A simple closed-form model for fracture of CFRP panel with shallow surface scratch confirmed by comprehensive flexural/tensile tests

Comprehensive tests using more than 200 CFRP laminate specimens with and without shallow surface scratches (20 μm - 3 mm) have been performed under three-point-bending (3-p-b) and direct tensile conditions. Critical flexural loads of scratched 3-p-b specimens have been linked to the tensile strength f_t of CFRPs by a simple closed-form solution of a non-Linear Elastic Fracture Mechanics (non-LEFM) model for composite failures, which models the crack tip damage using the characteristic composite microstructure C_ch (ply thickness of CFRP). The average f_t measured from 30 direct tensile tests is virtually identical to that from 170 different 3-p-b tests with only 2% relative error, indicating potential applications of the simple closed-form solution in structural integrity analysis for scratched CFRP components. The statistical reliability has been combined into the predictive model, which can be important when not only the mean strength but also the prediction interval is required.