Transverse Cracking of M40J/PMR-II-50 Composites under Thermal—Mechanical Loading: Part I — Characterization of Main and Interaction Effects using Statistical Design of Experiments

In this study, a novel conduction heating-based thermal cycling apparatus combined with large deflection bending is developed and utilized to identify the critical controlling parameters for microcracking of [90/0]1s, M40J/ PMR-II-50 high modulus carbon fiber/polyimide composite laminate under synergistic environmental conditions. The synergistic test involves four controlling parameters namely, average in-plane mechanical strains (0 and 0.488%), thermal cycling temperature amplitudes (—196—23 °C and —196—250°C), number of thermal cycles (1 and 8), and heating rate (1 and 4°C/min). The 2k factorial design is used for the four factors to provide their quantitative primary and interaction effects on crack density with a minimum number of experiments. The experimental results indicate that the number of thermal cycles is the primary controlling factor (41%), while the thermal cycling temperature amplitude (25%) or the in-plane strain (22%) is the secondary factor. The number of thermal cycles also exhibits a significant interaction effect on the development of microcracks when it was combined with either the temperature amplitude of thermal cycling (7%) or mechanical in-plane strain (5%).