Proposing a new semi-nondestructive measurement of non-equiaxial residual stress field using indentation technique without reference value of hardness under non-stress state

Abstract

A new procedure using indentation technique was proposed in this study for semi-nondestructive measurement of non-equiaxial residual stress field. The stress evaluation formula using the Vickers and Knoop indenters was constructed based on the addition rule. In the newly proposed procedure, the Vickers and Knoop indenters are used so that the procedure does not require the reference value of hardness or indentation load under non-stress state. In this regard, however the proposed procedure requires two constants for stress determination. One is the load ratio between Vickers and Knoop indenters and the other is the conversion factor determining the relation between existing residual stress and load change due to the existing residual stress. The two constants were quantified by the measurement of the indentation load - depth curve and the existing residual stress using X-ray diffraction method. The accuracy of stress determination using the newly developed procedure was validated using welded specimens of high strength steel with different non-equiaxial stress fields. As the results, it was confirmed that the developed stress measurement using indentation technique provided good agreement with the X-ray stress measurement. Thus the newly developed procedure using indentation technique is expected to be a useful semi-nondestructive technique for determining the non-equiaxial residual stress at welds.

Keywords

• indentation technique
• semi-nondestructive stress measurement
• non-equiaxial stress field
• weld residual stress
• vickers indenter
• knoop indenter