RSs(Residual stress)in engineering components can lead to dimensional instability,distortion during life cycle or in some cases catastrophic failure.RSs in AM(additive manufacturing)parts are a consequent of thermal expansion during heating,thermal contraction during solidification of each laser pass,and volume change due to phase transformations.Currently,most RS measurement techniques are destructive or semi-DT(destructive tests)based on releasing the RS by drilling or slitting the sample while X-ray or neutron diffraction techniques are considered as nondestructive techniques but require the use of powerful beams and slicing a small sample of the detected part.In this paper,a novel nondestructive RS measuring technique is presented,using fs(Femto-Second)laser trenching up to 250μm depth.The fs-laser trenching relaxes surface stresses violating the stress balance that is measured by a bidirectional SG(strain gauge).In this work,RSs induced in low carbon steel samples using an IPG Photonics YLR500-AC-Y14500 W YAG laser(simulating the last pass of SLM)were directly measured by proposed method.The results show the precision and accuracy of the fs-laser trenching and SG technique,that can be applied to evaluate RS in wrought and cast metals as well.This novel method still needs to be validated and be supported by a model.
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