인장 및 압축 등방 잔류응력 측정을 위한 누프 압입시험의 응력환산계수 결정

• Published in: Corrosion science and technology Vol. 20; no. 6; pp. 484 - 490
• Main Authors: 정민재, Min Jae Jeong, 김영천, Young-cheon Kim
• Format: Journal Article
• Language: Korean
• Published: 한국부식방식학회 31.12.2021
• Subjects: Equibiaxial stress; FEM; Knoop indentation; Residual stress; Stress conversion factor; 금속공학; Equibiaxial stress; Stress conversion factor; Residual stress; Knoop indentation; FEM
• ISSN: 1598-6462; 2288-6524
• DOI: 10.14773/cst.2021.20.6.484

Instrumented indentation testing has been widely used for residual stress measurement. The Knoop indentation is mainly selected for determining anisotropic mechanical properties and non-equibiaxial residual stress. However, the measurement of equibiaxial stress state and compressive residual stress on a specimen surface using Knoop indentation is neither fully comprehended nor unavailable. In this study, we investigated stress conversion factors for measuring Knoop indentation on equibiaxial stress state through indentation depth using finite element analysis. Knoop indentation was conducted for specimens to determine tensile and compressive equibiaxial residual stress. Both were found to be increased proportionally according to indentation depth. The stress field beneath the indenter during each indentation test was also analyzed. Compressive residual stress suppressed the in-plane expansion of stress field during indentation. In contrast, stress fields beneath the indenter developed diagonally downward for tensile residual stress. Furthermore, differences between trends of stress fields at long and short axes of Knoop indenter were observed due to difference in indenting angles and the projected area of plastic zone that was exposed to residual stress.