No abstract

No abstract

In reality most welded components are loaded with a combination of different variable forces and moments that often cause a state of multiaxial stress in the fatigue‐critical areas. If the multiaxial loading is non‐proportional, traditional deformation‐based hypotheses are not able to give a reliable lifetime prediction. This investigation is a cooperation between three German research institutes to build an experimental database for the verification of different concepts of lifetime prediction. In accordance with former investigations, a flange‐tube connection made of steel P460 was used. The test program was divided into constant amplitude and variable amplitude tests. The ratio between the nominal bending and shear stress is 1. For the variable amplitude tests, a Gaussian‐standard is used. A lifetime prediction software for multiaxial state of cyclic stress was developed. The software has a modular structure and allows calculations with different hypotheses and methods. The calculations are based on the local elastic stresses. This is an acceptable method for high‐cycle fatigue. In this work, two general types of calculation, the Integral Approach and Critical Plane Approach and a local stress‐based modification of the von Mises Criterion, the hypothesis of effective equivalent stress (EESH) are shown. The damage accumulation is performed with the elementary Miner’s rule (S–N curve without fatigue limit). The statistical distributions of the damage sums are also shown.

Estimation of Endurance Limit under Multiaxial LoadingMultiaxial criteria for endurance limit prediction of metallic materials will be discussed in this paper.The Shear Stress Intensity Hypothesis SIH is improved under consideration of the variable fatigue limit ratio zwlow and mean stress effects. Fatigue behaviour under synchronous and nonsynchronous stresses and influences such as mean stresses, out-of-phase stresses, different frequencies, nonsinusoidal stress time function are analysed theoretically and verified with test results. The prediction according to SIH shows good agreement with the test results. Based on an extensive statistical investigation it can be recommended to use the SIH for "crack free materials" and the normal stress hypothesis NSH for "materials with cracks".For components the hypothesis SIH and NSH are developed under consideration of the notch effect. In this study a concept for the prediction of endurance limit under multiaxial loads has been developed.

No abstract