Dislocation mechanisms of mean stress effect on cyclic plasticity

The goal of the present paper is to discuss the reliability of a strain-based multiaxial Low-Cycle Fatigue (LCF) criterion in estimating the fatigue lifetime of metallic structural components subjected to multiaxial sinusoidal loading with zero and non-zero mean value. Since it is well-known that a tensile mean normal stress reduces the fatigue life of structural components, three different models available in the literature are implemented in the present criterion in order to take into account the above mean stress effect. In particular, such a criterion is formulated in terms of strains by employing the displacement components acting on the critical plane and, then, by defining an equivalent strain related to such a plane. The Morrow model, the Smith-Watson-Topper model and the Manson-Halford model are applied to define such an equivalent strain. The effectiveness of the new formulations is evaluated through comparison with some experimental data reported in the literature, related to biaxial fatigue tests performed on metallic specimens under in-and out-of-phase loadings characterised by non-zero mean stress values.

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A New Crack Initiation Life Prediction Method for Arbitrary Multiaxial Loading Considering Mean Stress Effect

Fatigue '96 ◽

10.1016/b978-008042268-8/50044-7 ◽

1996 ◽

pp. 1007-1012 ◽

Cited By ~ 5

Author(s):

W. Ott ◽

O. Baumgart ◽

K.H. Trautmann ◽

H. Nowack

Keyword(s):

Crack Initiation ◽

Life Prediction ◽

Prediction Method ◽

Stress Effect ◽

Mean Stress ◽

Multiaxial Loading ◽

Mean Stress Effect ◽

Crack Initiation Life

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S–N curves for fatigue life estimation of friction stir welded 19501 aluminum alloy T-joint

Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science ◽

10.1177/0954406218760056 ◽

2018 ◽

Vol 233 (2) ◽

pp. 664-674

Author(s):

Prakash Chandra Gope ◽

Harshit Kumar ◽

Himanshu Purohit ◽

Manish Dayal

Keyword(s):

Aluminum Alloy ◽

Fatigue Life ◽

Fatigue Strength ◽

Weld Zone ◽

Stress Effect ◽

Mean Stress ◽

Friction Stir ◽

Fracture Surfaces ◽

Mean Stress Effect ◽

Metallic Bonding

In this study, the mechanical properties and fatigue life of 19501 aluminum alloy friction stir welded T-joint is investigated. Tensile properties of friction stir welded joint show that there is a marginal reduction of about 5% in strength and ductility as compared to unwelded 19501 aluminum alloy. Fatigue test results of T-joint specimen at two stress ratios of 0 and -1 show that there is a reduction of 15% in fatigue strength due to change of stress ratio from -1 to 0. Also, higher variation is seen in fatigue strength in low cycle zone than the high cycle zone. Effect of mean stress on fatigue life is discussed on the basis of different mean stress effect models. Morrow’s mean stress effect model is found to be better than other models. Micrographs from the fracture surfaces of retreating side, mid weld zone, and advancing side of the T-joint indicates that fracture surfaces are cleavage fracture. Different sizes of inter-metallic bonding are seen in the micrographs, which indicate that fracture is initiated due to breaking of the brittle inter-metallic bonding.

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