Role Of Strain Rate Research Articles

The role of strain rate in microstructure evolution, deformation heterogeneity and cracking mode of high-pressure die-casting Al7Si0.2Mg alloy

The quasi-static and dynamic deformation behaviours of high-pressure die-casting (HPDC) Al7Si0.2 Mg alloy were studied in this work. Competing effects among porosities, α-Al(Fe/Mn)Si phase, eutectic phase and α-Al dendrites on strain concentration and crack propagation at different strain rates were investigated using X-ray computed tomography (CT), scanning electron microscopy (SEM), in-situ electron backscattering diffraction (EBSD), and high-resolution digital image correlation (HR-DIC). The results indicate that yield strength and ductility of Al7Si0.2 Mg alloy were improved at high strain rates compare to quasi-static loading. Weak zones, including porosities and particle interfaces, primarily contributed to deformation heterogeneity under quasi-static tension, whereas both weak zones and Al matrix played a role under dynamic loading. Moreover, crack propagation was hardly observed on porosities during dynamic deformation, thereby reducing the sensitivity of ductility to porosity. The slip and rotation of α-Al dendrites became more pronounced during dynamic deformation. As a result, the area fraction of fractured eutectic phase increased dramatically and surpassed the area fraction of α-Al(Fe/Mn)Si phase, which became the dominant factor of crack propagation during dynamic deformation.

The Dynamic Recrystallization in a Hot‐Compressed Al–Zn–Mg–Cu–Sc–Zr Alloy: The Role of Strain Rate

The effects of strain rates (0.001–1 s−1) on the microstructures and mechanical performance of the novel Al–Zn–Mg–Cu alloy through hot compression at 300 °C are investigated in detail. With the increase of strain rate, the dislocation density increases from 0.06 × 1013 to 3.77 × 1013 m−2, which promotes the dynamic precipitation kinetics. And the volume fraction of η precipitates is calculated by the differential scanning calorimetry curves increasing from 1.36% to 3.94%. Both dislocations and precipitates promote to increase the hardness of the Al–Zn–Mg–Cu alloy. The large number of η precipitates in high‐strain‐rate samples hinders the recrystallization process by impeding the movement of dislocations and grain boundaries, decreasing the volume fraction of recrystallized grains to 3.1%. Continuous/discontinuous dynamic recrystallization occurs preferentially at low strain rates, and discontinuous dynamic recrystallization is rarely observed in high‐strain‐rate samples. In addition, because the process of continuous dynamic recrystallization promotes the transformation from low‐angle grain boundaries to high‐angle grain boundaries, more continuous dynamic recrystallized grains and less low‐angle grain boundaries can be observed in low‐strain‐rate samples.

Role of strain rate in phase stability and deformation mechanism of non-equiatomic Fe38-xMn30Co15Cr15Ni2Gdx high-entropy alloy

Excellent combination of strength and ductility makes metastable high entropy alloys (HEAs) stand out from multi-principal elements alloys. In this study, micro-alloying Gd element is effectively solid solutionized in metastable single FCC phase FeMnCoCrNi HEA system, to bring the FCC phase stability decreased that causes a pronounced FCC → HCP phase transformation during compression. In order to decouple the temperature effect from the influence of dynamic strain rate on phase transformation, a wide strain rate range is adopted from 10 −3 –10 −1 s −1 to 1000–5000 s −1 . The results show that the increased strain rate and adiabatic temperature rise both can restrain the phase transformation. Under low strain rates (10 −3 –10 −1 s −1 ), phase transformation is activated in all tested samples and gradually suppressed with the increase of strain rates, because the rate-induced shear bands inhibit the growth of the HCP phase. The reduction of strain hardening during phase transformation is related to the increase of local thermal activation volume due to disentangling of dislocations. Under dynamic strain rates (1000–5000 s −1 ), the phase transformation is completely substituted by deformation twinning due to the significant adiabatic temperature rise. The present work provides insights into the influence of strain rate on phase stability and deformation mechanism in a wide strain rate range. • Solid solution of Gd decreases the FCC phase stability bringing pronounced FCC → HCP phase transformation during quasi-state compression. • Phase transformation related dislocation dissociation enlarges the thermally activated volume causing the decrease in strain hardening rate. • Under low strain rates (10 −3 –10 −1 s −1 ), the increased strain rates activate shear bands earlier that hinder the growth of the HCP phase, it is a rate-related effect on phase transformation. • Under high strain rates (1000–5000 s −1 ), adiabatic temperature rise enhances the phase stability which is a thermo-related effect, co-works with the rate-related effect, making the phase transformation completely suppressed.

Mechanical Behavior of Polymer Nanocomposites via Atomistic Simulations: Conformational Heterogeneity and the Role of Strain Rate.

Polymer nanohybrids with a high fraction of nanofillers have been found to exhibit improved mechanical properties compared to the neat polymer homogeneous systems. Since polymer-based materials are characterized by a broad range of relaxation times, it is expected that their response under external load would depend on the actual rate of the applied deformation. In this work, we investigate the heterogeneous mechanical behavior in glassy poly(ethylene oxide)/silica nanoparticles (PEO/SiO2) nanocomposites via detailed atomistic molecular dynamics simulations. Our goal is to unravel the effect of strain rate on the mechanism of polymer nanocomposite reinforcement, within the glassy state, by directly probing the mechanical properties at the molecular level. By applying tensile deformations with various strain rates we clearly demonstrate that the value of the applied strain rate strongly affects the mechanical properties of the PEO/SiO2 model systems, inducing a transition from a rubber-like behavior, at low strain rate, to a more brittle one, at high strain rates. Then, we further investigate the mechanical heterogeneity in glassy PEO/SiO2 systems by probing directly the stress and strain fields for various conformations of adsorbed (trains, tails, loops, and bridges), and free polymer chains. Our data emphasize the importance of both train and bridge conformations on the mechanical reinforcement of the polymer nanocomposites. Last, we also probe the mobility of various chain conformations, under different applied strain rates, and their contribution to the overall mechanical behavior of the nanocomposite, during the deformation process.

A new look at tensile yielding in isotactic polypropylene: role of strain rate and thermal softening

A new look at tensile yielding in isotactic polypropylene: role of strain rate and thermal softening

Role of Strain Rate in Phase Stability and Deformation Mechanism of Non-Equiatomic Fe38-Xmn30co15cr15ni2gdx High-Entropy Alloy

Role of Strain Rate in Phase Stability and Deformation Mechanism of Non-Equiatomic Fe38-Xmn30co15cr15ni2gdx High-Entropy Alloy

The role of strain rate and texture in the deformation of commercially pure titanium at cryogenic temperature

In this work, we explore the effect of strain rate and crystallographic texture on the hardening behaviour and ductility of grade 2 commercially pure titanium (CP–Ti) plate at both room (298 K) and cryogenic temperature (123 K). EBSD technique was used to characterise the microstructural features and analyse the deformation twins and active slip systems in α-Ti. Using the SEM fractography, the necking resistance was estimated by measuring the reduction of cross-sectional area. As the strain rate decreases, the elongation was improved with the enhancement of strain-hardening and necking resistance, whereas this behaviour was relatively strain rate insensitive at 298 K. Consequently, the total elongations were increased from 38% (298 K) to 65% (123 K), and from 28% (298 K) to 35% (123 K) in tension parallel and transverse to the rolling direction of the plate, respectively. The combined effect of strain rate and (cryogenic) temperature affected the transition of deformation mechanisms involved in the twinning and dislocation slip, thereby leading to the three or four multi-stage strain-hardening behaviour. The results reveal that in addition to the dislocation slip, the deformation twinning contributed to the strain-hardening, and improvement of total elongation of α-titanium at cryogenic temperature.

Effect of the potential function and strain rate on mechanical behavior of the single crystal Ni-based alloys: A molecular dynamics study* *Project supported by National Science and Technology Major Project of China (Grant No. 2017-IV-0003-0040), Fundamental Research Funds for the Central Universities in NWPU, China (Grant No. 31020180QD088), the National Natural Science Foundation of China (Grant Nos. 12002275 and 51904015),

Molecular dynamics has been widely used to study the fundamental mechanism of Ni-based superalloys. However, the effect of the potential function and strain rate on mechanical behavior has rarely been mentioned in the previous molecular dynamics studies. In the present work, we show that the potential function of molecular dynamics can dramatically influence the simulation results of single crystal Ni-based superalloys. The microstructure and mechanical behavior of single crystal Ni-based superalloys under four commonly used potential functions are systematically compared. A most suitable potential function for the mechanical deformation is critically selected, and based on it, the role of strain rate on the mechanical deformation is investigated.

DEM numerical tests on dry granular specimens: the role of strain rate under evolving/unsteady conditions

In this paper, the mechanical behaviour of an ideal dry granular material under both evolving and steady conditions has been studied. Triaxial loading both constant volume and constant pressure Discrete Element (DEM) tests on periodic cells have been performed. The role played by strain rate, void ratio and imposed pressure has been analysed. The aim of the paper is to obtain a numerical data set, at present totally absent in the literature, useful for the definition of constitutive relationships capable of reproducing phase transitions (from solid-to-fluid and vice versa) taking place in granular materials. The novelty of the data set obtained derives also from the type of loading tests performed, referred as heating, cooling and cyclic, in which different strain rate histories are imposed, inspired to what locally occurs in flowing granular masses, accelerating and decelerating according to the slope inclination. The numerical results are interpreted by considering state variables (granular temperature and fabric) and the energies evolution (elastic and kinetic fluctuating) to put in evidence phase transition processes. Again, this interpretation of the results is fundamental to conceive upscaled constitutive relationships based on thermodynamic theories. The numerical results have allowed to highlight the role of the strain acceleration/deceleration, and the evolution of the directional properties of the microstructure even in the collisional regime (never described up to now). Cooling constant volume tests results provide a description, not available in the literature, of the evolving response of the material under pure collisional conditions.

Mechanical properties of 2D blue phosphorus and temperature effect

Blue phosphorus is an emerging 2D material that exhibits finite electronic band gap and may find promising applications in advanced semiconducting devices. Comparing to its allotrope, black phosphorus, mechanical properties of blue phosphorus have not been explored in detail. Here we report molecular dynamics simulations of mechanical responses of blue phosphorus under uniaxial tensile, biaxial tensile and shear loadings. It is found that blue phosphorus shows less anisotropic effect as compared to black phosphorus, the room temperature Young’s modulus is about 122.3 GPa and 121.6 GPa along armchair and zigzag directions, respectively, shear modulus is about 27.1 GPa and 28.6 GPa, respectively, along armchair and zigzag directions. Temperature effect on mechanical responses is also systematically studied within a range of 5–400 K. It is found that temperature reduces both Young’s modulus and fracture strain and fracture strength of blue phosphorus, owing to the interplay between thermal energy and strain energy applied to the models. Brittle fracture mode is found in blue phosphorus in all loading conditions, with varied crack nucleation and propagation modes. The role of strain rate on the mechanical properties is examined and found to systematically modify the ultimate stress and ultimate strain of BlueP. Structural details including bond length and bond angle variations to external strain are analyzed to gain deeper insights into the underlying mechanisms.

(Invited) Interfacial Engineering of Solid-State Batteries: Coupled Electrochemical, Morphological, and Mechanical Evolution

Solid-state batteries have seen a dramatic increase in research in recent years because of their ability to address safety challenges associated with flammable liquid electrolytes, and the potential to enable Li metal anodes. However, all solid-state interfaces present unique challenges, including high interfacial impedances, accommodation of mechanical stresses due to solid-solid interfacial contact, and (electro)chemical instabilities that can evolve during dynamic cycling conditions1.To address these challenges, our group focuses on gaining new fundamental insights into the coupled phenomena occurring at interfaces, and applies this knowledge to rationally design interfacial composition and structure to address the root cause of performance limitations. In this talk, I will first present a multi-modal in situ/operando characterization approach to study Li metal-solid electrolyte interfaces during cycling2-4. Mechanistic insight will be provided into solid-electrolyte interphase (SEI) evolution, as well as nucleation and growth dynamics of the Li metal anode during cycling. In addition to these coupled morphological/chemical/electrochemical phenomena, the unique mechanical properties of Li metal will be discussed in the context of solid-state battery interfaces4-5.Equipped with this fundamental knowledge, I will describe the rational design of interlayers at the Li metal-SE interface using Atomic Layer Deposition (ALD). Examples will be presented in both bulk solid-state battery interfaces, and thin film electrolytes deposited by ALD3,6-7. Through this interdisciplinary approach of fundamental materials chemistry and applied engineering, strategies to address future interfacial challenges will be addressed, pointing towards rational design and manufacturing of optimized interfaces.1) K. B. Hatzell, X. C. Chen, C. L. Cobb, N. P. Dasgupta, M. B. Dixit, L. E. Marbella, M. T. McDowell, P. P. Mukherjee, A. Verma, V. Viswanathan, A. S. Westover, W. G. Zeier “Challenges in Lithium Metal Anodes for Solid State Batteries” ACS Energy Lett. 5, 922 (2020).2) Gupta, E. Kazyak, N. Craig, J. Christensen, N. P. Dasgupta, J. Sakamoto, “Evaluating the Effects of Temperature and Pressure on Li/PEO-LiTFSI Interfacial Stability and Kinetics” J. Electrochem. Soc. 165, A2801 (2018).3) A. L. Davis, R. Garcia-Mendez, K. N. Wood, E. Kazyak, K.-H. Chen, G. Teeter, J. Sakamoto, N. P. Dasgupta “Electro-Chemo-Mechanical Evolution of Sulfide Solid Electrolyte/Li Metal Interfaces: Operando Analysis and ALD Interlayer Effects” J. Mater. Chem. A 8, 6291 (2020).4) E. Kazyak, R. Garcia-Mendez, W. S LePage, A. Sharafi, A. L. Davis, A. J. Sanchez, K.-H. Chen, C. Haslam, J. Sakamoto, N. P. Dasgupta “Li Penetration in Ceramic Solid Electrolytes: Operando Microscopy Analysis of Morphology, Propagation, and Reversibility” Matter 2, 1 (2020).5) W. S. LePage, Y. Chen, E. Kazyak, K.-H. Chen, A. J. Sanchez, A. Poli, E. M. Arruda, M. D. Thouless, N. P. Dasgupta “Lithium Mechanics: Roles of Strain Rate and Temperature and Implications for Lithium Metal Batteries” J. Electrochem. Soc. 166, A89 (2019).6) E. Kazyak, K.-H. Chen, K. N. Wood, A. L. Davis, T. Thompson, A. J. Sanchez, X. Wang, C. Wang, J. Sakamoto, N. P. Dasgupta, “Atomic Layer Deposition of the Solid Electrolyte Garnet Li7La3Zr2O12” Chem. Mater. 29, 3785 (2017).7) E. Kazyak, K.-H. Chen, A. L. Davis, S. Yu, A. J. Sanchez, J. Lasso, A. R. Bielinski, J. Sakamoto, D. J. Siegel, N. P. Dasgupta, “Atomic Layer Deposition and First Principles Modeling of Glassy Li3BO3-Li2CO3 Electrolytes for Solid-State Li Metal Batteries” J. Mater. Chem. A 6, 19425 (2018).

A New General Paradigm for Understanding and Preventing Li Metal Penetration through Solid Electrolytes

Summary The use of lithium (Li) or sodium (Na) metal anodes together with highly ion-conductive solid electrolytes (SEs) could provide batteries with a step improvement in volumetric and gravimetric energy densities. Unfortunately, these SEs face significant technical challenges, in large part because Li and Na dendrites can penetrate through SEs, leading to short circuits. The ability of such a soft material (Li or Na metal) to penetrate through ceramic is surprising from the point of view of models widely used in the Li-battery field. We introduce a concept, new to the battery field, for preventing penetration of lithium dendrites through SEs by putting the SE surfaces into a state of residual compressive stress. For a sufficiently high compressive stress, cracks have difficulty forming, and cracks that do form are forced to close, inhibiting dendrite penetration. This approach is widely used to solve commercially important stress corrosion cracking problems in metals and static fatigue problems in ceramics and glasses (e.g., Gorilla Glass). However, the technique will not be useful for SEs if the Li-ion transport rate through a SE is substantially reduced when the SE is under compression. Our molecular dynamics calculations for Li-ion transport through a common SE demonstrate that the introduction of even very high residual compressive stresses (∼10 GPa) has only a modest effect on Li-ion transport kinetics, suggesting that this approach is viable and capable of providing a new paradigm for developing high-performance and mechanically stable SEs.

Investigating the Mechanical Properties of Na Metal for Solid-State Batteries

In recent years, increasing power density and reducing cost has fueled interest in developing all solid-state batteries. Na metal anodes have garnered attention because of its abundance and high theoretical capacity (1165 mA h g–1) [1]. However, similar to solid-state Li-ion conductors, it has been reported that dendrite growth through Na-ion conductors also occurs. It has been hypothesized that dendrite propagation through the electrolyte is dependent upon the elastic and plastic properties of the alkali metal anode [2]. Therefore, a better understanding of the mechanical properties of bulk Na can promote the further development of Na-based solid-state batteries.In this study, several analyses were performed to gain insight into the mechanical properties of Na metal. Tensile and compressive tests were performed by using a load frame contained in an inert atmosphere. From the resulting stress-strain graphs, the yield strength was determined to be 0.283 MPa. An acoustic technique was employed to determine that the elastic modulus of Na was 4.6 GPa. Because Na has a relatively low melting point (98°C), the deformation mechanism of Na during battery operation is likely dominated by creep. To investigate the creep behavior of Na, tension creep measurements were performed. The creep exponent of Na was determined to be n = 7.4. Lastly, to better understand the mechanical behavior of Na at the various interfaces in a solid-state battery, compression tests were performed on varying substrates. Three interfaces were examined: Oil/Na (simulating a frictionless interface), current collector/Na, and Na/Na-β’’-alumina.We believe the mechanical measurements in this work will provide new insights into in the design requirements for solid-state batteries utilizing Na metal anodes.REFERENCE 1. Sun, B., Li, P., Zhang, J., Wang, D., Munroe, P., Wang, C., ... & Wang, G. (2018). Dendrite‐Free Sodium‐Metal Anodes for High‐Energy Sodium‐Metal Batteries. Advanced Materials, 30(29), 1801334.2. LePage, W. S., Chen, Y., Kazyak, E., Chen, K. H., Sanchez, A. J., Poli, A., ... & Dasgupta, N. P. (2019). Lithium Mechanics: Roles of Strain Rate and Temperature and Implications for Lithium Metal Batteries. Journal of The Electrochemical Society, 166(2), A89-A97.

Lithium Metal Anodes: Operando Observation of Nucleation, Dendrite Growth, and Dead Lithium Formation

Lithium (Li) metal anodes have experienced a resurgence of research in recent years, which has been fueled by advances in electrolyte chemistry (both solid and liquid), interfacial engineering, and rational design of electrode architectures1. This has enabled Coulombic efficiency values to push above 99.5%, and cycle life to extend into relevant ranges for transportation applications2. However, while performance metrics are beginning to approach relevant values for consideration of their use in electric vehicles, several fundamental questions remain on how Li metal anodes dynamically evolve during cycling, especially at high current densities. Towards this goal, there is a continued need for new methods to understand the evolving morphology from nucleation, to growth, to irreversible capacity loss.In this talk, operando optical microscopy will be discussed as an enabling platform to study the coupled chemical, electrochemical, mechanical, and morphological evolution of Li metal during plating and stripping. By time synchronization of the morphological evolution of Li metal anodes with electrochemical signatures during cycling, significant insights can be obtained into the mechanistic origins of poor performance3-4. Both cross-sectional and plan-view perspectives on the electrode surface will be described, which allow for a full 3-dimensional understanding of nucleation and growth processes. Video imaging of Li metal propagation in both liquid and solid electrolytes will be presented, and the critical role of mechanical stress evolution in Li metal morphology will be described5-6. A focus will be on the formation of “dead Li”, which form as a result of electronic isolation of metallic Li from the electrode surface3. Finally, strategies to modify surface chemistry and electrode geometry will be described, providing design rules for interfacial engineering of optimized electrodes2.1) Wood, K. N.; Noked, M.; Dasgupta, N. P. Lithium Metal Anodes: Toward an Improved Understanding of Coupled Morphological, Electrochemical, and Mechanical Behavior. ACS Energy Lett. 2017, 2 (3), 664–672.2) Chen, K.-H.; Sanchez, A. J.; Kazyak, E.; Davis, A. L.; Dasgupta, N. P. Synergistic Effect of 3D Current Collectors and ALD Surface Modification for High Coulombic Efficiency Lithium Metal Anodes. Adv. Energy Mater. 2019, 9 (4), 1802534.3) Wood, K. N.; Kazyak, E.; Chadwick, A. F.; Chen, K.-H.; Zhang, J.-G.; Thornton, K.; Dasgupta, N. P. Dendrites and Pits: Untangling the Complex Behavior of Lithium Metal Anodes through Operando Video Microscopy. ACS Cent. Sci. 2016, 2 (11) 790-801.4) Chen, K.-H.; Wood, K. N.; Kazyak, E.; LePage, W. S.; Davis, A. L.; Sanchez, A. J.; Dasgupta, N. P. Dead Lithium: Mass Transport Effects on Voltage, Capacity, and Failure of Lithium Metal Anodes. J. Mater. Chem. A 2017, 5 (23), 11671–11681.5) LePage, W. S.; Chen, Y.; Kazyak, E.; Chen, K.-H.; Sanchez, A. J.; Poli, A.; Arruda, E. M.; Thouless, M. D.; Dasgupta, N. P. Lithium Mechanics: Roles of Strain Rate and Temperature and Implications for Lithium Metal Batteries. J. Electrochem. Soc. 2019, 166 (2), A89–A97.6) Gupta, A.; Kazyak, E.; Craig, N.; Christensen, J.; Dasgupta, N. P.; Sakamoto, J. Evaluating the Effects of Temperature and Pressure on Li/PEO-LiTFSI Interfacial Stability and Kinetics. J. Electrochem. Soc. 2018, 165 (11), A2801–A2806.

Effects of temperature and strain rate on plastic deformation mechanisms of nanocrystalline high-entropy alloys

The nanocrystalline high-entropy alloys (HEAs) can be regarded as ideal substitution materials for use in aero engines due to their outstanding mechanical properties. Owing to the crucial importance on the evaluation of mechanical properties in nanocrystalline HEAs, the identification of the plastic deformation mechanism remains a challenging topic. Considering the fact that nanocrystalline HEAs suffer from the high-temperature service, the roles of strain rate and temperature on their deformation characteristics should be examined. Here, we report the impact of strain rate and temperature on the mechanical properties and deformation behaviors of nanocrystalline HEAs. This issue was investigated by a series of molecular-dynamics tensile tests at different strain rates ranging from 5 × 107 to 1 × 1010 s−1 and temperatures ranging from 10 to 1,200 K. The results show that the dislocation slip controls the preferred deformation mechanism at low temperatures and high strain rates. When the temperature rises and strain rate reduces, grain-boundary sliding dominates the primary deformation mechanism at elevated temperatures. Moreover, the occurrence of the face-centered-cubic (fcc) to body-centered-cubic (bcc) phase transformation can effectively enhance the plasticity of HEAs. The synergistically-integrated experimental and modeling efforts at the nanoscale will help understand, control, and optimize the mechanical behaviors of nanocrystalline HEA systems, thereby enabling the development of advanced nanocrystalline HEAs.

The role of strain rate in the dynamic response of materials

The role of strain rate in the dynamic response of materials

Lithium Mechanics: Roles of Strain Rate and Temperature and Implications for Lithium Metal Batteries

The lack of a reliable rechargeable lithium metal (Li-metal) anode is a critical bottleneck for next-generation batteries. The unique mechanical properties of lithium influence the dynamic evolution of Li-metal anodes during cycling. While recent models have aimed at understanding the coupled electrochemical-mechanical behavior of Li-metal anodes, there is a lack of rigorous experimental data on the bulk mechanical properties of Li. This work provides comprehensive mechanical measurements of Li using a combination of digital-image correlation and tensile testing in inert gas environments. The deformation of Li was measured over a wide range of strain rates and temperatures, and it was fitted to a power-law creep model. Strain hardening was only observed at high strain rates and low temperatures, and creep was the dominant deformation mechanism over a wide range of battery-relevant conditions. To contextualize the role of creep on Li-metal anode behavior, examples are discussed for solid-state batteries, “dead” Li, and protective coatings on Li anodes. This work suggests new research directions and can be used to inform future electrochemical-mechanical models of Li-metal anodes.

Role of strain rate in the strain-induced crystallization (SIC) of natural and synthetic isoprene rubber

The role of strain rate ( $${{\dot \varepsilon }}$$ ) in the strain-induced crystallization (SIC) of vulcanized natural rubber (NR) and synthetic isoprene rubber (IR) was studied using in situ wide-angle X-ray scattering (WAXS) (synchrotron X-ray radiation). We developed homemade extension equipment and coupled it with the synchronized time-resolved X-ray detector system. The nucleation rate (I) was determined for a wide range of $${{\dot \varepsilon }}$$ values (0.0075 s−1–330 s−1) based on the increase in the scattering intensity (IX) as a function of time (t). We found that I is proportional to $${\dot{\varepsilon }}$$ ( $$I \propto \dot \varepsilon$$ ). Based on this result, we concluded that $$\dot \varepsilon$$ plays an important role in the kinetic mechanism of the SIC of NR and IR. The role of strain rate ( $$\dot \varepsilon$$ ) in strain induced crystallization (SIC) of vulcanized natural rubber (NR) and synthetic isoprene rubber (IR) was studied by in-situ wide angle X-ray scattering (WAXS). The nucleation rate (I) was determined by measuring the slope on the plot of the scattering intensity (IX) as a function of time (t). Various I values were determined for various $$\dot \varepsilon$$ . On the plot of I vs. $$\dot \varepsilon$$ , we found that I is proportional to $$\dot \varepsilon$$ ; I ∝ $$\dot \varepsilon$$ .

The role of strain rate, local extinction, and hydrodynamic instability on transition between attached and lifted swirl flames

The coupling between fluid strain rate, local flame extinction, hydrodynamic instability, and flame lift-off was studied in premixed swirl flames using multi-kHz repetition-rate OH* chemiluminescence (CL), OH planar laser induced fluorescence (PLIF), and stereoscopic particle image velocimetry (S-PIV). Over 50 different combinations of fuel composition (CH4/H2 ratio), equivalence ratio, and reactant preheat temperature were studied, allowing systematic variation of the reactant-to-product density ratio, laminar flame speed, and Lewis number. Depending on the test conditions, the flame could either be stably attached to the nozzle, stably lifted, or intermittently transitioning between attached and lifted states. Transition between stabilization states was linked with the transition between convective instability and absolute instability at the flame base; formation of an m=1 (m denotes the azimuthal wavenumber) globally unstable wave was associated with the lifted flame, which was manifested by a helical precessing vortex core (PVC). The minimum bulk velocity at which the flame was stably lifted was linearly correlated with the laminar flame extinction strain rate, while none of the other commonly reported key parameters governing hydrodynamic instability was able to collapse the data alone. Hence, lift-off was associated with a relatively constant Damköhler number based on the bulk fluid strain rate and extinction strain rate. The roles of local strain and extinction on the transition process were further elucidated by the cases with intermittent lift-off/reattachment. The probability of the flame being in the lifted state was roughly linearly correlated with the degree of local extinction at the flame base while the flame was still in the attached state. Moreover, this probability also was linearly related to the ratio of fluid-dynamic strain rate to extinction strain rate, but not the fluid-dynamic strain rate itself. These results demonstrate the importance of predicting extinction and hydrodynamic stability for predicting the attachment state of swirl flames.

Normal fault growth in layered basaltic rocks: The role of strain rate in fault evolution

Conceptual models for the evolution of dilatant faults in volcanic rift settings involve a step-wise growth pattern, involving upward propagation of subsurface faults, and surface monocline formation, which are breached by subvertical, open faults. Immature, discontinuous normal faults are considered representative of the early stages of mature, linked faults that accommodate extensional strains. We consider the evolution of surface-breaking normal faults using a comparison of the distribution and geometry of normal faults from two volcanic rift zones: the Koaʻe fault system, Hawaiʻi, and the Krafla fissure swarm, NE Iceland. Field mapping highlights similarities to current predicted geometries, but also prominent differences that are not reconciled by current models. Variable deformation styles record magma supply changes within the rift zones, which drive local strain rate gradients. Building on existing studies, we present a conceptual model of fault growth that accounts for spatial and temporal changes in strain rate within the deforming regions. We propose that faults in separate rift systems may not advance through the same stages of evolution and that faults within individual rift systems can show differing growth patterns. Variations in surface strains may be indicative of subsurface magmatic system changes, with important implications for our understanding of volcano-tectonic coupling.