Creep-fatigue Crack Initiation Research Articles

Local Approach : Numerical Simulations of Creep and Creep-Fatigue Crack Initiation and Crack Growth in 316L SPH Austenitic Stainless Steel

This study deals with the evaluation of local approach to assess the mechanical integrity of cracked components submitted to cyclic and steady load at elevated temperature. In this approach, a fracture criterion based on calculated intergranular damage ahead of the crack tip is introduce to simulate both crack initiation and crack propagation in 316 L type austenitic stainless steel. This numerical method, based on finite element computations is firstly described. Then numerical results are compared with sets of experimental data for two specimen geometries during load controlled tests. A damage criterion in good agreement with previous studies leads to promising load-displacement response, crack initiation and crack growth curves.

Ｎｉ基超合金単結晶におけるクリープ‐疲労き裂の初生成長挙動

The fatigue and creep-fatigue crack initiation and growth behaviors of Ni-base single crystal superalloy TMS 12 were investigated at room temperature and 920°C using double edge notched specimens. At room temperature the fatigue incipient crack growth from the notch occurred by failure on the (111) plane, and the crack growth was not dependent on the number of cycles. At 920°C the crack growth behavior did not exhibit anisotropic fracture, which is caused from multiple slips. Under creep-fatigue and creep, rhombic cavities were observed at the crack tip vicinity. Alpha wolfram precipitates were observed at the sites of cavities. Cracks initiated from the interface rafted γ' and γ at alpha wolfram precipitates in (100) plane, which formed square-type cavities.

環状切欠き材の高温多軸クリープ疲労

This paper describes the notch effect in multiaxial creep-fatigue loadings for a type 304 stainless steel at an elevated temperature. Push-pull and reversed torsion creep-fatigue tests with hold-times of 3, 10 and 30min. were carried out at 873K for three types of notched specimens. The effect of stress concentration was more significant in torsion than in tension. The notch root local displacement (NRD) approach in combination with the frequency modified fatigue life equation provides a satisfactory data correlation for the creep-fatigue crack initiation life in tension and torsion.