Effects of strain's error on residual stresses calculated by HDM

The hole-drilling method is an effective and popular semi-destructive technique for residual stress (RS) measurement. It consists in drilling a very small hole into the specimen. Consequently, RS relaxes in the hole and stresses in the surrounding region change causing strains also to change. A strain gage rosette, specifically designed and standardized measures these strains. Using stress–strain relationships, the RS field is calculated from the measured strains. In the case of not uniform RS, an incremental technique is used in which relieved strains are measured during a series of small hole depth increments. In contrast to the uniform stress case, not uniform stress calculations are extremely sensitive to errors in the measured strain: small strain measurement errors can cause significant variations in calculated stresses, particularly for stresses far from the surface. This paper presents a detailed analysis of the influence of the strain measurement error on the computed stresses. Particular emphasis is placed on the analysis of the influence of both the number of total steps and the type of step increment. Both the integral and power series stress calculation methods are investigated, and their different responses to measurement errors are described.