Calibration of residual stress measurements obtained from EDM hole drilling method using physical material properties

Abstract

When using the electrodischarge machining (EDM) hole drilling method to measure residual stress, the stress induced by the metallurgical transformation layer formed during the drilling process can lead to significant measurement errors. In this study, it is shown that provided the dielectric fluid retains a high level of purity, the stress induced during the drilling process is determined primarily by the thermal conductivity and carbon equivalent of the specimen. Accordingly, these two material properties are used as the basis of two calibration equations designed to compensate the residual stress measurement obtained using the EDM hole drilling method. It is shown that the calibration equations reduce the discrepancy between the actual simulated residual stress values produced by the prestress loadings and the measured residual stress values to less than 8 MPa. The calibration equations provide a significant improvement in the accuracy of the measurement results obtained using the EDM hole drilling technique.

Keywords:

• EDM
• HOLE DRILLING STRAIN GAGE METHOD
• RESIDUAL STRESS
• THERMAL CONDUCTIVITY
• CARBON EQUIVALENT
• RECAST LAYER