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J. Eng. Mater. Technol. 2018;140(3):031001-031001-9. doi:10.1115/1.4039108.

Magnesium alloys with rare earth (RE) elements addition, modified with zirconium are used for cast, light-weight solutions for components applied at temperature up to 250–300 °C. Computational methods are often used by the foundries to decrease the cost of a new product start-up. The commercially available magmasoft software is widely used to simulate a casting process. Nevertheless, its database does not contain complete data for modern alloys. We present the results of our investigations on the thermo-physical properties of a EV31A magnesium alloy and the simulation of a sand casting process with applied data. We compared the simulation and technological trials, recognized problems occurring during the simulation, and applied corrections. Our final simulations gave acceptable results. The differences between the technological tests and the simulation were caused by factors that are difficult to model in the simulation, such as the presence of nonmetallic inclusions and the degree of modification of the liquid alloy.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2018;140(3):031002-031002-13. doi:10.1115/1.4038801.

This paper presents a combined experimental and theoretical analysis focusing on the individual roles of microdeformation mechanisms that are simultaneously active during the deformation of twinning-induced plasticity (TWIP) steels in the presence of hydrogen. Deformation responses of hydrogen-free and hydrogen-charged TWIP steels were examined with the aid of thorough electron microscopy. Specifically, hydrogen charging promoted twinning over slip–twin interactions and reduced ductility. Based on the experimental findings, a mechanism-based microscale fracture model was proposed, and incorporated into a visco-plastic self-consistent (VPSC) model to account for the stress–strain response in the presence of hydrogen. In addition, slip-twin and slip–grain boundary interactions in TWIP steels were also incorporated into VPSC, in order to capture the deformation response of the material in the presence of hydrogen. The simulation results not only verify the success of the proposed hydrogen embrittlement (HE) mechanism for TWIP steels, but also open a venue for the utility of these superior materials in the presence of hydrogen.

Commentary by Dr. Valentin Fuster
J. Eng. Mater. Technol. 2018;140(3):031003-031003-14. doi:10.1115/1.4038672.

Hybrid micro-architected materials with unique combinations of high stiffness, high damping, and low density are presented. We demonstrate a scalable manufacturing process to fabricate hollow microlattices with a sandwich wall architecture comprising an elastomeric core and metallic skins. In this configuration, the metallic skins provide stiffness and strength, whereas the elastomeric core provides constrained-layer damping. This damping mechanism is effective under any strain amplitude, and at any relative density, in stark contrast with the structural damping mechanism exhibited by ultralight metallic or ceramic architected materials, which requires large strain and densities lower than a fraction of a percent. We present an analytical model for stiffness and constrained-layer damping of hybrid hollow microlattices, and verify it with finite elements simulations and experimental measurements. Subsequently, this model is adopted in optimal design studies to identify hybrid microlattice geometries which provide ideal combinations of high stiffness and damping and low density. Finally, a previously derived analytical model for structural damping of ultralight metallic microlattices is extended to hybrid lattices and used to show that ultralight hybrid designs are more efficient than purely metallic ones.

Topics: Damping , Stiffness , Polymers
Commentary by Dr. Valentin Fuster

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