Electronic structure, phase stability and chemical bonding in Th2_2Al and Th2_2AlH4_4

We present the results of theoretical investigation on the electronic structure, bonding nature and ground state properties of Th$_2$Al and Th$_2$AlH$_4$ using generalized-gradient-corrected first-principles full-potential density-functional calculations. Th$_2$AlH$_4$ has been reported to violate the "2 \AA rule" of H-H separation in hydrides. From our total energy as well as force-minimization calculations, we found a shortest H-H separation of 1.95 {\AA} in accordance with recent high resolution powder neutron diffraction experiments. When the Th$_2$Al matrix is hydrogenated, the volume expansion is highly anisotropic, which is quite opposite to other hydrides having the same crystal structure. The bonding nature of these materials are analyzed from the density of states, crystal-orbital Hamiltonian population and valence-charge-density analyses. Our calculation predicts different nature of bonding for the H atoms along $a$ and $c$. The strongest bonding in Th$_2$AlH$_4$ is between Th and H along $c$ which form dumb-bell shaped H-Th-H subunits. Due to this strong covalent interaction there is very small amount of electrons present between H atoms along $c$ which makes repulsive interaction between the H atoms smaller and this is the precise reason why the 2 {\AA} rule is violated. The large difference in the interatomic distances between the interstitial region where one can accommodate H in the $ac$ and $ab$ planes along with the strong covalent interaction between Th and H are the main reasons for highly anisotropic volume expansion on hydrogenation of Th$_2$Al.Comment: 14 pages, 9 figure

Development of a Hybrid Manufacturing Cell; Integration of Additive Manufacturing with CNC Machining

The application of Additive Manufacturing (AM) for production of injection molding tools and tooling inserts enables significant improvements in regards to, for example, product quality and cycle times. However, the AM based production of tools and inserts is most often far from being rapid and the inserts are usually considerably more expensive than conventionally produced. A combination of AM with CNC milling in a hybrid process route allows for the application of each process to the production of the section of the product geometry for which it is most advantageous. However, this approach also multiplies the number of process steps and therefore also the limiting factors and possible causes of failure. This paper describes the development of a Hybrid Manufacturing cell by integration of AM with conventional CNC milling in a robust, streamlined production sequence.Mechanical Engineerin

Directional fatigue behaviour of maraging steel grade 300 produced by laser powder bed fusion

Surfaces of metals produced by additive manufacturing (AM) are known to be rough and populated with defects, this is, in particular, true for downward-facing (down-skin) surfaces. When dealing with the fatigue of as-built surfaces produced by AM, fatigue is typically initiating from surface defects. In this work, the fatigue behaviour of maraging steel grade 300 (18Ni300) produced by laser beam powder bed fusion (PBF-LB) is investigated. Fatigue initiation from surfaces built both up- and down-skin are investigated. This is done by using specimens where all surfaces are machined, except the one at interest. Specimens were built in 10 orientation ranging from 0° (horizontal, up-skin) to 135° (down-skin). The surface roughness was measured for all orientations; high surface roughness was found for down-skin surfaces while wavy surfaces were found for up-skin surfaces. The fatigue behaviour was found to be correlated to the build orientation and the surface roughness. © 2021 The Author(s

Mechanical Properties of Biocompatible 316L Steel Rhombic Dodecahedron Lattice Structures

Additive manufactured lattice structures have the potential of enhancing many of today’s engineered products manufactured by traditionally methods. The former provides the capability of altering the mechanical, thermal and acoustic properties of structures through the use of lattices. However, more investigation is needed to better understand the manufacturability and the mechanical behavior of sandwich structures. This paper investigates the influence of strut size on the global stiffness and the compressive strength using compression testing of sandwich structures. Digital Image Correlation (DIC) analysis is applied to determine the local strain distribution during the compression test. It is found that the compressive strength increases linearly with increased lattice strut diameter. Moreover, based on DIC the maximum strains are observed in the strut connection regions.Mechanical Engineerin

Cation Ordering and Oxygen Release in LiNi0.5-xMn1.5+xO4-y (LNMO): In Situ Neutron Diffraction and Performance in Li Ion Full Cells

Covers thorough study showing the possible strategies to decouple effect of oxygen deficiency, the presence of Mn3+ and degree of cation ordering in the high power positive electrode material for lithium ion batteries, LiNi0.5Mn1.5O4.</div