Abstract
The unexpected failures of structural materials in very high cycle fatigue (VHCF) regime have been a critical issue in modern engineering design. In this study, the VHCF property of a Cr-Ni-W gear steel was experimentally investigated under axial loading with the stress ratio of R = −1, and a life prediction model associated with crack initiation and growth behaviors was proposed. Results show that the Cr-Ni-W gear steel exhibits the constantly decreasing S-N property without traditional fatigue limit, and the fatigue strength corresponding to 109 cycles is around 485 MPa. The inclusion-fine granular area (FGA)-fisheye induced failure becomes the main failure mechanism in the VHCF regime, and the local stress around the inclusion play a key role. By using the finite element analysis of representative volume element, the local stress tends to increase with the increase of elastic modulus difference between inclusion and matrix. The predicted crack initiation life occupies the majority of total fatigue life, while the predicted crack growth life is only accounts for a tiny fraction. In view of the good agreement between the predicted and experimental results, the proposed VHCF life prediction model involving crack initiation and growth can be acceptable for inclusion-FGA-fisheye induced failure.
Highlights
In consideration of the current economics and energy resources, a great number of machinery parts or components, such as axle, wheel, gear, blade, etc., are expected to have a very high cycle fatigue (VHCF) life beyond 107 cycles [1,2]
Main conclusions obtained in this study ar8e3s5u2mmarized as follows: (1) The Cr‐Ni‐W gear steel exhibits the constantly decreasing S‐N property without traditional fatigue limit, and the fatigue strength corresponding to 109 cycles is around 485 MPa
Main conclusions obtained in this study are summarized as follows: (1) The Cr-Ni-W gear steel exhibits the constantly decreasing S-N property without traditional fatigue limit, and the fatigue strength corresponding to 109 cycles is around 485 MPa
Summary
In consideration of the current economics and energy resources, a great number of machinery parts or components, such as axle, wheel, gear, blade, etc., are expected to have a very high cycle fatigue (VHCF) life beyond 107 cycles [1,2]. Some methods or models combined with Paris law [14,15,16], FGA size [15,17,18], cumulative damage [19], stress ratio [16,20] and tensile strength [7,19] are proposed to predict fatigue life or strength in the VHCF regime These empirical methods or models are not necessarily appropriate for the experimental results of any steel, they to some extent reflect the failure behaviors of materials under a given condition. Based on the definition of crack initiation and grow processes, a fatigue life model involving both crack initiation and growth was established to evaluate the VHCF life for inclusion-FGA-fisheye induced fatigue failure
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