A bi-material property based FE modelling method for progressive damage analyses of composite double-lap bolted joints

A bi-material property method was proposed to describe mechanical properties of the unidirectional composite lamina. It divided the lamina into the fiber layer and the resin layer, which have different material properties and are responsible for the intra-laminar and inter-laminar properties, respectively. Furthermore, a finite element modelling method with the composite lamina simulated by the bi-material property method was presented. Combined with a Hashin-type failure criterion and a micromechanics-based material degradation model, a novel progressive damage model (PDM) was constructed for typical double-lap bolted joints. To validate the novel PDM, four double-lap, single-bolt joints with various width-to-hole-diameter ratios were designed and quasi-static tensile tests of the joints were performed. Numerical results of the novel PDM show better agreements with the experimental outcomes than the traditional PDMs. Besides, the novel PDM can describe the inter-laminar damage more precisely via a more reasonable simulation for the inter-laminar property of the lamina, and can also obtain more accurate deformation of the hole along the thickness direction of the laminate. Furthermore, influences of the width-to-hole-diameter ratio W/D on failure behaviours of the double-lap, single-bolt joint were revealed, and an optimal width-to-hole-diameter ratio was recommended for engineering practice. Combined with our previous study on effects of the end-distance-to-hole-diameter ratio E/D, a failure mode map with varying W/D and E/D was determined for the double-lap bolted joint. It is helpful for designers to seek safer designs of composite bolted joints because the W/D and E/D are key geometrical parameters that significantly affect failure behaviours of the joints.