Effect of Manufacturing Induced Fiber Break on Local Tensile Failure in Composites

Abstract

Fiber breakages are commonly found during composites manufacturing process. In the current study, the effect of manufacturing induced fiber break on local tensile failure in unidirectional (UD) composites is investigated numerically. In the finite element (FE) model, a broken fiber is placed centrally in a hexagonally packed UD composite and is assumed to be perfectly bonded to the matrix. Since the stress perturbation caused by a single fiber breakage is local, only the six most affected nearest-neighbor fibers are modeled and are placed as a ring of concentric axisymmetric cylinder embedded in the matrix. The discrete fiber region is surrounded by a concentric outer cylinder ring of homogenized composite. The entire FE model is subjected to axial tensile loading. Upon loading, it is found that matrix crack would most likely initiate perpendicular to fiber axis by cavitation due to tri-axial stress state near fiber break, and the thermal residual stress is found to promote the cavitation process. Once the matrix crack initiates from fiber break, fracture mechanics methodology is adopted by using extended finite element method (XFEM) to simulate the matrix crack propagation. The stress concentration factors (SCF) along the neighboring fibers are calculated during matrix crack propagation and obtained results show that the maximum SCF is the highest when matrix crack reaches a neighboring fiber. Finally, the statistical consideration regarding neighboring fiber failure is incorporated and it is found that the initial fiber breakage, together with the matrix cracking that follows, greatly enhance the probability of neighboring fiber failing at the local region close to the original fiber-break plane, which indicates that a planar fracture plane is expected if final tensile failure of UD composite starts from a manufacturing induced fiber break.