Large Compressive Strain Research Articles

Superlubricity of molybdenum disulfide subjected to large compressive strains

The friction between a molybdenum disulphide (MoS2) nanoflake and a MoS2 substrate was analyzed using a modified Tomlinson model based on atomistic force fields. The calculations performed in the study suggest that large deformations in the substrate can induce a dramatic decrease in the friction between the nanoflake and the substrate to produce the so-called superlubricity. The coefficient of friction decreases by 1–4 orders of magnitude when a high strain exceeding 0.1 is applied. This friction reduction is strongly anisotropic. For example, the reduction is most pronounced in the compressive regime when the nanoflake slides along the zigzag crystalline direction of the substrate. In other sliding directions, the coefficient of friction will reduce to its lowest value either when a high tensile strain is applied along the zigzag direction or when a high compressive strain is applied along the armchair direction. This anisotropy is correlated with the atomic configurations of MoS2.

Strain tuning of negative capacitance in epitaxial PbZr<sub>0.2</sub>Ti<sub>0.8</sub>O<sub>3</sub> thin films

In order to continue Moore’s Law, the reducing of power consumption is concerned by many researchers, and the discovery of ferronegative negative capacitance effect (NCE) provides a solution. Strain engineering has been widely studied as an effective means to regulate the physical properties of ferroelectric thin films. But the relevant mechanism of strain to ferroelectric negative capacitance regulation is not clear. Recently, the experimental results have shown that it is possible to stabilize the transient NCE in resistance-ferroelectric networks. In this work, we use the Landau-Khalatnikov theory to study the microscopic domain evolution and the influence of strain and temperature on NCE in a ferroelectric film. It is shown that compressive strain enhances NCE while NCE becomes weaker under a tensile strain. However, a larger compressive strain will give rise to a higher coercive voltage that hinders the NCE from forming. In addition, under a certain strain, the NCE becomes stronger at lower temperature. This work provides the theoretical basis for designing the negative capacitance devices and scaling towards nanoscale dimensions in future.

Dose and Recovery Response of Patellofemoral Cartilage Deformations to Running.

Background:Running is a common recreational activity that provides many health benefits. However, it remains unclear how patellofemoral cartilage is affected by varied running distances and how long it takes the cartilage to recover to its baseline state after exercise.Hypothesis:We hypothesized that patellofemoral cartilage thickness would decrease immediately after exercise and return to its baseline thickness by the following morning in asymptomatic male runners. We further hypothesized that we would observe a significant distance-related dose response, with larger compressive strains (defined here as the mean change in cartilage thickness measured immediately after exercise, divided by the pre-exercise cartilage thickness) observed immediately after 10-mile runs compared with 3-mile runs.Study Design:Descriptive laboratory study.Methods:Eight asymptomatic male participants underwent magnetic resonance imaging of their dominant knee before, immediately after, and 24 hours after running 3 and 10 miles at a self-selected pace (on separate visits).Results:Mean patellar cartilage thicknesses measured before exercise and after the 24-hour recovery period were significantly greater than the thicknesses measured immediately after both the 3- and 10-mile runs (P < .001). This relationship was not observed in trochlear cartilage. Mean patellar cartilage compressive strains were significantly greater after 10-mile runs compared with 3-mile runs (8% vs 5%; P = .01).Conclusion:Patellar cartilage thickness decreased immediately after running and returned to its baseline thickness within 24 hours of running up to 10 miles. Furthermore, patellar cartilage compressive strains were dose-dependent immediately after exercise.Clinical Relevance:These findings provide critical baseline data for understanding patellofemoral cartilage biomechanics in asymptomatic male runners that may be used to optimize exercise protocols and investigations targeting those with running-induced patellofemoral pain.

The mechanical behavior and collapse of graphene-assembled hollow nanospheres under compression

Recently, much interest has been attracted in the graphene-assembled hollow nanospheres (GAHNs) because of outstanding multi-functional properties. This paper systematically explores the compressive mechanical behaviors and gas bearing capability of GAHNs by a coarse-grained molecular dynamics (CGMD) simulation combining with in-situ compressive test. It was found that the GAHNs possess excellent compressive elasticity (experimentally recoverable strain can reach ∼ 58%). Under large compressive strain (>90%), the GAHNs also display obvious plastic deformation owing to inter-layer slippage between graphene nanosheets. In addition, the morphology of force measurement tip (FMT) plays critical roles on the compressive failure modes of GAHNs. When FMT is sharp, it can pierce through the shell of GAHN, whereas the blunt one compels GAHN to collapse. The thermal expansion process of GAHNs was investigated by CGMD simulation. With the increase of ambient temperature, the internal pressure of GAHN increased until a crack appears. To further understand this expansion failure, an in-situ scratching experiment was designed and the tearing strength of shell of GAHN was estimated to be ∼748 MPa. This work provides an in-depth understanding on intrinsic mechanical properties of GAHNs and broadens their potential applications.

Isogeometric shape optimization of missing rib auxetics with prescribed negative Poisson’s ratio over large strains using genetic algorithm

This paper presents an isogeometric shape optimization framework using genetic algorithm to design 2D auxetic structures with prescribed Poisson’s ratio over large tensile or compressive strains in the nonlinear deformation regime. The design domain is parametrized using NURBS to allow smoother shape variation of the structure and enable accurate fabrication of the optimized structures. The versatility of the framework is illustrated through the optimization of a missing rib structure with four ligaments under different loading conditions. The manufacturability of specimens using the NURBS and PolyJet 3D printing technology is also shown. The first example focuses on achieving constant negative Poisson’s ratio up to -0.7 within the applied tensile strain of 50% under plane stress condition. As auxetics experiments under large compressive strain are rarely performed and published, the second example demonstrates the optimization for compressive loading. The Poisson’s ratio determined from experiments matches well with the numerical results. The experiments highlight that for very flexible materials, deformation under self-weight and contacts between adjacent unit cells are significant factors in compression, and further investigations are needed.

Facile Fabrication of 3D Porous Sponges Coated with Synergistic Carbon Black/Multiwalled Carbon Nanotubes for Tactile Sensing Applications.

Recently, flexible tactile sensors based on three-dimensional (3D) porous conductive composites, endowed with high sensitivity, a wide sensing range, fast response, and the capability to detect low pressures, have aroused considerable attention. These sensors have been employed in different practical domain areas such as artificial skin, healthcare systems, and human–machine interaction. In this study, a facile, cost-efficient method is proposed for fabricating a highly sensitive piezoresistive tactile sensor based on a 3D porous dielectric layer. The proposed sensor is designed with a simple dip-coating homogeneous synergetic conductive network of carbon black (CB) and multi-walled carbon nanotube (MWCNTs) composite on polydimethysiloxane (PDMS) sponge skeletons. The unique combination of a 3D porous structure, with hybrid conductive networks of CB/MWCNTs displayed a superior elasticity, with outstanding electrical characterization under external compression. The piezoresistive tactile sensor exhibited a high sensitivity of (15 kPa−1), with a rapid response time (100 ms), the capability of detecting both large and small compressive strains, as well as excellent mechanical deformability and stability over 1000 cycles. Benefiting from a long-term stability, fast response, and low-detection limit, the piezoresistive sensor was successfully utilized in monitoring human physiological signals, including finger heart rate, pulses, knee bending, respiration, and finger grabbing motions during the process of picking up an object. Furthermore, a comprehensive performance of the sensor was carried out, and the sensor’s design fulfilled vital evaluation metrics, such as low-cost and simplicity in the fabrication process. Thus, 3D porous-based piezoresistive tactile sensors could rapidly promote the development of high-performance flexible sensors, and make them very attractive for an enormous range of potential applications in healthcare devices, wearable electronics, and intelligent robotic systems.

Ligament size dependency of strain hardening and ductility in nanoporous gold

Nanoporous (NP) metals with ligament sizes up to a few tens of nm show exceptional mechanical properties such as high strength and stiffness per weight. While their elasticity and yield strength have been the subject of numerous studies, less is known about the plastic deformability of these materials under large compressive and tensile strains. In this study, the effect of ligament size is investigated using large-scale atomistic simulations to probe the elastic response, plastic response, and deformation mechanisms of nanoporous gold under uniaxial compression and tension to strains in excess of 60 percent. This paper explores the full range of the material response under uniaxial loading, focusing on the modifications to strain hardening under compression and ductility and delayed failure under tension. It was found that the elastic modulus experiences a compression-tension asymmetry that decreases with ligament size increase. Under compression, strain hardening is found to be ligament size dependent. This size dependency can be explained by the coupling effect of the change in surface area to solid volume ratio evolution and defects accumulation. Under tension, the material shows higher ductility with ligament size increase causing a delay in failure. This is attributed to differences in dislocation density. The results reported in this work will help in evaluating the effect of ligament size on the material response, and eventually enhance the design of novel nanoporous foams with tailored mechanical response.

Strength and plasticity of amorphous ceramics with self-patterned nano-heterogeneities

Amorphous ceramics with superb strength and irradiation tolerance are promising candidate materials for nuclear industry. However, the brittle-like behavior extremely limits their applications. Here, we demonstrate that Fe–SiOC amorphous ceramic composites (ACCs) with self-patterned Fe-rich nanoclusters fabricated by co-sputtering Fe and amorphous SiOC ceramic not only exhibits exceptional, homogeneous plasticity at room temperature but also remains high strength and good irradiation tolerance. Flow strength of Fe–SiOC ACCs decreases but plasticity increases with the increase in Fe content. Moreover, the strength and plasticity of Fe–SiOC ACCs can be further tailored by subsequent annealing and ion irradiation associated with the change in their microstructure. High temperature annealing tunes amorphous Fe-rich nanoclusters into crystalline Fe nanoparticles, significantly enhancing flow strength of Fe–SiOC ACCs without loss of plasticity. Ion irradiation does not apparently modify the microstructure and reduce plasticity of Fe34at.%-SiOC ACC, but slightly enhances their flow stress. For instance, annealed Fe34at.%-SiOC ACC has flow true stress exceeding 4.0 GPa at a large uniform compressive strain of 55% without plastic flow instability and cracking. The spatially distributed Fe-rich heterogeneities (amorphous nanoclusters and crystalline nanoparticles) plastically co-deform with amorphous SiOC matrix and discretize shear transformation zones in amorphous ceramics, thus preventing the shear-banding instability and significantly enhancing compressive plasticity. The plastic co-deformation between Fe-rich nano-heterogeneities and amorphous SiOC ceramic matrix is achieved due to interface constraint, preventing cracking and ensuring homogeneous plastic deformation of Fe–SiOC ACCs. These findings suggest that patterning nanoscale metal-rich heterogeneities can tailor mechanical properties of amorphous ceramics.

The Mechanical Response of Wet Volcanic Sand to Impact Loading, Effects of Water Content and Initial Compaction

The effects of water content and initial compaction on the dynamic response of volcanic sand from Mount Etna were investigated by a series of experiments on a long Split Hopkinson Pressure Bar apparatus capable of generating stress pulses of duration exceeding one millisecond. The dynamic stress–strain characteristics were determined until large final compressive strains were achieved. An experimental protocol for the preparation of samples characterised by different initial porosity and moisture content was defined in order to reproduce, in a laboratory environment, granular volcanic aggregates representative of naturally occurring soils in different initial density and water content states. It was found that, for limited amounts of water content, the dynamic response of the investigated volcanic wet sand is more compliant than in dry conditions. Conversely, highly saturated samples exhibit a steep increase in stiffness occurring at strains when the dynamic compressive behaviour becomes dominated by the response of the nearly incompressible water. The presence of water has negligible effect on the mechanical behaviour when the samples are loaded at quasi static strain rates. The grain size distribution and morphology of samples tested in different conditions were evaluated and compared by means of edge detection analysis techniques applied to high contrast images.

Temperature dependence on the domain structure of epitaxial PbTiO3 films grown on single crystal substrates with different lattice parameters

Epitaxial PbTiO3 (PTO) thin films were deposited on different single crystal (100)KTaO3 [KTO], (110)DyScO3 [DSO], (110) GdScO3 [GSO] and (001)SrTiO3 [STO] substrates. Temperature dependence of the lattice parameters and the domain structure showed a systematic change with misfit strains (Sm) of PTO films, explored by high-resolution X-ray diffraction measurements. Fully (001)-orientation films on STO and fully (100)-orientation films on KTO substrates were confirmed, and the elevated phase transition temperature (Tc) was confirmed in PTO films induced by both large compressive (STO) and tensile strains (KTO). While, for PTO films grown on GSO substrates with small tensile strains, Tc is similar to the powder data. And, ferroelastic domain structure changed from (100)-orientation to (100)/(001)-orientations was observed during decreased temperature. The temperature dependence of domain structures PTO films with the different Sm are in good agreement with thermodynamic calculation for the temperature–Sm diagram of ferroelastic domain structure.

Relationships among rheological, sensory, and wear behaviors of cheeses.

Studying rheological and sensory behaviors of cheese provides structural and texture-related information that could be useful for a better understanding of the complex wear behaviors of cheese and their relationships with cheese industrial and oral processing behaviors. Thus, the objective of this study was to determine the relationships of rheological and sensory properties with cheese wear. Rheological tests including large amplitude oscillatory shear, strain sweeps at different temperatures (5, 15, and 25°C), and large-strain compression at room temperature (22 ± 2°C) were conducted for cheeses with varying fat contents (40, 50, 52, and 54% fat-in-dry-matter aged for different periods (15, 30, 45, and 60 d). Descriptive sensory analysis was used to evaluate cheese sensory texture attributes. Overall, fat content, testing temperature, and aging time had significant impact on cheese viscoelastic parameters. Higher temperature, aging time, and fat content led to lower rigidity and greater extent of nonlinear viscoelastic behaviors in the cheeses. Mass loss showed negative correlations with critical strain (γc ), critical stress (σc ), complex modulus (G* ), and fracture stress, but had positive correlations with phase angle (δ) and fracture strain. Sensory data showed that texture attributes were affected by cheese fat content and aging time and had significant correlations with mass loss at high normal force and sliding speed. This study showed that rheology and sensory data can be used to provide fundamental information on the wear behaviors of cheese and other soft materials.

Ice templated nanocomposites containing rod-like hematite particles: Interplay between particle anisotropy and particle–matrix interactions

We demonstrate that the mechanical response of ice templated nanocomposite scaffolds prepared from ellipsoidal hematite particles is determined by both the particle aspect ratio and the interaction between the particles and the matrix polymer. We ice template aqueous dispersions of hematite particles, polyethyleneimine, and diepoxy crosslinker and crosslink the polymer in the frozen state. This protocol results in the formation of elastic macroporous monoliths capable of complete recovery from large compressive strains. Hematite particles show an inversion of their surface charge with pH: they are negatively charged at a basic pH and positively charged under acidic conditions. This allows us to change the interaction between hematite particles and crosslinked matrix polymer that they are embedded in, simply by immersing the monoliths in aqueous solutions with different pH’s. We report that under basic conditions, viz, when polyethyleneimine adsorbs on the particle surface, there is a decrease in the monolith modulus with an increase in the particle aspect ratio. We demonstrate that this correlates with a change in the mechanism of monolith response: from wall compression for isotropic particles to wall bending for anisotropic particles with an aspect ratio of 4. Under acidic conditions (pH = 2), where hematite particles show a positive zeta potential, the monolith modulus increases with the aspect ratio of the ellipsoidal fillers. Understanding the interplay between filler aspect ratio and filler–matrix interaction has important implications for the control of nanocomposite mechanical properties.

Comparative Study of Boron Precursors for Chemical Vapor‐Phase Deposition‐Grown Hexagonal Boron Nitride Thin Films

Two different boron precursors, diborane (B2H6) and trimethyl boron ((CH3)3B, TMB), are investigated for chemical vapor‐phase deposition (CVD)‐grown hexagonal boron nitride (h‐BN) on α‐Al2O3 (0001) substrates. The BN layer grown using TMB includes a large amount (2 × 1020 cm−3) of carbon atoms, which is 60 times higher than that in the BN layer grown using B2H6. The X‐ray diffraction 2θ/ω scans for BN film grown using B2H6 exhibit the h‐BN (002) peak. The BN film obtained using TMB includes turbostratic BN (t‐BN). The E2g Raman peak frequencies in B2H6 and TMB h‐BN are observed at 1368.8 and 1369.7 cm−1, respectively. The Raman peak shift to a higher frequency indicates that a larger compressive strain is induced using TMB than using B2H6. The full width at half maximum of the B2H6 and TMB Raman peak frequencies is 21.8 and 42.7 cm−1, respectively. The cathodoluminescence spectra of B2H6 h‐BN show the band‐edge emissions at 225 and 232 nm, whereas only a 300 nm broadband is obtained in TMB h‐BN. It is suggested that the carbon atoms in TMB prevent the formation of highly crystalline h‐BN thin films.

Deposition-Temperature-Mediated Selective Phase Transition Mechanism of VO2 Films

A clear experimental explanation of the contribution of Mott and Peierls transitions to the insulator–metal transition (IMT) characteristics in vanadium dioxide (VO2) is still lacking. Examining the crystal and electronic structures of epitaxial VO2 films grown at various deposition temperatures, a Mott or a Peierls transition was observed. The VO2 film deposited at 500 °C showed suppressed Peierls transition characteristics because of the large in-plane compressive strain in the insulating phase. The VO2 films deposited at 600 and 650 °C had a higher IMT temperature because of the relaxation of both the in-plane and out-of-plane strain, and there were abundant V4+ states. Therefore, it was related to a collaborative Mott–Peierls transition. Finally, the VO2 film deposited at 720 °C showed a suppressed Mott transition because of the abundance of V3+ states in the insulating phase. Furthermore, an analysis of the electronic structure of the insulating and metallic phases using in situ X-ray photoelectron spectroscopy and X-ray absorption spectroscopy provide a complete band diagram to support the above explanation of the deposition-temperature-dependent IMT characteristics.

Highly regular rosette-shaped cathodoluminescence in GaN self-assembled nanodisks and nanorods

Self-assembled GaN nanorods were grown by metal-organic chemical vapor deposition. A highly regular rosette-shaped cathodoluminescence pattern in the GaN nanorods is observed, where its origin is helpful to deepen the understanding of GaN nanorod growth. The pattern forms at the very early stages of nanorod growth, which consists of yellow luminescence at the edges and the non-luminous region at six vertices of the hexagon. To clarify its origin, we carried out detailed cathodoluminescence studies, electron microscopy studies and nanoscale secondary ion mass spectrometry at both the nanorod surface and cross-section. We found the pattern is not related to optical resonance modes or polarity inversion, which are commonly reported in GaN nanostructures. After chemical composition and strain analysis, we found higher carbon and nitrogen cluster concentration and large compressive strain at the pattern area. The pattern formation may relate to facet preferential distribution of non-radiative recombination centers related to excess carbon/nitrogen. This work provides an insight into strain distribution and defect-related emission in GaN nanorod, which is critical for future optoelectronic applications.

High‐Performance Bismuth‐Doped Nickel Aerogel Electrocatalyst for the Methanol Oxidation Reaction

AbstractLow‐cost, non‐noble‐metal electrocatalysts are required for direct methanol fuel cells, but their development has been hindered by limited activity, high onset potential, low conductivity, and poor durability. A surface electronic structure tuning strategy is presented, which involves doping of a foreign oxophilic post‐transition metal onto transition metal aerogels to achieve a non‐noble‐metal aerogel Ni97Bi3 with unprecedented electrocatalytic activity and durability in methanol oxidation. Trace amounts of Bi are atomically dispersed on the surface of the Ni97Bi3 aerogel, which leads to an optimum shift of the d‐band center of Ni, large compressive strain of Bi, and greatly increased conductivity of the aerogel. The electrocatalyst is endowed with abundant active sites, efficient electron and mass transfer, resistance to CO poisoning, and outstanding performance in methanol oxidation. This work sheds light on the design of high‐performance non‐noble‐metal electrocatalysts.

High-Performance Bismuth-Doped Nickel Aerogel Electrocatalyst for the Methanol Oxidation Reaction.

Low-cost, non-noble-metal electrocatalysts are required for direct methanol fuel cells, but their development has been hindered by limited activity, high onset potential, low conductivity, and poor durability. A surface electronic structure tuning strategy is presented, which involves doping of a foreign oxophilic post-transition metal onto transition metal aerogels to achieve a non-noble-metal aerogel Ni97 Bi3 with unprecedented electrocatalytic activity and durability in methanol oxidation. Trace amounts of Bi are atomically dispersed on the surface of the Ni97 Bi3 aerogel, which leads to an optimum shift of the d-band center of Ni, large compressive strain of Bi, and greatly increased conductivity of the aerogel. The electrocatalyst is endowed with abundant active sites, efficient electron and mass transfer, resistance to CO poisoning, and outstanding performance in methanol oxidation. This work sheds light on the design of high-performance non-noble-metal electrocatalysts.

Electron-lattice interplay in LaMnO3 from canonical Jahn-Teller distortion notations

LaMnO$_3$ is considered as a prototypical Jahn-Teller perovskite compound, exhibiting a metal to insulator transition at $T_{JT} = 750K$ related to the joint appearance of an electronic orbital ordering and a large lattice Jahn-Teller distortion. From first-principles, we revisit the behavior of LaMnO$_3$ and show that it is not only prone to orbital ordering but also to charge ordering. Both charge and orbital orderings appear to be enabled by rotations of the oxygen octahedra and the subtle competition between them is monitored by a large tetragonal compressive strain, that is itself a Jahn-Teller active distortion. Equally, the competition of ferromagnetic and antiferromagnetic orders is slave of the same tetragonal strain. Our results further indicate that the metal to insulator transition can be thought as a Peierls transition that is enabled by spin symmetry breaking. Therefore, dynamical spin fluctuations in the paramagnetic state stabilize the insulating phase by the instantaneous symmetry breaking they produce and which is properly captured from static DFT calculations. As a basis to our discussion, we introduce canonical notations for lattice distortions in perovskites that distort the oxygen octhedra and are connected to charge and orbital orderings.

Combined compression-tension strain sensor over 1 µε-20 mε by using non-uniform multiple-core-offset fiber.

Combined compression-tension strain sensors with a range of 1 micro to a maximum of 20 milli-strain based on non-uniform multiple-core-offset fibers have been realized. A large strain range with high resolution is ideal for monitoring deformation of steel structures where a large compressive and tensile strain co-exists. Thanks to core-offset splicing of non-uniform fiber segments, unique asymmetric waveguides reduce the degeneracy of each section, realizing a reflection spectrum with a large range and irregular shape. Furthermore, enhanced multi-mode interference induced from high-order modes in silica cladding and air results in the large strain range with high resolution in both compression and tension regions. The sensitivity of 7.93 pm/µε with a strain step of 1.7 µε is achieved for micro-strain measurement. For milli-strain measurement, a strain coefficient of 1.298 nm/mε over a tensile strain of 13.2 mε is realized; in the compressive strain case, a coefficient of -1.251nm/mε over compression of 20.1 mε is observed.

Strain-Modulated Slater-Mott Crossover of Pseudospin-Half Square-Lattice in (SrIrO_{3})_{1}/(SrTiO_{3})_{1} Superlattices.

We report on the epitaxial strain-driven electronic and antiferromagnetic modulations of a pseudospin-half square-lattice realized in superlattices of (SrIrO_{3})_{1}/(SrTiO_{3})_{1}. With increasing compressive strain, we find the low-temperature insulating behavior to be strongly suppressed with a corresponding systematic reduction of both the Néel temperature and the staggered moment. However, despite such a suppression, the system remains weakly insulating above the Néel transition. The emergence of metallicity is observed under large compressive strain but only at temperatures far above the Néel transition. These behaviors are characteristics of the Slater-Mott crossover regime, providing a unique experimental model system of the spin-half Hubbard Hamiltonian with a tunable intermediate coupling strength.