Size effects and hydrothermal aging on mode I interlaminar fracture toughness of thick composite laminates

Abstract The effects of specimen thickness and hydrothermal aging on the Mode I interlaminar fracture toughness ( G _{I c} ) of thick composite laminates are analyzed. Unidirectional specimens with different thicknesses are tested, and the influence of specimen thickness on G _{I c} is revealed using finite element simulation. In subsequent experiments, the specimens are subjected to hydrothermal aging treatment in a thermostat water bath at 80°C. The moisture absorption behavior of specimens with varying thicknesses is systematically analyzed using a two‐stage moisture absorption model. Experimental results indicate that as the thickness increases, the stable Mode I fracture toughness values increase from 66.14 to 186.01 J/m ² . A fiber bridging region increase is the key factor leading to the size effects on G _{I c} according to the experimental and finite element simulation results. Thickness has a significant impact on the moisture absorption behavior of the specimens. The initial fracture toughness ( G _init ) and steady‐state fracture toughness ( G _prop ) of specimens with different thicknesses increase after hydrothermal aging due to the toughening of thematrix. Highlights The size effects on G _{I c} for thick composite laminates are studied. The growth of the fiber bridging region enhances G _Ic with the increase of specimen thickness. The toughening of the matrix leads to the increase of G _{I c} after hydrothermal aging.