Experimental and Numerical Study of Mode II Delamination in Laminated Composite Beams

Thesis (Master's)--University of Washington, 2019The use of laminated composites is becoming increasingly ubiquitous in many industries as this material has a high strength-to-weight ratio, and offers customization and flexibility in design. However, delamination damage, which reduces the strength and stiffness of the material, is common and often difficult to detect during inspection. The integration of delamination failure considerations into the design and analysis process is of the utmost importance, and therefore necessitates experimental characterization of delamination, as well as structural-scale numerical models which accurately predict delamination behavior. In this thesis the end loaded split (ELS) specimen was used to experimentally investigate mode II delamination, which is less well understood than mode I delamination. Force-displacement data was used to characterize the mode II critical strain energy release rate, as well as to study the capabilities of two crack growth models: the virtual crack closure technique (VCCT), and cohesive zone model (CZM). The numerical model results demonstrated good agreement with the experimental test data, however neither the experimentally determined mode II critical strain energy release rates, nor the crack growth simulations were free of size effects. In an effort to establish a more robust material model to characterize mode II delamination, through-thickness displacement field data was analyzed, but was found to lack the resolution necessary to accurately capture cracked, or even uncracked beam behavior