Transient Response Dynamic Module Modifications to Include Static and Kinetic Friction Effects

A methodology that supports forced transient response dynamic solutions when both static and kinetic friction effects are included in a structural system model is described. Modifications that support this type of nonlinear transient response solution are summarized for the transient response dynamics (TRD) NASTRAN module. An overview of specific modifications for the NASTRAN processing subroutines, INITL, TRD1C, and TRD1D, are described with further details regarding inspection of nonlinear input definitions to define the type of nonlinear solution required, along with additional initialization requirements and specific calculation subroutines to successfully solve the transient response problem. The extension of the basic NASTRAN nonlinear methodology is presented through several stages of development to the point where constraint equations and residual flexibility effects are introduced into the finite difference Newmark-Beta recurrsion formulas. Particular emphasis is placed on cost effective solutions for large finite element models such as the Space Shuttle with friction degrees of freedom between the orbiter and payloads mounted in the cargo bay. An alteration to the dynamic finite difference equations of motion is discussed, which allows one to include friction effects at reasonable cost for large structural systems such as the Space Shuttle. Data are presented to indicate the possible impact of transient friction loads to the payload designer for the Space Shuttle. Transient response solution data are also included, which compare solutions without friction forces and those with friction forces for payloads mounted in the Space Shuttle cargo bay. These data indicate that payload components can be sensitive to friction induced loads

Suppression of axionic charge density wave and onset of superconductivity in the chiral Weyl semimetal Ta₂Se₈I

A Weyl semimetal with strong electron-phonon interaction can show axionic coupling in its insulator state at low temperatures, owing to the formation of a charge density wave (CDW). Such a CDW emerges in the linear-chain-compound Weyl semimetal Ta2Se8I below 263 K, resulting in the appearance of the dynamical condensed-matter axion quasiparticle. In this paper, we demonstrate that the interchain coupling in Ta2Se8I can be varied to suppress the CDW formation with pressure, while retaining the Weyl semimetal phase at high temperatures. Above 17 GPa, the Weyl semimetal phase does not survive, and we induce superconductivity, due to the amorphization of the iodine sublattice. Structurally, the quasi-one-dimensional Ta-Se chains remain intact and provide a channel for superconductivity. We highlight that our results show a near-complete suppression of the gap induced by the axionic charge density wave at pressures inaccessible to previous studies. Including this CDW phase, our experiments and theoretical predictions and analysis reveal the complete phase diagram of Ta2Se8I and its relationship to the nearby superconducting state. The results demonstrate Ta2Se8I to be a distinctively versatile platform for exploring correlated topological states. © 2021 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society

An Experimental Study on the Ordered Alloy Ni_2Cr

The ordered alloy Ni_2Cr has been investigated by means of electron diffraction, electron microscopy, calorimetry, resistometry and tensile tests. The formation of the Pt_2Mo type superstructure is revealed by an electron diffraction study on the single crystalline specimens. The size of ordered domains is of the order of magnitude of several hundred A even in the well annealed state. The so-called \u27K-state\u27 which is characterized by the initial increase in electrical resistivity upon isothermal annealing is attributed to the existence of very fine ordered domains. Superdislocations consisting of triple dislocations are sometimes observed in various stages of ordering, and the mechanical properties are briefly discussed in the light of electron microscopic observation. The energy and entropy of transformation are evaluated as about 1.0 kcal/g・atom and 1.2 cal/g・atom-deg on the alloy of 32.1 at% Cr annealed at 500℃ for about 3000 hr

EFFECT OF THE VANADIUM ADDITION ON THE GRAIN SIZE AND MECHANICAL PROPERTIES OF THE COPPER-ALUMINIUM-ZINC SHAPE MEMORY ALLOYS

The effects of vanadium addition on the β-grain size, pseudo-elastic and shape memory behaviour and fracture mode of the copper-aluminium-zinc shape memory alloys with different vanadium contents were investigated. It was found that the vanadium addition is very effective in reducing β-grain size. In the specimen hot-rolled and recrystallized for several ten minutes at 1073K, the maximum mean grain size was only 300 µm. When the annealing time is shorter, i.e. a few minutes, it reaches 200 µm. The minimum β-grain size 100 to 150 µm of the specimen in the recrystallized state was obtained by combination of vanadium addition and cold-rolling. The recoverable pseudo-elastic strain of the specimen having four-five grains along its thickness was found to be up to 5%, and recoverable shape memory strain up to 5.5%, both are near the mean theoretical values of polycrystalline materials. It was found that grain boundary cracking, which is usually observed in copperbase β-brass alloys and is considered to be the most undesirable failure of these alloys, was remarkably suppressed by vanadium addition

SURFACE ENERGY AND EQUILIBRIUM SHAPE OF L12-TYPE A3B ORDERING ALLOYS

Calculation of surface energy of L12-type A3B ordering alloy was made on the basis of a broken bond model using Bragg-Williams approximation. Prior to the calculation of surface energy, calculation of broken bond density in the same alloy was made. Numerical results for Cu3Au alloy were presented as functions of surface orientation and degree of order. Applying Wulff's theorem to calculated γ-plots of the alloy, their external equilibrium shapes for the alloy with various degree of order (η) were predicted

ORDERING AND DISORDERING PHENOMENA AT/NEAR THE SURFACE OF D1a TYPE ORDERING ALLOYS

Ordering and disordering phenomena at/near the surface of D1a type ordering alloys (Ni4Mo and Ni4W) were studied by field-ion microscopy experimentally and by theoretical calculation based on a broken bond model and Bragg-Williams approximation. The main experimental results are as follows : (i) an ordered phase nucleates preferentially at surfaces with certain low index orientation based on the fcc matrix (immediately below Tc), (ii) surface layers of specimens become disordered (around 0.9Tc) and (iii) faceting based on the ordered structure occurs (around 0.8Tc). In the theoretical calculations, (i) surface energy, (ii) surface free energy, (iii) equilibrium degree of order and (iv) surface nucleation rate were obtained. The calculated results explain peculiar phenomena in the above experimental results

EFFECTS OF HEAT TREATMENT ON MECHANICAL BEHAVIOR OF Ti-Ni ALLOYS

Aging effects on the transformation temperatures and the deformation behavior of Ti-Ni alloys have been studied by electrical resistivity measurement, tensile test and transmission electron microscopy. Main interest was in the influence of alloy composition and aging treatment on the pseudo-elasticity and the shape memory effect. It was found that Ms temperature and mechanical behavior of nickel-rich off-stoichiometric (>50.7at%Ni) Ti-Ni alloys were sensitive to heat-treatment, while those of a near-stoichiometric (50.4at%Ni) alloy were not. Precipitates were observed in the off-stoichiometric alloys after aging

ATOM PROBE FIM STUDY OF SHORT RANGE ORDER IN Ni RICH Ni-W AND Ni-Mo-W ALLOYS

True picture of short range order of Ni rich Ni-W and Ni-Mo-W alloys has been studied by an atom probe FIM. The presence of solute rich regions having about 50at% solute concentration has been found in the Ni-W alloy and in the Ni-Mo-W alloy. The details of these regions are described. Partitioning of Mo and W atoms in the interior and also at the interface, of (Mo+W) rich regions in ternary Ni-Mo-W alloy has been also studied