Onset-of-growth behavior of mode II delamination in a carbon fiber composite under spectrum fatigue loads

摘要

End notched flexure (ENF) test specimens of unidirectional IMA/M21 carbon fiber composite were fabricated using standard autoclave process. A teflon insert was used to simulate a delamination at the mid plane. Three point bend tests were conducted under a modified mini-FALSTAFF spectrum load sequence with various reference strain energy release rate, G(ref) to determine the onset-of-growth of mode II delamination. The onset life was identified as 5% increase in compliance during the fatigue test. Onset fatigue life was observed to increase with decreasing, G(ref). Further, the onset-of-growth was predicted using empirical models. For this purpose, the mode II fracture toughness, G(IIc) and the constant amplitude fatigue data, G(max)-N-onset curves at two different stress ratios were determined and used to construct a constant onset life diagram (COLD). Following the general procedure of damage estimation, the onset-of-growth was predicted using the COLD and compared with experimental results. (C) 2015 Elsevier Ltd. All rights reserved.