Effects of ply thickness and 0°-layer ratio on failure mechanism of open-hole and filled-hole tensile tests of thin-ply composite laminates

Thin-ply technology provides increasing possibilities for composite structures, expanding the design space for ply thickness and laminate layup. This study examines the effects of ply thickness and the 0°-layer ratio on the strength and damage behavior of thin-ply composite laminates. We conducted open-hole tensile (OHT) and filled-hole tensile (FHT) tests on laminates with various ply thicknesses and 0°-layer ratios, observing the internal damage via X-ray radiography. It was confirmed that the damage retardation effect of the thin-ply reduced both the OHT and FHT strengths. Furthermore, the results revealed that laminates with a higher 0°-layer ratio have higher strengths and the failure of laminates with a higher 0°-layer ratio transitioned to splitting-dominated failure. Finite element analysis of the fastener restraint indicated that the fastener restraint alleviated the stress concentration in the 0°-layer around the hole, potentially leading to a difference in the OHT and FHT strengths.