Accurate evaluation of the fracture parameters is crucial for estimating the behaviour of the mechanical components in service condition. Experimental observations are extremely useful to provide accurate and reliable information for modern structural integrity analysis. The stress intensity factor (SIF) is a key parameter for understanding the fatigue crack propagation behaviour of structures prone to linear elastic failure. The SIF has been widely studied and a number of experimental, numerical and analytical methods have been developed and continue being developed to improve the estimation of the SIF for different loading conditions and component geometries. Digital Image Correlation (DIC) is a simple and versatile method for full-field quantification and can be used to measure experimentally the displacement data from a surface of a component being strained. By combining the experimentally evaluated displacement data with analytical solutions such as Westergard's, Muskhilishvili's and Williams' series, one is able to evaluate the SIF in cracked components. However, the selection of the experimental parameters and the limitations of the approach (e.g. the maximum permitted plasticity at the crack tip) are still a controversial concept. This work concentrates on three main topics: optimization the experimental DIC parameters for SIF evaluation, continuous measurement of SIF by DIC and evaluation of crack tip field under complex loading conditions (biaxial loading) with and without the presence of overloads. A multipoint over-deterministic method is employed to combine an elastic model based on Williams' solution for displacement distribution around the crack tip with the experimentally full field measurement of displacement at the crack tip by DIC. Different parameters such as number of terms in Williams' series, size of the field of view and the best location of the area of interest are examined in the optimisation stage.
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