Interlaminar Mode II Toughness of Unidirectional CF-Epoxy Laminates Made of out of Autoclave Prepregs

Fatigue delamination of CF unidirectional laminates made of low temperature and vacuum bag cured prepreg, (out of autoclave-OOA), with MTM46 epoxy system was investigated under Mode II loading condition and the coefficients of the corresponding Paris equations were determined. The tests were carried out with the use of ENF beam specimens under displacement controlled conditions and at room temperature with the frequency, f=5Hz, and cycle parameter R=0.1. The crack length, a, was calculate based on the specimen compliance changes. For each specimen, for the entire range of load cycles, i.e. 1 nnmax, the a (n) relationship was approximated with the help of a single sigmoidal function and then the da/dn (n) relationship was determined. In addition, for the comparison purpose the 7-point approximation procedure recommended by ASTM E647 for the same purpose was applied. The differences in results produced by both the data reduction variants were presented for important variants stages and discussed.