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.