A novel methodology for determining creep crack initiation and growth properties using FEM with notched small punch specimens

0547003 - ÚFM 2022 RIV NL eng J - Journal Article
Li, Y. - Dymáček, Petr - Hurst, R. - Stevens, P.
A novel methodology for determining creep crack initiation and growth properties using FEM with notched small punch specimens.
Theoretical and Applied Fracture Mechanics. Roč. 116, DEC (2021), č. článku 103112. ISSN 0167-8442. E-ISSN 1872-7638
R&D Projects: GA MŠMT(CZ) LQ1601
Institutional support: RVO:68081723
Keywords : fracture mode transition * toughness * steel * tests * Residual life assessment * Creep crack initiation (CCI) * Creep crack growth (CCG) * C*-integral * Stress intensity factor * Reference stress * Limit load * Small punch test * Notched specimen
OECD category: Materials engineering
Impact factor: 4.374, year: 2021
Method of publishing: Limited access
https://www.sciencedirect.com/science/article/pii/S0167844221002159?via%3Dihub

Determination of material properties on creep crack initiation (CCI) and creep crack growth (CCG) using small punch tests is still a virgin field to be exploited. Spanish and Czech researchers have carried out pioneering work and put forward an approach to correlate the notched specimen with the standard CT specimen. The advantage is that, the formulas of C*-integral for CT specimen are available and can be used directly. However, building a big data pool with both SP and CT tests within the creep region is a daunting task and hence it is worthwhile to derive C*-integral formulas for notched specimens themselves. The research is novel in that it proposes a methodology to derive the key parameter C*-integral for notched small punch specimens directly without supporting known CT tests. A 3D finite element model (FEM) for through-wall notched specimen with different crack lengths is build, and a general formulas for stress intensity factor (SIF) K, and limit load PL are obtained to calculate C*-integral for notched specimen. Experiments on notched specimens are carried out for stainless steel Sanicro 25 at temperature 700 degrees C. By using general formulas derived in this study, the key parameter C*-integral is obtained. The relation between C*-integral and the creep initiation time ti can be drawn as a straight line in a double logarithmic coordinate. The relation between C*-integral and the creep crack rate a appears to follow the same tendency. Material constants for CCI and CCG can be derived according to the power law using least square fitting. The proposed method is not fully developed and further validating experiments will be necessary to complete the research.
Permanent Link: http://hdl.handle.net/11104/0323367