An Enhanced Calibration Scheme for the EDM Hole-Drilling Strain Gage Method for the Measurement of Residual Stress in Ferrous Materials

Abstract

Recent studies revealed that EDM hole-drilling strain gage method is applicable for the measurement of residual stress in materials with higher hardness and toughness. However, the metallurgical transformation layer formed on the wall of the hole induces an additional stress and therefore generates a measurement error. Usually this error can be calibrated by estimating and reducing the hole-drilling induced extra stress, IS . However, the value of IS is highly sensitive to the EDM parameters. Accordingly, the current study aimed at lowering IS by optimizing the working parameters of pulse current, pulse-on duration and pulse-off duration with experiments. An inverse power law relationship was constructed to predict the magnitude of the hole-drilling induced stress where was referred. A convenient calibration method was proposed where calibration factor can be easily determined. The calibrated results revealed good accuracy where deviation is no more than 10 MPa. The accuracy of the proposed calibration scheme was confirmed in study.

Effect of Material Physical Properties on Residual Stress Measurement by EDM Hole-Drilling Method

“…As a result, some form of calibration procedure is required to compensate for this additional residual stress such that an accurate assessment of the original residual stress within the workpiece can be obtained. In previous studies by the current group, it was shown that the value of the hole-drilling induced stress is independent of the original stress intensity within the component, and as a result, the measured value of the residual stress can be calibrated by subtracting the value of the residual stress induced by a hole-drilling operation in a stress-free specimen of the equivalent type [8,9]. However, this technique, while undeniably effective, incurs considerable time, manpower, and material costs.…”