Validation of a Continuum Damage Model for predicting the axial-crush response of CFRP composite material

In this work, the validation of the Finite Element (FE) analysis code PAM-Crash for the simulation of crashworthy composite structures is proposed. The investigation follows the principles of the Building Block Approach (BBA): FE analyses are supported at an increasing level of geometrical complexity by experimental campaigns. The investigation starts with multiple sets of coupon level testing on carbon fiber-epoxy UD material, followed by the quasi-static axial crushing of a self-supporting specimen. Tests performed include: tension, compression, in-plane shear and delamination modes I and II. A continuum damage mechanics (CDM) model is implemented starting from elementary load cases, then scaling up to the self-supporting specimens. The phenomenological meso-model for the intra-ply post-failure behaviour is based on the studies of Ladevèze, as later revised by Johnson and Pickett. In addition, a cohesive zone model is used to account for the delamination phenomena. Influence of different simulation strategies and simulation settings are discussed within the body of this work: a model comprising a single multilayered shell element, a staked set of shells representing the single constituent ply connected by inter-ply cohesive elements, and lastly, an intermediate solution using sub laminate groups. Influence of mesh size, friction coefficients and crushing velocity are also discussed. Results show that the CDM model alone is not able to correctly simulate the complex load cases, but calibration strategies of the material card are necessary to fit the experimental data. The required manual tuning limits the predictive quality of the model, as the characterisation effort alone is unable to describe the energy absorption characteristic of the different physical phenomena occurring during crushing. In addition, due to the different features of the proposed numerical approach, the contribution on Specific Energy Absorption (SEA) of the different crushing modes is discussed. A sensitivity analysis of different card parameters on simulation results is finally discussed in order to propose a framework for future investigation.