The paper presents method for determined S-N curve used only static properties of material. To verified this algorithm, material C45+C was tested to provide reference fatigue characteristics. Tests was carrying out with rotating bending by equipment own design. Test machine was checked for correct working according standard ISO 1143. Verification of analytical method has been realized by statistical calculation assume null hypothesis that coefficient of slope of straight line and absolute term estimated by proposed algorithm is equal to coefficient of slope and absolute term estimated from experimental data. Calculated value of statistics has shown that there is no reason to reject null hypothesis for proposed method.

In this paper, the sensitivity to the type of loads (axial and bending loading) of selected construction materials (AW6063 T6 aluminum alloy, S355J2+C structural steel, and 1.4301 acid-resistant steel) in high-cycle fatigue was verified. The obtained S-N fatigue characteristics were described by a probabilistic model of the 3-parameters Weibull cumulative distribution function. The main area of research concerned the correct implementation of the weakest link theory model. The theory is based on a highly-stressed surface area and a highly-stressed volume in the region of the highest stresses. For this purpose, an analytical model and a numerical model based on the finite element method were used. The model that gives the lowest error implemented in specific test conditions was determined on the basis of high-cycle fatigue analysis. For the analyzed materials, it was a highly-stressed volume model based on the weakest link theory.

The paper presents a standard approach to the determination of the S-N curve. It also presents an alternative approach requiring fewer samples. The proposed method was verified based on test results for steel S3555J2+C. The tests were performed by rotating bending. Based on the resulting curves, it was determined that a sufficiently accurate S-N curve could be obtained using 9 samples, which is fewer than the standard 14 samples. In addition, a different scatter band depending on sample loading level within its limited durability range. It can be obtained using the 3-parameter Weibull distribution.

This paper presents the results of the static tensile and fatigue life tests under rotating bending of round 1.4301 (AISI 304) steel samples. The fatigue tests were carried out on smooth and notched samples with three different rounding angles with a shape factor of 1.4, 2 and 2.6. A fatigue life was determined for samples with different shape factors subject to identical loads. The results showed that the scatter of fatigue test results decreases with an increase in shape factor. To evaluate the cracking properties (cracking mode and mechanism), microstructure and fractographic tests of the fractured samples were carried out.

The study presents two approaches to plotting an S-N curve based on the experimental results. The first approach is commonly used by researchers and presented in detail in many studies and standard documents. The model uses a linear regression whose parameters are estimated by using the least squares method. A staircase method is used for an unlimited fatigue life criterion. The second model combines the S-N curve defined as a straight line and the record of random occurrence of the fatigue limit. A maximum likelihood method is used to estimate the S-N curve parameters. Fatigue data for C45+C steel obtained in the torsional bending test were used to compare the estimated S-N curves. For pseudo-random numbers generated by using the Mersenne Twister algorithm, the estimated S-N curve for 10 experimental results plotted by using the second model, estimates the fatigue life in the scatter band of the factor 3. The result gives good approximation, especially regarding the time required to plot the S-N curve.

Verification of analytical models of the S-N curve within limited fatigue life