The influence of material shear nonlinearity on multidirectional laminates in terms of failure envelopes

Influence of material shear nonlinearity on multidirectional laminates in terms of failure envelopes was investigated. In applying classic laminate theory, elastic constants were employed in transverse and longitudinal directions, while initial shear modulus was substituted by the secant shear modulus, which was achieved by means of Ramberg-Osgood model. The fracture curves were generated from maximum stress, Tsai-Wu and Puck criteria. The similarities and differences between nonlinear and linear shear models can be expressed in terms of symmetric balanced laminates [±θ°]2s and asymmetric laminates [0°2/±θ°], which are both arranged by material E-glass/MY750 oriented at different directions. All σ1 - σ2 failure envelopes due to material nonlinearity extend outward in tensile and compressive directions, but the phenomenon is not obvious with increasing ply angles. Similarly, the differences of all σ1 - τ12 failure envelopes between nonlinear shear analysis and linear shear analysis are decreasing with increased ply angles. Ply orientations and loading directions are involved in the effect of nonlinear shear properties on failure envelopes. According to the failure modes obtained from maximum stress criterion, it is reasonably derived that the influence of material shear nonlinearity will lead whether the failure envelopes from the other two failure criteria are more conservative or not.