Determination of the residual stress for cracked plates of fiber-metal composite materials

Abstract

The hybrid composite materials, fiber-metal laminates, FML (Fiber Metal Laminates), consist of thin sheets of aluminum alternately with unidirectional fiber layers embedded in an epoxy resin matrix. In this work the residual strength on two geometries of plate with crack is determined from fracture toughness J, such obtained by testing as simulation using a linear elastic finite element calculation (FEM) model to develop a prediction of the behavior of fracture toughness. For the simulation of the crack propagation in the FML specimen, a 2D model with cohesive elements was applied. Two different types of formulation of cohesive elements were used to simulate the failure mechanism presented by hybrid composite materials, in the presence of crack propagation. The results obtained with the FEM models that predict the progression of the crack, in terms of the loaddisplacement graph, have been compared with the results of elasto-plastic fracture mechanics tests, applying the J integral criterion according to the ASTM E-1820 standard. In the tests as in the FEM model, CARALL composite C(T) specimens were used, made from 1050 aluminum and NCT-301 unidirectional carbon fibers impregnated with epoxy resin. A 4/3 arrangement is used (Al-0-Al-90-Al-0-Al), with 0 and 90 being the orientation of the carbon fiber with respect to the lamination direction of the aluminum alloy. On the other hand, based on the results of J, in terms of the instability toughness parameter (Jc), both from the FEM simulation predictive model and from the J test, the residual strength is calculated in a flat plate with surface crack geometry.