Abstract
In the context of high cycle fatigue (HCF), the experimental characterization of the fatigue properties is often performed by using specimens in a virgin state (i.e., without preliminary loading), and with a constant stress amplitude for each specimen. However, the load history applied to a real structure is more complex and the fatigue life prediction remains a difficult task because of the time dedicated to the classical fatigue tests (i.e., the specimen is loaded until failure) and the dispersion of fatigue lives. The load history effects on the HCF properties is characterized using an alternative method: self-heating measurements under cyclic loadings. This method is based on the observation of the mean steady state temperature evolution of a specimen under a successive series of cyclic loadings with increasing stress amplitude for each loading series. A probabilistic two-scale model was developed from the self-heating method able to predict HCF properties. Some self-heating tests are performed to study the influence of a load history effects. It seems that the plasticity is the most influential factor. So, the evolution of the plasticity is observed at the surface of the material under cyclic loading. There is a significant evolution in function of the plastic pre-strain.
Highlights
The standard method to characterize high cycle fatigue properties of steel grade requires one month of tests
An initial series of cyclic loading has a slightly influence and this influence can explain the difference between the fatigue limit determined from a two blocks fatigue test
If a such as fatigue test is performed with the first block amplitude higher than the second one, the fatigue limit determined is lower than if the two blocks are inverted
Summary
The standard method to characterize high cycle fatigue properties of steel grade requires one month of tests. To reduce the time of characterization, some fast methods have been developed, such as the self-heating method. This method, associated with a two scales probabilistic model, allows to obtain the fatigue limit with only one specimen in less than one day. This kind of model assumes that the damage is mainly due to microplasticity activation. Many steel grades have been studied with the self-heating method [1,2]. To go deeper in this way, and to expand the two scales probabilistic model, two kind of load history are studied with the self-heating method: a plastic pre-straining and a cyclic-pre-loading
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