Measurement of Residual Stresses in Parts Created by Shape Deposition Manufacturing
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Residual stress build-up is a concern in any solid freeform fabrication process involving successive deposition of uncured or molten material, due to differential contractions caused by solidification or curing. The most detrimental effect of residual stresses is typically part warping, which can lead to unacceptable losses in part tolerance. In many processes residual stress build-up is a fundamental barrier to the consistent manufacture of high-quality artifacts. In this paper, two methods of measuring residual stresses in parts created by Shape Deposition Manufacturing (SDM) with microcasting are described. First, a technique for measuring warping in deposited plateshaped specimens is detailed, which can be used to determine residual stress resultants as well as to quantify gross effects of processing changes on residual stress magnitudes. Next, x-ray diffraction procedures are described by which residual stresses in deposited layers can be measured at discrete in-plane locations as a function of depth. Measured results for 308L stainless steel deposits determined from each method are interpreted in the context of residual stress modeling results obtained numerically in a separate research effort. The measured results provide insight into the effects on residual stress of both the material deposition path and the discrete droplet-bydroplet nature of the microcasting deposition process. The insights provided here may also be applicable to other processes involving successive material deposition.