Prediction of Residual Stresses in L-PBF Ti-6Al-4V Fatigue Specimens Using a Thermo-Mechanical Finite Element Model

Laser Powder Bed Fusion (L-PBF) is an additive manufacturing process that is becoming widely adopted in the automotive, aerospace, and biomedical industries. It uses a laser to melt metal in the form of powder to build parts in a layer-by-layer fashion based on an imported CAD geometry. The constant remelting of previous layers can produce unwanted thermally induced residual stresses in the part due to large thermal gradients, which can drastically reduce the fatigue life of the material. Predicting these residual stresses within the as-built part would be advantageous because one could better understand how the part will perform in an industrial setting. This study aims to use a combined thermo-mechanical finite element model to simulate the printing of fatigue specimens using L-PBF. The specimens are built based on Ti6Al4V material properties using a set of nominal process parameters. After the mechanical model of the specimen containing the induced residual stresses is created, the fatigue life of the part will be analyzed using constant amplitude stress-controlled loadings in FE-safe, and the results will be compared with that of a wrought Ti-6Al4V specimen.https://scholarsjunction.msstate.edu/fea/1005/thumbnail.jp

The Variation of Mechanical Properties of M300 Maraging Steel Manufactured with Varying Process Parameters in Laser Powder Bed Fusion

Laser power bed fusion (L-PBF) is a type of additive manufacturing (AM) that uses layers of powdered metal and a laser to manufacture a part in a layer-by-layer fashion. L-PBF uses a variety of process parameters that ultimately determine the overall quality and mechanical properties of a print. The ability to alter parameters allows for the utilization of various metals in this form of AM. Maraging 300 steel (M300) is a material of particular interest due to its combined tensile strength and high strength-to-weight ratio. By using an assortment of parameters and comparing the resulting mechanical properties it can be determined which process parameters result in a more favorable part to be used in a variety of applications. A favorable process parameter set was selected for future use. This study aims to determine which process parameters result in the best overall mechanical properties of M300 manufactured using L-PBF.Mechanical Engineerin

Increased Recruitment but Impaired Function of Leukocytes during Inflammation in Mouse Models of Type 1 and Type 2 Diabetes

BACKGROUND: Patients suffering from diabetes show defective bacterial clearance. This study investigates the effects of elevated plasma glucose levels during diabetes on leukocyte recruitment and function in established models of inflammation. METHODOLOGY/PRINCIPAL FINDINGS: Diabetes was induced in C57Bl/6 mice by intravenous alloxan (causing severe hyperglycemia), or by high fat diet (moderate hyperglycemia). Leukocyte recruitment was studied in anaesthetized mice using intravital microscopy of exposed cremaster muscles, where numbers of rolling, adherent and emigrated leukocytes were quantified before and during exposure to the inflammatory chemokine MIP-2 (0.5 nM). During basal conditions, prior to addition of chemokine, the adherent and emigrated leukocytes were increased in both alloxan- (62±18% and 85±21%, respectively) and high fat diet-induced (77±25% and 86±17%, respectively) diabetes compared to control mice. MIP-2 induced leukocyte emigration in all groups, albeit significantly more cells emigrated in alloxan-treated mice (15.3±1.0) compared to control (8.0±1.1) mice. Bacterial clearance was followed for 10 days after subcutaneous injection of bioluminescent S. aureus using non-invasive IVIS imaging, and the inflammatory response was assessed by Myeloperoxidase-ELISA and confocal imaging. The phagocytic ability of leukocytes was assessed using LPS-coated fluorescent beads and flow cytometry. Despite efficient leukocyte recruitment, alloxan-treated mice demonstrated an impaired ability to clear bacterial infection, which we found correlated to a 50% decreased phagocytic ability of leukocytes in diabetic mice. CONCLUSIONS/SIGNIFICANCE: These results indicate that reduced ability to clear bacterial infections observed during experimentally induced diabetes is not due to reduced leukocyte recruitment since sustained hyperglycemia results in increased levels of adherent and emigrated leukocytes in mouse models of type 1 and type 2 diabetes. Instead, decreased phagocytic ability observed for leukocytes isolated from diabetic mice might account for the impaired bacterial clearance

Prediction of Residual Stresses in L-PBF Ti-6Al-4V Fatigue Specimens Using a Thermo-Mechanical Finite Element Model

Laser Powder Bed Fusion (L-PBF) is an additive manufacturing process that is becoming widely adopted in the automotive, aerospace, and biomedical industries. It uses a laser to melt metal in the form of powder to build parts in a layer-by-layer fashion based on an imported CAD geometry. The constant remelting of previous layers can produce unwanted thermally induced residual stresses in the part due to large thermal gradients, which can drastically reduce the fatigue life of the material. Predicting these residual stresses within the as-built part would be advantageous because one could better understand how the part will perform in an industrial setting. This study aims to use a combined thermo-mechanical finite element model to simulate the printing of fatigue specimens using L-PBF. The specimens are built based on Ti6Al4V material properties using a set of nominal process parameters. After the mechanical model of the specimen containing the induced residual stresses is created, the fatigue life of the part will be analyzed using constant amplitude stress-controlled loadings in FE-safe, and the results will be compared with that of a wrought Ti-6Al4V specimen