Abstract
In this study, Linear Elastic Fracture Mechanics (LEFM) approach is used to evaluate the fatigue strength of a box-shaped welded structure. A parametric study is also undertaken to study the effect of various weld parameters on the fatigue strength, such as lack of weld metal penetration, load position, and plate thicknesses. FRANC3D software was adopted to obtain the stress intensity factor values for two types of full-length and intermediate crack sizes, located at the critical region of the weld of the box-shaped structure. It was concluded that the LEFM approach could capture the crack propagation from the weld root reasonably well under the given conditions and estimate residual fatigue life of the welded structures conservatively. Compared to fatigue life estimations by nominal stress method (1,714,564 cycles) or effective notch stress method (63,385 cycles), the LEFM approach can estimate the residual life more accurately. Especially for intermediate (4 mm) lack of penetration (LOP) of weld metal case (589,198 cycles) in comparison to the experiments (1,216,595 cycles). The parametric study showed that the fatigue life increases with increase in the thickness of flanges, lesser LOP in the weld root, and when load is applied more toward the center of the plate.
Highlights
There are many methods for evaluating the fatigue life of welded structures [1]
Triamlumlerda and Lenwari [13] simulated the fatigue crack propagation (FCP) in steel I-beams numerically. They reported the effects of initial crack size, fillet weld size, stiffener dimension, and web-gap length on the FCP. All these efforts show the applicability of using Linear Elastic Fracture Mechanics (LEFM) in fatigue life estimation of welded structures specially when there is a lack of penetration (LOP) in the weld root
It was found that the fatigue strength of the box-shaped structure increases with the increase in weld metal penetration and increase in the thicknesses of flange and web plates, while eccentric loading leads to a reduction of fatigue strength. & A commercial software, FRANC3D, is used in conjunction with ANSYS to simulate the propagation of semielliptical cracks as LOP defects in the circumferential weld root of the box-welded structures
Summary
There are many methods for evaluating the fatigue life of welded structures [1]. In addition to direct experimental methods, procedures based on S-N curves and fatigue crack propagation (FCP) considerations are frequently used. The fatigue strength of joints that fail from the root depends on many variables such as weld throat size, plate thickness, and depth of weld penetration. They reported the effects of initial crack size, fillet weld size, stiffener dimension, and web-gap length on the FCP All these efforts show the applicability of using LEFM in fatigue life estimation of welded structures specially when there is a LOP in the weld root. Limited studies have used LEFM to evaluate the fatigue strength and life of large welded structures [5, 6, 10, 15, 16]. & The effect of weld metal penetration, thickness of plates (e.g., flanges and webs) and load position (e.g., centric or eccentric) on fatigue strength of the welded box-shaped structures are studied. It was found that the fatigue strength of the box-shaped structure increases with the increase in weld metal penetration and increase in the thicknesses of flange and web plates, while eccentric loading leads to a reduction of fatigue strength. & A commercial software, FRANC3D, is used in conjunction with ANSYS to simulate the propagation of semielliptical cracks as LOP defects in the circumferential weld root of the box-welded structures
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