Parametric analysis of enhancement of Z-pins on asymmetric delamination of Z-pinned laminated composites——ModeⅡdelamination toughness

It was assumed that the friction between the fiber Z-pins and the surrounding matrix，during its pull-out process，provides the bridging forces to enhance the delamination toughness of the laminates. Based on the currently available Z-pin micro-model，a Z-pin element was developed and a beam element model was proposed in this paper to study the effect of Z-pins on modeⅡdelamination toughness of Z-pinned end notched flexure (ENF) specimens. A contact element was also introduced on the delamination crack surface in the proposed finite element model to avoid the unrealistic penetration of the two substrate beams. The numerical results showed that the Z-pins can significantly improve the modeⅡdelamination toughness of the Z-pinned laminated ENF specimens. However，fewer enhancements on modeⅡdelamination toughness are obtained when the delamination crack is close to the surface of ENF specimens. The thickness of the thinner substrate beam is the key parameter to determine the enhanced modeⅡdelamination toughness of ENF specimens.