The effect of prepreg ply thickness in carbon fiber reinforced composites on intralaminar toughness and shear strength in cryogenic environments for liquid hydrogen storage tanks

This study investigates the effect of prepreg ply thickness on the intralaminar toughness and shear strength of carbon-fiber reinforced polymer (CFRP) in room temperature and cryogenic environments. A toughened epoxy resin, optimized for ultra-low temperatures, was impregnated with unidirectional carbon-fibers at 45, 70, and 140 g/m 2 areal weights. The intralaminar energy release rates in modes I and II, along with the interlaminar shear strength, were evaluated under liquid nitrogen ( in-situ ) testing conditions to assess the performance of these composites in cryogenics. Optical and scanning electron microscopy correlated fiber-matrix distribution and regularity with failure modes and performance. While G IC decreased from 296 K to 77 K, ILSS was notably higher in cryogenic environments. Both intralaminar toughness and interlaminar strength were improved by thinner plies, especially at 77 K. Thus, highlighting the importance of fiber-matrix uniformity in optimizing delamination and shear properties under cryogenic conditions, where sensitivity to irregularities increases.