High Strain Deformation Research Articles

Controlled single bubble cavitation collapse results in jet-induced injury in brain tissue

Multiscale damage due to cavitation is considered as a potential mechanism of traumatic brain injury (TBI) associated with explosion. In this study, we employed a TBI relevant hippocampal ex vivo slice model to induce bubble cavitation. Placement of single reproducible seed bubbles allowed control of size, number, and tissue location to visualize and measure deformation parameters. Maximum strain value was measured at 45 µs after bubble collapse, presented with a distinct contour and coincided temporally and spatially with the liquid jet. Composite injury maps combined this maximum strain value with maximum measured bubble size and location along with histological injury patterns. This facilitated the correlation of bubble location and subsequent jet direction to the corresponding regions of high strain which overlapped with regions of observed injury. A dynamic threshold strain range for tearing of cerebral cortex was estimated to be between 0.5 and 0.6. For a seed bubble placed underneath the hippocampus, cavitation induced damage was observed in hippocampus (local), proximal cerebral cortex (marginal) and the midbrain/forebrain (remote) upon histological evaluation. Within this test model, zone of cavitation injury was greater than the maximum radius of the bubble. Separation of apposed structures, tissue tearing, and disruption of cellular layers defined early injury patterns that were not detected in the blast-exposed half of the brain slice. Ultrastructural pathology of the neurons exposed to cavitation was characterized by disintegration of plasma membrane along with loss of cellular content. The developed test system provided a controlled experimental platform to study cavitation induced high strain deformations on brain tissue slice. The goal of the future studies will be to lower underpressure magnitude and cavitation bubble size for more sensitive evaluation of injury.

Realizing Ultrafine Grained Steel by Simple Hot Deformation Using Dynamic Transformation and Subsequent Dynamic Recrystallization Mechanisms

We have found a new strategy for ultra grain refinement without high strain deformation by combining dynamic transformation (DT) and dynamic recrystallization (DRX) mechanisms. Through simple thermomechanical processes using a total plastic strain of 0.92 at elevated temperatures, ultrafine grained microstructures having mean grain sizes down to 0.35 microns could be obtained in a 10Ni-0.1C steel. DRX phenomenon occurring in the dynamically transformed ferrite significantly reduced the strain necessary for the formation of ultrafine grains. The DRX of DT ferrite showed an unconventional temperature dependence, which suggested an optimal condition for grain refinement. The obtained UFG steel exhibited superior mechanical properties, for example, the tensile strength of 970 MPa and the total elongation over 20% at the same time.

Microstructural and textural evolution of high-purity titanium under dynamic loading

The evolution of microstructure and texture during room temperature compression of high-purity titanium was studied under dynamic loading. X-ray diffraction (XRD) was used to examine the changes in the macrotexture while electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to characterize the microstructural evolution. Dynamic loading was found to enhance the activity of deformation twins; four types of primary twins were activated, including 101¯2, 112¯1, 112¯2 and 112¯4 twins. In addition, 112¯2–101¯2 and 101¯2–112¯2 secondary twins were also formed from a 10% thickness reduction. The newly formed [0001] TD orientation texture component was attributed to the 112¯2 primary twins. Although deformation twinning was the dominant deformation mechanism at the beginning of deformation, slip became dominant with increasing strain. Dislocations with Burgers vectors of ⟨c+a⟩ type character was predicted to accommodate strain along c-axis at higher deformation strain. The ⟨a⟩, pyramidal ⟨c+a⟩ and 112¯2–101¯2 secondary twins contributed to the formation of a basal texture at 40% thickness reduction. The twin boundary (TB) thickening resulted from a high density of dislocation interactions with the TB, which destroyed the misorientation relationship of the TB. The TB gradually evolved into TB segments or completely transformed into conventional high angle boundaries.

High strain deformation of austenitic steel for enhancing erosion resistance

Marine and off-shore components including propellers, pumps, valves, pipelines and other submerged surfaces are subjected to severe degradation by erosion. Impingement of solid particles mixed in a liquid, referred as slurry, leads to significant material loss and shortens the life span of components. Tailoring the surface properties of materials is an economical way for addressing their degradation. Surface modification through high strain-rate deformation is widely used to enhance functional properties of materials. However, surface modification, particularly at low temperature, is extremely challenging for high strength materials such as stainless steel and has not been investigated comprehensively so far. In the present work, high strain-rate deformation of austenitic steel, SS316L, was performed by innovative submerged friction stir processing technique. For comparative studies, friction stir processing was also performed under ambient cooling conditions. Electron back scatter diffraction studies showed significant grain refinement for the sample processed under submerged conditions. The erosion behavior of as-received and processed steel was investigated using slurry erosion tests. Erosion tests were performed at constant impact velocity of 20 m/s and particle size, while varying the impingement angles. The sample processed under submerged conditions showed nearly two times higher erosion resistance compared to as-received steel. The enhancement in erosion resistance is explained using structural rejuvenation achieved at high strain-rate deformation. All the samples showed similar erosion mechanisms with micro-cutting and ploughing being evident at acute angles and platelet mechanism at normal impingement angle. Erosion phenomena showed a strong correlation with material's hardness at oblique impingement angle while, erosion behavior at normal impingement is explained by the flow work given as hardness to elastic modulus ratio. The study provides fundamental insights into material design for advanced structural applications.

Influences of high strain rate, low temperature, and deformation direction on microstructural evolution and mechanical properties of copper

Step-wise deformations are applied to pure copper along uniaxial direction or multiaxial directions in three conditions of speed and temperature: static and room temperature, dynamic and room temperature, or dynamic and low temperature. Through examinations of total 36 deformation stages, the influences of strain rate, temperature, and deformation direction on microstructural evolution and mechanical properties are investigated. According to the results, the deformation mechanism at extreme conditions (high strain rate and low temperature) changes from only dislocation slip to dislocation slip and deformation twinning. Although deformation-direction change has no significant effect on the final mechanical properties and total dislocation densities measured from X-ray diffraction results, the evolutions of grain-boundary misorientation and geometrically necessary dislocations (GNDs) are clearly influenced. The trend of microstructural evolution, i.e. larger grain size and lower GND densities by multi-axial deformation than the uniaxial case, is reversed when twinning occurred. Based on the results, we suggest four evolution models: uniaxial or multi axial cases with dislocation slip, or with dislocation slip and deformation twining. Even if the homogenous and almost fully twinned microstructure producing improved mechanical strength was obtained by applying the extreme deformations, poor ductility of the processed specimen were observed.

Combination of dynamic transformation and dynamic recrystallization for realizing ultrafine-grained steels with superior mechanical properties.

Dynamic recrystallization (DRX) is an important grain refinement mechanism to fabricate steels with high strength and high ductility (toughness). The conventional DRX mechanism has reached the limitation of refining grains to several microns even though employing high-strain deformation. Here we show a DRX phenomenon occurring in the dynamically transformed (DT) ferrite, by which the required strain for the operation of DRX and the formation of ultrafine grains is significantly reduced. The DRX of DT ferrite shows an unconventional temperature dependence, which suggests an optimal condition for grain refinement. We further show that new strategies for ultra grain refinement can be evoked by combining DT and DRX mechanisms, based on which fully ultrafine microstructures having a mean grain size down to 0.35 microns can be obtained without high-strain deformation and exhibit superior mechanical properties. This study will open the door to achieving optimal grain refinement to nanoscale in a variety of steels requiring no high-strain deformation in practical industrial application.

Numerical modeling of mullions in the Taili high deformation zone, North China: Implications for the rheology of granitic rocks

This paper presents a combined field measurement and finite element modeling analysis of the mullions occurring on the contact of two granitic rocks with different grain size in the Taili High-Strain Deformation Zone (THDZ), West Liaoning of North China. All of the field data are located in the plot zone of the modeling results. Numerical modeling results indicate that: (1) The inter-angle between the tangent lines cross the cusp point and the ratio R of amplitude and width of mullions are the most effective parameters to describe the geometric shape and evolution of mullions, as well as useful indicators of the rheology of rocks. (2) The competence contrast controls the growth rate of mullions under shortening. It determines the possible ratio R of final mullions. Moreover, decreasing of the cusp angle in high competence contrast materials is faster than that in low competence contrast model. (3) The initial disturbance is an essential factor for the generation of mullions. Those contacts with higher initial disturbance will develop into mullions more easily and have a high growth rate during the same shortening deformation regime. (4) The rheology and deformation behavior of the granitic rocks in the study area are primarily controlled by the grain sizes of quartz and feldspar. The effective viscosity ratio of biotite adamellite and granitic gneisses is about 0.01–0.5. The deformation mechanisms of these granitic rocks should be dominated by a grain-size-sensitive diffusion creep.

Texture balancing in a fcc/bcc multilayered composite produced by accumulative roll bonding

The high strain deformation and recrystallization behaviour of a Fe/Ni multilayered composite sheet fabricated by accumulative roll bonding has been investigated. The comparable initial hardness and subsequent strain hardening behaviour of the Ni and Fe layers reduces the flow compatibility related challenges at the bonding interfaces, thereby generating parallel layers of uniform thickness during rolling to true strains up to 4.18. Typical body centred cubic (α- and γ-fibres) and face centred cubic (β-fibre) rolling textures were generated in the Fe and Ni layers, respectively. During annealing at 700 °C, recrystallization takes place homogenously in the Ni layers but commences initially by particle stimulated nucleation at oxide debris present at the interface of adjacent Fe layers. After recrystallization, the texture of the Ni layers is similar to the starting material prior to ARB, but considerable texture modification occurs in the Fe layers. For both metals, oriented growth of nucleated grains has the greatest influence on the final annealing textures, which generates the classic Cube texture in Ni and a {511}<1 5 10> texture in Fe. While these final textures of the individual Fe and Ni layers are not conducive to good formability, texture-based Schmidt factor calculations of the combined layers show an overall balance in texture components that points to a reduction in planar anisotropy. The ability to fabricate multilayered textured sheets by this route is a promising way of controlling the anisotropy of both strength and ductility.

Dependence of bulk viscosity of polypropylene on strain, strain rate, and melt temperature

The relations between bulk viscosity, strain, strain rate and melt temperature of polypropylene are investigated in uniaxial compression similar to the measurement of PVT diagram of a polymer. A new and more practical bulk viscosity model for the simulation of injection molding is proposed. The bulk viscosity increased with the increase of compression deformation and decreased when the compression speed and the melt temperature are higher. This dependency is attributed to the orientation and occupancy of the molecule within the free interstitial space. In addition, the magnitude of the bulk viscosity was found to be significantly greater than the shear viscosity at high compression deformation and low strain rate. Thus, not only shear viscosity but also the bulk viscosity should be considered in the simulation of the packing-holding stage of the plastic injection molding process. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

Elucidating microstructural evolution and strengthening mechanisms in nanocrystalline surface induced by surface mechanical attrition treatment of stainless steel

Surface mechanical attrition treatment (SMAT) is a high strain and strain rate severe plastic deformation (SPD) technique for surface nanocrystallization of metals. The aim of this study was to investigate the mechanism of nanocrystallization and strengthening in a medium stacking fault energy 316 L austenitic stainless steel during SMAT. The paramount role of microband and shear band formation in nanocrystallization is outlined, as opposed to deformation twinning previously reported in low SFE austenitic stainless steels. Shear bands undergo dynamic recrystallization and recrystallization twinning to produce ultra-fine grains in contrast to twin-twin intersections in low SFE stainless steel. The ultra-fine grains further sub-divide into smaller cells with initially low misorientation. Nanocrystallization occurs when misorientation between these cells increases with further strain. The additivity of strengthening by dislocation density and grain size is studied. Dislocation density was neglected in previous studies while studying strengthening mechanisms in SMAT processed materials. This study illustrates that dislocation density cannot be ignored as the strengthening mechanism in SMAT process. The grain size and dislocation density both significantly contribute to overall strengthening in SMAT processed microstructure.

High-strain deformation and fluid infiltration diachronism of the middle crust: New Devonian–Permian Alice Springs ages (365–290 Ma) of shear zones in the Strangways Metamorphic Complex, Central Australia

The Proterozoic granulite-facies Strangways Metamorphic Complex (SMC) in the Arunta Region of Central Australia was partially hydrated during the Devonian–Carboniferous (380–320Ma) Alice Springs Orogeny by amphibolite-greenschist-facies high-strain deformation. Stable and radiogenic isotope analyses on coeval muscovite and biotite from shear-zone samples of the SMC were performed to analyse the composition and date the timing of fluid circulation and cooling.Stable isotope data (δ18O and δD) indicate that in the south of the SMC, the source of fluids appear to be the thick successions of Neoproterozoic Heavitree Quartzite, while another source in the north and central part of the SMC may be related to meteoric fluids. The heterogeneous δ18OFluid and homogenous δDFluid values for muscovite reflect changes in water/rock ratios with initial high values in the south and lower in the north, possibly suggesting a migration of fluids from south to north (as indicated by the evolving δ18OFluid and homogenous δDFluid values). Rb/Sr muscovite ages of 365–340Ma approximate the time of crystallization and fluid infiltration. They also indicate that the shear zones were active at different times during the Alice Springs Orogeny and that some were active prior to the peak Carboniferous amphibolite-facies metamorphism. 40Ar/39Ar muscovite ages of 350–325Ma are mostly interpreted as cooling ages. Rb/Sr biotite ages of 335–290Ma are interpreted as cooling ages at ~300°C (Sr closure temperature for biotite) and extend the activity of the Alice Springs Orogeny until the Permian.Cooling histories of the Wallaby Knob and Harry Creek shear zones, which serve as the tectonic boundaries of the SMC to the north and south respectively, indicate slow cooling (<3.5°CMa−1) for c. 30Ma (360–330Ma) at both boundaries continuing until 290Ma in the western portion of the Harry Creek shear zone. This slow cooling is associated with passive exhumation (i.e. erosion). Rapid cooling (20–10°CMa−1) then occurred over c. 10Ma (330–320Ma) in the Wallaby Knob shear zone and in the east portion of the Harry Creek shear zone. This change in cooling rate is associated with the combined initiation in the Carboniferous of dextral and thrusting deformation by the Pinnacles Bore and Erontonga shear zones.

Effect of indentation temperature on nickel-titanium indentation-induced two-way shape-memory surfaces

This study investigated the effect of temperature on indentation-induced one-way and two-way shape memory properties in Ti-50.3at% Ni alloy. Indentation temperatures ranged from below the martensite finish temperature (Mf) to above the austenite finish temperature (Af) with the explicit intent of varying the indented phase. Samples used in the study were characterized by differential scanning calorimetry and transmission electron microscopy (TEM). The topographical behavior of the shape memory effect was investigated through Vickers indentation and laser scanning 3D confocal measurements. The magnitudes of deformation recovery associated with the one-way and two-way shape-memory effect (OWSME, TWSME) decreased with increasing indentation temperatures, which is a reflection of the decreasing volume of material experiencing martensitic reorientation during indentation. Indented and subsequently planarized samples exhibited TWSME protrusions when thermally cycled. Laser scanning measurements were used to characterize the height of the protrusions as increasing depths of material were polished away, which provided insight into the overall affected volume beneath the indent. As indentation temperatures increased, both the height of the protrusions, and consequently the polish depth necessary to completely remove the effect, decreased. TEM investigations revealed that directly underneath a nanoindent the microstructure was very fine due to the high-strain deformation; this was contrasted with a much coarser grain size in the undeformed bulk material. Overall these results strongly imply that the deformation recovery associated with the OWSME and TWSME can be maximized by indenting at temperatures at Mf or below because the volume of deformed microstructure beneath the indent is maximized. This finding has important practical value for any potential application that utilizes indentation-induced phase transformation deformation recovery in NiTi.

Atomistic clustering-ordering and high-strain deformation of an Al0.1CrCoFeNi high-entropy alloy.

Computational investigations of structural, chemical, and deformation behavior in high-entropy alloys (HEAs), which possess notable mechanical strength, have been limited due to the absence of applicable force fields. To extend investigations, we propose a set of intermolecular potential parameters for a quinary Al-Cr-Co-Fe-Ni alloy, using the available ternary Embedded Atom Method and Lennard-Jones potential in classical molecular-dynamics simulations. The simulation results are validated by a comparison to first-principles Korringa-Kohn-Rostoker (KKR) - Coherent Potential Approximation (CPA) [KKR-CPA] calculations for the HEA structural properties (lattice constants and bulk moduli), relative stability, pair probabilities, and high-temperature short-range ordering. The simulation (MD)-derived properties are in quantitative agreement with KKR-CPA calculations (first-principles) and experiments. We study AlxCrCoFeNi for Al ranging from 0 ≤ x ≤2 mole fractions, and find that the HEA shows large chemical clustering over a wide temperature range for x < 0.5. At various temperatures high-strain compression promotes atomistic rearrangements in Al0.1CrCoFeNi, resulting in a clustering-to-ordering transition that is absent for tensile loading. Large fluctuations under stress, and at higher temperatures, are attributed to the thermo-plastic instability in Al0.1CrCoFeNi.

A technique for studying the response of materials to high rate, high strain deformation

A gas-gun technique is described in which a thick-walled cylinder of a chosen solid may be collapsed over a wide range of effective strains, and at shear strain-rates of the order 104 s−1. Two variants of the basic concept are described. Initially a 70 mm bore gun was used to dynamically collapse stainless steel 304 cylinders to a wide range of final effective strains. Early-stage shear bands were observed to intersect the inner circumference of the collapsed cylinder. However, although the configuration provides a useful vehicle for studying high rate, high strain deformation it has the disadvantage that the strain vs. time field experienced by the sample is complex. In addition, the 70 mm bore size limited the diameter of the specimen tube studied and hence diagnostic access to the collapsing cylinder wall was not possible. Therefore the Sandia hydrocode CTH was used to modify the initial configuration to generate a simpler strain history in the sample. This refinement of the original concept was used to implode cylinders of the titanium alloy Ti–6Al–4V using a larger 100 mm bore gas launcher. The velocities of the inner surfaces of the imploding cylinders were measured using optical velocimetry from which the macroscopic strain and shear strain-rate were determined as a function of time. The samples were sectioned after the tests, revealing severe localised adiabatic shear patterns. The gas-gun technique is shown to be a versatile configuration with potential for easily varying the specimen's initial geometry and the strain-rates at which it is collapsed.

Recovery Kinetics in Commercial Purity Aluminum Deformed to Ultrahigh Strain: Model and Experiment

A new approach to analyze recovery kinetics is developed from a recent model, and microstructural observations are introduced to supplement hardness measurements. The approach involves two steps of data fitting, and the second step of fitting enables an estimation of the apparent activation energy for recovery. This approach is applied to commercial purity aluminum (AA1050) cold rolled to ultrahigh strain (99.6 pct reduction in thickness) and annealed at temperatures from 413 K to 493 K (140 °C to 220 °C). The annealing data fit the recovery model well, and the analysis shows that the apparent activation energy increases during recovery and approaches 190 kJ/mol at the end of recovery, suggesting that solute drag is an important rate-controlling mechanism. The recovery rate for the highly strained Al is found to be higher than that for Al deformed to a lower strain, an effect which is related to an increase in the stored energy (driving force). These findings form the basis for a discussion of recovery mechanisms and the increase in the apparent activation energy during annealing, suggesting an application of the model when optimizing the structure and strength through annealing of nanostructured materials produced by high strain deformation.

In-situ measurement of texture development rate in CaIrO3 post-perovskite

The rate of crystallographic preferred orientation (CPO) development during deformation of post-perovskite is crucial in interpreting seismic anisotropy in the lowermost mantle but the stability field of MgSiO3 post-perovskite prevents high-strain deformation experiments being performed on it. Therefore, to constrain the rate of CPO development in post-perovskite, we deformed CaIrO3, a low-pressure analogue of MgSiO3 post-perovskite, in simple shear at 3.2GPa and 400°C to a shear strain (γ) of 0.81. From X-ray diffraction patterns acquired during deformation, we invert for CPO as a function of strain. By comparing the CPO that develops with visco-plastic self-consistent (VPSC) models we constrain the critical resolved shear stresses (CRSS) of the non-primary slip-systems in CaIrO3 to be of order 6 times stronger than the primary [100](010) slip system. This value is significantly less than has been assumed by previous studies and if applicable to MgSiO3 implies that seismic anisotropy in the D″ layer develops slower than has previously been assumed.

Influence of high strain rates on the structure and mechanical properties of high‐manganes austenitic TWIP‐type steel

The purpose of this paper is to determine the influence of high strain rates on the structure and mechanical properties of high‐Mn austenitic TWIP steel. Low and high strain deformation rates in the range of 0.001 s–1 to 1000 s–1 have a significant effect on the forming of the structure and mechanical properties of high‐manganese austenitic steel. Also, the strain energy per unit volume of advanced high‐Mn TWIP steel containing Mn, Al and SI, with Nb and Ti microadditions, increases considerably in dynamic conditions. This group of steels not only shows excellent strength, but also excellent formability due to twinning, thereby leading to a unique combination of strength, ductility and formability when compared with conventional dual phase steels or transformation induced plasticity TRIP steels. The microstructure of the investigated steel was determined in metallographic investigations using scanning and high‐resolution transmission electron microscopies (HRTEM). Results obtained in static and dynamic conditions for new developed high‐manganese austenitic steel indicate their possible employment for the constructional elements of vehicles, especially passenger cars, to take advantage of the significant growth of their strain energy per unit volume. This guarantees a reserve of plasticity in the zones of controlled energy absorption during possible collision resulting from the activation of twinning induced by cold working, which may lead to a significant growth of the passive safety of these vehicles' passengers.

The golden ark: arsenopyrite crystal plasticity and the retention of gold through high strain and metamorphism

AbstractQuantitative electron backscatter diffraction analysis and ion microprobe imaging of gold‐rich arsenopyrites provide the first insights into the crystal plasticity and element mobility behaviour of arsenopyrites through metamorphism (340°–460° and 2 kbar). Remarkably, the gold‐rich arsenopyrites remained structurally and chemically robust during high strain deformation. It was only during a superimposed lower strain deformation event, at a high angle to the preferred orientation of the arsenopyrites, that small amounts of crystal plasticity affected the arsenopyrites. During the low strain event, a dissolution–reprecipitation reaction resulted in loss of gold from the crystal lattice, facilitated by localised domains of recrystallisation, most likely due to fluid percolation along sub‐ and new grain boundaries. We suggest that the abundance and rheologically robust nature of gold‐rich arsenopyrite in giant gold deposits, affected by greenschist–amphibolite metamorphism, is actually critical in the preservation of those deposits.

Influence of deformation and fluids on Ar retention in white mica: Dating the Dover Fault, Newfoundland Appalachians

White mica 40Ar/39Ar analyses may provide useful constraints on the timing of tectonic processes, but complex geological and thermal histories can perturb Ar systematics in a variety of ways. Ductile shear zones represent excellent case studies for exploring the link(s) between dynamic re-/neo-crystallization of white mica and coeval enhanced fluid flow, and their effect on 40Ar/39Ar dates. White mica 40Ar/39Ar dates were collected from compositionally similar granites that record different episodes of deformation with proximity to the Dover Fault, a terrane-bounding strike-slip shear zone in the Appalachian orogen, Newfoundland, Canada. 40Ar/39Ar data were collected in situ by laser ablation and by step heating single crystals. Results were compared to each other and against complementary U–Pb zircon and monazite, and K-Ar fault gouge analysis.Although step-heat 40Ar/39Ar is a widely applied method in orogenic settings, this dataset shows that relatively flat step-heat 40Ar/39Ar spectra are in contradiction with wide spreads in in-situ40Ar/39Ar dates from the same samples, and that plateau dates in some cases yielded mixed dates of equivocal geological significance. This result indicates that the step-wise release of Ar from white mica likely homogenizes and obscures spatially-controlled Ar isotope reservoirs in white mica from sheared rocks. In contrast, in situ laser ablation 40Ar/39Ar analysis preserves the spatial resolution of 40Ar reservoirs that have been variably reset by deformation and fluid interaction. This study therefore suggests that laser ablation is the best method for dating the timing of deformation recorded by white mica. Final interpretation of results should be guided by microstructural analysis, estimation of deformation temperature, chemical characterization of white mica, and complementary chronometers.Overall the dataset shows that granitic protoliths were emplaced between 430 and 422Ma (U–Pb zircon). High strain deformation along the Wing Pond Shear Zone occurred between ca. 422–405Ma (U–Pb monazite and 40Ar/39Ar). Subsequent patchy Ar loss in white mica occurred locally during low T shear (<400 C), and via post-deformation fluid interactions. Low-temperature reactivation of the Dover Fault, a narrow segment of the Wing Pond shear zone, occurred at ca. 385Ma (40Ar/39Ar). K-Ar dating of authigenic illite in fault gouge from the broadly co-linear brittle Hermitage Bay Fault indicates that slip along the terrane boundary persisted until at least the Mississippian.

Recent Advances in Stretchable and Transparent Electronic Materials

Recent technological advances have made a myriad of soft and flexible electronic devices possible. The essential materials behind many of these devices and systems are electrical conductors that are compliant and retain their conductivity at high strain deformation. These so‐called “compliant conductors” are the class of materials that enable stretchable and flexible electrodes, interconnects, and other components utilized in soft electronics. Creating conductors with high compliance, conductivity, and transparency is not a trivial matter, since these properties are often mutually exclusive. Furthermore, engineering reliable compliant conductors with a desired set of properties that remain fairly unchanged over long service lifetimes is an additional criterion that merits careful attention. These challenges have been addressed through at least two primary approaches. The first has been to create conducting composites that are intrinsically stretchable, typically by filling elastomers with conductive particles, or by depositing conductive particles on or just beneath the surface of elastomers. The second strategy has been to build conducting structures capable of reversible bending or stretching. In this review, the key research efforts toward the development of compliant conductors, including transparent conductors, are surveyed for application in flexible and highly stretchable electronic and electromechanical devices.