'Coaxing effect' of prior cycling stress on material fracture mechanics performance

The fatigue crack growth rate tests were carried out using aluminum alloy materials served in high-speed train for years, and the relationship of fatigue crack growth rate da/dN and the stress intensity factor ΔK was shown in a broken form in logarithmic coordinates. Compared with the non-service material, the crack growth rate decreases at the initial stage. Aiming at this phenomenon, the aluminum alloy materials were applied here to investigate the behavior of fatigue crack growth under 10⁷ prior cycling stress. The influence of prior cycling stress under fatigue limit on the material fracture mechanics performance was studied in details. The results show that the curves of da/dN vs ΔK of prior cycling stress materials present a broken form in the low ΔK period. The regression analyses of the test data illustrate that the prior cycling stress plays a positive role in the fracture performance, and the prior cycling stress has 'coaxing effect' on the fatigue crack of materials.