Omnidirectional thermal-electric signatures of functional illusion device with anisotropic geometry.

The omnidirectional thermal-electric signatures induced by the anisotropic functional illusion device and the corresponding camouflage device are reported. We first theoretically derive the anisotropic effective parameters of confocal elliptical bilayer core-shell structure for constructing the functional illusion device. Then, the thermal-electric signatures of the functional illusion device with camouflage device are presented numerically. In addition, we further transform the monolayered structure of the camouflage device into an alternating multilayered one to enrich the omnidirectional illusion effects. The results show that the functional illusion device with monolayered structure could realize omnidirectional thermal-electric illusion effects perfectly. When the monolayered structure is replaced by the alternating multilayered one, the functional illusion device with alternating multilayered structure could achieve different illusion effects with different scattering signatures under different directional heat flux and electric current launching. This article may open a new avenue to realize omnidirectional illusion effects of functional device in multiphysical fields.

Design of an omnidirectional camouflage device with anisotropic confocal elliptic geometry in thermal-electric field.

The designed confocal elliptical core-shell structure can realize the omnidirectional camouflage effect without disturbing temperature and electric potential profiles as the directions of heat flux and electric current change. Based on the anisotropy of the confocal ellipse, the anisotropic effective parameters of the confocal elliptical core-shell structure are derived under different heat flux and electric current launching. Then, the matrix material should be anisotropic as the effective parameters to satisfy the omnidirectional camouflage effect, which is demonstrated numerically. In addition, we present a composite structure to realize the anisotropic matrix. The experimental results show that the camouflage device embedded in the composite structure can eliminate the scattering caused by the elliptical core under different directions of heat flux and electric current, thus achieving the omnidirectional thermal-electric camouflage effect experimentally. The omnidirectional camouflage effect in thermal and electric fields can greatly widen the application fields of this device with anisotropic geometry.

Synergy Effect and Symmetry-Induced Enhancement Effect of Surface Multi-Defects on Nanohardness by Quasi-Continuum Method.

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.

Assessment of predicted aircraft engine non-volatile particulate matter emissions at Hangzhou Xiaoshan International Airport using an integrated method.

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.

Shape Effect of Surface Defects on Nanohardness by Quasicontinuum Method.

Nanoindentation on a platinum thin film with surface defects in a rectangular shape and triangular shape was simulated using the quasicontinuum method to study the shape effect of surface defects on nanohardness. The results show that the nanohardness of thin film with triangular defects is basically larger than those with rectangular defects, which is closely related to the height of the surface defects at the boundary near to the indenter. Moreover, the triangular defect might have an enhancement effect on nanohardness by a certain size of the defects and the boundary orientation of the defect, where such an enhancement effect increases as the defect grows. Furthermore, the nanohardness decreases when the defect is folded from wide to narrow in the same atom cavity, and particularly expresses a more obvious drop when the height of the defects increases. In addition, larger sizes of the rectangular defect induce more reduction in nanohardness, while the nanohardness of the triangular surface defect is sensitive to the periodic arrangement of atoms changed by the boundary orientation of the defect, which is well explained and demonstrated by the calculation formula theory of necessary load for dislocation emission.

Atomistic Study of Interactions between Intrinsic Kink Defects and Dislocations in Twin Boundaries of Nanotwinned Copper during Nanoindentation.

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.

Multiscale Analysis of Size Effect of Surface Pit Defect in Nanoindentation.

The nanoindentation on a pit surface has been simulated using the quasicontinuum method in order to investigate the size effect of surface pit defect on the yield load of thin film. Various widths and heights of surface pit defect have been taken into account. The size coefficient has been defined as an index to express the influence of the width or height of surface pit defect. The results show that as the size coefficient of width (of height) increases, at first the yield load of thin film decreases extremely slowly, until the size coefficient of width equals approximately one unit (half unit), at which point the yield load experiences an obvious drop. When the size coefficient of width (of height) reaches approximately two units (one unit), the yield load is almost the same as that of the nanoindentation on a stepped surface. In addition, the height of surface pit defect has more influence than the width on the yield load of thin film.

Temperature-Dependent Transformation Thermotics: From Switchable Thermal Cloaks to Macroscopic Thermal Diodes.

The macroscopic control of ubiquitous heat flow remains poorly explored due to the lack of a fundamental theoretical method. Here, by establishing temperature-dependent transformation thermotics for treating materials whose conductivity depends on temperature, we show analytical and simulation evidence for switchable thermal cloaking and a macroscopic thermal diode based on the cloaking. The latter allows heat flow in one direction but prohibits the flow in the opposite direction, which is also confirmed by our experiments. Our results suggest that the temperature-dependent transformation thermotics could be a fundamental theoretical method for achieving macroscopic heat rectification, and it could provide guidance both for the macroscopic control of heat flow and for the design of the counterparts of switchable thermal cloaks or macroscopic thermal diodes in other fields like seismology, acoustics, electromagnetics, and matter waves.

Multiscale simulation of indentation, retraction and fracture processes of nanocontact.

The process of nanocontact including indentation and retraction between a large Ni tip and a Cu substrate is investigated using quasicontinuum (QC) method. The multiscale model reveals that significant plastic deformation occurs during the process of nanocontact between Ni tip and Cu substrate. Plastic deformation is observed in an area as large as 20 nm wide and 10 nm thick beneath Ni tip during the indentation and retraction. Also, plastic deformation at a deep position in the Cu substrate does not disappear after the neck failure. The analysis of generalized planar fault energy curve shows that there is a strong tendency for deformation twinning in Cu substrate. However, deformation twinning will be retarded during indentation due to the high stress intensity caused by stepped surface of Ni tip. The abrupt drop of load curve during tip retraction is attributed to the two different fracture mechanisms. One is atomic rearrangement near the interface of Ni tip and Cu substrate at the initial stage of neck fracture, the other is shear behavior of adjacent {111} planes at the necking point. A comparison of the critical load and critical contact radius for neck fracture is also made between theoretical values and our numerical results.

Effects of Crystalline Anisotropy and Indenter Size on Nanoindentation by Multiscale Simulation.

Nanoindentation processes in single crystal Ag thin film under different crystallographic orientations and various indenter widths are simulated by the quasicontinuum method. The nanoindentation deformation processes under influences of crystalline anisotropy and indenter size are investigated about hardness, load distribution, critical load for first dislocation emission and strain energy under the indenter. The simulation results are compared with previous experimental results and Rice-Thomson (R-T) dislocation model solution. It is shown that entirely different dislocation activities are presented under the effect of crystalline anisotropy during nanoindentation. The sharp load drops in the load-displacement curves are caused by the different dislocation activities. Both crystalline anisotropy and indenter size are found to have distinct effect on hardness, contact stress distribution, critical load for first dislocation emission and strain energy under the indenter. The above quantities are decreased at the indenter into Ag thin film along the crystal orientation with more favorable slip directions that easy trigger slip systems; whereas those will increase at the indenter into Ag thin film along the crystal orientation with less or without favorable slip directions that hard trigger slip systems. The results are shown to be in good agreement with experimental results and R-T dislocation model solution.