Extreme Strain Research Articles

Atomistic study on tensile fracture of densified silica glass and its dependence on strain rate* *Project supported by Beijing Institute of Technology Research Fund Program for Young Scholars.

Densification is a major feature of silica glass that has received widespread attention. This work investigates the fracture behavior of densified silica glass upon uniaxial tension based on atomistic simulations. It is shown that the tensile strength of the silica glass approximately experiences a parabolic reduction with the initial density, while the densified samples show a faster power growth with the increase of strain rate. Meanwhile, the fracture strain and strain energy increase significantly when the densification exceeds a certain threshold, but fracture strain tends to the same value and strain energy becomes closer for different densified samples at extreme high strain rate. Microscopic views indicate that all the cracks are formed by the aggregation of nanoscale voids. The transition from brittleness fracture to ductility fracture can be found with the increase of strain rate, as a few fracture cracks change into a network distribution of many small cracks. Strikingly, for the high densified sample, there appears an evident plastic flow before fracture, which leads to the crack number less than the normal silica glass at the high strain rate. Furthermore, the coordinated silicon analysis suggests that high strain rate tension will especially lead to the transition from 4- to 3-fold Si when the high densified sample is in plastic flow.

Enantioselective Synthesis of Cyclopropanone Equivalents and Application to the Formation of Chiral β‐Lactams

AbstractCyclopropanone derivatives have long been considered unsustainable synthetic intermediates because of their extreme strain and kinetic instability. Reported here is the enantioselective synthesis of 1‐sulfonylcyclopropanols, as stable yet powerful equivalents of the corresponding cyclopropanone derivatives, by α‐hydroxylation of sulfonylcyclopropanes using a bis(silyl) peroxide as the electrophilic oxygen source. This work constitutes the first general approach to enantioenriched cyclopropanone derivatives. Both the electronic and steric nature of the sulfonyl moiety, which serves as a base‐labile protecting group and confers crystallinity to these cyclopropanone precursors, were found to have a crucial impact on the rate of equilibration to the corresponding cyclopropanone. The utility of these cyclopropanone surrogates is demonstrated in a mild and stereospecific formal [3+1] cycloaddition with simple hydroxylamines, leading to the efficient formation of chiral β‐lactam derivatives.

Enantioselective Synthesis of Cyclopropanone Equivalents and Application to the Formation of Chiral β-Lactams.

Cyclopropanone derivatives have long been considered unsustainable synthetic intermediates because of their extreme strain and kinetic instability. Reported here is the enantioselective synthesis of 1-sulfonylcyclopropanols, as stable yet powerful equivalents of the corresponding cyclopropanone derivatives, by α-hydroxylation of sulfonylcyclopropanes using a bis(silyl) peroxide as the electrophilic oxygen source. This work constitutes the first general approach to enantioenriched cyclopropanone derivatives. Both the electronic and steric nature of the sulfonyl moiety, which serves as a base-labile protecting group and confers crystallinity to these cyclopropanone precursors, were found to have a crucial impact on the rate of equilibration to the corresponding cyclopropanone. The utility of these cyclopropanone surrogates is demonstrated in a mild and stereospecific formal [3+1] cycloaddition with simple hydroxylamines, leading to the efficient formation of chiral β-lactam derivatives.

Mechanical properties of electrochemically lithiated Sn

Sn is a promising Li ion battery anode with high theoretical capacity, but it can easily pulverize due to repeated application of extreme volumetric strain of 260% during cycling. Sn is a low melting point metal with low modulus and therefore has previously been proposed to be a fracture resistant anode due to its the ability to relax stresses via plasticity and creep deformations. In this study, intrinsic mechanical properties of lithiated Sn at various stages in the lithiation were evaluated using nanoindentation experiments using a special setup. In order to avoid oxidation of the highly reactive lithiated Sn, nanoindentation was performed on specimens submerged in a mineral oil bath. After careful calibration, hardness and modulus of different phases of lithiated Sn were evaluated. With an increase in the lithium content, both the modulus and hardness of the lithiated Sn decreased, as expected, where the modulus and hardness are 28.6 GPa and 0.37 GPa, respectively, for fully lithiated Sn (Li22Sn5) and 58.0 GPa and 0.77 GPa, respectively, for unlithiated Sn. This is the first report on the mechanical properties of lithiated Sn, which is expected to be of importance in theoretical analysis of the diffusion induced stresses in Sn anodes.

Seasonal Changes In Cardiovascular Function, Risk Factors, And Oxidative Stress Of Wildland Firefighters

Wildland firefighters (WLFF) experience extreme physiological strain throughout a typical season due to intense occupational demands and consistent woodsmoke exposure. There is a rationale to indicate that accumulated physiological strain, and oxidative stress, throughout a WLFF season has the potential to negatively alter cardiovascular function and risk factors. PURPOSE: The purpose of the study was to examine the effects of a season on cardiovascular function, risk factors, and markers of oxidative stress in WLFF. METHODS: Fourteen members of a Type I interagency hotshot crew participated in the study (males: n=13, females: n=1, age: 30.1 years ± 4.8). Pre- and post-seasonal resting measurements (May, October) were obtained for heart rate variability (lnRMSSD, lnHF, lnHF, LF:HF), pulse wave velocity (PWV), blood lipid panels (TC, TG, LDL, HDL), metabolic biomarkers (blood glucose, HbA1c), blood pressure (SBP, DBP) and blood oxidative stress (3-nitrotyrosine, 8-isoprostane). Paired samples t-tests were used to identify differences among pre- and post- seasonal values. RESULTS: There were no seasonal effects observed on resting heart rate variability, PWV, 3-nitrotyrosine, 8-isoprostane, TC, TG, LDL, blood glucose, SBP, or DBP (p>0.05). A significant reduction occurred in HDL (Pre: 53 mg/dL ± 14, Post: 45 mg/dL ± 18, p=0.043) and HbA1c increased (Pre: 5.2% ± 0.2, Post: 5.3% ± 0.2, p=0.034) from pre- to post-season. CONCLUSION: These data suggest a WLFF season did not impact resting markers of heart rate variability, pulse wave velocity, and oxidative stress. Alterations in metabolic biomarkers of cardiovascular risk factors (HDL and HbA1c) demonstrate unfavorable seasonal changes, suggesting that the WLFF season may increase cardiovascular risk.

Liquid Metal Based Island‐Bridge Architectures for All Printed Stretchable Electrochemical Devices

AbstractThe adoption of epidermal electronics into everyday life requires new design and fabrication paradigms, transitioning away from traditional rigid, bulky electronics towards soft devices that adapt with high intimacy to the human body. Here, a new strategy is reported for fabricating achieving highly stretchable “island‐bridge” (IB) electrochemical devices based on thick‐film printing process involving merging the deterministic IB architecture with stress‐enduring composite silver (Ag) inks based on eutectic gallium‐indium particles (EGaInPs) as dynamic electrical anchors within the inside the percolated network. The fabrication of free‐standing soft Ag‐EGaInPs‐based serpentine “bridges” enables the printed microstructures to maintain mechanical and electrical properties under an extreme (≈800%) strain. Coupling these highly stretchable “bridges” with rigid multifunctional “island” electrodes allows the realization of electrochemical devices that can sustain high mechanical deformation while displaying an extremely attractive and stable electrochemical performance. The advantages and practical utility of the new printed Ag‐liquid metal‐based island‐bridge designs are discussed and illustrated using a wearable biofuel cell. Such new scalable and tunable fabrication strategy will allow to incorporate a wide range of materials into a single device towards a wide range of applications in wearable electronics.

Isolation and identification of halophilic and halotolerant bacteria from the sediments of the Qeshm Island mangrove forest

Due to specific environmental and ecological conditions, mangrove forests are known as marine transitional zones between sea and land, and, as such, they host organisms with high ecological plasticity. The mangrove forests of Qeshm Island (Iran) are relatively pristine habitats and represent an ideal target for investigating patterns of either aquatic or benthic biodiversity. To provide insights on microbial diversity in this area, nineteen halophilic and halotolerant bacteria were isolated from the sediments in 2017 during low tide. The extracted bacterial strains were studied morphologically by streaking, initial observation of colonies and bacterial staining, and characterized using a battery of biochemical tests including KOH, MR, VP, urease, TSI, S/I/M, Mac, LIA, ODC, ADH, oxidase, catalase, and tryptophan deaminase. The optimum growth of halophilic bacteria was observed in salt concentrations from 5 to 20% NaCl, whereas the extreme halophilic Gram-positive strain grew in salt concentration of up to 30% NaCl. Molecular analyses were also carried out on four halophilic strains and one extreme halophilic gram-positive bacteria. Phylogenetic taxonomy analysis, after 16S rDNA gene Sanger sequencing, revealed that the halophilic bacteria were closely related to the strain types of the genus Bacillus including Bacillus licheniformis, Bacillus velezensis, Bacillus Paralicheniformis and Bacillus sp. with 99% bootstrap value. The extreme halophilic strain was associated to strains of Planococcus plakortidis with 100% bootstrap value.

Production enhancement of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in Halogeometricum borinquense, characterization of the bioplastic and desalination of the bioreactor effluent

Polyhydroxyalkanoates (PHAs) are a replacement of conventional single-use plastics. Bioprocess conditions of the extreme halophilic archaeon Halogeometricum borinquense strain RM-G1 were selected resulting in the synthesis of 66.80 ± 1.69 % PHA (of cell dry mass) in 72 h using glycerol and tryptone as carbon and nitrogen sources respectively, yielding volumetric productivity of 0.206 ± 0.006 gL−1 h−1 in a repeated batch process in a small-scale bioreactor where 20 % of the production medium was used as the inoculum for the subsequent batch. The purified PHA was characterized as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with 10.21 mol% 3-hydroxyvalerate content possessing glass transition temperature -12.6 °C, degradation temperature 285 °C, number average molecular weight 156,899 Da, weight average molecular weight 288,723 Da, polydispersity index 1.8 and melting temperatures 139.1 °C and 152.5 °C. Maximum (21.7 ± 0.6 L m-2 h−1) and average (17.2 ± 0.6 L m-2 h−1) flux values were their respective highest and crystallization time was its least (3.0 ± 0.16 h) when ΔT was 90 °C and polytetrafluoroethylene membrane was applied for desalination of the bioreactor effluent by Direct Contact Membrane Distillation. While using polyvinylidene fluoride membrane, maximum 25.5 ± 0.5 L m-2 h−1 and average 18.6 ± 0.2 L m-2 h−1 fluxes were obtained and crystallization time decreased (3.25 ± 0.16 h) even when ΔT was lowered by 20 °C.

Microscopic insight into the structural transition of single crystal iron under the ramp wave loading

The microscopic dynamics of the BCC to HCP/FCC structural transition (ST) in single crystal iron induced by ramp waves (RWs) has been investigated in detail with atomistic simulations. Firstly, the microstructure change during the RW propagation is demonstrated and the differences between the [001], [011] and [111] loadings are revealed. It is found that the ST products under the [001] loading tends to form lamellar twins along the (100) or (010) planes with the evolution of grain boundary, although the nucleation number will increase with the RW convergence. Nevertheless, the new phase grains under the [011] and [111] loadings are much smaller than that under the [001] loading, because more equivalent {011} planes are activated. The size of new grains is also found to reduce with the RW propagation distance, indicating a significant dependence on the loading strain rate. As a result, the maximal shear stress of the new hase can approach to zero after the ST for the [011] and [111] loadings. Besides, the change of temperature indicates the increase of entropy during the RW convergence, and the temperature and potential energy approximately keep a linear increase with the propagation distance. The modulus softening before the ST is found for all the three loading directions, which can lead to a stress climbing region and a following stress relaxation region in front of the ST wave (STW). By adjusting the piston acceleration, we further explore the strain rate effect in the range of 5×109∼1011 s−1. Interestingly, the ST pressure (PST) is almost the same value for the three loading directions although there exists a significant difference in the deviator stress. What’s more, PST approximately satisfies a linear change with the extreme strain rate, instead of the power function with an index less than 1. Finally, by tracing the stress variation and atomic motion of a certain crystal plane, we show the different ST dynamic paths when the strain rate exceeds 1010 s−1 and then the strain rate effect is better interpreted.

Application of Relay C−H Oxidation Logic to Polyhydroxylated Oleanane Triterpenoids

Summary Although clinical applications of abundant feedstock triterpenoids such as oleanolic acid are limited because of poor solubility and bioavailability, synthetic access to higher hydroxylated oleanane terpenoids is challenging. We now report the use of relay C−H oxidation logic to mimic the processes carried out in nature by P450 monooxygenase enzymes. To this end, we used the C-23-OH as natural handle for a hydrogen-atom transfer to access C-6, enabling the first syntheses of highly oxidized natural products uncargenin C and protobassic acid as well as uncovering the anti-leukemic activity of a synthetic intermediate.

An experimental study of flexural behavior of glulam beams made out of thermally treated fast-growing poplar laminae.

In this study, to improve the structural applications of glued laminated timber (glulam) in high RH environment according to its relatively lower MOE, fast-growing poplar laminae with a thickness of 35 mm were thermally treated at 20oC for 3.5 h. The effects of thermal treatment and RH in the surrounding environment on laminae strength class was conducted. Afterward, 12 full-scale same-grade composition glulam beams made out of untreated and thermally treated poplar laminae were prepared. The four-point bending tests were conducted to reveal the effects of laminae thermal treatment and RH in the surrounding environment on flexural properties of glulam beams with a span-depth ratio of 18. The results showed that the strength class of fast-growing poplar laminae was negatively related to RH in the surrounding condition, and thermal treatment can contribute to the increase in strength class. In 90% RH, strength class increased from untreated laminae ME7 to the heat-treated ME10, according to China standard. The relationship between bending properties of glulam beams and RH in the surrounding environment was negatively correlated, as well as thermal treatment, whereas MOE was improved significantly after thermally pretreated, especially in high RH. In 90% RH, MOE of glulam beams made of thermally pretreated laminae was 29.57% higher than the untreated beams with an MOR reduction of 8.82%. The results of characteristic load-deformation curves, characteristic load-strain curves, average extreme fiber strain, and the failure mode can support each other in this study. Industrial thermal treatment technology to laminae improved the MOE of glulam beams significantly in high RH with a reduction in MOR, and glulam beam made out of thermally treated fast-growing poplar laminae can be used in construction, but need checking in MOR or be used for a limited range of structural elements.

Isolation of an elusive phosphatetrahedrane.

This exploratory synthesis investigation was undertaken to determine the viability of replacing a single carbon vertex with another p-block element in a highly strained tetrahedrane molecule. Phosphorus was selected for this purpose because the stable molecular form of elemental phosphorus is tetrahedral. Our synthetic strategy was to generate an unsaturated phosphorus center bonded to a substituted cyclopropenyl group, a situation that could lead to closure to provide the desired phosphatetrahedrane framework. This was accomplished by dehydrofluorination of the in situ generated fluorophosphine H(F)P(C t Bu)3. Tri-tert-butyl phosphatetrahedrane, P(C t Bu)3, was then isolated in 19% yield as a low-melting, volatile, colorless solid and characterized spectroscopically and by a single-crystal x-ray diffraction study, confirming the tetrahedral nature of the molecule's PC3 core. The molecule exhibits unexpected thermal stability.

Multi-Arch-Structured All-Carbon Aerogels with Superelasticity and High Fatigue Resistance as Wearable Sensors.

Compressible and ultralight all-carbon materials are promising candidates for piezoresistive pressure sensors. Although several fabrication methods have been developed, the required elasticity and fatigue resistance of all-carbon materials are yet to be satisfied as a result of energy loss and structure-derived fatigue failure. Herein, we present a two-stage solvothermal freeze-casting approach to fabricate all-carbon aerogel [modified graphene aerogel (MGA)] with a multi-arched structure, which is enabled by the in-depth solvothermal reduction of graphene oxide and unidirectional ice-crystal growth. MGA exhibits supercompressibility and superelasticity, which can resist an extreme compressive strain of 99% and maintain 93.4% height retention after 100 000 cycles at the strain of 80%. Rebound experiments reveal that MGA can rebound the ball (367 times heavier than the aerogel) in 0.02 s with a very fast recovery speed (∼615 mm s-1). Even if the mass ratio between the ball and aerogel is increased to 1306, the ball can be rebound in a relatively short time (0.04 s) with a fast recovery speed (∼535 mm s-1). As a result of its excellent mechanical robustness and electrical conductivity, MGA presents a stable stress-current response (10 000 cycles), tunable linear sensitivity (9.13-7.29 kPa-1), and low power consumption (4 mW). The MGA-based wearable pressure sensor can monitor human physiological signals, such as pulses, sound vibrations, and muscular movements, demonstrating its potential practicability as a wearable device.

Mechanisms-Based Transitional Viscoplasticity

When metal is subjected to extreme strain rates, the conversation of energy to plastic power, the subsequent heat production and the growth of damages may lag behind the rate of loading. The imbalance alters deformation pathways and activates micro-dynamic excitations. The excitations immobilize dislocation, are responsible for the stress upturn and magnify plasticity-induced heating. The main conclusion of this study is that dynamic strengthening, plasticity-induced heating, grain size strengthening and the processes of microstructural relaxation are inseparable phenomena. Here, the phenomena are discussed in semi-independent sections, and then, are assembled into a unified constitutive model. The model is first tested under simple loading conditions and, later, is validated in a numerical analysis of the plate impact problem, where a copper flyer strikes a copper target with a velocity of 308 m/s. It should be stated that the simulations are performed with the use of the deformable discrete element method, which is designed for monitoring translations and rotations of deformable particles.

Strain Modulated Superlattices in Graphene.

Numerous theoretically proposed devices and novel phenomena have sought to take advantage of the intense pseudogauge fields that can arise in strained graphene. Many of these proposals, however, require fields to oscillate with a spatial frequency smaller than the magnetic length, while to date only the generation and effects of fields varying at a much larger length scale have been reported. Here, we describe the creation of short wavelength, periodic pseudogauge-fields using rippled graphene under extreme (>10%) strain and study of its effects on Dirac electrons. Combining scanning tunneling microscopy and atomistic calculations, we find that spatially oscillating strain generates a new quantization different from the familiar Landau quantization. Graphene ripples also cause large variations in carbon-carbon bond length, creating an effective electronic superlattice within a single graphene sheet. Our results thus also establish a novel approach of synthesizing effective 2D lateral heterostructures by periodically modulating lattice strain.

Effect of sample orientation on the microstructure and microhardness of additively manufactured AlSi10Mg processed by high-pressure torsion

For the first time, high-pressure torsion (HPT) was applied to additively manufactured AlSi10Mg built in two directions (vertical and horizontal) by selective laser melting (SLM), and the influence of extreme torsional strain on the porosity, microstructure and microhardness of the alloy was investigated. ImageJ analysis indicates that significant porosity reduction is achieved by 1/4 HPT revolution (low strain). Optical microscopy (OM) and scanning electron microscopy (SEM) observations reveal the steady distortion and elongation of the melt pools, the continuous elongation of the cellular-dendritic Al matrix and breakage of the eutectic Si phase network with increased HPT revolutions. Microhardness measurements indicate that despite the significant increase in hardness attained from HPT processing, hardness saturation and microstructural homogeneity are not achieved even after 10 HPT revolutions. X-ray diffraction (XRD) line broadening analysis demonstrates increased dislocation densities with increased HPT revolutions, which contributes to the considerably higher hardness values compared to as-received samples.

Extreme Strain Fluctuations in Polycrystalline Materials

The stochastic structure of polycrystalline materials causes a high inhomogeneity of the kinematic and force fields in grains of materials and large fluctuations of these fields. The inhomogeneity and fluctuations are insignificant in some cases, but they become crucial in the study of various critical phenomena whose occurrence strongly depends on the type of material microstructure. Fluctuations mainly arise due to the elastic interaction of grains, which has a long-range effect. Therefore, it is necessary to account for the interaction of a large number of grains, which is difficult to do using conventional methods (direct computer modeling and others). In the present paper, inhomogeneous mesostrain fluctuations in grains of polycrystalline materials were estimated using a field-theoretical approach to a boundary-value problem of microheterogeneous material deformation. Particular attention is paid to the calculation of extreme fluctuations that are important for some critical phenomena, such as, e.g., crack initiation under gigacycle fatigue when the macrostress amplitude and the mean stresses in grains are much lower than the quantities included in any macroscopic damage or fatigue criteria. Phe maximum mesostrains in grains can exceed several times the macrostrains. Extreme fluctuations in a grain are generated in grain clusters of specific configuration. Phe applied approach makes it possible to predict patterns of such clusters. Extreme fluctuations in the bulk grains of a polycrystalline body are much higher than in the surface grains, due to which the behavior of the material surface layers and bulk volumes is different. Quantitative data are given for the case of uniaxial tension of polycrystalline zinc.

On the Strength of Hair across Species

Summary The hair of mammals varies in diameter across species from ∼60 μm in humans to over ∼400 μm in giraffes and elephants. Here, we establish that the tensile strength of hair generally decreases with increasing diameter. Although there is a commonality in the morphology of the hair in such differing species as they all possess a cortex surrounded by cuticles, there are also significant differences in the hierarchical structure that contribute to the observed differences in strength. In this work, the internal structure of the hair from different species is examined, with some unique peculiarities in javelina and capybara hair uncovered. The dimensional dependence of hair strength is compared using Weibull predictions. The good correlation of the strength of hair using such Weibull analysis suggests that the failure strength is dictated by the probability distribution of flaws within the cortex.

Damage Mechanism of Cu6Sn5 Intermetallics Due to Cyclic Polymorphic Transitions.

The formation of high-melting-point Cu6Sn5 interconnections is crucial to overcome the collapse of Sn-based micro-bumps and to produce reliable intermetallic interconnections in three-dimensional (3D) packages. However, because of multiple reflows in 3D package manufacturing, Cu6Sn5 interconnections will experience cyclic polymorphic transitions in the solid state. The repeated and abrupt changes in the Cu6Sn5 lattice due to the cyclic polymorphic transitions can cause extreme strain oscillations, producing damage at the surface and in the interior of the Cu6Sn5 matrix. Moreover, because of the polymorphic transition-induced grain splitting and superstructure phase formation, the reliability of Cu6Sn5 interconnections will thus face great challenges in 3D packages. In addition, the Cu6Sn5 polymorphic transition is structure-dependent, and the η′↔η polymorphic transition will occur at the surface while the η′↔ηs↔η polymorphic transition will occur in the deep matrix. This study can provide in-depth understanding of the structural evolution and damage mechanism of Cu6Sn5 interconnections in real 3D package manufacturing.

Tantalum strength at extreme strain rates from impact-driven Richtmyer-Meshkov instabilities.

Recently, Richtmyer-Meshkov instability (RMI) experiments driven by high explosives and fielded with perturbations on a free surface have been used to study strength at extreme strain rates and near zero pressure. The RMI experiments reported here used impact loading, which is experimentally simpler, more accurate to analyze, and which also allows the exploration of a wider range of conditions. Three experiments were performed on tantalum at shock stresses from 20 to 34 GPa, with six different perturbation sizes at each shock level, making this the most comprehensive set of strength-focused RMI experiments reported to date on any material. The resulting estimated average strengths of 1200-1400 MPa at strain rates of 10^{7}/s exceeded, by 40% or more, a common power law extrapolation from data at strain rates below 10^{4}/s. Taken together with other data in the literature that show much higher strength at simultaneous high rates and high pressure, these RMI data isolated effects and indicated that, in the range of conditions examined, the pressure effects are more significant than rate effects.