An investigation of variability among residual stress measurement techniques and prediction of machining induced distortion
Poerner, Nathan W.
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The primary objective of this research was to compare and contrast the effectiveness of several Residual Stress (RS) measurement techniques. This was achieved by preparing a series of samples with known RS distribution and comparing the results from different measurement techniques. This round robin study verified the RS distribution of the samples relative to predicted distributions obtained via Finite Element Analysis (FEA). Among the methods examined, all but X-ray diffraction showed a consistently accurate measurement of the RS profile. The secondary objective of this study was to investigate the sensitivity of the slitting technique for residual stress measurement to the type of machining method used for creating the slit. Slitting RS measurements were made on samples with known RS distributions, while employing two different machining methods for creating the slit, namely, electrical discharge machining (EDM) versus computer numerically controlled (CNC) milling. It was shown that CNC milling could be utilized with a reasonable degree of accuracy in place of wire EDM to obtain data for determination of RS distribution. The final objective of this study was to determine whether FEA could accurately predict machining distortion caused by removal of material from a component having a known RS distribution. This was done by comparing FEA results with actual experimental measurements of machining distortion, conducted on specimens with known RS distributions. Comparison of the experimental machining distortion values with the predicted values showed a deviation between the results deep into the cut. Thus, it was concluded that there needs to be improvements made in the modeling of the machining process.