Abstract
There are several types of fatigue testing machines under multiaxial loading. Each type of testing machine has its own characteristic, but most of multiaxial fatigue studies have been performed by a using push-pull and reversed torsion fatigue testing machine with a hollow cylinder specimen. This testing machine can perform multiaxial fatigue tests under not only proportional loading but also non-proportional loading where principal directions of stress and strain are changed in a cycle. However, the principal strain ratio range performable is -1≤ε_3/ε_1≤-v, where ε_1 and ε_3 are the maximum and the minimum principal strains and v Poisson's ratio. Since structural components under service loading undergo wider principal strain ratios, fatigue testing machines which can perform the wider multiaxial stress and strain states are necessary to evaluate the multiaxial fatigue damage precisely. This study developed two types of fatigue testing machines for multiaxial fatigue. One is a biaxial testing machine using a cruciform specimen. The other one is a testing machine using the hollow cylinder specimen added combining push-pull and reversed torsion loadings with cyclic internal and external pressures.
