Topic
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.
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12 Aug 2015-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of severe plastic deformation induced by multiple sliding impacts by the specimen surface produced at ultrasonic impact treatment (UIT) on the stress-controlled fatigue response of the powder metallurgy Ti-6Al-4V alloy is studied.
Abstract: The effect of severe plastic deformation induced by multiple sliding impacts by the specimen surface produced at ultrasonic impact treatment (UIT) on the stress-controlled fatigue response of the powder metallurgy Ti–6Al–4V alloy is studied in this paper. Specimens of Ti–6Al–4V alloy were produced from Ti hydride precursor powders via the cost-effective blended elemental powder metallurgy technique. Structure investigations were performed by XRD, TEM, LM and SEM techniques. After UIT, fatigue strength was increased by about 60% on the base of 107 cycles, and lifetime was prolonged by two orders of magnitude at applied stress amplitudes of 300–400 MPa. The UIT process leads to approx. four times decrease in the surface roughness parameters. Increased by 65 and 20% microhardeness magnitudes are respectively registered on the top surface and on the depth of 100 μm. The UIT induced compressive stresses achieve about two thirds of the alloy yield stress. The hardness increase is shown to be coupled with the increased dislocation density, essentially refined of α+β microstructure and with randomization in α-grains orientations. Observations of cross-sections of the UIT processed specimens revealed the pores free near-surface layer of approx. 200 μm thick, which is formed thanks to micro-pore closure process promoted by high shear strains produced at the UIT induced sliding impacts. Analysis of fracture surfaces revealed subsurface cracks initiations and numerous fracture steps indicating on the cracks branching and deflection in the surface layers of the UIT processed specimens instead of superficial crack initiation and the grain boundary cleavages mainly observed in the pristine samples. Experimentally registered magnitudes of fatigue limit were successfully predicted by accounting for the effective stress intensity factor range ΔKth and observed by TEM microstructural units responsible for fatigue fracture (α-phase colonies, α-grains or micro-pores) and compared with literature data on PM Ti–6Al–4V alloy. Enhanced fatigue strength and prolonged lifetime of PM Ti–6Al–4V alloy after the UIT process are concluded to be associated with (i) minimized surface roughness; (ii) compressive residual stresses; (iii) UFG and nano-scale α+β microstructure; and (iv) micro-pore healing.
103 citations
25 Feb 2006-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the influence of root flaws on the fatigue strength and life of friction stir (FS) welds was investigated, and it was found that there was always existed flaws at the roots of FS welds because of unsuitable welding parameters and the vertical length of the flaws is about 0.31-0.33mm.
Abstract: The fatigue experiment of friction stir (FS) welds in 2024-T3 aluminum alloys were performed to investigate the influence of root flaws on the fatigue strength and life of FS welds. The test results of welds with flaws (flawed welds) were compared with the results suggested by the International Institute of Welding (IIW) recommendations and the welds without root flaws (flaw-free) in the published research reports. It was found that there was always existed flaws at the roots of FS welds because of unsuitable welding parameters and the vertical length of the flaws is about 0.31–0.33 mm for the FS butt-welded joint of 4 mm in thickness. The fatigue life of flawed welds is 33–80 times shorter than that of flaw-free welds, and the fatigue characteristic values have decreased from 120.6 MPa for flaw-free welds to 54.7 MPa for flawed welds at 2 × 106 cycles.
103 citations
TL;DR: In this paper, two kinds of ultra-high strength steel sheets having different ductility were used to join two different types of die having different shape and diameter and depth of the die.
103 citations
TL;DR: A Weibull analysis revealed an important size effect in bone and predicted this effect with an accuracy of 12% and concluded that large bones will have a fatigue strength much lower, by a factor of 2–3, than that measured by conventional tests.
102 citations
TL;DR: In this article, the upper and lower limits of life are estimated using the proposed life equations, where the upper life limit is obtained by assuming that the dominant cracking mechanism is Case A and the lower life limit, which is the case B, is derived from the amount of dissipated energy over life cycles.
102 citations