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.

A Total Strain Energy Density Theory for Cumulative Fatigue Damage

Abstract: La rupture par fatigue dans les regimes de haut et bas cycle, le dommage cumulatif, et la sequence de chargement peuvent etre exprimes en fonction d'un simple parametre de dommage Le critere de dommage est base sur la densite d'energie de deformation totale par cycle (somme de l'energie de deformation elastique et plastique) Les phases d'amorcage et de propagation de fissures sont inclues dans cette approche Application a l'acier A-516 pour recipient sous pression Comparaison avec les resultats experimentaux

On ‘multi-stage’ fatigue life diagrams and the relevant life-controlling mechanisms in ultrahigh-cycle fatigue

Abstract: In recent years, several fatigue studies on different metallic materials have indicated that fatigue failures can occur even at amplitudes below the conventional high-cycle fatigue (HCF) fatigue limit in the gigacycle or ultrahigh-cycle fatigue (UHCF) range (number of cycles to failure in excess of ca. 10 7 -10 8 ). In the latter case, fatigue failures were observed to originate from internal defects (non-metallic inclusions). The S-N curves displayed a multi-stage shape, sometimes with a second lower fatigue limit in the UHCF range. The present paper specifies the conditions under which internal and/or surface fatigue failure can occur at low load levels below the conventional HCF fatigue limit. The relevant fatigue thresholds are discussed for two classes of materials, namely pure single-phase metallic materials (type I) without internal defects and materials such as steels or cast materials (type II) with internal defects (inclusions or pores). In the case of type II materials, the probability of surface versus internal fatigue is discussed in terms of the volume density, size and location of the inclusions and the relevant cracking mechanisms. It is argued that, in both type I and type II materials, multi-stage S-N curves or Manson-Coffin plots can be expected under certain conditions.

Low-Cycle Fatigue Behavior of Reinforcing Steel

Abstract: ASTM A615 grade 40 ordinary deformed‐steel reinforcing bars with a specified minimum yield strength of 276 MPa (40 ksi) and ASTM A722 high‐strength prestressing thread bars with a specified ultimate strength of 1,083 MPa (157 ksi) were experimentally evaluated for their low‐cycle fatigue behavior under axial‐strain‐controlled reversed cyclic tests with strain amplitudes ranging from yield to 6%. All tests were performed on virgin (unmachined) specimens to closely simulate seismic behavior in structural concrete members. A methodology is suggested to identify incipient (first‐cracking) failure of test specimens. The experimental data were evaluated with existing fatigue models, which related stress‐strain quantities to the failure life. Additional energy‐based fatigue models are proposed that relate various stress and/or strain quantities to the dissipated energy. The study demonstrates that the modulus of toughness and low‐cycle fatigue life for both the low‐ and high‐strength materials are similar. Based...

Fatigue damage characterization in carbon fibre composite materials using an electrical potential technique

Abstract: Changes in electrical resistance during static and fatigue loading of unidirectional and cross ply carbon fibre reinforced polymer composites have been studied. The carbon fibres in the study were T300 and the matrix resins were Hexcel 914 and 920. It was found that changes in resistance during static tensile testing were about three per cent of the original resistance of the samples, while fatigue testing caused resistance changes of up to 10% of the original resistance, immediately prior to final failure. The initial linear portion of the resistance increase on static testing was reversible and could be attributed to reversible elastic strains in the fibres; later non-linear changes were a consequence of fibre fracture and were irreversible. Changes in resistance during fatigue also contained both reversible and non-reversible components. It was found that during fatigue testing the initial changes in resistance caused by the first few thousand cycles could be correlated with the eventual life. Samples with large initial resistance change had reduced lives compared with those with small changes in resistance. Fatigue lives of composite laminates may thus be predicted from monitoring of initial resistance changes. Many of the results could be explained via the parallel resistance model of conduction in composite laminates.

Crack initiation mechanism of extruded AZ31 magnesium alloy in the very high cycle fatigue regime

Abstract: Ultrasonic fatigue testing as well as conventional fatigue testing has been conducted on commercial extruded AZ31 magnesium alloy. The S-N curve for this alloy appears to have a continuous decreasing trend in the very high cycle regime. Fatigue strength at 109 cycles is 88.7 +/- 4.1 MPa. The ratio of endurance limit at one billion cycles to the tensile strength (sigma(-1)/sigma(b)) is 0.301. Fatigue failure mainly originated from the specimen surface or near surface, where deformation twins were found after cyclic loading. Fatigue cracks were observed along twin bands. Based on cyclic deformation irreversibility caused by twinning, fatigue damage mechanisms are proposed in terms of surface/near surface crack initiation. (C) 2008 Elsevier B.V. All rights reserved.