Prediction of Matrix Failure in Fibre Reinforced Polymer Composites

Recent development has enabled fibre and matrix failure in a fibre reinforced composite material to be predicted separately. Matrix yield/failure prediction is based on a Von Mises strain and first strain invariant criteria. Alternative matrix failure criteria for enhanced prediction accuracy are discussed in this paper. The proposed failure envelope formed with basic failure criteria intersects with uniaxial compression, pure shear and uniaxial tensile test data points smoothly. For failure of typical neat resin, significant improvement of prediction accuracy compared with measured material data is demonstrated. For a unit cell with a fibre and surrounding matrix with typical material properties, a FEM analysis indicates a significant improvement in prediction accuracy in the pure shear load case and a marginal improvement in the biaxial tensile load case. This paper also provided a preliminary discussion about the issues when material nonlinearity of the matrix material is involved. 1. Introduction Fibre reinforced polymer matrix composites are being increasingly used for aircraft structures because of their superior structural performance (such as high strength, high stiffness, long fatigue life, and low density). Some recently developed military helicopters have nearly all-composite airframe structures (such as Eurocopter Tiger and Bell/Boeing V22). In the conventional laminate theory widely used to predict the strength of fibre reinforced polymer composites, the laminae are treated as homogeneous orthotropic materials. Recent development has made it possible to extend the conventional laminate theory to predict separately the failure of the polymer matrix and fibres. In essence, this is through a microstructural analysis conducted on a unit cell of the composite material that contains a fibre and surrounding polymeric matrix to determine the correlation between the stress-strain states of the whole cell and its matrix and fibre components. This correlation is then used in a structural analysis to predict matrix or fibre failure. In a linear finite element method, the failure of the polymer matrix and fibres can be separately predicted during postprocessing of the results from a computation based on the conventional laminate theory, by correlating the element of stress-strain state with matrix and fibre stress-strain states. In principle, this micromechanical approach may also predict the interfacial failure between the fibre and matrix. Significant work in the aforementioned area was reported by Gosse and his coworkers [1, 2]. In their approach, it