Fatigue Life Of Welded Specimens Research Articles

Fatigue Studies of Welded Stainless Steel 304L: Effect of Manufacturability and Weld Type, Choice of Fatigue Model, and Comparison to Pristine Material

Abstract This study investigates fatigue life and fracture in welded stainless steel 304L (SS 304L) resulting from load-controlled fatigue. This was done for specimens from two welding manufacturers. Mechanical testing was carried out using a MTS test frame in uniaxial tension. Specimens fabricated in 3 weld configurations (butt, lap, butt-with-backer) were cycled at stress ratio R = 0.1, frequency f = 5 Hz, and experienced varying mean tensile stress. A comparison of the fatigue life of welded and unwelded (or pristine) specimens determined that the fatigue life of welded specimens is considerably shorter. The microstructure in the parent material (PM), heat affected (HAZ) and fusion zones (FZ) was analyzed using SEM, and results suggest that, for a limited number of specimens (backer welds), fracture in the (FZ) was primarily the result of Zener-Stroh cracks. Most welded specimens fractured at the weld-HAZ interface (weld toe), and we postulate that stress concentrations primarily due to abrupt geometrical change at the weld interface led to crack initiation there. Additional stress concentrations at welding induced defects (resulting from high temperature) such as second phase particles, fatigue induced defects, and pre-existing impurities are responsible for crack initiation, crack growth, and eventual fracture. Comparison of unwelded and welded SN curve data using numerical curve fitting methods reveal that the fatigue life of pristine SS 304L follows the expected sigmoid shape found in literature (specifically the Chandran fatigue model), while that of welded SS 304L deviates considerably in low cycle fatigue (LCF) and follows the Basquin power law equation.

The influence of heat treatment on the behavior of fatigue crack growth in welded joints made of S355 under bending loading

The work concerns on the results of the tests of the growth of the fatigue crack experiment. All specimens were subjected to bending at constant load using S355 steel. Rectangular cross-section specimens were weakened by external notches and fillet welded joints. The tests were carried out under cyclic bending without and with mean load values. Additionally, the impact of heat treatment on fatigue lifetime was investigated. Crack initiation and propagation stages were observed on the specimens’ surface using a light microscope. This research also shows microstructures with cracks of welded connectors and with changes in the material after heat treatment as well as their effect on the fatigue lifetime of joints. The highest durability was demonstrated by specimens without heat treatment. On the other hand, a similar fatigue crack growth mechanism was observed in different weld types. The numerical analysis also explains similar fatigue crack growth mechanism by equivalent stress intensity factors values. The fatigue life of welded specimens without heat treatment for both stress R-ratios was higher than for specimens after heat treatment.

High pressure rolling of low carbon steel weld seams: Part 2 – Roller geometry and residual stress

Large residual stresses are an undesirable but inevitable side effect of fusion welding operations, and localised high pressure rolling of the weld seam is a proposed method for eliminating them. In this study, neutron diffraction has been used to map the residual stresses within low carbon steel weld seams treated with high pressure rolling. The effect on the residual stress distribution of using different roller types was determined, along with the influence of these different rollers on final weld seam geometry. Rolling was found to completely change the residual stress state in the weld, creating large compressive longitudinal residual stresses. It was effective for this purpose regardless of whether it was applied directly to the weld seam or to regions either side of it. The fatigue life of welded specimens was shown to be reduced by rolling; however, it is suggested that this is due to geometric and metallurgical effects.

The Influence of Vibratory Treatment on the Fatigue Life of Welds: A Comparison with Thermal Stress Relief

Abstract: A comparison has been made between the fatigue lives of welded specimens a) in the as welded condition b) after heat treatment, and c) after post‐weld vibration. By comparison with the as‐welded specimens, the fatigue lives of the thermally relieved specimens were found to decrease by 43%, while the vibration treated specimens showed an increase of between 17% and 30%. While these findings are interesting in that they offer a way of extending the fatigue lives of welded joints, they confirm the view that the mechanism of residual stress relieving in the vibratory stress relief (VSR) method, and its relationship with fatigue life is poorly understood.

Fatigue characteristics of ‘bead-on-plate’ of aluminum and AlZnMg alloy

Fatigue life of ‘bead-on-plate’ on commercially pure aluminum and AlZnMg alloy have been investigated. In both cases, the fatigue life of ‘Bead-on-Plate’ specimen was drastically reduced. But when the same weld-bead was flushed off, a marginal improvement in fatigue life was observed. For AlZnMg alloy, the post weld heat treatment was less effective than flushing of weld-bead for improving the fatigue life of welded specimens. Results are analyzed with the help of S- N diagrams and microphotographs.