High-resolution 3D weld toe stress analysis and ACPD method for weld toe fatigue crack initiation

S Chaudhuri,B G Mellor,J Crump,P A S Reed

doi:10.1007/s40194-019-00792-3

S Chaudhuri, B G Mellor + Show 2 more

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https://doi.org/10.1007/s40194-019-00792-3

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Abstract

Weld toe fatigue crack initiation is highly dependent on the local weld toe stress-concentrating geometry including any inherent flaws. These flaws are responsible for premature fatigue crack initiation (FCI) and must be minimised to maximise the fatigue life of a welded joint. In this work, a data-rich methodology has been developed to capture the true weld toe geometry and resulting local weld toe stress-field and relate this to the FCI life of a steel arc-welded joint. To obtain FCI lives, interrupted fatigue test was performed on the welded joint monitored by a novel multi-probe array of alternating current potential drop (ACPD) probes across the weld toe. This setup enabled the FCI sites to be located and the FCI life to be determined and gave an indication of early fatigue crack propagation rates. To understand fully the local weld toe stress-field, high-resolution (5 μm) 3D linear-elastic finite element (FE) models were generated from X-ray micro-computed tomography (μ-CT) of each weld toe after fatigue testing. From these models, approximately 202 stress concentration factors (SCFs) were computed for every 1 mm of weld toe. These two novel methodologies successfully link to provide an assessment of the weld quality and this is correlated with the fatigue performance.

Highlights

Introduction and backgroundRecommended for publication by Commission XIII - Fatigue of Welded Components and Structures1.1 Weld toe geometryStress-concentrating geometrical features inherent to welding are one of the primary causes of the low fatigue strengths of welded joints compared to the unwelded material
The stress-concentrating features can be broadly classified as macro- or micro-sized; the former considers the weld bead geometry as described by the plate thickness, leg attachment length and weld toe angle and radius (Fig. 1) whilst the latter considers weld toe flaws, which typically consist of undercuts and spatter
The work presented in this paper describes the development of a process that combines state-of-the-art techniques available: to non-destructively resolve the “true” weld toe profile of non-load carrying welds, produce high-resolution weld toe stress concentration factors (SCFs) distributions and identify crack initiation under fatigue cycling using Alternating current potential drop (ACPD)

Summary

Introduction

Stress-concentrating geometrical features inherent to welding are one of the primary causes of the low fatigue strengths of welded joints compared to the unwelded material. To estimate stress concentration factors (SCFs) for simplified weld profiles, various parametric solutions can be found in the literature [7,8,9,10,11,12]. These are based on linear-elastic finite element modelling and are valid for specific ranges of geometrical parameters.

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