Damage trends in cryogenically cycled carbon/polymer composites

Influence of stacking sequence on leakage characteristics through CFRP composite laminates

“…Matrix cracks which play a role in leak path were not necessarily long enough to be detected by C-scans. Bechel et al [4] microscopically observed short cracks in 45°of CF/polymer (0/ 45/À45/90) S laminates after thermal cycles, which initiated from neighboring matrix cracks in adjacent layers. It was speculated that some of the cracks in the specimens C1 and C2 were too small to be detected in the C-scan image but connected the cracks in adjacent layers forming leak path.…”

“…Several studies [2,3] have shown that severe thermal strain at cryogenic temperature of liquid hydrogen might induce matrix cracks at relatively low mechanical loads. Even though the CFRP laminates are not mechanically loaded, thermal cycle between room temperature and cryogenic temperature induce matrix cracks in carbon fiber/toughened epoxy resin composites [4]. The continuous chain of connected matrix cracks in the CFRP laminates would cause the gas leakage [5], and the leak rate through damaged laminates is significantly higher than the diffusion rate through undamaged laminates [6,7].…”

Damage characterisation of cryogenically cycled carbon fibre/PEEK laminates

“…Due to the multiaxial nature of thermal loading, cracks may form in both the outer and inner ply groups [2,3] and may occur below the failure strength of the bulk material [4]. Overlapping microcracks in adjacent plies contribute to the formation of leakage paths through a damaged laminate, with factors such as stacking sequence, laminate thickness, and edge effects all affecting crack density and permeability [5][6][7][8][9][10]. With subsequent thermal cycles or increased amplitude of loading, delaminations may initiate from existing transverse cracks or from free edges.…”

A Self-sealing Fiber-reinforced Composite

“…Additional studies by Bechel and Kim [4] and Bechel et al [5] investigated how the density of thermally induced cracks varied with the number of cycles, ply thickness, and ply orientation. A later study, also by Bechel et al [6], examined how permeability of helium gas through the composite changed with the number of thermal cycles and adjacent ply orientation.…”