Strength analysis in L-angle section of carbon-fiber-reinforced plastic by measuring distributions of out-of-plane strain and stress

This study provides an engineering-valid and simple strength evaluation method for the L-angle part in carbon-fiber-reinforced plastic (CFRP) laminates. A four-point bending test according to ASTM D6415 was performed on L-angle specimens made of pseudo-isotropically laminated CFRP, and the full-field strain distribution at the curvature was measured using digital image correlation. A two-dimensional finite element model was constructed to simulate the four-point bending test, load–displacement curve, and maximum principal strain distribution; all agreed with the experimental results. The theoretical equation for calculating the stress distribution at the curvature agreed with the maximum out-of-plane stress at the 30.5-MPa bend and the stress distribution in the stacking direction obtained from the analytical results. Furthermore, the relationship between the load and the changed angle of the curvature part replicated satisfactory experimental results, and delamination occurred when the angle of the bent part reached 1.5°, indicating the rotation angle of those parts can diagnose the integrity in curved portions. Therefore, the proposed model can qualitatively explain the failure mode of bent sections.