Finite Element Approach for Analyzing Manufacturing Defects in Composite Materials

Abstract

Fiber composite materials provide low material weights in combination with high material stiffness and strength. The fiber stiffness and strength characterize mainly the behavior of unidirectional composites plies. Critical phenomena for composite structures are defects caused by the manufacturing and processing technologies. One such phenomenon which is often detected is fiber misalignment. The paper presents an appropriate 3D finite element model for the analysis of the effects of in-plane and out-of-plane graded fiber waviness on the stiffness and strength values of a laminate which consists of unidirectional plies under shear and tensile loading conditions. The classical laminate theory (CLT) is utilized as analytical model to predict the unidirectional fiber stiffness as a function of in-plane and out-of-plane fibers waviness. Furthermore the undula-tions of fiber are represented by Fourier series. The 3D linear Hashin failure criterion implemented in ABAQUS is functioned by means of a user subroutine file (i.e. UMAT) to predict the influence of misaligned fibers on the strength of a compos-ite laminate under pure shear and pure tensile loading conditions along and transverse to the fiber direction. In this investigation, parametric studies are carried out on the sensitivity of the effect of fiber misalignment on the stiffness and strength. These parameters are, e.g., material properties, vary-ing degree of fibers and plies waviness, different ply orientation, ply-up of laminate, width and thick-ness of laminate, volume fiber fraction variation with fiber waviness, and mesh size.