It is challenging how to identify the origin of fatigue life in pearlitic steel under cyclic impacts. In this paper, resorting to molecular dynamics simulations, we demonstrate that impact fatigue originates from local atomic disordering at the ferrite-cementite interface. This disordering triggers the nucleation and growth of voids, ultimately leading to spalling failure under cyclic impact loading. The disordering mechanism is incorporated into an Arrhenius-type activation model, which accurately captures the exponential relationship between fatigue life and impact velocity. This study thus establishes a clear link between the impact fatigue behavior of pearlitic steel and its microstructural evolution from an atomistic perspective, providing an intuitive framework for understanding fatigue processes in materials.

By implementing an intragranular distribution strategy for Al2O3 nanoparticles, an Al2O3/Al composite with ultra-high strength-ductility synergy was fabricated. The research shows that nano Al2O3 particles in hot-pressed composites were mainly located at grain boundaries, while hot extrusion promoted grain boundary migration, facilitating the migration of nano Al2O3 particles into the grains. A critical model related to materials (including reinforcement content, size) and hot deformation parameters was proposed to describe the grain boundary migration and intragranular behavior of nano reinforcements, which provides a criterion for intragranular distribution regulation. The tensile results indicate that the intragranular nano Al2O3 particles triggered highly efficient Orowan strengthening, significantly enhancing the strength. Meanwhile, the intragranular nano Al2O3 particles induced more uniform proliferation of dislocations, effectively promoting the coordinated deformation between the grain boundaries and the grain interior, thereby enhancing the elongation. Finally, a prepared 3 vol. % Al2O3/2009Al composite exhibits a yield strength exceeding 700 MPa and an elongation of up to 9 %, achieving a synergistic enhancement of both high strength and high ductility in metal matrix nanocomposites.

High-pressure environments require that power supplies of electronic devices can withstand high pressure without a hard shell. While compact reduced graphene oxide (rGO) electrodes enhance pressure tolerance, they suffer from compromised capacitance and power output due to the decreased ion-accessible surface area and blocked or collapsed ion channels. To overcome this challenge, carbon quantum dots (CQDs) were uniformly embedded into rGO film to create a compact yet porous electrode. This was achieved via a hydrothermal reaction to form a rGO/CQDs hydrosol by bonding CQDs to rGO nanosheets, followed by a subsequent vacuum filtering. The "spacer" function of CQDs improves the ion-accessible surface area, ion migration, and compressive strength of the rGO/CQDs films. Molecular dynamics simulations further confirm that embedded CQDs enhance both Young's modulus and the diffusion coefficient of hydronium ions within the rGO/CQDs films. Thus, at an ultra-high pressure of 360 MPa, the prepared rGO/CQDs films retained an impressive 81.2% of their initial capacitance (219.7 F cm-3 at 0.8 mA cm-2). The rGO/CQDs-based supercapacitors retained a high volumetric power density of 59.4 W cm-3 at 180 MPa. These findings demonstrate the great potential of rGO/CQDs films for pressure-tolerant power supply devices. Uniform CQD-embedded rGO films were made through hydrothermal reaction and vacuum filtration. CQDs boost ion transport and compressive strength. Remarkably, the films retain 81.2% capacitance under ultrahigh pressure (360 MPa).

The fatigue behavior of a high-strength bearing steel tempered under three different temperatures was investigated with ultrasonic frequency and conventional frequency loading. Three kinds of specimens with various yield strengths exhibited obvious higher fatigue strengths under ultrasonic frequency loading. Then, a 2D crystal plasticity finite element method was adopted to simulate the local stress distribution under different applied loads and loading frequencies. Simulations showed that the maximum residual local stress was much smaller under ultrasonic frequency loading in contrast to that under conventional frequency at the same applied load. It was also revealed that the maximum local stress increases with the applied load under both loading frequencies. The accumulated plastic strain was adopted as a fatigue indicator parameter to characterize the frequency effect, which was several orders smaller than that obtained under conventional loading frequencies when the applied load was fixed. The increment of accumulated plastic strain and the load stress amplitude exhibited a linear relationship in the double logarithmic coordinate system, and an improved fatigue life prediction model was established.

The fragmentation caused by cracks spreading along grain boundaries seriously deteriorates the cycling performance of high nickel (Ni >= 90%) layered cathode materials for lithium-ion batteries (LIBs). In this study, heterogeneous nucleation was utilized to epitaxially grow LiNbO3 layer onto LiNi0.90Co0.05Mn0.05O2 (NCM90). Importantly, the LiNbO3 layer was compatible with the highly reactive surface of NCM90. The formation process of LiNbO3 solid embryos was calculated and discussed based on crystal solidification theory, and the distribution of solid embryos revealed thin zone crystallization and aggregation zone grain pinning. More interestingly, the surface stiffness and surface Young's modulus of the NCM90 were significantly enhanced, and the grain movement (fragmentation) caused by the non-uniform contraction of the unit cell was bound correspondingly at high cut-off voltages. Originating from the binding effect of the coating layer, the value of surface hoop internal stress of NCM90 decreased by 22.88% to inhibit the cracking and reduce the loss of NCM90 during cycling. At the potential range of 3.0-4.3 V at 50 mA g(-1), the specific discharge capacity of the optimized NCM90 increased from 109.3 mAh g(-1) to 147.4 mAh g(-1) after 200 cycles. It is believed that this study provides a simple, convenient but effective strategy to restrain the fragmentation of high nickel layered cathode materials for LIBs.

Hardness decreases as indentation depth increases at both the nano- and micro-meter scales. By incorporating interfacial contributions, the indentation size effect can provide valuable information on the deformation behaviors of Ni-based single-crystal superalloys. In this paper, through experimental studies and atomistic simulations, we examine the indentation size effect and mechanical behaviors of Ni-based single-crystal superalloys. The results demonstrate that the indentation size effect, in conjunction with the Ni3Al/Ni interfacial network, is effectively captured by a modified Nix–Gao model. Molecular dynamics simulations further reveal the underlying atomistic mechanisms and microstructural evolution during nanoindentation. These findings provide new insights into the deformation behavior of Ni-based single-crystal superalloys and support their wide applications in the aerospace industry.

The century-long problem of conversion of plastic work to heat is controversial and challenging. In this work, 2D and 3D molecular simulations of crystal Cu are carried out to study the micro-mechanism of plastic work converting to heat. The results show that heat generation comes along with lattice restoration, transferring part of potential energy of defects, i.e., stored energy of cold work (SECW), to kinetic energy. As a result, specific crystallographic defects generate amounts of heat corresponding to variations of their SECW. If the change of microstructure and temperature are only detected at the surface of the system, the time lag of heat generation will be observed. The simulation results are indispensable accompaniments of experimental research, unveiling how plastic heat is affected by the type, propagation path, and density of defects, providing nano-scale explanations for the time lag of temperature rising in experiments.

Ni/Ni3Al heterogeneous multilayer structures are widely used in aerospace manufacturing because of their unique coherent interfaces and excellent mechanical properties. Revealing the deformation mechanisms of interfacial structures is of great significance for microstructural design and their engineering applications. Thus, this work aims to establish the connection between the evolution of an interfacial misfit dislocation (IMD) network and tensile deformation mechanisms of Ni/Ni3Al multilayer structures. It is shown that the decomposition of IMD networks dominates the deformation of Ni/Ni3Al multilayer structures, which exhibits distinct effects on crystallographic orientation and layer thickness. Specifically, the Ni/Ni3Al (100) multilayer structure achieves its maximum yield strength of 5.28 GPa at the layer thickness of 3.19 nm. As a comparison, the (110) case has a maximum yield strength of 4.35 GPa as the layer thickness is 3.01 nm. However, the yield strength of the (111) one seems irrelevant to layer thickness, which fluctuates between 10.89 and 11.81 GPa. These findings can provide new insights into a deep understanding of the evolution and deformation of the IMD network of Ni/Ni3Al multilayer structures.

An electrode often gets hot as it is operated. However, the critical temperature to trigger its failure remains elusive. Using finite element simulations, we have shown that a silicon anode cracks with the increase of temperature. The critical temperature to initiate a crack is positively correlated to the thickness of the silicon film, while the crack density is on the contrary. The mechanism is attributed to the mismatch of material properties between the silicon film and its substrate. The dependency of damage rate on the thickness of silicon films is also discussed. The findings provide a guidance for designing an electrode with a better resistance to thermal load.

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To comprehensively describe the size and strain rate dependent yield strength of monocrystalline ductile materials, a theoretical model was established based on the dislocation nucleation mechanism. Taking Ni3Al as an example, the model firstly fits results of molecular dynamics simulations to extract material dependent parameters. Then, a theoretical surface of yield strength is constructed, which is finally verified by available experimental data. The model is further checked by available third part molecular dynamics and experimental data of monocrystalline copper and gold. It is shown that this model can successfully leap over the huge spatial and temporal scale gaps between molecular dynamics and experimental conditions to get the reliable mechanical properties of monocrystalline Ni3Al, copper and gold.

In this paper, from both experimental and atomistic simulation perspectives, we have systematically elaborated on the formation of stacking fault tetrahedrons that induces the pop-in events in Ni-based single crystal superalloys under nanoindentation. The magnitude of a displacement burst is proportional to the number and size of stacking fault tetrahedrons. The external work and strain energy stored in dislocations are further discussed in order to ascertain the energy conversion during pop-in events. The findings can provide new insights into a deep understanding of the pop-in events in Ni-based single crystal superalloys and benefit their wide applications in the aerospace industry.

The development of science and technology has put forward higher and higher requirements for material properties. It is an effective way to achieve the best performance in a specific direction by ordering the internal structure of materials. However, the traditional one-way freezing technology cannot achieve the preparation of two-dimensional ordered structure. B4C layered scaffolds with single orientation were prepared by bidirectional freezing method. The layered scaffolds were filled with polydimethylsiloxane (PDMS) to prepare the two-dimensional layered boron carbide and organo-silicate composites with anisotropy. The layered scaffolds maintain an obvious two-dimensional ordered ttlayered structure in the composites. There is an alternate arrangement structure of PDMS and B4C skeleton at the growth plane of A in the composite material. It is a stacked structure like ocean waves at the growth plane of B. The layered scaffold maintains an obvious two-dimensional ordered layered structure in the composite material. The maximum in-plane anisotropy ratio of dynamic modulus of the composite can reach 12.9, and the dynamic modulus shows obvious Payne effect. It provides some new methods and ideas for the preparation of anisotropic composite material systems.

Semiconductor quantum dots (QDs) are promising materials for stress/strain sensing applications owing to their pressure-dependent photoluminescence (PL) and nanoscale size, while the impact of stress and microstructure on their optical properties still awaits in-depth investigations under more realistic loading conditions. Herein, bare CuInS2 QDs and core- shell structured CuInS2/ZnS QDs are investigated under repetitive pressure loadings to elucidate the pressure-dependent PL responses over many pressure cycles. The CuInS2/ZnS QDs not only show higher PL intensity but also exhibit a reliable and simple relationship between PL emission peak energy (E-PL) and external pressure (P), which is desirable for actual application in stress/strain sensing. Specifically, the E-PL-P relationship of bare CuInS2 QDs changes after the first loading-unloading cycle, while the EPL-P relationship of CuInS2/ZnS QDs shows repeatable trajectories under different cycles. This research provides experimental support for designing QD-based stress/ strain sensing materials and explains how the shell and surface microstructure will affect the mechanical-luminescence responses of

We show that repeatable energy absorption can be obtained via the reversible wurtzite-to-hexagonal phase transformation of ZnO nanopillars at room temperature. The effect is demonstrated using molecular dynamics simulations and available experimental data. With uniaxial compressive strains up to 22.1% along the [0001] orientation, a ZnO nanopillar with a lateral dimension of 5.5 nm can produce average specific energy absorption on the order of 26.7 J g(-1) under quasistatic cyclic loading and 11.1 J g(-1) under rapid loading. The theoretical maximum of the specific energy absorption is 41.0 J g(-1) which can be approached at nanopillars with lateral sizes above 55 nm. These values are comparable to that of widely used aluminum foams. The effects of inversion domain boundaries and sample size on the repeatable energy absorbing capacity are discussed. The findings open an avenue for ZnO nanostructures in mechanical energy absorption and dissipation applications.

The apparent activation energy of a nanostructure is difficult to directly measure experimentally. In this letter, we present a computational method for estimating the apparent activation energy of a range of semiconductor nanostructures. This method allows the activation energy to be obtained from experimentally measured average activation time or propagation speed at various temperatures of the phase boundary associated with the transformation. The approach entails analyzing the mobility of the transformation in question using a model based on the Arrhenius relation. The specific analysis carried out uses the {0110} inversion domain boundary in wurtzite ZnO nanopillars as example. Molecular dynamics simulations are conducted over the temperature range of 300-900 K of the corresponding available experimental data. The approach and analysis offer a means for experimentally establishing the apparent activation energy of the {0110} inversion domain boundary in a variety of wurtzite-structured II-VI, III-V and IV-IV binary compounds.

Experimental determination of the frictional properties of a microsized fiber wrapped around a cylinder has been of long-standing interest to the academic community. The purpose of the current experiments was to explore the diameter dependence of such microsized fibers in nonlubricated friction using a highly accurate tribometer. For this work, NbTi superconducting material was used for the fibers and polyvinyl chloride (PVC) was used as the cylinder material. Significant effects were observed in the kinetic friction coefficient for different fiber diameters, normal forces, and sliding speeds. Moreover, the effects of fiber diameter on the frictional stability were measured. Smaller fiber diameters and low sliding speeds both produced poor frictional stability. The most likely explanation for the observed stick-slip phenomena is hypothesized to be a combination of creep mechanics and plastic deformation of the junctions on the contacting surfaces.

The acceleration precursor of catastrophic rupture in rock‐like materials is usually characterized by a power law relationship, but the exponent exhibits a considerable scatter in practice. In this paper, based on experiments of granites and marbles under quasi‐static uniaxial and unconfined compression, it is shown that the power law exponent varies between −1 and −1/2. Such a changeable power law singularity can be justified by the energy criterion and a power function approximation. As the power law exponent is close to the lowest value of −1, rocks are prone to a perfect catastrophic rupture. Furthermore, it is found that the fitted reduced power law exponent decreases monotonically in the vicinity of a rupture point and converges to its lower limit. Therefore, the upper bound of catastrophic rupture time is constrained by the lowest value of the exponents and can be estimated in real time. This implies that, with the increase of real‐time sampling data, the predicted upper bound of catastrophic rupture time can be unceasingly improved.

Multifunctional polymer composites with both high dielectric constants and high thermal conductivity are urgently needed by high-temperature electronic devices and modern microelectromechanical systems. However, high heat-conduction capability or dielectric properties of polymer composites all depend on high-content loading of different functional thermal-conductive or high-dielectric ceramic fillers (every filler volume fraction ≥ 50%, i.e., ffiller ≥ 50%), and an overload of various fillers (fthermal-conductive filler + fhigh-dielectric filler > 50%) will decrease the processability and mechanical properties of the composite. Herein, series of alumina/barium titanate/polypropylene (Al2O3/BT/PP) composites with high dielectric- and high thermal-conductivity properties are prepared with no more than 50% volume fraction of total ceramic fillers loading, i.e., ffillers ≤ 50%. Results showed the thermal conductivity of the Al2O3/BT/PP composite is up to 0.90 W/m·K with only 10% thermal-conductive Al2O3 filler, which is 4.5 times higher than the corresponding Al2O3/PP composites. Moreover, higher dielectric strength (Eb) is also found at the same loading, which is 1.6 times higher than PP, and the Al2O3/BT/PP composite also exhibited high dielectric constant ( ε r = 18 at 1000 Hz) and low dielectric loss (tan δ ≤ 0.030). These excellent performances originate from the synergistic mechanism between BaTiO3 macroparticles and Al2O3 nanoparticles.

Instrumented indentation is a method that has been widely used to obtain material properties at micro and nano scale, yet creditable indentation size effect at real nano-scale and its mechanism are still unsolved. This paper summarizes our recent work on progresses in experimental and simulation approaches to this problem. By confirming the crystalline orientations and the surface roughness of the sample, obtaining the tip radius of the indenters, as well as considering tip radius in large-scale molecular simulation, the gap between the experiment and simulation results is bridged, and these two results can be cross verified with each other, which leads to a reliable hardness trend over the indentation depth at nano-scale. Two opposite size effects are observed, and their different mechanisms are revealed, as the conventional size effect results from the plastic behavior such as dislocation nucleation and propagation in the sample beneath the indenter, while the initial reverse size effect is due to the combined effect of the indenter roundness and elastic behavior of the material. Systematic investigation on the efficiency and fidelity of MD and MS is carried out, on problem of the dislocation evolution during indentation, the influence of the relaxation time and convergence resolution on the load curve and dislocation patterns are studied, and suggestion on choice of two simulation methods and the relaxation time and convergence resolution are given.