An Experimental Investigation into Additive Manufacturing-Induced Residual Stresses in 316L Stainless Steel
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Additive manufacturing (AM) technology provides unique opportunities for producing net-shape geometries at the macroscale through microscale processing. This level of control presents inherent trade-offs necessitating the establishment of quality controls aimed at minimizing undesirable properties, such as porosity and residual stresses. Here, we perform a parametric study into the effects of laser scanning pattern, power, speed, and build direction in powder bed fusion AM on residual stress. In an effort to better understand the factors influencing macroscale residual stresses, a destructive surface residual stress measurement technique (digital image correlation in conjunction with build plate removal and sectioning) has been coupled with a nondestructive volumetric evaluation method (i.e., neutron diffraction). Good agreement between the two measurement techniques is observed. Furthermore, a reduction in residual stress is obtained by decreasing scan island size, increasing island to wall rotation to 45 deg, and increasing applied energy per unit length (laser power/speed). Neutron diffraction measurements reveal that, while in-plane residual stresses are affected by scan island rotation, axial residual stresses are unchanged. We attribute this in-plane behavior to misalignment between the greatest thermal stresses (scan direction) and largest part dimension.
KeywordsResidual Stress Digital Image Correlation Additive Manufacturing Tensile Residual Stress Residual Stress Measurement
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This work was funded by the Laboratory Directed Research and Development Program at LLNL under project tracking code 13-SI-002 and has been assigned the document release ID #LLNL-JRNL-654740.
The authors would like to acknowledge the guidance and expertise of Ms. Mary M. LeBlanc (LLNL) in mechanical characterization techniques and digital image correlation methodology. Dr. Bjørn Clausen and Dr. Thomas A. Sisneros (LANL, Lujan Center) are recognized for their time and expertise in neutron diffraction. The authors also recognize Dr. Bassem el-Dasher, Dr. Robert Ferencz, and Dr. Neil Hodge (LLNL) for their guidance in planning these experiments—and, in particular, Dr. Neil Hodge for melt pool geometry predictive capabilities, as well as Dr. Chandrika Kamath (LLNL) for process optimization expertise and Dr. John Elmer (LLNL) for his advice and expertise. Mr. Gregory J. Larsen and Mr. Paul Alexander are recognized for their drafting efforts and processing expertise, respectively. Dr. Karl Fisher provided the RUS measurements of elastic modulus used in this study.
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