Fatigue limit

About: Fatigue limit is a research topic. Over the lifetime, 20489 publications have been published within this topic receiving 305744 citations. The topic is also known as: endurance limit & fatigue strength.

Standardization of fretting fatigue test methods and equipment

Abstract: Papers contained in this book are grouped under the topics of the fundamental aspects of fretting fatigue testing (conceptual framework and mechanics of contact), methods and equipment for fretting fatigue testing, environmental and surface conditions, and nonconventional materials and test methods. Papers are presented on the problems of fretting fatigue testing, a critical appraisal of testing methods in fretting fatigue, the determination and control of contact pressure distribution in fretting fatigue, and fretting fatigue analysis of strength improvement models with grooving or knurling on a contact surface. Other papers include a critical review of fretting fatigue investigations at the Royal Aerospace Establishment, techniques for the characterization of fretting fatigue damage, improving fretting fatigue strength at elevated temperatures by shot peening in steam turbine steel, the fretting fatigue properties of a blade steel in air and vapor environments, and fretting fatigue of carbon-fiber-reinforced epoxy laminates.

The fatigue limit and its elimination

Abstract: The classical fatigue limit of ferrous metals is a consequence of testing materials at a constant range of cyclic stress and determining the cyclic stress range below which fatigue failures do not occur. This classical fatigue limit of a material is equated to the condition for which fatigue cracks can not propagate beyond microstructural barriers. This paper discusses the causes, leading to the elimination of this fatigue limit, including the introduction of transitory cyclic-dependent mechanisms and time-dependent processes that will permit a previously non-propagating crack to grow across the different threshold states expressed in terms of linear-elastic fracture mechanics (LEFM), elastic-plastic fracture mechanics (EPFM) and microstructural fracture mechanics (MFM). These transitory mechanisms and processes include different loading and environmental conditions, which in a long-life engineering plant (e.g. 30 years lifetime) can lead to apparently premature failures. Of greater concern is the creation of a new crack-initiation zone, i.e. a transfer from a surface-generated crack to an internal-generated crack that eventually dominates the fatigue failure event. The impact of these conditions on the elimination of the classical fatigue limit necessitates changes in Design Codes of Practice, and such changes are discussed in relation to the extremely long-lifetime regime (10 7

A review of the as-built SLM Ti-6Al-4V mechanical properties towards achieving fatigue resistant designs

Abstract: Ti-6Al-4V has been widely used in both the biomedical and aerospace industry, due to its high strength, corrosion resistance, high fracture toughness and light weight. Additive manufacturing (AM) is an attractive method of Ti-6Al-4V parts’ fabrication, as it provides a low waste alternative for complex geometries. With continued progress being made in SLM technology, the influence of build layers, grain boundaries and defects can be combined to improve further the design process and allow the fabrication of components with improved static and fatigue strength in critical loading directions. To initiate this possibility, the mechanical properties, including monotonic, low and high cycle fatigue and fracture mechanical behaviour, of machined as-built SLM Ti-6Al-4V, have been critically reviewed in order to inform the research community. The corresponding crystallographic phases, defects and layer orientations have been analysed to determine the influence of these features on the mechanical behaviour. This review paper intends to enhance our understanding of how these features can be manipulated and utilised to improve the fatigue resistance of components fabricated from Ti-6Al-4V using the SLM technology.

IIW recommendations for the fatigue assessment of welded structures by notch stress analysis: IIW-2006-09

Abstract: The notch stress approach for fatigue assessment of welded joints is based on the highest elastic stress at the weld toe or root. In order to avoid arbitrary or infinite stress results, a rounded shape with a reference radius, instead of the actual sharp toe or root, is usually assumed. Different proposals for reference radii exist, e.g. Radaj proposed a fictitious radius of 1 mm to consider micro-structural support effects for steel. The present guideline reviews different proposals for reference radii together with associated S-N curves. Detailed recommendations are given for the numerical analysis of the notch stress by the finite or boundary element method. Several aspects are discussed, such as the structural weakening by keyhole-shaped notches and the consideration of multiaxial stress states. Regarding the fatigue strength, appropriate S-N curves are presented for different materials. Finally, four examples illustrate the application of the approach, as well as the variety of structures that can be analysed and the scatter of results obtained from different models.