Abstract
The Stress concentration factor (SCF) induced by the machined surface is more complex than that resulting from macro-geometry discontinuities and has great effect on fatigue life of structure. However, another important parameter, stress gradient (SG), was always ignored. The notch roots or valleys of the wave surface constitute fatigue hot points, where cracks occur, so it is essential to study the SCF and SG at valleys rather than just the root-mean-square SCF variable. In this work, a new method for evaluating the influences of surface topography on fatigue propriety of the random machined surfaces was given. An analytical method using Fourier transformation to simulate machined surface topography is presented. Analytical formulae for SCF and SG for random machined surfaces are derived subjected to a general loading and validate these formulae via finite element method (FEM). Joint probability-distribution function for SCF and SG at the valleys of the random machined-surface topography of the machined sample was obtained after different cycles fatigue test. This method gave us how the surface topography effect the fatigue properties of machined components. Fatigue test of machined sample for a single crystal nickel based alloy were established for validated this method. The obtained results should be useful in studying and evaluating fatigue properties of machined components.
Highlights
The stress concentration factor (SCF) is an important parameter in the application of mechanical engineering and knowledge of this parameter and the stress distribution around notches is important for engineers engaged in the design or fatigue-life prediction of engineering components [1,2,3,4]
The stress concentration induced by the machined surface is more complex than that resulting from macro-geometry discontinuitiesand is characterized by the occurrence of multiple hotspots
In the present work, we propose a method to evaluate the influences of surface topography on fatigue propriety of the random machined surfaces
Summary
The stress concentration factor (SCF) is an important parameter in the application of mechanical engineering and knowledge of this parameter and the stress distribution around notches is important for engineers engaged in the design or fatigue-life prediction of engineering components [1,2,3,4]. The fatigue stress concentration factor, related to SG and SCF, can describe the relationship between surface topography and fatigue life. In the present work, we propose a method to evaluate the influences of surface topography on fatigue propriety of the random machined surfaces. This paper is organized as follows: an approach for simulations of the machined surface from the measured data was given, the analytical solutions of SCF and SG, obtained via Fourier transformation, in the section 4, validation of these solutions under uniform loading via finite element simulations was presented, a 2D joint probability-distribution function of SCF and SG associated with the machined-surface topography was given, different fatigue test cycles for the proposed method to evaluate the influences of surface topography on fatigue propriety of the random machined surfaces in the section 6.
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