More insights into fatigue crack growth from experiments on steels and aluminium alloys—Thresholds

The paper deals with the influence of the R-ratio on the fatigue crack propagation threshold of different metallic materials. Based up on threshold data of steels, aluminium-alloys and two particulate-reinforced aluminium-alloys the threshold behaviour has been analyzed and a new model to describe the threshold behaviour has been deduced. With this model, which contains two quantities that can be deduced from special fatigue crack propagation tests, the threshold behaviour of different kind of materials can be explained. Finally, the existence of the threshold can be attributed to specific elastic parameters of the materials (shear modulus) and their microstructure.