Explicit-Implicit Schemes for Calculating the Dynamics of Layered Media with Nonlinear Conditions at Contact Boundaries

In this paper we consider the problem of dynamic loading of a deformable solid medium con- taining slip planes with nonlinear slip conditions on them. An explicit-implicit scheme was constructed for the numerical solution of the constitutive system of equations, which exactly reduces to correcting the stress tensor values after performing the elastic step. An implicit approximation of the constitutive relations containing a small parameter in the denominator of the nonlinear free term was used with the second order of the approximation. The correction procedure is applicable for those cases when the viscosity parameter of interlayers providing the sliding mode of the contact boundaries is not small. The solution of the problem of the seismic waves propagation in an inhomogeneous fractured geological massif in a two-dimensional case was obtained numerically

Fracture of Be and Its Alloys - Webb Space Telescope Revisited

NASA/ESA/CSA joint venture James Webb Space Telescope is about to be launched. It is hypothesized to operate in near-infrared range. It is also hypothesized to unveil early star formation, galaxies, and universe due to its orbit, point in orbit and orbital motion. It has been under manufacturing for over 20 years at a staggering cost of 10 billion US dollars (most expensive scientific experiment in history). Beryllium (Be) is chosen to be element for construction of its main mirrors due to its high stiffness, low density, low linear coefficient of thermal expansion (α) in cryogenics and high thermal conductivity. It is followed by gold (Au) layer deposition on its (Be) surface to enhance its sensitivity towards infrared radiation as later is hypothesized to bear superior properties. However, serious mistakes have been made in selecting this material for this application. Owing to its crystal structure (hexagonal close packed (hcp)), slip planes (basal, prismatic and pyramidal) and mechanisms of their activation, Be necessitates easy fracture at cryogenic temperature. It has anisotropic properties and prone to transverse fracture under tensile loading. Furthermore, its ductile to brittle transition temperature is very low making it entirely unsuitable for such an application. It is one of most expensive metals on planet. This study constitutes revisiting these fundamental properties and mechanisms which were entirely ignored during materials selection thus rendering whole project useless.

Anelastic Behaviour of Commercial Die-Cast Magnesium Alloys: Effect of Temperature and Alloy Composition

The anelastic deformation, resulting from partial reversal of {101¯2} twinning, is studied at room temperature to 150 °C on several commercial die-cast magnesium alloys for the first time. The magnitude of anelastic strain decreases with increasing temperature. For inter-alloy comparison, AZ91 shows the largest maximum anelastic strain, while AM40 and AM60 show similar maximum anelastic strain. The phenomenon is discussed in terms of solid solution softening and hardening of slip planes and how they influence twinning. T5-aged AE44 consistently shows smaller magnitude of anelasticity compared to as-cast AE44, suggesting that the precipitates formed during ageing may decrease the twin-boundary mobility and further suppress untwinning. Presence of anelasticity poses a challenge to yield strength measurement using the conventional 0.2% offset method, and a more accurate and consistent method of using a higher offset strain or a lower modulus is proposed in this study.

Crystal Structure Defects and Imperfections

Alloying, heat treating, and work hardening are widely used to control material properties, and though they take different approaches, they all focus on imperfections of one type or other. This chapter provides readers with essential background on these material imperfections and their relevance in design and manufacturing. It begins with a review of compositional impurities, the physical arrangement of atoms in solid solution, and the factors that determine maximum solubility. It then describes different types of structural imperfections, including point, line, and planar defects, and how they respond to applied stresses and strains. The chapter makes extensive use of graphics to illustrate crystal lattice structures and related concepts such as vacancies and interstitial sites, ion migration, volume expansion, antisite defects, edge and screw dislocations, slip planes, twinning planes, and dislocation passage through precipitates. It also points out important structure-property correlations.

Crystalline Imperfections—Problems and Solutions

This chapter provides readers with worked solutions to more than 25 problems related to compositional impurities and structural defects. The problems deal with important issues and challenges such as the design of low-density steels, the causes and effects of distortion in different crystal structures, the ability to predict the movement of dislocations, the influence of impurities on defects, the relationship between gain size and material properties, the identification of specific types of defects, the selection of compatible metals for vacuum environments, and the effect of twinning planes on stacking sequences. The chapter also includes problems on how the formation of precipitates can produce slip planes and how grain boundaries can act as obstacles to dislocation motion.

Numerical Study and Experimental Validation of Deformation of FCC CuAl Single Crystal Obtained by Additive Manufacturing

The importance of taking into account directional solidification of grains formed during 3D printing is determined by a substantial influence of their crystallographic orientation on the mechanical properties of a loaded material. This issue is studied in the present study using molecular dynamics simulations. The compression of an FCC single crystal of aluminum bronze was performed along the <111> axis. A Ni single crystal, which is characterized by higher stacking fault energy (SFE) than aluminum bronze, was also considered. It was found that the first dislocations started to move earlier in the material with lower SFE, in which the slip of two Shockley partials was observed. In the case of the material with higher SFE, the slip of a full dislocation occurred via successive splitting of its segments into partial dislocations. Regardless of the SFE value, the deformation was primarily occurred by means of the formation of dislocation complexes involved stair-rod dislocations and partial dislocations on adjacent slip planes. Hardening and softening segments of the calculated stress–strain curve were shown to correspond to the periods of hindering of dislocations at dislocation pileups and dislocation movement between them. The simulation results well agree with the experimental findings.

Anisotropic shock responses of nanoporous Al by molecular dynamics simulations

Mechanical responses of nanoporous aluminum samples under shock in different crystallographic orientations (<100>, <111>, <110>, <112> and <130>) are investigated by molecular dynamics simulations. The shape evolution of void during collapse is found to have no relationship with the shock orientation. Void collapse rate and dislocation activities at the void surface are found to strongly dependent on the shock orientation. For a relatively weaker shock, void collapses fastest when shocked along the <100> orientation; while for a relatively stronger shock, void collapses fastest in the <110> orientation. The dislocation nucleation position is strongly depended on the impacting crystallographic orientation. A theory based on resolved shear stress is used to explain which slip planes the earliest-appearing dislocations prefer to nucleate on under different shock orientations.

New Analog Experiment for Convergent Regime an example of planet Mercury

&lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;p&gt;We conduct a series of experiments to understand the nature of thrust faulting as a result of global thermal contraction in planetary bodies such as Mercury. The spatial scales and patterns of faulting due to contraction are still not very well understood. However, the problem is complicated even for the homogeneous case where the crustal thickness and material properties do not vary spatially. Previous research showed that the thrust faulting patterns are non-random and are arranged in long systems. This is probably due to the regional-scale stress patterns interacting with each other, leading to the creation of coherent structures. We first conduct 1-Axis experiments where we simulate the contraction of the substratum using an elastic ribbon. On top of this we place the material for which the friction, cohesion and thickness can be controlled for each experiment. The shared interface between the frictional-cohesive material and the shortening elastic substratum dictates undulations and finally the generation of slip planes in the upper layer. We discuss the spatial distribution of these patterns spatially. We then speculate the interaction of such patterns on a 2D plane.&lt;/p&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;div&gt;&amp;#160;&lt;/div&gt; &lt;/div&gt;&lt;div&gt; &lt;div&gt;&amp;#160;&lt;/div&gt; &lt;/div&gt;

What steers deformation within fold-and-thrust belts: insights from the carbonate multilayer footwall of the Belluno Thrust, Italian eastern Southern Alps

&lt;p&gt;Despite significant recent progress in the understanding and quantification of the parameters controlling deformation modes in carbonate multilayers within fold-and-thrust belts, the details of early deformation and faulting during the initial stages of large-scale thrusting remain poorly documented and understood. Aiming to narrow this knowledge gap, we have chosen to study the relatively low-strain carbonate multilayer footwall of the Belluno Thrust (BT), one of the most external and S-vergent thrusts of the eastern Southern Alps (Italy). The BT footwall is composed of a c. 600 m thick Meso-Cenozoic multilayer succession of shallow water carbonate and pelagic sedimentary units characterized by strong mineralogical heterogeneity, with calcite (32-98%), sheet silicates (1-27%), and quartz (1-37%) as principal components. Its structural framework reflects cumulative strain due to multiple deformation events and is defined by the superposition of different structures such as i) south-verging asymmetric folds, ii) faulted folds, cut by slip planes with centimetric to metric throw, iii) SC-C&amp;#8217; fabrics in the marly layers, and iv) cataclastic domains. &amp;#160;Structures recording the early shortening increments are generally well preserved mesoscopic upright folds. Asymmetric folds with gently N-dipping backlimbs and steeply S-dipping (or even overturned N-dipping) forelimbs, record further shortening of the early upright and symmetrical folds. Strain is strongly partitioned within the marly layers, with discrete faults commonly defined by multiple slip surfaces forming duplex geometries and SC-C&amp;#8217; fabrics and exploiting millimetric to centimetric marly beds as detachment layers. Thrusts and diffuse reverse faults not associated with any cataclasite localise along the backlimbs of the asymmetric folds, suggesting dominant layer-parallel shortening. Cataclasites develop instead along the thrust surfaces that cut across the steeply dipping (locally even overturned) forelimbs, where cataclastic flow becomes the dominant deformation mechanism. On the vertical forelimbs, cataclasis and strain localisation are commonly associated with veins, which contributed to harden the rock system. &amp;#160;&lt;/p&gt;&lt;p&gt;Based on our systematic observations, we propose that deformation progressively evolved from folding and layer-parallel shortening (initial phases) to faulting and cataclasis (final phases) as a function of the dynamic interplay of the following factors: i) the geometrical relationships between fault orientation, fold attitude (forelimb and backlimb domains) and stress field, ii) the lithotype, which we conveniently account for by referring to the ratio between the cumulative thickness of the outcrop marly layers and the total measured stratigraphic thickness, iii) the involvement of fluids during deformation, iv) the mineral assemblage of the involved layers and v) the geometric framework of the domain localising strain with respect to the principal stress axes orientation. We conclude that these parameters play a major role in guiding strain localisation and partitioning during continuous shortening within fold-and-thrust belts. They also govern the transition from overall aseismic creep to coseismic rupturing at the scale of mesoscopic structures and, possibly, of the entire belt.&lt;/p&gt;

Finding and Characterising Active Slip Systems: A Short Review and Tutorial with Automation Tools

The behaviour of many materials is strongly influenced by the mechanical properties of hard phases, present either from deliberate introduction for reinforcement or as deleterious precipitates. While it is, therefore, self-evident that these phases should be studied, the ability to do so—particularly their plasticity—is hindered by their small sizes and lack of bulk ductility at room temperature. Many researchers have, therefore, turned to small-scale testing in order to suppress brittle fracture and study the deformation mechanisms of complex crystal structures. To characterise the plasticity of a hard and potentially anisotropic crystal, several steps and different nanomechanical testing techniques are involved, in particular nanoindentation and microcompression. The mechanical data can only be interpreted based on imaging and orientation measurements by electron microscopy. Here, we provide a tutorial to guide the collection, analysis, and interpretation of data on plasticity in hard crystals. We provide code collated in our group to help new researchers to analyse their data efficiently from the start. As part of the tutorial, we show how the slip systems and deformation mechanisms in intermetallics such as the Fe7Mo6 μ-phase are discovered, where the large and complex crystal structure precludes determining a priori even the slip planes in these phases. By comparison with other works in the literature, we also aim to identify “best practises” for researchers throughout to aid in the application of the methods to other materials systems.