A B S T R A C T Mean stress effects in finite-life fatigue are studied for a number of sets of experimental data for steels, aluminium alloys and one titanium alloy. Specifically, the agreement with these data is examined for the Goodman, Morrow, Smith-Watson-Topper and Walker equations. The Goodman relationship is found to be highly inaccurate. Reasonable accuracy is provided by the Morrow and by the Smith-Watson-Topper equations. But the Morrow method should not be used for aluminium alloys unless the true fracture strength is employed, instead of the more usual use of the stress-life intercept constant. The Walker equation with its adjustable fitting parameter γ gives superior results. For steels, γ is found to correlate with the ultimate tensile strength, and a linear relationship permits γ to be estimated for cases where non-zero mean stress data are not available.Relatively high-strength aluminium alloys have γ ≈ 0.5, which corresponds with the SWT method, but higher values of γ apply for relatively low-strength aluminium alloys.For both steels and aluminium alloys, there is a trend of decreasing γ with increasing strength, indicating an increasing sensitivity to mean stress.A = intercept constant at 1 cycle for a stress-life curve b = exponent constant for a stress-life curve b w = exponent constant for a Walker method stress-life fit c = exponent constant for a plastic strain versus life curve d = intercept constant for multiple linear regression E = elastic modulus m 1 , m 2 = slope constants for multiple linear regression n = number of data points for an s z calculation N * = life for a given ε a for the σ m = 0 case N * w = value of N * from the Walker method N f = fatigue life; cycles to failure R = stress ratio, R = σ min /σ max s z = stress deviation; the standard deviation of z for a set of data z = normalized stress-direction deviation of a data point relative to a stress-life curve σ = stress range, σ = 2σ a ε a = strain amplitude ε ar = strain amplitude for σ m = 0 ε f = intercept constant at 1/2 cycle for a plastic strain versus life curve Correspondence: N. E. Dowling.

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Many advanced high-strength steels rely on a metastable austenite phase for improvements in strength and formability. To date, no method has demonstrated the ability to provide accurate austenite phase fraction measurements in textured steels. Several techniques have been proposed, such as averaging the intensity of several peaks and/or summation of intensity from several sample orientations. The series of numerical experiments performed in this work sought to quantify the effects of texture on the measurement of the austenite phase fraction, with an emphasis on techniques suitable for laboratory X-ray diffraction. Simulated diffraction profiles were created with the following variables: texture components for the ferrite and austenite phases, the sharpness of each of the texture components, the number of peaks used for averaging in the phase fraction calculation, and the sampling scheme used for sample orientation summation in the phase fraction calculation. The resulting phase fraction calculations showed that texture, the number of peak pairs and the sampling method have a drastic effect on phase fraction measurements, causing significant bias errors. Hexagonal grids produced minimal bias errors and demonstrated a robust method of measuring phase fractions in textured materials.

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