Analytical Prediction of Mechanical Performance of Structural Organic Matrix Composites with Sharp Radii Features

Abstract

An analytical approach for progressive damage prediction was developed for structural organic matrix composites (OMCs) with sharp radii features. Structural OMCs offer advantages in reduced weight and high mechanical performance. However, OMC structures with complex part geometries encounter frequent occurrence of defects due to multi-step reactions and void formation during manufacturing process cycles. Defect-driven analysis is particularly important for OMCs with sharp radii features. Porosity plays a significant role in the generation of microcracking and leads to the degradation of effective mechanical properties and fatigue life of engineering applications. In this work, a custom ANSYS® user subroutine was used to model the damage progression in canted-T shaped subelements with various porosity levels. The porosity was predicted based on incomplete step reaction using a composite process model. The relationship of property reduction as a function of porosity was established and quantified. The progressive damage finite element model, based on a custom algorithm that accounted for shear stress-strain nonlinearity, predicted different failure modes using both strength based and fracture toughness based failure criteria. Failure mode based stiffness loss, implemented at the element level using a nonlinear constitutive law, accounted for the current damage state. This model was used to perform a series of mechanical failure analyses to simulate laboratory test conditions. The predicted results showed a good correlation with experimental results for the entire nonlinear load deflection response, as well as the damage progression and local failure modes as observed by digital image correlation (DIC). Also studied and analyzed was the effect of local porosity on the damage initiation and progression at the sharp radii of the canted-T subelement using this custom ANSYS® model.