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The thermal–electric bifunctional devices with isotropic and anisotropic geometries are designed in this paper, which can realize different control functions (invisible sensors and cloaks) of thermal and electric fields. We first theoretically achieve the bifunctions of invisible sensors and cloaks with isotropic and anisotropic geometries. When the material parameters of the core and matrix and the geometric parameters of the core, inner shell, and outer shell are determined, the thermal–electric invisible sensors could be realized. Meanwhile, the invisible sensors will degrade to invisible cloaks as the inner shell material is insulating. The simulations applying the derived material parameters have also been conducted to verify the thermal–electric bifunctions of different circular and confocal elliptical devices. The results show that the thermal–electric bifunctional devices can effectively control the thermal and electric fields, and these devices exhibit perfect performance of the thermal–electric functions of invisible sensors and cloaks. This work presents a new method to realize thermal–electric bifunctional devices and opens a new window to the development of multi-physics field. [ABSTRACT FROM AUTHOR]

A novel interfacial resistance-free (IRF) bifunctional camouflage (transparent and invisible) device is proposed in this paper. The thermal and electric conductivities of the shell and background are the same to eliminate the interfacial resistance. The IRF bifunctional camouflage device can operate in thermal–electric fields based on the neutral inclusion method. The distribution of isotherm and equipotential lines are studied quantitatively by the simulations. It is confirmed that the IRF bifunctional camouflage device with arbitrary natural materials can effectively achieve not only the invisible function but also the transparent function in thermal–electric fields. This method provides a window to the realization of bifunctions and the development of multi-physics fields. [ABSTRACT FROM AUTHOR]

Cr(VI) in wastewater poses a serious threat to human health, so there is an urgent need to remove it using a cost-effective way. Herein, we report a composite electrode material of homemade paulownia biochar and MoS2 (PBC@MoS2) for the efficient and selective removal of Cr(VI) from wastewater. PBC@MoS2 has an excellent ability to selectively remove Cr(VI) by electrosorption under the coexistence of different anions and cations (385.74 mg g−1 at voltage = 1.2 V, spacing = 1 mm, and initial concentration = 60 mg L−1). It can achieve 98.75% desorption and regeneration of the electrode within 1 h, and after 5 cycles of adsorption/desorption, it still maintains 97.02% of the original adsorption capacity. The characterization analysis shows that the removal process of Cr(VI) has both electrosorption and reduction effects, which can reduce 85.4% of the highly toxic Cr(VI) to the less toxic Cr(III). This is facilitated by the large specific surface area and special two-dimensional sheet structure of PBC@MoS2 composites. The results of this work can provide data support for the design of high-performance CDI systems for the removal of Cr(VI) from wastewater. [ABSTRACT FROM AUTHOR]

Assessing the aircraft engine nonvolatile particulate matter (nvPM) emissions during landing and take-off (LTO) cycles is significant for airport air quality management. However, presently few prior studies have examined aircraft engine nvPM emissions on a daily basis for optimizing flight operations at airports. Therefore, based on the latest first-order approximation method of engine nvPM emissions, we introduce the engine emission data and aircraft flight data to establish an integrated method for estimating daily aircraft engine nvPM emissions at airports. This method can be applied to obtain different engine nvPM mass and number emissions in each phase of the LTO cycle, and therefore the total nvPM mass and number emissions in different time periods can be estimated for the analysis of the sources and trends of daily aircraft engine nvPM emissions during LTO cycles at Hangzhou Xiaoshan International Airport. Results show that the highest aircraft engine nvPM mass and number emissions are generally predicted to occur in the climb and taxi/ground idle phase, respectively. The proportion of total engine nvPM mass and number emissions in each phase of the LTO cycle could also be estimated, specifically the take-off phase (21% & 6%), climb phase (52% &15%), approach phase (8% & 27%), and taxi/ground idle phase (19% & 52%). In addition, the trends of hourly engine nvPM mass and number emissions during LTO cycles within a day are similar, but the predicted highest total hourly engine nvPM mass and number emissions occur in different time periods (7:00–8:00 a.m. & 11:00–12:00 a.m.) at the airport, and the total hourly engine nvPM mass and number emissions at 6:00 a.m. to 17:00 p.m. are generally higher than those of the rest periods. These results are valuable for optimizing flight operations for mitigating the environmental impact of aircraft engine nvPM emissions. Implications: The integrated method for estimating engine nvPM mass and number emissions in the LTO cycle based on FOA4.0 method reported in this study is effective to assess the sources and trends of daily aircraft engine nvPM emissions during LTO cycles at airports, which is valuable for optimizing flight operations considering the environmental impact of aircraft engine nvPM emissions. When the relevant aircraft flights, engine parameters, and engine nvPM emission databases embedded in the integrated method for any airport are established, the method is feasible to assess the sources and trends of aircraft engine nvPM emissions during LTO cycles at any time period in the airport. [ABSTRACT FROM AUTHOR]

For the electrolysis of aquatic hydrogen process efficiently in alkaline solution, the synthesis of high-activity and low-cost electrocatalyst are needed to reduce the high reaction energy barrier of HER. In this paper, a cost-effective MoS 2 /Cu 1.8 S/NiS@MoS X heterostructure catalyst was synthesized simply by a one-step hydrothermal method. In the preparation process, Cu mesh was used instead of traditional copper salts as a Cu source, enabling the spontaneous formation of Cu 1.8 S and NiS together on a large specific surface area MoS x substrate, which helps to accelerate the dissociation of H 2 O. The catalyst had an overpotential as low as 87 mV at 10 mA/cm2 and only 31 mV was increased after 1000 cycles of CV test in 1 M KOH solution. The characterization analysis showed that the heterogeneous structure of the catalyst contained a large amount of bridging S 2 2− and vacancy defects, which greatly promoted the catalyst stability and catalytic effect. • A heterostructure catalyst with excellent HER activity was synthesized. • The MoS 2 /Cu 1.8 S/NiS@MoS X catalyst was prepared using Cu mesh as a Cu source. • High synergism of Cu 1.8 S with NiS induces a large quantity of bridging S 2 2− active sites in MoS X. [ABSTRACT FROM AUTHOR]

To figure out the effect of kink-like defects on twin boundaries, BCC Ta with three different kinds of microstructures: single crystal (SC), perfect twin boundaries (PTB) and defective twin boundaries (DTB), are studied under nanoindentation. Both indenter load and hardness in PTB are enhanced by twin boundaries but reduced in DTB due to intrinsic kink-like defects. According to atomic surface morphology, the relative sink-in depth in DTB is lower than that in PTB but higher than that in SC. By comparing atomic images of prismatic loops in three different stages, it can be found that kink-like defects in DTB perform two opposite functions: acceleration and delay. In initial plastic stage, defective twin boundaries can accelerate pinching-off event and nucleation. In transmission stage, dislocation backward emission is advanced by defective twin boundaries. In obstruction stage, the symmetry of coherent twin boundaries will be broken and asymmetrical shear loops are formed, which will delay prismatic loops moving across twin boundaries. Dislocations of 1 2 〈 111 〉 are the main factor of nanoindentation in [ 1 ¯ 1 ¯ 2 ] direction. Kink-like defects will lead to less drops in DTB on dislocation densities than that in PTB. These findings are helpful to reveal the influence of intrinsic kink-like defects in BCC nanotwinned materials. [Display omitted] • Nanoindentation on nanotwinned Ta with intrinsic kink-like defects is studied. • Kink-like defects prevent twinning partial slip on the top twin boundary. • Prismatic loops will be either accelerated or delayed by kink-like defects. [ABSTRACT FROM AUTHOR]

Quasi-continuum method is applied to investigate the anisotropic behavior of nanoscale adhesive contact when a Ni tip indents into and then pulls out of single crystal Cu substrates. For 1 ¯ 10 substrate, the Ni tip exhibits excellent brittle behavior. Interface fracture is mainly characterized by atomic rearrangement since few slip planes are available. For (001) substrate, Shockley partials and deformation twins are both observed during the indentation process. Interface fracture is dominated by atomic slip which leads to the ductile fracture of the interface. As for (111) substrate, the nanocontact leads to significant plastic deformation of the substrate and the piling up of Cu atoms as well as the wetting of the Ni tip. This is because the Ni tip and Cu substrate share the same crystal orientations and the misfit effect between them is less evident. These anisotropic adhesive behaviors illustrate the importance of choosing a proper crystal contact surface to prevent wearing in micro-electro-mechanical systems. Distinctive nanocontact-induced deformation mechanisms and fracture mechanisms are revealed and analyzed. We found that available slip systems should be paid enough attention to for adhesive contact at nanoscale. It is recommended that adhesive contact between the Ni tip and Cu substrate with the same orientations should be avoided in order to reduce wearing. Some of the results found in our work are also validated by similar or related experiments by other researchers. [ABSTRACT FROM AUTHOR]

A new method is proposed to perform the multiscale simulation of nanoindentation with wedge indenter. We designed a potential field to model the wedge indenter based on the repulsive force-field approach which was used to model round indenters. A smooth curve representing the indenter tip is used to avoid the singularity of an ideal wedge indenter. Simulation with our approach correctly shows essential features of wedge nanoindentation. The load responses during retraction is confirmed by elastic model based on the Oliver-Pharr approach. Significant indentation size effect that the contact hardness decreases with the increase of contact depth is compared with existing models. The atomic configurations of the film shows that perfect dislocations nucleate under the indenter with Burges vectors perpendicular to the indentation direction. The strain distribution under the indenter shows that the length of plastic zone in the indentation direction is much larger than the contact width. [ABSTRACT FROM AUTHOR]

Abstract: Anisotropic plastic deformation beneath surface step during nanoindentation process is investigated applying the quasicontinuum (QC) method. Microscopic mechanisms of effects of surface step on FCC Al , (111), and (001) planes under the action of a cylindrical indenter are systematically studied. For steps on plane, dislocations nucleation and emission beneath surface steps is the main plastic deformation characteristic; for steps on (111) plane, the crystal lattice beneath the step undergoes severe distortion and rotation; for steps on (001) plane, deformation twinning and dislocation lock can be observed beneath the surface step. Load–displacement responses of various orientations and roughness are discussed in detail. The concept of geometrically necessary displacement is proposed to describe step flattening process. Strain energy for nanoindentation on stepped and flat surfaces under various crystal orientations is analyzed and compared to further investigate the effect of crystal anisotropic plastic deformation. The description about the atomistic behavior beneath surface step and the discussion about the anisotropic plastic deformation of surface step are meaningful for understanding the influence of surface step on the nanoindentation tests. [Copyright &y& Elsevier]

Abstract: Nanoindentation simulations on flat and stepped surfaces are respectively investigated using the quasicontinuum method based on the embedded-atom method potential. Effect of surface step considering indenter size and step height is studied. Results show that the critical load for the first dislocation emission will be decreased with the increase of step height. However, the effect of surface step will be weakened if the indenter size continues to increase. Initial atomistic structures after dislocation nucleation and emission are discussed systematically. The initial dislocations are not quite identically nucleated under the stepped surface. Stress distribution analysis reveals that the shear stress in the slip planes close to the step is much larger than the shear stress in the slip planes far from the step for nanoindentation on the stepped surface. The multiscale simulation results are consistent with experimental results and analytic solutions. The conclusions about step effect considering indenter size and step height are helpful for understanding the microscopic mechanism of nanoindentation tests on thin films with surface step. [Copyright &y& Elsevier]

Abstract: The quasicontinuum (QC) multiscale method is used to investigate anisotropic fracture behaviors of body-centered cubic (BCC) rare metal tantalum (Ta) loaded in Mode I and different fracture mechanisms are discussed from nanoscopic to continuum perspectives to have a deep understanding of brittle and ductile fracture. Initial crack deflection, brittle fracture by cleaving along low surface energy plane, ductile fracture as a result of dislocation emission and fracture accompanied by deformation twinning are all observed near crack tips of different crystal orientations. Particularly, some of these fracture mechanisms are found to be consistent with the latest experimental results. By examining different fracture behaviors, we find the surface energy and the available slip planes play a combined role in determining the fracture mechanisms near a crack tip. Both isotropic and anisotropic critical stress intensity factors are derived and compared for different crack orientations. A straightforward criterion that is proved to be applicable is used to distinguish brittle fracture from ductile fracture. [Copyright &y& Elsevier]

The flow around two square cylinders arranged side by side has been investigated through lattice Boltzmann method under different Reynolds numbers and various space ratios (s = d/D, d is the separation distance between two cylinders, D is the characteristic length) from 1.0, 1.1 to 2.7, including 18 space ratios. It is found that the flip-flop regime occurs at small space ratios and the synchronized regime occurs at large space ratios. Wide and narrow wakes at small spacing are formed and intermittently change behind the cylinders, and the biased flow in the gap is bistable. The frequency of vortex shedding is different in two wakes. The upper frequency is smaller than the lower frequency for small space ratios (s < 1.4), and the time-averaged drag and lift coefficients of cylinders are also different. When the space ratios increase, two distinct vortex streets occur behind the cylinders, and the frequency of vortex shedding is almost equal in two wakes. Also the difference of time-averaged drag and lift coefficients of the cylinders decreases with the increase in space ratios; in this case the flow shows synchronized regime. The transition between flip-flop and synchronized regimes occurs at s = 1.5. When s < 1.5, the flow shows flip-flop regime; otherwise, it shows synchronized regime. When s = 2.0 and 2.5, the curves for the time-averaged drag and lift coefficient with different Reynolds numbers are smooth. When s = 1.5 and 1.8, the curves are also smooth under Re ≤ 140, but that will be fluctuant under Re > 140 because of the nonlinear interaction between the wakes, and the instability of flow becomes stronger with the increase in Reynolds numbers. On the other hand, the vortex shedding type from the cylinder occurs in-phase when s < 2.5 and s = 2.5 for Re < 190, whereas that occurs anti-phase when s = 2.5 for Re ≥190. In addition, the pressure varies a little on the left surfaces and greatly on the right surfaces of both cylinders with the increase in Reynolds number at s = 2.5. [ABSTRACT FROM AUTHOR]

Abstract: A lattice Boltzmann model is proposed for the simulation of the statistical evolution of numerous microvoids under high stress triaxiality subjected to dynamic loadings. It considers the size distribution of microvoids during ductile fracture based on the balance law of microvoids’ number. A series of lattice Boltzmann equations governing the statistical evolution of microvoids are derived by using distribution function and multi-scale technique. Numerical results show that after a given time of evolution, microvoids in rate-sensitive materials are small and compact, whereas microvoids in rate-insensitive materials appear to be big and sparse, and the porosity in rate-insensitive material increases faster than that in rate-sensitive material. These numerical results might put insight into the mechanism of ductile fracture. [Copyright &y& Elsevier]

Abstract: A new biodegradable starch graft-copolymer, starch-g-poly(ε-caprolatone) (St-g-PCL), was synthesized in situ by the ring-opening graft-polymerization of a ε-caprolactone (CL) monomer onto starch granules in the presence of Sn(Oct)2. The polymerization was carried out in three different polymerization methods: in bulk, in toluene suspension or in suspension/bulk polymerization, where a suspension/bulk process resulted in highest PCL grafting efficiency in 40wt%. The structure of St-g-PCL was characterized by IR, DSC, SEM and WAXD. Both of the CL monomer and amylose corn starch were of industrial grade, without further purifications. The medium-resistance of St-g-PCL and the mechanical properties of the PCL composite blending with St-g-PCL were better than that of the PCL/starch blending composite. [Copyright &y& Elsevier]

The quasicontinuum method has been applied to probe the thin film with surface multi-defects, which is commonly seen in nanoimprint technique and bulk micromachining. Three unilaterally distributed multi-defect models and six bilaterally distributed multi-defect models of Pt thin film have been carried out in nanoindentation. The results show that the nanohardness gradually decreases as the number of unilaterally distributed multi-defects increases, along with the increasingly low decline rate of the nanohardness. The synergy effect of the unilaterally distributed multi-defects has been highly evidenced by the critical load revision for dislocation emission of Pt thin film, and it is predicted into a universal form with the synergy coefficient among the existing multi-defects for FCC metals. Moreover, the nanohardness obviously increases when the bilaterally distributed multi-defects form into symmetrical couple, and it could be even greater than the one with defect-free surface, due to the symmetry-induced enhancement effect on nanohardness. The symmetry-induced enhancement coefficient has been brought out and has well explained the symmetry-induced enhancement effect of bilaterally distributed multi-defects on the nanohardness by a prediction formula. Furthermore, the characteristic length of symmetric relations has been brought out to calculate the symmetry-induced enhancement coefficient and it has been effectively predicted to equal to the sum of the adjacent distance between the surface defect and the indenter, the defect depth near the indenter, and the defect width for FCC metal. [ABSTRACT FROM AUTHOR]

In order to study the effects of kink-like defects in twin boundaries on deformation mechanisms and interaction between dislocations and defects in twin boundaries under localized load, nanotwinned Cu with two defective twin (TDT) boundaries is compared with the nanotwinned Cu with two perfect twin (TPT) boundaries, and nanotwinned Cu with single defective twin (SDT) boundary and single perfect twin boundary by simulating spherical nanoindentations using molecular mechanics. The indenter force-depth and hardness-contact strain responses were analyzed. Results show that the existence of intrinsic defects in twin boundary could reduce the critical load and critical hardness of nanotwinned material. A quantitative parameter was first proposed to evaluate the degree of surface atom accumulation around the indenter during nanoindentation, and it can be inferred that the surface morphology in TDT changes more frequently than the surface morphologies in TPT and SDT. The atomistic configurations of incipient plastic structures of three different models were also analyzed. We found that the intrinsic defects in twin boundary will affect the incipient plastic structures. The formation of twinning partial slip on the defective twin boundary happens before the contact of the dislocation and twin boundary. The kink-like defects could introduce Frank partial dislocation to the twin boundary during interaction between dislocation and twin boundary, which was not detected on the perfect twin boundary. In addition, the area of twinning partial slips on the upper twin boundary in the incipient plastic structures in SDT and TDT are larger than the twinning partial slip area in TPT, which results in the reduction of the critical hardness in SDT and TDT. The kink-like defects could also block the expansion of twinning partial slip on the twin boundary. Furthermore, we investigated the dislocation transmission processes in three different models. It is found that the dislocation transmission event could be delayed in model containing single defective twin boundary, while the transmission process could be advanced in model containing two consecutive defective twin boundaries. The quantitative analysis of dislocation length was also implemented. Result shows that the main emitted dislocation during nanoindentation is Shockley partial, and the dislocation nucleation in SDT and TDT is earlier than the dislocation nucleation in TPT due to the existence of defects. It is inferred that the intrinsic defects on twin boundaries could enhance the interaction between dislocations and twin boundaries, and could strongly change the structure evolution and promote the dislocation nucleation and emission. These findings about kink-like defects in twin boundaries show that the inherent kink-like defects play a crucial role in the deformation mechanisms and it should be taken into consideration in future investigations. Single defective twin boundary structure is recommended to delay the transmission and block the expansion of twin boundary migration. Some of the results are in good agreement with experiments. [ABSTRACT FROM AUTHOR]

High-energy lasers can cause severe damage to conventional materials in an extremely short time. Highly reflective coatings are effective against damage, but they cannot withstand high laser power densities. In this study, a composite coating with two characteristics, namely, reflection and energy consumption, was designed and prepared. TiO 2 and BN powders, as light reflective media, were introduced into a boron-modified phenolic resin (BPF) to prepare an anti-laser composite coating. The results show that the initial reflectivity of the composite coating can reach 78.8% at a wavelength of 1064 nm. After damage-free protection for 0.4 s, ablation occurred in the irradiation region. Owing to the formation of residual char, which is the pyrolysis product of BPF, the coating maintained its protective performance. When the composite coating was irradiated at 1000 W/cm2 for 10 s, the back-surface temperature was 186 °C, which indicates decent anti-laser performance. We also studied the role of BN by setting a control experiment. The high conductivity and energy consumption caused by the evaporation of B 2 O 3 , which is the oxidation product of BN, helped in improving the anti-laser performance. The residual char with high porosity and degree of graphitization proved to be effective to isolate laser energy. This study provides a new design for protection of conventional materials against laser damage. [ABSTRACT FROM AUTHOR]

Abstract: Multiscale simulations using the quasicontinuum (QC) method with the embedded-atom method (EAM) potential are performed to examine the mechanical response of Cu–Ag bilayer film during nanoindentation tests. An attempt is made, from the viewpoint of collective interaction among misfit dislocations on the interface, to account for the strengthening and weakening mechanisms of interface on Cu–Ag bilayer film. The details of misfit dislocation nucleation, motion and collective interaction on Cu/Ag and Ag/Cu interfaces are discussed systematically, respectively. The investigation shows that the property and performance of Cu–Ag bilayer film mainly depend on the mechanical property of upper film. Both the strengthening and weakening effects are closely related to the collective interaction among misfit dislocations on the interface. Due to the pinning effect of interface on misfit dislocation, both the local interface migration and the voids can be observed at the core region of misfit dislocations. For nanoindentation on Cu/Ag bilayer film, the plastic deformation is localized chiefly in the lower Ag substrate and the void will disappear with the redistribution of misfit dislocations, which indicate that there are distinct protective and strengthening effects of the upper Cu film on the lower Ag substrate. While, for nanoindentation on Ag/Cu bilayer film, both the upper Ag film and the lower Cu substrate experience plastic deformation and the voids will not disappear, which imply that there are an obvious weakening effect of the upper Ag film on the lower Cu substrate. In addition, the multiscale simulation results are consistent with the experimental results. [Copyright &y& Elsevier]

Abstract: The quasi-continuum multiscale method (QC) is applied to investigate position effect of cylindrical indenter on nanoindentation into Cu thin film. Load–displacement responses reflect that indenter position influences the critical load and critical displacement distinctly. The microscopic deformation mechanism shows that it is the retarding of dislocation nucleation beneath the indenter that actually leads to a relative lower critical load. Once the plastic deformation is retarded, the load–displacement curve will undulate several times until dislocations nucleate at the retarded region. It is found that the critical loads periodically change with indenter positions. The period equals to the distance between two adjacent atomic planes in [111] direction. An improved elastic model is proposed to predict the critical load in consideration of the effect of indenter position. The agreement between QC simulation and the present model has shown the effectiveness of the improved model. [Copyright &y& Elsevier]

Abstract: Poiseuille number of rarefied gas flow in channels with designed roughness is studied and a multiplicative decomposition of Poiseuille number on the effects of rarefaction and roughness is proposed. The numerical methodology is based on the mesoscopic lattice Boltzmann method. In order to eliminate the effect of compressibility, the incompressible lattice Boltzmann model is used and the periodic boundary is imposed on the inlet and outlet of the channel. The combined bounced condition is applied to simulate the velocity slip on the wall boundary. Numerical results reveal the two opposite effects that velocity gradient and friction factor near the wall increase as roughness effect increases; meanwhile, the increments of the rarefaction effect and velocity slip lead to a corresponding decrement of friction factor. An empirical relation of Poiseuille number which contains the two opposite effects and has a better physical meaning is proposed in the form of multiplicative decomposition, and then is validated by available experimental and numerical results. [Copyright &y& Elsevier]

In this paper, the evolution of microstructure and the role of twin boundary during the fracture process of nano-twinned Ag are studied through molecular dynamics simulation. The fracture process of nano-twinned Ag with multiple twin boundaries is compared with both the fracture process of single crystal Ag and nano-twinned Ag with single twin boundary. Results demonstrate that multiple twin boundaries can significantly improve the strength of material by influence the propagation of crack and dislocation as observed by experiments. By comparing the stress–strain relationship and evolution of microstructure, we found that the elastoplastic transition in single crystal Ag is characterized by dislocation emission from the crack tip, while the elastoplastic transition in nano-twinned Ag is characterized by dislocation crossing the twin boundary. According to crack-resistance curves and observation results of microstructure evolution, multiple twin boundaries can significantly improve the fracture toughness of nano-twinned Ag compared to single twin boundary. The role of twin boundary in the fracture process is mainly to influence the propagation of crack and dislocation. The crack tip in single crystal Ag gradually gets blunt with the nucleation and emission of dislocations, while the crack in nano-twinned Ag propagates by cleavage. To explain this phenomenon, the generalized stacking fault energies and surface energies of both nano-twinned Ag and single crystal Ag are calculated and compared. It is shown that twin boundary can influence the energy barrier for atomic slip while have no influence on the generation of fracture surface. Twin boundary can also change the propagation direction of dislocations and stacking faults. Stacking faults propagate along (1 1 1) planes in matrix grain and propagate along (1 1 1 ¯) planes in twin grain, showing a tortuous shape. In this process, dislocations accumulate on the twin boundary, leading to high local dislocation density and high strength of nano-twinned material, which is agreement with experiments and simulations. Our study is helpful for understanding the relationship between microscopic deformation and macroscopic properties of nano-twinned crystal material. • The fracture processes of nano-twinned Ag and single crystal Ag are compared. • Multiple twin boundaries can improve the strength and fracture toughness of material. • Different characteristics of elastoplastic transition are revealed. • The cracks of nano-twinned Ag and single crystal Ag show different behaviors. • The effects of twin boundary on the propagation of stacking faults are revealed. [ABSTRACT FROM AUTHOR]

For manipulating heat flow efficiently, recently we established a theory of temperature-dependent transformation thermotics which holds for steady-state cases. Here, we develop the theory to unsteady-state cases by considering the generalized Fourier's law for transient thermal conduction. As a result, we are allowed to propose a new class of intelligent thermal metamaterial — switchable concentrator, which is made of inhomogeneous anisotropic materials. When environmental temperature is below or above a critical value, the concentrator is automatically switched on, namely, it helps to focus heat flux in a specific region. However, the focusing does not affect the distribution pattern of temperature outside the concentrator. We also perform finite-element simulations to confirm the switching effect according to the effective medium theory by assembling homogeneous isotropic materials, which bring more convenience for experimental fabrication than inhomogeneous anisotropic materials. This work may help to figure out new intelligent thermal devices, which provide more flexibility in controlling heat flow, and it may also be useful in other fields that are sensitive to temperature gradient, such as the Seebeck effect. [ABSTRACT FROM AUTHOR]