Investigation of trapezoidal corrugated aramid/epoxy laminates under large tensile displacements transverse to the corrugation direction

Corrugated structures are noted for their exhibition of extreme anisotropic stiffness properties which may be useful in aircraft morphing wing skin applications. As part of a wider study to compare the stiffness properties of corrugated laminates made from different materials and geometries, anomalous experimental results were obtained with trapezoidal corrugated aramid/epoxy laminates subjected to large tensile deformations transverse to the corrugation direction. This study investigates the local failure mechanisms of these specimens that explain the obtained experimental results. Static and cyclic experimental testing identified three stages of behaviour in the structure's stress vs. global strain response. The majority of the displacement comes from the second stage. This was attributed to the aramid fibre compressive properties and delaminations in the corrugated unit cell corner region. This local phenomenon is comparable to a pseudo-plastic hinge that allows large deformations over relatively constant stress levels. This behaviour is thought not to occur in glass and carbon fibre corrugated laminates because it was related specifically to the aramid fibre response. Analytical and numerical analysis showed that the equivalent transverse tensile elastic modulus of the corrugated laminate can be predicted; while the complete three-stage behaviour can also be modelled using non-linear finite element analysis with local elastic-plastic material definitions.