NONLINEAR ANALYSES OF HOMOGENEOUS, SYMMETRICALLY DELAMINATED SINGLE LEG BENDING SPECIMENS

Energy release rates obtained by geometrically linear and geometricall y nonlinear finite element analyses of homogeneous, symmetrically dela minated single leg bending specimens are presented for a variety of ma terials, specimen geometries and fixture dimensions. It is shown that certain test geometries will exhibit strong nonlinear effects; thus, c ritical energy release rates obtained from tests of these geometries, using data reduction procedures that are based on linear theory, may c ontain significant errors. The nonlinear finite element results are us ed to develop empirical relationships between energy release rate as p redicted by the nonlinear analyses and those predicted by linear analy ses. These empirical relationships are shown to be valid over a wide r ange of specimen material properties, material property ratios (e.g., Young's modulus to shear modulus) and geometric properties of both the specimen and fixture, including fixture roller diameters. Thus, the e mpirical relationships may be used in a quantitative manner to design tests in order that significant nonlinear effects do not occur prior t o fracture, and hence linear data reduction procedures remain valid. A lternatively, the empirical relationships may be used to interpret tes t results where nonlinear behavior occurs. Both uses are illustrated b y example for typical laminated composite materials.