Experimental and Simulation of Compression after Impact (CAI) Tests for Thermoplastic Composite Materials

Abstract Damage caused by low velocity impacts in composite materials may go undetected, resulting in significant damage being unnoticeable. This phenomenon has been studied using experiments and simulations on a typical composite material, Toray T1225 LM-PAEK UD Tape, following impacts with varying energy levels. To the authors’ knowledge, there is a lack of information on thermoplastics and compression after impact (CAI) in the publicly available literature, and there have been insufficient results and discussions regarding CAI tests on thermoplastic composite materials at the relatively high levels of impact used, especially with the rise in the use of thermoplastic materials for the advanced air mobility market. This paper provides experimentally gathered data and describes a numerical approach to aid in the prediction of CAI strength for materials that are of interest to the advanced air mobility market. It has been observed that compressive strength decreases significantly even for a range of damage growth and levels of impact energy. This decrease occurs with damage (dent depth) below 0.1 inches (2.54 mm (mm)) and impact energy well below 30 Joules, even though the resulting damage may be barely visible. Finite element (FE) simulation was carried out to better understand the development and growth of damage in the composite material during the CAI tests. There exist a few restrictions to implement a high-fidelity CAI model. Dynamic instability resulting from the impact must be suppressed during compression by employing mass scaling with a significantly low target time increment. The complexity of problems and need for detail make current models take days to run, even on high performance computing (HPC) clusters. Therefore, a “simplified” CAI test was implemented in ABAQUS using symmetric boundary conditions (BCs), even when the composite had +/-45° plies and lacked full symmetry. This approach allowed testing different quarters of the full CAI specimen to identify which one showed the most damage and lowest compressive strength. The design ultimate load (DUL) has been selected based on the experimental and simulation results, considering a safety factor suitable for the ranges of static loadings when barely visible impact damage (BVID) occurs.