Dr Wei Tan
BEng, PhD


Research Group News



Our new paper titled ‘A physically-based constitutive model for the shear-dominated response and strain rate effect of carbon fibre reinforced composites’ has been published in the leading composite journal 'Composites Part B: Engineering'. This is the first time in the literature to demonstrate how the well-known crystal plasticity framework can be used to predict the plastic deformation and strain rate effect of composite materials. By analogy,  the plastic deformation of a composite lamina is assumed to be due to fibre slip along certain slip systems within the matrix. Reviewers comment "The paper is an excellent contribution to the literature. It is clear and concise, and the technical approach is very good" and "This is a very good manuscript, both regarding scientific content, novelty and thoroughness in the analysis". 

Carbon Fibre Reinforced Plastics (CFRP) are finding increasing utilisation in lightweight transportation vehicles due to their high specific stiffness and strength. They often fails catastrophically in a brittle manner without warning. Under transverse or shear loading, the main response of a unidirectional (UD) CFRP is controlled by matrix, exhibiting large non-linear shear-dominated deformation and subsequent matrix cracking. This non-linear hardening effect allows composite structures to bear loading under strain over 20%, which may create an additional safety margin to engineering structures . It is therefore essential to understand the origin of non-linear stress strain responses of CFRP to determine design allowables for engineering composite structures.

Impact resistance and crashworthiness are the typical safety measures for CFRP used in the transportation vehicles. In the bird-strike or crash events of transport vehicles, strain rates of structural components are in the range of 100–1000/s. Experimental results found that both the moduli and strengths of CFRP varied with the strain rate. To accurately assess the impact tolerance of composite structures, it is important to consider the strain rate effect in their constitutive models.

To develop a micro-mechanically motivated constitutive model for CFRP composites, accurately capturing the fibre rotation and the strain rate effect, we shall understand the deformation mechanisms of CFRP composite. Experimental observations suggest this non-linear behaviour is mainly achieved by the shearing of the matrix along the fibre direction with evident fibre rotations.

By ananolgy, we developed a micromechanical model to capture the matrix shearing and fibre rotation of CFRP under finite strain and different strain rates, inspired by the crystal plasticity theory. Strain rate dependency of the shear modulus and yield strength of matrix is modelled through scaling functions. We then validate the predictive capabilities of this micromechanical model against the measured stress-strain responses of unidirectional (UD) and cross-ply composite laminates.  

This work reveals the origin of the hardening response through analytical and finite element analysis. It provides a computational tool to predict the shear deformation of carbon fibre composites which will contribute to the development of damage tolereant composite structures.