This paper presents the experimental application of using the digital image correlation method to determine the stress intensity factors (SIFs) for load-carrying fillet welded cruciform joints. A non-contact optical experiment using a commercial digital camera was conducted to measure the crack opening displacements (CODs) in un-penetrated region of the fillet welded cruciform joint details. The photos taken from the non-contact optical experiment were processed by the digital image correlation (DIC) method, which used the cross-correlation relation in statistics for 2-D displacement-field measurement, to obtain the crack opening displacements. The measured crack opening displacements were inserted into the proposed least-squares procedure to derive the stress intensity factor KI. The test results verify the existing BS 7910 formula for fillet welded cruciform joints, and show that the presented experimental method is able to give satisfactory stress intensity factor evaluation for load-carrying fillet welded cruciform joints. This method can be applied to any cracked detail where the Irwin's series solution for crack-tip displacement fields is valid. Due to its simplicity and portability, the presented experimental method is applicable to field measurement of stress intensity factors directly from a detail of interest at the site, which is very useful for fracture and fatigue evaluation of details in structures like steel bridges or offshore structures.
Fillet welds are widely used in steel structures. Weld defects of fillet welds, such as undercut or overlap in the weld toe and incomplete joint penetration in the weld root, usually result in stress concentrations and act as crack initiation points during tensile or cyclic loading. Therefore, analytical or numerical solutions for the stress intensity factors (SIFs) at fillet weld roots or toes have been studied extensively in the past.
