Effect of the Melt Pool Boundary Network on the Anisotropic Mechanical Properties of Selective Laser Melted 304L

Anisotropic mechanical properties are a well-known issue in selective laser melted parts. The microstructure produced by selective laser melting (SLM) is directional, including the solidified melt pool structures and grains. This work investigates the melt pool boundary’s effects on 304L stainless steel’s compressive properties. 304L stainless steel solid cylinders were built using a pulse laser SLM machine in four directions using three hatch angle rotations: 0°, 67°, and 105°. The twelve samples were compression tested, and the results were analyzed. Numerical models were also created with the different hatch angles and directions. The melt pool boundary network (MPBN) in each build was tracked using the model across multiple planes. Results showed that both the hatch angle and build orientation influenced the concentration of melt pool boundaries present in the manufactured samples. A weak negative correlation of compressive strength to the melt pool boundaries’ concentration was also observed, indicating that the melt pool boundary concentration negatively affected the material’s strength. Local anisotropic plastic deformation was also observed in some of the compressed samples. In those samples, it was observed that directions that plastically deformed more also contained higher concentration of the melt pool boundaries.

Investigation on the ductile fracture of a high-strength dual-phase steel with anisotropic damage mechanics model

In this study, a hybrid experimental and numerical investigation is implemented to characterize the plasticity and ductile fracture behavior of a high-strength dual-phase steel. Uniaxial tensile tests are conducted along the three typical directions of rolled sheet metals for the anisotropic plastic behavior, while the hydraulic bulge test is applied for the flow behavior under equiaxial biaxial tension. Further tensile tests are conducted on various featured dog-bone specimens to study the fracture behavior of the material from the uniaxial to plane-strain tension. On the numerical side, the evolving non-associated Hill48 (enHill48) plasticity model considering anisotropic hardening and plastic strain ratio evolution is employed to describe the anisotropic plastic deformation. The extended enHill48 model with damage and fracture formulation is further calibrated and validated in the study to describe the ductile fracture behavior of the steel under various stress states. Through a comparison of the results based on the evolving anisotropic model with the isotropic Mises model, it is concluded that even for materials that show only minor initial plastic anisotropy, it could develop a non-negligible influence on the large plastic deformation and the prediction of both deformation and fracture shows profound improvement with the evolving anisotropic plasticity model.

Anisotropic Plastic Behavior of Additively Manufactured PH1 Steel

Metals made by additive manufacturing (AM) have intensely augmented over the past decade for customizing complex structured products in the aerospace industry, automotive, and biomedical engineering. However, for AM fabricated steels, the correlation between the microstructure and mechanical properties is yet a challenging task with limited reports. To realize optimization and material design during the AM process, it is imperative to understand the influence of the microstructural features on the mechanical properties of AM fabricated steels. In the present study, three material blocks with 120×25×15 mm3 dimensions are produced from PH1 steel powder using powder bed fusion (PBF) technology to investigate the anisotropic plastic deformation behavior arising from the manufacturing process. Despite being identical in geometrical shape, the manufactured blocks are designed distinguishingly with various coordinate transformations, i.e. alternating the orientation of the block in the building direction (z) and the substrate plate (x, y). Uniaxial tensile tests are performed along the length direction of each specimen to characterize the anisotropic plastic deformation behavior. The distinctly anisotropic plasticity behavior in terms of strength and ductility are observed in the AM PH1 steel, which is explained by their varied microstructure affected by the thermal history of blocks. It could also be revealed that the thermal history in the AM blocks is influenced by the block geometry even though the same process parameters are employed.

Anisotropic Plastic Behavior in an Extruded Long-Period Ordered Structure Mg90Y6.5Ni3.5 (at.%) Alloy

The Mg90Y6.5Ni3.5 alloy composed almost completely of the Long-Period-Stacking-Ordered (LPSO) phase has been prepared by casting and extrusion at high temperature. An elongated microstructure is obtained where the LPSO phase with 18R crystal structure is oriented with its basal plane parallel to the extrusion direction. Islands of α-magnesium are located between the LPSO grains. The mechanical properties of the alloy are highly anisotropic and depend on the stress sign as well as the relative orientation between the stress and the extrusion axes. The alloy is stronger when it is compressed along the extrusion direction. Under this configuration, the slip of <a> dislocations in the basal plane is highly limited. However, the activation of kinking induces an increase in the plastic deformation. In the transversal extrusion direction, some grains deform by the activation of basal slip. The difference in the yield stress between the different stress configurations decreases with the increase in the test temperature. The evolution of internal strains obtained during in-situ compressive experiments reveals that tensile twinning is not activated in the LPSO phase.

Evaluation of landfast ice simulations with basal stress parameterization using the Regional Arctic System Model

&lt;p&gt;The landfast ice (LFI) is an important component of the Arctic environment, especially in regions of shallow shelfs North of Alaska and Siberia. Its presence affects the transfer of energy between the atmosphere and the ocean. Its outer edge continuously interacts with the moving pack ice. One of the mechanisms of LFI formation &amp;#8211; grounded ice keels, acting as anchor points &amp;#8211; was parametrized in the version 6 of Los Alamos sea ice model (CICE) Consortium.&amp;#160; The parametrization is based on the bathymetry data, ice concentration and the mean ice thickness in a grid cell. It enables determination of the critical thickness, required for large ice keels to reach the bottom and calculation of the basal stress. A series of experiments using the Regional Arctic System Model (RASM) with CICEv6 has been conducted. In addition to sea ice model, RASM includes the atmosphere (WRF), ocean (POP), land hydrology (VIC), and river routing scheme (RVIC) components controlled by a flux coupler (CPL). LFI simulations using two different rheologies: elastic-visous-plast (EVP) and elastic-anisotropic-plastic (EAP) have been evaluated in the fully coupled and forced sea ice - ocean configurations. &amp;#160;Also, sensitivity studies with varying values of the LFI free parameters have been performed. Results are compared against landfast ice extent data from the National Snow &amp; Ice Data Center. In the optimal configuration, including the basal stress parameterization, the model reproduces observed landfast ice in East Siberian, Laptev Sea, and along the coast of Alaska. However, some areas continue to be problematic &amp;#8211; like the Kara Sea where LFI is underestimated and the area around the New Siberian Islands, where landfast ice growth is too high. In the former case, the ice arching might be the major landfast ice formation mechanism there, whereas in the latter case the model internal stress distribution might not be adequate to allow realistic sea ice drift between the islands.&lt;/p&gt;