Thermally Induced Transverse Cracking in Graphite-Epoxy Cross-Ply Laminates

Abstract

Thermally induced transverse cracking in T300/5208 graphite-epoxy cross-ply laminates was investigated experimentally and theoretically. The six laminate configura tions studied were: [0/903] s, [02/902]s, [03/90] s, [90/03]s, [902/02] s, and [903/0]s. The thermal load required to initiate transverse cracking was determined experimentally and compared to theoretical prediction. Experimental results for the accumulation of transverse cracks, under cyclic thermal loading between —250°F and 250°F for up to 500 thermal cycles, are presented. The calculated in situ transverse lamina strength was deter mined to be at least 1.9 times the unidirectional lamina transverse tensile strength. All laminate configurations exhibited an increase in crack density with increasing thermal cycles.

Finite Element Modeling of Thermal Cycling Induced Microcracking in Carbon/Epoxy Triaxial Braided Composites

“…Figure 5 shows that the main damage in the material was the splitting of fiber bundles and that the microcracks developed in the direction of fiber orientation. This is similar to traditional laminates of which transverse cracks are the main damage induced by thermal cycles [9] . The microcracks were reported to span the entire cross section.…”

“…It was found that the damage was more extensive in 934 epoxy resin composites and included skin/core delamination. Adam et al [9] emulated the effect of a space environment for T700/5208 carbon epoxy resin specimens with various symmetrical lay-ups. He noted that no crack saturation was observed even after 500 cycles.…”

Thermomechanical Fatigue of Polymer Matrix Composites

“…Fiber splitting has also been reported in some materials [17]. Crack densities are generally observed to increase with the number of cycles until a saturation value is achieved [17,[22][23].…”

“…Unconstrained thermal cycling has been shown to induce microcracking in the transverse plies of polymer matrix composites [7,[15][16][17][18][19][20][21][22][23][24]. Fiber splitting has also been reported in some materials [17].…”

“…Crack densities are generally observed to increase with the number of cycles until a saturation value is achieved [17,[22][23]. Delaminations initiated by transverse ply microcracks have been reported [17,19,22] [16]. Toughening by the introduction of flexible segments into the epoxy network has been shown to improve resistance to microcracking [16], presumably by dissipating localized residual stresses.…”