Prediction of Constant-Amplitude Fatigue Life to Failure under Pulsating-Tension(R Greater Than or Equal to O) by Use of the Local-Strain-Approach

摘要

The aim was to compare Local Strain Approach (LSA) life prediction with pulsating-tension tests to failure. It is shown that, in the case of pulsating tension, the ratio N(sub i)/N(sub f) does not change considerably with the stress level and therefore LSA calculation can be of use for predicting S-N lines for R greater than or equal to O. The accuracy of the prediction is associated with choice of the K-value in Neuber's relation K(sub sigma) x K(sub epsilon) equals K(exp 2). The K-values which give the best life predictions were close to those of the corresponding notch factors for pulsating-tension (R = S(sub min)/S(sub max) = O). Because of the size and surface effects (which were not taken into account in LSA) and in view of the difficulty in knowing whether the specimen with a given K(sub F) value has exactly the same material parameters as those used in the LSA calculations, it is preferable to use a K-value proved to give predictions in agreement with a related pulsating-tension test. This K-value may be used for various combinations of S(sub a) and S(sub m) (S(sub a) greater than or equal to S(sub m) and S(sub max) less than S(sub y)). The results are valid for a specific specimen material, geometry, size, and surface finish.