Damage Evolution in CFRP Laminates with Varied Initial Damages Under Combined Compression-Shear Revealed by Stressing State Theory

Independent compression-shear testing of large-span CFRP laminates is difficult because conventional setups couple shear with axial loading and distort the force-transfer paths. This study develops an innovative pulley-block loading system that applies compressive and shear loads independently. Based on stressing state theory, strain data were renormalized to construct stressing state matrices, allowing the damage evolution could be treated as a system evolution problem. A clustering algorithm was employed to identify phase transition loads in the evolution process, including elastic-plastic branching points, damage initiation points and damage evolution points. These points were further used to identify differences in damage evolution and force-transfer characteristics among specimens with different initial damages. Tests on three specimens (undamaged, impact damage and pre-embedded damage) show that both damage types reduce the load-carrying capacity. Pre-embedded damage had a stronger influence on early-stage stress redistribution, whereas impact damage accelerates later-stage damage evolution. The proposed framework provides an efficient approach to evaluating the damage and stressing state of CFRP laminates and offers references for load-bearing assessment, and subsequent structural design.