Experimental and numerical investigation on the size effect of interlaminar shear strength for thick composites

The study investigates the variation of interlaminar shear properties for unidirectional glass fiber reinforced polymer (GFRP) composites with different thickness using the short-beam shear (SBS) test in conjunction with DIC. To verify the scaling principle and clarify possible mechanisms of the interlaminar shear strength size effect , the quantitative parameters for characterizing randomly distributed irregular voids are proposed. It is seen that the variation of probability for void characteristics with thickness is one of the mechanisms for the interlaminar shear strength size effect. Furthermore, a micromechanical representative volume element (RVE) model with randomly distributed irregular voids is developed for numerical verication. The analysis indicates that the weakest link is related to not only the void size but also the void irregularity and void concentration. The void concentration has a pronounced negative impact on shear strength due to the intersection of the microcracks around the voids. • The Weibull model has been verified for the interlaminar shear strength of GFRP composites. • The variation in void characteristics with thickness is one of the mechanisms for the size effect. • The void irregularity and concentration need to be considered in the definition of the weakest link. • High void concentration has a pronounced negative impact on the interlaminar shear strength.