A cohesive zone model for predicting delamination suppression in z-pinned laminates

Abstract

This paper presents a cohesive zone model based finite element analysis of delamination resistance of z-pin reinforced double cantilever beam (DCB). The main difference between this and existing cohesive zone models is that each z-pin bridging force is governed by a traction-separation law derived from a meso-mechanical model of the pin pullout process, which is independent of the fracture toughness of unreinforced laminate. Therefore, two different traction-separation laws are used: one representing the toughness of unreinforced laminate and the other the enhanced delamination toughness owing to the pin bridging action. This approach can account for the large scale bridging effect and avoid using concentrated pin forces, thus removing the mesh dependency and permitting more accurate analysis solution. Computations were performed using a simplified unit strip model. Predicted delamination growth and load vs. displacement relation are in excellent agreement with the prediction by a complete model, and both models are in good agreement with test measured load vs. displacement relation. For a pinned DCB specimen, the unit strip model can reduce the computing time by 85%.

Experimental characterisation of mixed mode traction–displacement relationships for a single carbon composite Z-pin

“…Approaches to describe the through thickness reinforced (TTR) pin bridging mechanisms analytically have been attempted by a number of [13][14][15][16][17]. In all these cases the TTR bridging models have been calibrated against experimental data carried out either on mode I pin array pull-out tests [16], standard mode I fracture toughness tests [7], T-Joint pull-out tests [2,5,6,15] or mode I and mode II single pin tests [11,14].…”

Micro-mechanical finite element analysis of Z-pins under mixed-mode loading

“…These are derived from experiments, simplified FE models or semi-analytical models of single Z-pins [6][7][8][9][10].…”

An experimental investigation into multi-functional Z-pinned composite laminates

“…Early FEA approaches have been based on the virtual crack closure technique [24], with nonlinear spring elements distributed on the delamination surfaces to model the bridging action of Z-pins. More recent techniques are based on the formulation of cohesive zone models whereby the response of individual Z-pins is homogenised at interface level [28,29]. The interface cohesive constitutive behaviour is based on traction-displacement laws derived from single Z-pin experiments or models.…”