Analysis of cyclic deformation under non-proportional tension and torsion loading.

The knowledge of cyclic deformation behaviour is essential for fatigue analysis of industrial components. However such knowledge is difficult to obtain for nonproportional loading situation. Although notch deformation can be analysed by methods such as Neuber, but these methods are not suitable for critical non-proportional loading paths encounted in industrial components.The aim of this research was to study the cyclic deformation of a medium carbon steel EN 8. It is essential to find the plastic strain ranges under cyclic loads as it is used for fatigue life prediction under variable amplitude tension-torsion multiaxial, proportional and non-proportional loops. Hysteresis loops were obtained experimentally for different loading conditions of uniaxial, torsional, proportional and non-proportional loads. Finite element analyses were also performed. Experiment and the FEA results obtained using ABAQUS code were compared. Neuber predictions were performed for uniaxial load and torsion loads. Comparisons of analytical and finite element results show good correlation.The specimens used for the testing programme were solid cylindrical with a notch and made from EN8 medium carbon steel. A series of tests were conducted under various axial-torsion loading conditions. For the testing, a computer controlled biaxial ESH machine was used. Rosette strain gauges attached at the notch root were used to measure the three strain components.The hysteresis loops obtained from the experiment were compared with the Finite Element results for uniaxial, torsion, in-phase, out of phase and three other nonproportional paths. Considering the results obtained from different non-proportional multiaxial loading paths, Path-C non-proportional loading was found to be more damaging and Path-A was least damaging in both FEA and experiment cases.