Geometrically nonlinear determination of energy release rate and mode ratio in single leg bending tests

Geometrically linear and nonlinear finite element analyses are used to determine the energy release rate and mode ratio in simulated tests of unidirectional, symmetric, single leg bending (SLB) specimens. It is shown that the finite diameter loading rollers that are typically used in practical test set-ups cause this test to be inherently nonlinear. The differences between the linear and nonlinear results are presented parametrically as a function of material properties, specimen thickness, roller diameter, span length and crack length. These results are used, along with empirically derived equations, to develop an approach for designing SLB experiments where one will have a high degree of confidence in toughness values as obtained from conventional data reduction techniques, and for which relatively little specimen-to-specimen variation in mode ratio will be observed.