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In this study, best-fit fatigue curves are constructed considering material properties and loading modes. Three common fatigue test methods (rotating bending, axial load-controlled and strain-controlled) are compared, and their scopes of applications are clarified. The best-fit fatigue curves are given as a function of tensile strength and have been constructed based on the strain-controlled fatigue test data. The comparison of the best-fit fatigue curves with the axial load-controlled test data reveals that both deviated from each other for the carbon and low-alloy steels and the austenitic stainless steel. Therefore, the best-fit fatigue curves are reconstructed considering the data by the rotating bending fatigue test and the axial load-controlled fatigue test. In the case of the carbon and low-alloy steels, the best-fit fatigue curves are classified by two kinds of microstructures. In the case of the austenitic stainless steel, the best-fit fatigue curves are classified by two kinds of loading modes. Finally, design factors based on the reliability of best-fit fatigue curves are specifically presented.

Cylinder-crown integrated hydraulic press (CCIHP) is a new press structure. The hemispherical hydraulic cylinder also functions as a main portion of crown, which has lower weight and higher section modulus compared with the conventional hydraulic cylinder and press crown. As a result, the material strength capacity is better utilized. During the engineering design of cylinder-crown integrated structure, in order to increase the fatigue life, structural optimization on the basis of the adaptive macro genetic algorithms (AMGA) is first conducted to both reduce weight and decrease peak stress. It is shown that the magnitude of the maximum principal stress is decreased by 28.6%, and simultaneously the total weight is reduced by 4.4%. Subsequently, strain-controlled fatigue test is carried out, and the stress-strain hysteresis loops and cyclic hardening curve are obtained. Based on linear fit, the fatigue properties are calculated and used for the fatigue life prediction. It is shown that the predicted fatigue life is significantly increased from 157000 to 1070000 cycles after structural optimization. Finally, according to the optimization design, a 6300 kN CCIHP has been manufactured, and priority application has been also suggested. [ABSTRACT FROM AUTHOR]

Abstract: The low cycle fatigue (LCF) behaviour of a Cr–Mo–V matrix-type high-speed steel (matrix-type HSS), which was used as cold forging tool material, was investigated. Fatigue tests were conducted under strain-controlled cyclic loading conditions with different axial strain amplitude levels at room temperature. The tests indicated that hysteresis loops formed when the total strain amplitude was 1.5%, 1.0% and 0.75%. At total strain amplitudes that were less than 0.7%, there was no cyclic plastic deformation or hysteresis loop observed. The material fatigue behaviour was analysed specifically at the above three strain levels to investigate the cyclic plastic deformation of the material because the low cycle fatigue behaviour was of principal interest in this study. At all selected total strain amplitudes, the cyclic stress responses showed cyclic softening, and reached a “quasi-stabilised” softening state before the material finally ruptured from fatigue. The cyclic strain–stress relationship and the strain–life relationship were obtained through the test results, and related material parameters were calculated. Fractographic and metallographic analyses were also conducted in this study. The metallographic structure of the steel before and after heat treatment was examined. Two types of carbide phases were found in the steel. The fatigue damage process through the crack initiation and propagation was explained by observing the features of the fractures. [Copyright &y& Elsevier]

• Review of elastic modulus evaluation for fatigue design of metallic components. • Cyclic material parameters according to the elastic modulus of EN AW-7075. • Comparison of different evaluation methods for the elastic modulus of EN AW-7075. • Determination of the elastic modulus from linear elastic cyclic tests. The elastic modulus is a key parameter for the description of material properties when evaluating metallic components under service loads. In particular, when evaluating strain-controlled tests for the application of the strain-life approach, there are numerous different possibilities in standards for determining this material parameter. These can lead to different results and confront the user with a certain challenge in selecting the most suitable method. In this publication, an overview of different evaluation methods is given and a new evaluation method is presented, in which the elastic modulus is determined using the reversal points of a strain-controlled cyclic test under macroscopic linear-elastic deformation. This allows a simple and clear, widely user-independent determination of the elastic modulus. In addition, the differences between the new and the commonly used evaluation methods are shown, using the example of the aluminum alloy EN AW-7075, and their influence on the strain-life curve, the P SWT and P J damage parameter curves, and the cyclic stress-strain curve by Ramberg-Osgood are investigated. [ABSTRACT FROM AUTHOR]