Fracture Toughness Evaluation for Composite Delamination at a High Strain Rate and Tilted Specimen Design

This work investigates the high rate interlaminar delamination of an angle-ply carbon fiber reinforced plastics (CFRP) laminate by combining experimental in-situ monitoring and finite element analysis. Split Hopkinson Pressure Bar experiments with ultra-high-speed synchrotron x-ray phase contrast imaging were conducted to monitor the through-thickness fracture progression in the laminate at high strain rates. A cutting method was developed to prepare specimens with increased shear between layers during loading in the macroscopic compressive mode. The interlaminar delamination was simulated with three-dimensional models using Virtual Crack Closure Technique (VCCT) and Cohesive Zone Model to calculate fracture toughness and study the speed of crack growth. The fracture toughness of the CFRP laminates is suggested to decrease at high strain rates. The simulated results for the tilted specimen with critical energy release rate (ERR) values of G_IC = 14 J/m² and G_IIC = 156 J/m² showed good agreement with the experimental data, particularly when using a homogenized model of the test specimen at high strain rates. The VCCT model was finally used to predict a crack propagation speed of approximately 1.24 mm/µs.