Search Results

Both the experimental results and the analytical predictions of this study confirm that the poor fatigue performance of weldments with longitudinal attachments is due to poor weld quality which in turn leads to either a cold-lap or a very small weld toe radius. as well as to the combination of a very high 3-D stress concentration, and very high tensile residual stresses. Consequently, a specially designed stress-concentration-reducing part termed “stress diffuser” incorporated in the wrap-around welds at the ends of the longitudinal attachments increased the fatigue strength of longitudinal attachments to equal that of transverse attachments but only when cold-laps were eliminated. The fatigue life predictions made using the a two-stage Initiation-Propagation (IP) Model were in good agreement with the experimental results. Procedures for correcting for the curved shape of the crack path are investigated.

Fatigue tests have been conducted on low carbon steel butt welds containing lack of penetration defects. The growth of fatigue cracks from the lack of penetration defects was monitored by radiography. These measurements allowed the total fatigue life to be separated into periods of crack initiation and crack propagation. It was found that the rate of crack growth conformed to the expression: The initiation period was found to occupy approximately one-half of the total fatigue life and to consist of the cycle necessary to shake down the residual stresses in the weld and to form the lack of penetration defect into an active fatigue crack.

An empirical Three Stage Initiation-Propagation (TSIP) model has been developed which predicts the fatigue resistance of tensile-shear spot welds under constant amplitude loading. The improvements of tensile-shear spot weld fatigue resistance caused by changes in weld geometry, residual stresses and material properties variables are discussed with the aid of the model. The TSIP model suggests that, in addition to the influence of geometry, residual stresses at the site of crack initiation greatly influence the fatigue resistance of tensile-shear spot welds. The TSIP model predicts that material properties play a subtle role in determining the fatigue resistance of tensile-shear spot welds.

An empirical model has been developed which predicts the fatigue strength of weldments and considers the four important factors which affect the fatigue performance of weldments: geometry - the severity of the discontinuity; material properties - the fatigue properties of the material at the root of the discontinuity; the residual stress - the sign and magnitude of the residual stresses at the discontinuity; and loading type - axial and tending. Analytical and graphical aids for estimating the fatigue strength of weldments are given which may be useful to designers.