Revisiting Classical Issues of Fatigue Crack Growth Using a Non-Linear Approach

Materials

FernandoV. Antunes¹  MicaelF. Borges¹  DiogoM. Neto¹ 

[1] Department of Mechanical Engineering, Centre for Mechanical Engineering, Materials and Processes (CEMMPRE), University of Coimbra, 3030-788 Coimbra, Portugal;

关键词: fatigue crack growth;    constant amplitude loading;    crack closure;    overload;   

DOI  :  10.3390/ma13235544

来源: DOAJ

【 摘 要 】

Fatigue crack growth (FCG) has been studied for decades; however, several aspects are still objects of controversy. The objective here is to discuss different issues, using a numerical approach based on crack tip plastic strain, assuming that FCG is driven by crack tip deformation. DK was found to control cyclic plastic deformation at the crack tip, while K_max has no effect. Therefore, alternative mechanisms are required to justify models based on DK and K_max. The analysis of crack tip plastic deformation also showed that there is crack tip damage below crack closure. Therefore, the definition of an effective load range DK_eff = K_max − K_open is not correct, because the portion of load range below opening also contributes to FCG. Below crack closure, damage occurs during unloading while during loading the crack tip deformation is elastic. However, if the maximum load is decreased below the elastic limit, which corresponds to the transition between elastic and elasto–plastic regimes, there is no crack tip damage. Additionally, a significant effect of the crack ligament on crack closure was found in tests with different crack lengths and the same DK. Finally, the analysis of FCG after an overload with and without contact of crack flanks showed that the typical variation of da/dN observed is linked to crack closure variations, while the residual stresses ahead of crack tip are not affected by the contact of crack flanks.

【 授权许可】

Unknown