Effects of defects on mechanical properties in metal additive manufacturing: A review focusing on X-ray tomography insights

The local approach is one of the most important method developed in recent years for fatigue assessment of welded joints. The basic principle of local approach is taking the “local parameter" of the stress concentration region as a characteristic parameter to describe the fatigue behavior and to establish the general S—N curves expressed by the correlate local parameters and the loading cycles N which lead to the prediction of fatigue life and strength of welded components possible. The local approaches could effectively represent the practical fatigue performances of welded structures due to the inclusion of the local geometrical details of the welded joints. This method is recommended by the International Institute of Welding (IIW) and widely employed by various societies in Europe. Various local fatigue criteria for fatigue assessment are developed in recent years, such as notch stress intensity factor (N-SIF), equivalent stress intensity factor (E-SIF), critical distance method (CMD) which includes point method (PM), line method (LM), area method (AM) and volumetric method (VM). The principles, procedures and effect factors about the local approaches are discussed in this paper.

Review of the fatigue assessment of welded joints by local approaches

Probabilistic framework for fatigue life assessment of notched components under size effects

A new approach to correlate the defect population with the fatigue life of selective laser melted Ti-6Al-4V alloy

Fatigue strength improvement factors for high strength steel welded joints treated by high frequency mechanical impact

It is well known that the fatigue strength of welded structures is in general independent from the material strength In case of high-strength steels, however, a significant improvement in the fatigue behaviour can be realised through post-treatment processes This paper deals with the effect of high-frequency mechanical impact (HFMI) on the fatigue behaviour of a range of steels starting from mild construction steel (S355) to ultra high-strength steel (S960) The experiments involve fatigue tests at a stress ratio of R = 01 on butt welds, T-joints, and longitudinal attachments on 5 mm, thin-walled specimens The fatigue assessment was performed in accordance to the nominal and the notch stress approach taking the HFMI condition into account Finally, a novel method is outlined to evaluate the notch stress fatigue behaviour of HFMI-treated joints made of high-strength steel Applicability of this new HFMI notch stress approach is shown through fatigue assessment of about 330 HFMI post-treated specimens taken from both literature and own test results Further work focuses on the expansion of the introduced HFMI notch stress model for load spectra influence covering overloads and multiaxial fatigue

Fatigue enhancement of thin-walled, high-strength steel joints by high-frequency mechanical impact treatment

Stability of high frequency mechanical impact (HFMI) post-treatment induced residual stress states under cyclic loading of welded steel joints

This study shows the effect of hot isostatic pressing (HIP) on the porosity and the microstructure, as well as the corresponding fatigue strength of selectively-laser-melted (SLM) AlSi10Mg structures. To eliminate the influence of the as-built surface, all specimens are machined and exhibit a polished surface. To highlight the effect of the HIP treatment, the HIP specimens are compared to a test series without any post-treatment. The fatigue characteristic is evaluated by tension-compression high cycle fatigue tests under a load stress ratio of R = −1. The influence of HIP on the microstructural characteristics is investigated by utilizing scanning electron microscopy of micrographs of selected samples. In order to study the failure mechanism and the fatigue crack origin, a fracture surface analysis is carried out. It is found that, due to the HIP process and subsequent annealing, there is a beneficial effect on the microstructure regarding the fatigue crack propagation, such as Fe-rich precipitates and silicon agglomerations. This leads, combined with a significant reduction of global porosity and a decrease of micro pore sizes, to an improved fatigue resistance for the HIPed condition compared to the other test series within this study.

https://www.mdpi.com/2504-4494/3/1/16/pdf

Martin Leitner

Papers

Fatigue enhancement of thin-walled, high-strength steel joints by high-frequency mechanical impact treatment

Stability of high frequency mechanical impact (HFMI) post-treatment induced residual stress states under cyclic loading of welded steel joints

Effect of hip treatment on microstructure and fatigue strength of selectively laser melted AlSi10Mg

Residual stress state induced by High Frequency Mechanical Impact Treatment in different steel grades -numerical and experimental study

Application of modified Kitagawa-Takahashi diagram for fatigue strength assessment of cast Al-Si-Cu alloys