Increasing Shear Strain Research Articles

Transpressional deformation in the lithospheric mantle beneath the North Anatolian Fault Zone

We studied mantle xenoliths sampled from two late Miocene volcanic centers located immediately north of the North Anatolian Fault Zone (NAFZ) in western Turkey. The spinel lherzolite and harzburgite xenoliths equilibrated at temperatures ranging from 757 to 1019 °C, estimated from two-pyroxene geothermometry. Pressures estimated from the Cr-in-clinopyroxene geobarometer and pseudosection modelling range from 1.0 to 2.1 GPa, which correspond to depths of 38–75 km. We used X-ray computed tomography to quantify the three-dimensional shape preferred orientation of spinel grains. Spinel displays dominantly oblate fabric ellipsoids, consistent with flattening strain. Olivine crystallographic preferred orientation (CPO), determined by electron backscatter diffraction, exhibits chiefly axial-[010] and A-type patterns. The axial-[010] CPO pattern is consistent with the spinel fabric that shows flattening strain, and is primarily developed in xenoliths from the volcanic center nearer to the NAFZ. Obliquity of olivine CPO to the spinel lineation decreases with proximity to the NAFZ, suggesting an increase in shear strain. Our results favor an interpretation of transpressional deformation in the upper mantle below the NAFZ. We attribute this pattern to a restraining bend in the mantle section of the NAFZ.

Deformation characteristics of medium-dense sand-clay mixtures under a principal stress rotation

A moving wheel load induces a principal stress rotation (PSR) in pavement foundation geomaterials including subgrade/subbase soils. Simulating such a stress condition is not possible with stress path tests conducted with conventional cyclic triaxial (CT) equipment. More complex stress paths such as a heart-shaped stress path are required to determine the deformation characteristics of these under a PSR. A heart-shaped stress path can be simulated on a soil specimen in cyclic hollow cylinder (CHC) tests via user-defined waveforms for its stress components (axial stress, and torsional shear stress). In this study, a series of CT and CHC tests were performed to analyze the impact of a PSR on strain behaviors of medium-dense sand-clay mixtures. The specimens contained 0%, 5%, 10%, and 20% clay by weight and were prepared at an initial relative density of 50%. All specimens were anisotropically consolidated under K0≈0.5. It was determined that all CT specimens underestimated the strain performances (both axial strain and shear strain) of the sand-clay mixtures. On the other hand, a heart-shaped stress path was simulated successfully in CHC tests and thus, all specimens yielded more accurate strain results. At low clay content (≤10%), the impact of a PSR on strain performances of the sand-clay mixtures was observed to be less (axial strain (εz) < 0.12%, and shear strain (γzθ) < 0.8% after number of load cycles (N) = 5000) due to the low stress ratios (CVSR = 0.15 and η = 1/3). On the other hand, despite the low stress ratios, a PSR caused a rapid increase in axial strain and shear strain (εz = 5%, and γzθ > 0.8%) of the specimen containing 20% clay, which resulted in the failure of the specimen at N = 478. Results of this study clearly indicated that the effect of a PSR should be taken into consideration while evaluating the strain characteristics of the sand-clay mixtures that contain clay particularly at high contents (≥20%) under traffic loads.

Introduction of a New Parameter to Quantify the Fatigue Damage in Asphalt Mastics and Asphalt Binder

This study involves the quantification of fatigue damage in asphalt materials by introducing a new fatigue damage parameter denoted as the F parameter. One waste filler, i.e., red mud and an asphalt binder were chosen to blend the asphalt mastics at three filler contents of 10, 20, and 30% respectively with respect to the volume of binder and tested at temperatures of 5, 15, and 25 °C. The proposed parameter incorporates the effect of both peak shear stress as well as the failure strain, and hence, can better represent the fatigue damage. A lower value of F is recommended for a better fatigue resistant material. The F parameter was found increasing with the increment in filler content, which signifies higher degree of damage with a high level of stiffening. On the other hand, it consistently decreased with the increment in temperature. The behavior of the materials under the action of increasing shear strain was clearly justified by using the F parameter corresponding to different filler contents and the testing temperatures. In addition to that, the observations from the F parameter were also complemented by the fatigue diagrams. Hence, the proposed parameter is envisaged to be a promising fatigue damage indicator in future works.

(Nanocarbons Division Best Poster Award - 3rd Place) Intrinsic Shear Strain in Graphene Heterostructures Detected Via Raman Spectroscopy

Graphene’s electronic band structure is extremely sensitive to small perturbations in its crystal lattice. Because of this it is vital to correctly characterize strain, doping and defects in graphene through nondestructive measurements. Characterization through Raman Spectroscopy allows this nondestructive measurement. Graphene on Transition Metal Dichalcogenides (TMDCs) show increased shear strain which is not caused by defects introduced through the transfer method. We prove this using Raman analysis of graphene samples on silicon oxide and TMDC. Graphene shows G peak splitting and shift indicative strain increasing on top of TMDC when compared to nearby graphene on silicon oxide.Acknowledgement: Authors acknowledge the JSNN, a member of the Southeastern Nanotechnology Infrastructure Corridor (SENIC) and National Nanotechnology Coordinated Infrastructure (NNCI), supported by the NSF (ECCS-1542174), The PSU Two-Dimensional Crystal Consortium – Materials Innovation Platform 2DCC-MIP, supported by NSF cooperative agreement (DMR- 1539916). Authors are grateful to Dr. S. Aravamudhan (JSNN) and Dr. J. Redwing (2DCC MIP).

Near-surface frequency-dependent nonlinear damping ratio observation of ground motions using SMART1

The damping ratio is an important index used in soil nonlinearity studies and is mostly proportional to the shear strain increase. Previous researches indicated a frequency-independent damping in most cases. In this study, frequency-dependent damping was introduced from frequency-dependent Q calculated through the spectral ratio method of near-surface structures using the power spectrum of strong motion records in the Strong Motion Array in Taiwan Phase I (SMART1). The dense SMART1 recorded significant strong motions in the 1980s, which can be used to identify soil nonlinearity at near surfaces. A 40%–50% increase in frequency-dependent damping for SMART1 was identified, with strain increasing from 0.01% to 0.1% in near-surface regions. A large damping was also found in the shallow sediments with mean Vs below 600 m/s on the topmost 500 m layers in the SMART1 database at a frequency range of 3–8 Hz, which is independent of the magnitude scaling or near-field travel distance scaling relations.

Theoretical analysis of high strength and anti-buckling of three-dimensional carbon honeycombs under shear loading

Three-dimensional carbon honeycombs (3D C-honeycombs) are considered as a promising matrix material for new composites, while their mechanical behaviors under complex stress status remain unclear. Here, shear response of 3D C-honeycombs is systematically investigated with molecular dynamics (MD) simulations and mechanical analysis. Two deformation modes are observed for 3D C-honeycombs under in-plane and out-of-plane shear loading. A mechanical model is proposed to describe the deformation of 3D C-honeycombs under different shear loading, and agrees well with the MD simulations. Under in-plane shear loading, the initial elastic deformation is dominated by distortion of hexagon structures, shear modulus increases as increasing shear strain, and the tension of side walls leads to fracture. Under out-of-plane shear loading, the structure of 3D C-honeycombs can remain stable until fracture regardless of side wall buckling, and the tensile stress concentration at junctions gives rise to fracture. For both the two modes, the junction type has a negligible effect on shear strength of 3D C-honeycombs. The stability of junctions plays a dominant role in the shear response of 3D C-honeycombs, and thus the superb mechanical properties of graphene can be largely inherited by the 3D C-honeycombs.

Experimental investigation of dynamic shear behavior of typical silt sand in Rudong Offshore Wind Farm

The dynamic properties of typical silt sand in offshore wind farm are closely related to the stability of offshore wind farm foundations. This study investigates the dynamic behavior of typical silt sand in Rudong offshore wind farm of Jiangsu province based on dynamic triaxial testing and resonant column testing. Specifically, the dynamic properties including dynamic modulus, damping ratio, dynamic strength, dynamic strain, dynamic pore water pressures and stress-strain relationship of the silt sand are studied. It is found that the accumulated strain and pore pressure continuously increase with the increased cyclic number, which eventually leads to liquefaction failure. Soil specimen with a higher confining pressure is more likely to reach liquefaction with a lower number of loading cycles. It is also found that the Hardin-Drnevich model can be used to reflect the mechanism of the effect of confining pressure on the dynamic behavior of the silt sand. The dynamic shear modulus and damping ratio decrease and increase exponentially with the increase of shear strain, respectively.

Small strain stiffness within logarithmic contractancy model for structured anisotropic clay

Stiffness of soils in the small strain region is high and it decays nonlinearly with increasing shear strains or with mobilization of shear stresses. However, the commonly used critical state based constitutive models use a simple elastic formulation at small strains that falls short in the prediction of the small strain nonlinearity and anisotropy. This paper proposes a simple way for rendering the existing constitutive models with the capability to capture the small strain behaviour of soils. This is illustrated by proposing a new model for structured anisotropic clay extending an existing model that uses the framework of logarithmic contractancy called E-SCLAY1S. The proposed model is implemented into a Finite Element program as a user-defined soil model. The model predictions are compared with experimental data for various clays. Furthermore, the effect of nonlinearity is investigated for an excavation in soft clay.

Control of plastic deformation in Cu50Ta50 metallic glass by insertion of Cu crystalline cores

The tensile characteristics and deformation mechanisms of Cu-Ta metallic glasses with the insertion of Cu crystalline cores are investigated using molecular dynamics (MD) simulations. The effects of different Cu crystalline core diameters (D Cu ), experiment temperatures (T), and Cu crystalline core numbers (N) are studied. The results show that the plasticity of the Cu-Ta MGs is significantly improved by inserting Cu crystalline cores. The Shockley dislocations (<112>) make up the majority, and the FCC structures mainly transform into the HCP structures in the Cu crystalline cores. As increasing D Cu , the shear transformation zones (STZs) form more severely, the fraction of atoms with the high shear strain increases, and the tensile strength reduces. As increasing T, the STZs formation is fainter and most intense at 100 K, the fraction of atoms with the shear strain greater than 0.5 (f0.5) and the tensile strength reduce, while the fraction of atoms with the shear strain greater than 0.3 (f0.3) increases. As changing N, the STZs formations in the samples with the N = 2 and 8 are more pronounced, the f0.5 of the samples with the N = 1 and 8 are lower than those in the other cases, and the tensile strength reduces as the N increases.

Impact of Forward Osmosis Operating Pressure on Deformation, Efficiency and Concentration Polarisation with Novel Links to CFD.

Forward osmosis (FO) modules currently suffer from performance efficiency limitations due to concentration polarisation (CP), as well as pressure drops during operation. There are incentives to further reduce CP effects, as well as optimise spacer design for pressure drop improvements and mechanical support. In this study, the effects of applying transmembrane pressure (TMP) on FO membrane deformation and the subsequent impact on module performance was investigated by comparing experimental data to 3D computational fluid dynamics (CFD) simulations for three commercial FO modules. At a TMP of 1.5 bar the occlusion of the draw-channel induced by longitudinal pressure hydraulic drop was comparable for the Toray (16%) and HTI modules (12%); however, the hydraulic perimeter of the Profiera module was reduced by 46%. CFD simulation of the occluded channels indicated that a change in hydraulic perimeter due to a 62% increase in shear strain resulted in a 31% increase in the Reynolds number. This reduction in channel dimensions enhanced osmotic efficiency by reducing CP via improved draw-channel hydrodynamics, which significantly disrupted the external concentration polarization (ECP) layer. Furthermore, simulations indicated that the Reynolds number experienced only modest increases with applied TMP and that shear strain at the membrane surface was found to be the most important factor when predicting flux performance enhancement, which varied between the different modules. This work suggests that a numerical approach to assess the effects of draw-spacers on pressure drop and CP can optimize and reduce investment in the design and validation of FO module designs.

Laponite gels - visco-elasto-plastic analogues for geological laboratory modelling

Laponite® is a synthetic clay that, depending on concentration, temperature and curing time, forms a clear, transparent thixotropic fluid or brittle visco-elasto-plastic gel when mixed with water. Here we present the results of rheological and mechanical testing of gel-forming Laponite RD (LRD) to evaluate its suitability as a rock analogue in laboratory analogue experiments. Rheological tests of 2–4 wt% concentrations of LRD in deionised water were carried out at temperatures between 20 and 50 °C, and after curing times of 3 to 14 days. Our results show that LRD gels change from a brittle, elastic-dominant, linear viscoelastic material to a plastic material as shear strain increases. The linear viscoelastic region occurs at shear strains, γ < 10% after which the material yields and then undergoes strain hardening before a peak stress occurs at γ = 15–20%. LRD then strain softens up to γ < 26.2%, beyond which it behaves as a plastic material. Empirical equations are provided that predict increases in the Young's and complex shear moduli of LRD with increasing concentration and ageing time. LRD can be used to model elastic deformation when γ < 10% at a shear strain rate of 0.1 s−1 and plastic deformation when γ > 26.2%. LRD is an ideal material for modelling the behaviour of rocks during the emplacement of magma and the propagation of brittle fractures in the upper crust. Its ease of preparation, low surface tension, full transparency, chemical and biological stability and photoelastic properties provide further advantages for analogue laboratory modelling compared to other frequently used visco-elastic gels, such as pig skin gelatine.

Grain boundary migration and deformation mechanism influenced by heterogeneous precipitate

AbstractUnderstanding the interaction between heterogeneous precipitates and grain boundaries (GBs) is of great significance for tailoring the stability and mechanical properties of nanograined materials. In this work, the nanoscale interaction between the cylindrical precipitate and the migrating GB is investigated by atomic simulation. The results show that the resistance for GB migration can be increased by decreasing the direction angle $$\alpha$$ α (the angle between the axis of the precipitate and the tilt axis of GB). For the larger precipitate, the influence of direction angle is more pronounced. With the increase in shear strain, the interaction between the specific precipitate and GB changes the material deformation mechanism from “GB migration” to “GB migration accompanied with activated dislocations or GB deformation,” which contributes to the softening of the material. By simultaneously tuning the direction angle and size of heterogeneous precipitates, the GB deformation can be strongly inhibited and the stability of GBs can be significantly improved.

The effect of soil nonlinearity on high-frequency spectral decay and implications for site response analysis

This study uses recorded ground motions at soil sites over a range of shaking intensities to investigate the effects of soil nonlinearity on the high-frequency spectral decay, as quantified by the parameter [Formula: see text]. Equivalent-linear site response analyses indicate that [Formula: see text] should increase significantly with increasing shear strain and ground motion intensity due to increases in soil damping. However, using more than 2500 motions from 32 sites, this study shows that [Formula: see text] does not vary systematically with the induced shear strain but instead remains at its small-strain value. This observation indicates that high-frequency components of motion are consistent with small-strain damping, rather than the strain-compatible damping used in site response analysis. It is demonstrated that equivalent-linear site response analyses for large strains can be modified to generate surface motions with more realistic high-frequency content by scaling the predicted surface motion to fit the small-strain [Formula: see text] or by employing frequency-dependent soil properties that account for the frequency dependence of the induced strains.

Study on Dynamic Characteristics of Unsaturated Strongly Weathered Sericite Schist Residual Soil

Sericite schist residual soils are widely distributed on the shallow surface of western Yunnan, and most of them are in an unsaturated state. In order to study its dynamic characteristics, a resonance column tester was used to target the strongly weathered unsaturated sericite schist residuals in the Dali Railway. The soil carries out dynamic characteristic test to study. The results show that the confining pressure has a great influence on the dynamic characteristics of the specimen, the dynamic shear modulus increases with the increase of the confining pressure, the phenomenon that the damping ratio decreases with the increase of shear strain is more obvious. Using the Hardin-Drnevich model can better fit the dynamic shear modulus with shear strain. The application of the improved linear equation can better describe the relationship and analyse its mechanism.

Rheological Properties of Superparamagnetic Iron Oxide Nanoparticles

The present study focuses on the rheological properties of polyethylene glycol (PEG) modified, positively charged, and negatively charged superparamagnetic iron oxide nanoparticles (SPIONs) at different temperatures. We hypothesized that the surface properties of these nanoparticles in the water did not affect their rheological properties. These nanoparticles had not the same surface properties as SPIONs-PEG had not to charge on their surface whereas positively charged and negatively charged ones with amine and carboxyl groups as their surfaces had positive and negative surface charges, respectively. However, their rheological behaviors were not different from each other. The comparative rheological study of SPIONs revealed their pseudo-Newtonian behavior. The viscosity of SPIONs decreased with the increase in temperature. At low shear rates, the shear stress of SPIONs was independent of rate and increased with the increase of rate. Moreover, at high shear rates, the shear stress for PEG-SPIONs was more than those for positively charged and negatively charged SPIONs. These measurements also revealed that at high shear rates, the shear stress of samples decreased with the increase of temperature. The shear stress of samples decreased with the increase of shear strain and the temperature. We also observed that all the samples had the same amount of shear strain at each shear stress, which indicated the exact resistance of SPIONs to deformation. Furthermore, the shear modulus decreased with time for these nanoparticles. These results suggest that these nanoparticles are promising candidates with appropriate properties for fluid processing applications and drug vectors in biomedical applications.

Force attenuation properties of shear-thickening polymer (STP)-based hip protector in simulated sideways fall

Shear-thickening polymer (STP) has a unique property of increasing its viscosity with an increase in shear strain to attenuate the application of force, implying that it can be used as a material for hip protectors. This study introduces a new hip protector composed of STP and compares its force attenuation capacity to that of other commercial hip protectors in simulated sideways falls. The performance of the STP-based hip protector was analyzed against eight commercial hip protectors (Pelican, Posey, SafeHip, Hornsby, FallSafe, HipSaver, Impact Wear (Hard), Impact Wear (Soft)). The simulated sideways fall conditions were created by a drop weight impact testing system using an anatomical hip model. The machine was dropped from a 20 or 30 cm height resulting in impact energy of 25.1 J (low) or 44.1 J (moderate), respectively. At low impact energy, the commercial hip protectors showed an attenuation range from 21.6 % to 53.3 %, and the STP-based hip pad was able to attenuate the force by 42.7 %. At moderate impact energy, the commercial hip protectors showed an attenuation range from 23 % to 54.3 %, and the STP-based hip pad was able to attenuate the force by 32.6 %. The low coefficient of variance showed a high precision in the execution of the experiments. Although the STP-based hip protector was thinner than the average of commercial soft shell pads and retained comfortable fit, it showed comparable force attenuation capacity to the commercial ones for the low impact energy test. This study highlights that STP, in combination with a polyurethane foam layer, provides the best features in energy-absorption and shunting, showing that it can be used in hip protectors to gain a competitive advantage over others.

Dynamic Characterization of Tire Derived Aggregates

Despite the recent efforts in characterizing and investigating the dynamic properties of tire-derived aggregates (TDA) and its use in civil engineering applications, the size of TDA used in most of the previous work was significantly smaller than the TDA size range mentioned in ASTM D6270 standards. There are two types of TDA, Type A and Type B, in which the maximum aggregate size of Types A and B are 200 and 450 mm, respectively. Thus, the availability of experimental data and shear modulus reduction curves for the dynamic behavior of TDA of larger sizes are deemed necessary for practical engineers to assess and investigate the behavior of such material under dynamic loads. This paper provides the results of large-scale undrained cyclic triaxial tests performed on Type A TDA at large strain amplitudes. The tests were performed under confining pressures ranging from 25 to 200 kPa and shear strain levels ranging from 0.1% to 10%. Furthermore, each test consisted of successive stages in which the number of cycles and axial strain levels varied. The shear modulus of Type A TDA has a range of 245–1,796 kPa, with a decreasing trend with increasing shear strain amplitudes. Furthermore, the dampening ratios were found to range from 11% to 23.5%. Finally, the shear modulus reduction curves were obtained through curve fitting techniques and nonlinear regression.

A three-dimensional mechano-electrochemical material model of mechanosensing hydrogels

Mechanotransduction is the initiation of an electrochemical signal as a result of mechanical stimuli. It is found predominately in biological tissue and its mechanisms are well documented. In the gel like tissues of the body, such as articular cartilage and intervertebral discs, mechanotransduction regulates matrix building and degrading processes as well as keeping the tissues adequately hydrated, both with the aim of minimizing degradation. The electrochemical responses to mechanical loading at constant volume of an inanimate hydrogel could assist in the understanding of these processes.There is considerable evidence that the modulus of hydrated tissues and hydrogels depend explicitly on ionic concentration. By modeling the mechano-electrochemical relationship of a hydrogel, the coupling of the elastic and electrochemical energies can be quantified. In turn, the mechanisms that govern this phenomenon can be better understood. This study modifies the Flory-Rehner theory of gels, using material-specific experimental data as input. The results show up to a 11% difference in equilibrium swelling magnitude compared to the Flory-Rehner model. Furthermore, under isochoric deformation, an increase in electrical potential is shown with increasing shear strain, something which is not possible with conventional Flory-Rehner and Donnan theory. This aligns the continuum model presented here more closely with both experiment and microscopic theories. The mechanosensing capabilities as well as varying swelling responses in different solution concentrations highlight the models potential applications in both biological and technological settings.

Influences of grain size, alloy composition, and temperature on mechanical characteristics of Si100-xGex alloys during indentation process

We perform molecular dynamics simulations to explore the effects of grain size, alloy composition, and temperature on the mechanical characteristics of Si100-xGex alloys during the indentation process. The structural evolution, von Mises shear strain, von Mises stress, and dislocation in workpiece are evaluated to explain the transformation of the loading force. Moreover, hardness and Young's modulus are also computed to evaluate the mechanical characteristics of different specimens. The results present that the loading force, hardness, Young's modulus of single crystalline are higher than polycrystalline. Besides, the loading force and hardness reduce as the grain size reduces; this result reveals a reverse Hall-Petch relation. In the indentation process of small grain size workpiece, the dislocation freely migrates to the grain boundary and absorbed, leading the amount of dislocation movement significantly reduces, which will instead promote the migration and sliding at the grain boundaries. It is confirmed that the grain boundaries play an essential role in the deformation behavior of the material. For the purpose of study the effect of various alloy compositions on the mechanical characteristics of the Si100-xGex substrate, a series of various alloy compositions are conducted: Si20Ge80, Si40Ge60, Si50Ge50, Si60Ge40, and Si80Ge20. The results reveal that the hardness, and Young's modulus of specimens increase as the Si content increases. In addition, the influence of temperature is also investigated in this work. It is found that when the temperature increases, leading to the atomic displacement and shear strain increase, the total dislocation length and the number of defect atoms increase, which leads to the hardness and Young's modulus reduction.

Flow-to-Friction Transition in Simulated Calcite Gouge: Experiments and Microphysical Modeling.

A (micro)physical understanding of the transition from frictional sliding to plastic or viscous flow has long been a challenge for earthquake cycle modeling. We have conducted ring‐shear deformation experiments on layers of simulated calcite fault gouge under conditions close to the frictional‐to‐viscous transition previously established in this material. Constant velocity (v) and v‐stepping tests were performed, at 550°C, employing slip rates covering almost 6 orders of magnitude (0.001–300 μm/s). Steady‐state sliding transitioned from (strong) v‐strengthening, flow‐like behavior to v‐weakening, frictional behavior, at an apparent “critical” velocity (v cr) of ~0.1 μm/s. Velocity‐stepping tests using v < v cr showed “semi‐brittle” flow behavior, characterized by high stress sensitivity (“n‐value”) and a transient response resembling classical frictional deformation. For v ≥ v cr, gouge deformation is localized in a boundary shear band, while for v < v cr, the gouge is well‐compacted, displaying a progressively homogeneous structure as the slip rate decreases. Using mechanical data and post‐mortem microstructural observations as a basis, we deduced the controlling shear deformation mechanisms and quantitatively reproduced the steady‐state shear strength‐velocity profile using an existing micromechanical model. The same model also reproduces the observed transient responses to v‐steps within both the flow‐like and frictional deformation regimes. We suggest that the flow‐to‐friction transition strongly relies on fault (micro)structure and constitutes a net opening of transient microporosity with increasing shear strain rate at v < v cr, under normal stress‐dependent or “semi‐brittle” flow conditions. Our findings shed new insights into the microphysics of earthquake rupture nucleation and dynamic propagation in the brittle‐to‐ductile transition zone.