Determination of fracture mechanics parameters on a base of local displacement measurements

Abstract

New experimental technique for a determination of the stress intensity factor (SIF) and T-stress values is developed and verified. The approach assumes combining the crack compliance method and optical interferometric measurements of local deformation response on small crack length increment. Initial experimental information has a form of in-plane displacement component values, which are measured by electronic speckle-pattern interferometry at some specific points located near a crack tip. Required values of fracture mechanics parameters follow from the first four coefficients of Williams’ series. A determination of initial experimental data at the nearest vicinity of notch tip is the main feature of the developed approach. That is why it is not necessary to involve complex numerical models, which include global geometrical parameters, loading and boundary conditions of the object under study, in a stage of experimental data interpretation. An availability of high-quality interference fringe patterns, which are free from rigid-body motions, serves as a reliable indicator of real stress state around a crack tip. A verification of the technique is performed by comparing experimental results with analogous data of FEM modelling. Experimentally determined mode I SIF for DCB specimen with end crack is in 5 per cent agreement with the numerically simulated case. Proposed approach is capable of estimating an influence of the notch radius on fracture mechanics parameters. Comparing SIF and T-stress obtained for U notches of different radius both in actual and residual stress field confirms this statement.

Keywords

• Stress intensity factor
• T-stress
• crack compliance method
• In-plane displacement components
• Electronic speckle-pattern interferometry