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.

The effects of deep rolling and shot peening on fretting fatigue resistance of Aluminum-7075-T6

Abstract: The effect of shot peening (SP) and deep rolling (DR) on fretting fatigue life of Aliminum7075-T6 is investigated in this work. The results show that fretting fatigue reduces the normal fatigue life by 67%. For low cycle fatigue, SP while being superior to DR, increases the fretting fatigue life by 300% for the specimens tested in this work. For high cycle fatigue, however, the effect of DR on fretting fatigue resistance is more profound than SP such that an increase of about 700% is observed for DR. Numerical simulation of SP and DR is also performed in this work. The results indicate that DR gives rise to a larger compressive residual stress than SP under the conditions considered in the simulations. This agrees quantitatively with the experimental results obtained from high cycle fatigue tests.

Fatigue behavior of high-Mn TWIP steels

Abstract: Fatigue behavior of three high-Mn TWIP steels with the grain sizes between 4.5 and 55 μm were investigated in reversed plane bending in the high-cycle regime. Crack initiation and propagation stages were examined by optical, scanning electron and atom force microscopy. It was found that the fatigue limit, which is the stress amplitude leading to fatigue life beyond 2 × 10 6 cycles, is quite high, about 400 MPa, for these steels. This value is between 0.42 and 0.48 of the tensile strengths, similarly as for austenitic stainless steels. Refining the grain size still increases the fatigue resistance. Neither martensite is formed nor mechanical twinning takes place in the course of cycling, but intense slip bands are created with extrusions and intrusions. Fatigue cracks tend to nucleate at an early stage of fatigue life, and preferentially on grain and twin boundaries, especially in the intersection sites of slip bands and boundaries, besides slip bands. However, the crack propagation takes place mainly transgranularly creating ductile striations and protrusions on fracture surfaces.

Effect of microstructure on the fatigue of hot-rolled and cold-drawn NiTi shape memory alloys

Abstract: We present results from a systematic study linking material microstructure to monotonic and fatigue properties of NiTi shape memory alloys We consider Ni-rich materials that are either (1) hot rolled or (2) hot rolled and cold drawn In addition to the two material processing routes, heat treatments are used to systematically alter material microstructure giving rise to a broad range of thermal, monotonic and cyclic properties The strength and hardness of the austenite and martensite phases initially increase with mild heat treatment (300 °C), and subsequently decrease with increased aging temperature above 300 °C This trend is consistent with transmission electron microscopy observed precipitation hardening in the hot-rolled material and precipitation hardening plus recovery and recrystallization in the cold-drawn materials The low-cycle pseudoelastic fatigue properties of the NiTi materials generally improve with increasing material strength, although comparison across the two product forms demonstrates that higher measured flow strength does not assure superior resistance to pseudoelastic cyclic degradation Fatigue crack growth rates in the hot-rolled material are relatively independent of heat treatment and demonstrate similar fatigue crack growth rates to other NiTi product forms; however, the cold-drawn material demonstrates fatigue threshold values some 5 times smaller than the hot-rolled material The difference in the fatigue performance of hot-rolled and cold-drawn NiTi bars is attributed to significant residual stresses in the cold-drawn material, which amplify fatigue susceptibility despite superior measured monotonic properties