerical and experimental method for predicting interlaminar impact damage. A nanoindentation technique for measuring the stiffness properties of composites at a small length scale (nanometers) is leveraged to determine damage to composite laminates due to fast (microsecond) projectile impact. Specifically, nanoindentation is employed to measure the contact stiffness of an indenter and aerospace carbon/epoxy IM7/977-3 laminates with four different stacking sequences. Then, through a technique that combines nanoindentation and computational mechanics, an equivalent impact force approach is proposed to predict the upper-bound of interlaminar impact damage at impact energy levels of 5 and 10 Joules. Drop-weight impact experiments are conducted to validate the prediction results. In practical applications, estimating the upper-bound of damage is important for conservative and efficient damage tolerance designs, especially for thick composite laminates.