Comparing the In‐Plane Shear Behavior of Glass Fiber‐Reinforced and Carbon Fiber‐Reinforced Polymer Laminates With the Same Epoxy Matrix System in ±45° Tensile Tests

The in‐plane shear behavior of glass fiber‐reinforced and carbon fiber‐reinforced epoxy (GF‐ and CF‐epoxy) laminates manufactured with the same matrix system is investigated using quasi‐static ±45° tensile tests. Damage initiation and progression is monitored by optical crack detection for the translucent GF‐epoxy and by acoustic emission (AE) analysis for both materials. The study evaluates different criteria for determining the shear stress, , at failure to obtain ply level rather than laminate level strength values and examines the influence of the transverse stress component, , on measured at failure using classical laminate theory. In GF‐epoxy, optically observed crack initiation or first‐ply‐failure (FPF) coincides with a sharp increase in AE activity, enabling an AE‐based FPF criterion that more accurately represents ply strength than values from ASTM D3518. Besides the AE‐based detection, the ASTM D3039 transition point method provides the most reliable FPF estimates. GF‐epoxy exhibits lower at failure than CF‐epoxy, consistent with the higher resulting contribution arising from lower orthotropy. For both laminates, the shear modulus of elasticity depends on the selected shear angle, , range due to a gradual decrease in the – slope. In GF‐epoxy, maximum AE signal amplitude rate correlates well with optically measured crack density.