Evaluations of mixed-mode stress intensity factors for load-carrying fillet welded cruciform joints using the least-squares method

Abstract

This study presents the numerical and experimental applications of using the least-squares method (LSM) to evaluate the mixed-mode stress intensity factors (SIFs) of load-carrying fillet welded cruciform joints. In the numerical application, fillet welded cruciform joints of different combinations of geometric parameters (including weld leg size, initial lack of penetration size, and plate thickness) were systematically studied using the finite element method and the LSM. The derived SIF results were used to develop the general formulae of the opening mode (mode-I) and shearing mode (mode-II) SIFs, K _I and K _II, respectively. To validate the numerical results, five fillet welded cruciform joint specimens were fabricated and tested by a non-contact optical experiment using a commercial digital camera and the digital image correlation technique for image processing. The numerical and experimental mode-I SIF results were in good agreement with the results from the existing BS 7910 formula for fillet welded cruciform joints. In addition, the suggested non-contact optical experiment is simple and portable, making it well-suited for measuring mixed-mode SIFs directly from the welded details on site. This is very useful for fracture and fatigue evaluation and analysis of weld in existing or newly designed structures, such as steel bridges and offshore structures.

Keywords:

• cruciform joint
• stress intensity factor
• digital image correlation
• crack opening displacement

Acknowledgment

The authors gratefully acknowledge the financial support through the research grants (NSC96-2221-E-006-071 and NSC97-2221-E-006-140) awarded by the National Science Council, Taiwan, ROC.