A simple expression to estimate the fatigue endurance of welded joints

Mirco Daniel Chapetti,Ceferino Steimbreger,G Hénaff

doi:10.1051/matecconf/201816522024

Abstract

A simple expression is proposed to estimate the fatigue endurance of welded joints that can be used to understand and analyze in a simple way the influence of the main geometrical, mechanical and material effects (weld geometry, local geometry, material properties, residual stresses and size of defects). The proposed expression was derived from the results of the analysis of the fatigue strength of welds studied by means of a fracture mechanics approach that takes into account the fatigue behavior of short cracks by using the resistance curve method. For that purpose numerical simulation of transversely stressed butt, T and cruciform joints were performed.

Highlights

There exist several calculation methods for fatigue life analysis of welded joints, including the nominal stress method, hot spot method, notch stress method, local strain method, and fracture mechanics methods
To ensure that the full effect of the three key features dominating the fatigue life of welded joints are allowed for in design, most fatigue design rules consist of series of ∆σ–N curves based on data obtained from constant amplitude fatigue tests on actual weldments [35], and employ classification methods of specifying design curves in terms of the fatigue strength at a given number of cycles (e.g. 2x106 or 107)
The parameter Mk-200 represents the stress concentration generated by the configuration at a depth equal to 200 μm, which is taken as the initial crack length ai in the present analysis

Summary

Introduction

There exist several calculation methods for fatigue life analysis of welded joints, including the nominal stress method, hot spot method, notch stress method, local strain method, and fracture mechanics methods. An important consequence of the geometric stress concentrations associated with most welded joints, the severity of which is usually compounded by the presence of welding flaws, is that fatigue cracks readily initiate and the life is dominated by fatigue crack growth [3,4]. This accounts for the drastic reduction in fatigue life resulting from the presence of a weld. In this work a simple expression to estimate the fatigue endurance of welded joints is proposed on the bases of the results of previous analysis and results [7,8,9,10]

The fracture mechanics approach

Previous analysis and results

The simplifying hypotheses

The analysis

Concluding remarks