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An accurate life prediction is important to the design of a high-speed rotary blade subjected to multilevel cyclic loads. The widely used Miner's rule and uniaxial stress prediction method always deviate from actual life of the blade. A prediction method based on Chaboche's nonlinear damage evolution model is utilized to predict the multilevel cyclic fatigue life of a compressor blade subjected to start-up centrifugal force and working aerodynamic force. Chaboche's model is verified by comparing with experimental data of different materials. The blade life predicted by Chaboche's rule and Miner's rule are compared, and it is found that Miner's rule might overestimate the blade life under the typical loading spectrum of start-up centrifugal force and working aerodynamic force. To study the impact of multiaxial stress state on the blade life, the life predicted by uniaxial stress method is compared to that predicted by multiaxial stress method, and it demonstrates that the multiaxial stress state of the blade should not be neglected. Finally, the crack propagation of the blade under multiaxial fatigue loads is simulated successfully by element deletion technique, which is conducted by translating Chaboche's multiaxial model into a user defined UMAT program in ABAQUS. The predicted crack propagation life is compared with that predicted by an approximate Paris law method plate model. This research proves that the method to predict the blade life subjected to multilevel cyclic loads based on multiaxial Chaboche's model could provide a valuable reference for engineering blade fatigue design. [ABSTRACT FROM AUTHOR]

This article presents a modified Neuber’s rule to estimate the inelastic stress and strain at the toe of welded plate connections under large-scale cyclic yielding, caused by the low-cycle fatigue loadings. In contrast to the original Neuber’s rule, which usually overestimates the notch-tip elastic–plastic stress and strain as the applied nominal stress approaches or exceeds the material yield strength, the modified Neuber’s rule provides a convenient and accurate estimation of the stress and strain at the weld toe as an alternative to the time-consuming numerical computation. The numerical study covers the variations in both the geometric configuration and the material properties in the modified Neuber’s rule. This article also provides closed-form expressions for the two critical parameters in the modified Neuber’s rule to facilitate engineering applications. [ABSTRACT FROM AUTHOR]

Fretting fatigue is a mechanical failure process, which consists of two complex failure mechanisms. Fretting is caused by small relative movement between connected parts and fatigue is due to alternating bulk load. Fretting fatigue is highly non-linear and subjected to non-proportional loading condition. The multiaxial nature of stress at contact interface can be highly influenced by different phase difference between axial, tangential and contact load. In this study, the effect of different phase difference between axial and tangential load on fretting fatigue behaviour is investigated. Moreover, by applying cyclic contact load instead of constant contact load, its effect on fretting fatigue response and crack initiation lifetime is investigated. It was found that the phase difference affects the maximum location of dissipated energy along with fretting fatigue crack initiation lifetime. [ABSTRACT FROM PUBLISHER]

The paper proposes an approach for thermal stress evaluation and fatigue life assessment of work rolls in hot rolling mills. Temperature and thermal stress distributions are calculated with a simplified finite element approach, based on a plane model of work roll loaded on its boundary by rotating thermal actions for a typical hot rolling configuration. A transient of one hour is simulated and the calculated temperature field is next applied as thermal loading in elastic–plastic mechanical simulation, to get thermal stresses and elastic–plastic strains in work roll. Calculated cyclic stresses and strains are finally used to estimate work roll service life, based on Universal Slopes equation that is modified to account for the multiaxial stress state. A comparison of results by three multiaxial fatigue criteria is provided. The obtained results show that, according to such multiaxial criteria, stress multiaxiality would have a great effect on fatigue life, despite it is generally neglected in approaches usually adopted in literature. [ABSTRACT FROM PUBLISHER]

The transverse mechanical and failure behavior of unidirectional S2-glass/epoxy composites are investigated and reported for a wide range of strain rates from 10-4 to 104s-1 under multiaxial compressive loading conditions. The effect of stress multiaxiality is explored using the confining sleeve technique to impose varying degrees of lateral confinement. The lateral confinement has been found to significantly increase both the maximum attainable stress level and the strain to failure. Scanning electron microscopy (SEM) observations on recovered specimens reveal that the transverse failure occurs within localized shear bands through multiple fiber-matrix interface failure at the micro-scale. Based on the orientation of shear bands a Mohr-Coulomb type failure criterion is suggested to represent the transverse failure of unidirectional S2-glass/epoxy composites. [ABSTRACT FROM AUTHOR]

A multiaxial fatigue failure criterion for composite materials is presented in this paper along with an assessment of the capability it offers for design under multiaxial constant or variable amplitude stresses. The applicability of this criterion, based on the well known quadratic failure tensor polynomial criterion for static loading, is validated through comparisons with uniaxial and multiaxial fatigue experimental data. Static and fatigue tests were carried out during this study on glass/polyester specimens cut off-axis from a multidirectional laminate at different angles. The agreement between experimental values and theoretical predictions is good. The proposed criterion is also compared to existing fatigue criteria and an overall assessment of their performance is given. Some theoretical design considerations for the case of irregular stress spectra, introducing the concept of multiaxial Miner coefficient, are finally presented. [ABSTRACT FROM PUBLISHER]