Large Shear Strains Research Articles

Modeling shear stress response of bituminous materials under small and large strains

The paper at hand focuses on modeling the stress response of different mastics and asphalt binders exposed to small and large shear strains using Bergström-Boyce (BB) constitutive model as well as Finite Element (FE) approach. In this paper, a set of experiments based on Large Amplitude Oscillatory Shear (LAOS) test were designed and conducted to capture the state of strain dependence of bituminous mastics and binders over a broad spectrum of strain domain (0.5%, 10%, 20%, 30%, and 40%) pertaining linear and nonlinear regimes of such materials. Using the experimental data, the BB constitutive model was utilized to describe the attained behavior at two temperatures (30 °C and 40 °C) and varied strain amplitudes. The material properties derived from the BB model were further implemented into a Finite Element Model (FEM) using the ABAQUS platform to simulate the stress response of bituminous materials for a wide range of strain amplitudes. It has been shown that the bituminous mastics and binders have strong nonlinearity at high strain amplitudes, depicted graphically based on the progressive distortion from the elliptical form of Lissajous-Bowditch (LB) plot. Based on the observed goodness of fitting, the BB model well-described the experimental results for linear and nonlinear behaviors. Using the optimized parameters, it was confirmed that the BB model is well suited to build a numerical model that could reproduce stress responses derived from the LAOS results for a wide range of strain levels. The advantage of the methodology presented herein allows adaptable model constants of the BB model depending on the imposed level of strain and temperature and hence, the FEM can describe both linear and nonlinear behaviors of bituminous mastics and binders. From this paper, researchers can take advantage of capturing the stress response of binders and mastics under small and large strain amplitudes to stimulate the research on better representation of the complex behavior of asphalt mixes based on the role of mastic and asphalt binder.

Experimental investigation of the flexural mechanism and performance of channel steel tube slab structure under concentrated loads

Experimental studies about the flexural performance of channel steel tube slab (CSTS) structure subjected to concentrated loads were carried out, with considering various spacing of adjacent tubes, longitudinal spacing between the channel steel and missing tensile channel steel. A self-designed flexural device equipped with particle image velocimetry (PIV) technology was used to monitor continuous structure deformation and concrete cracking characteristics. In this study, the mechanism and performance of CSTS structure serving in underground engineering were analyzed, and a theoretical model for the bearing capacity of the CSTS structure was proposed. The results show that the failure mode of the test specimens exhibits ductile failure with an average ductility coefficient 2.52. The large shear strain of the concrete was obtained from PIV speckle contour, and it shows the same propagation trend compared with the main cracks appearing in the tests. In addition, the tensile channel steel along with decreasing the spacing of adjacent tubes can increase the bearing capacity of the specimens. The proposed theoretical model shows a reasonable prediction of the ultimate bearing capacity of specimens compared with the experimental results.

Dynamic Recrystallization Can Produce Porosity in Shear Zones

AbstractCreep cavities are increasingly recognized as an important syn‐kinematic feature of shear zones, but much about this porosity needs investigation. Largely, observations of creep cavities are restricted to very fine grained mature ultramylonites, and it is unclear when they developed during deformation. Specifically, a question that needs testing is should grain size reduction during deformation produce creep cavities? To this end, we have reanalyzed the microstructure of a large shear strain laboratory experiment that captures grain size change by dynamic recrystallization during mylonitization. We find that the experiment does contain creep cavities. Using a combination of scanning electron microscopy and spatial point statistics, we show that creep cavities emerge with, and because of, subgrain rotation recrystallization during ultramylonite formation. As dynamic recrystallization is ubiquitous in natural shear zones, this observation has important implications for the interpretation of concepts such as the Goetze criterion, paleopiezometery, and phase mixing.

Undrained cyclic simple shear simulation of liquefiable granular particles subjected to large shear strains up to 100% by 3D DEM

Undrained cyclic simple shear simulation of liquefiable granular particles subjected to large shear strains up to 100% by 3D DEM

Temperature Measurements with Depth and Physical Evidence for the Effect of High Temperature Gradients on Top-Down Fatigue Cracking

This paper presents the results of pavement temperature measurements with depth over a year obtained with a setup emulating the heat flow on a pavement with 305 mm (12 in.) of hot mix asphalt (HMA) and 152 mm (6 in.) of aggregate base. Several findings related to top-down fatigue cracking (TDFC) in Hawaii were obtained from these measurements. It was observed that pavement temperatures near the surface, which were both the lowest and the highest in the HMA depending on the time of day, were rarely below 20°C, and thus, that most cracking in Hawaii occurs at higher temperatures. It was also observed that passing rains can cause sudden temperature drops of the order of 15°C within short periods (15 min). HMA moduli estimated using measured temperature profiles indicate that high temperature gradients may lead to inverted moduli profiles that when loaded cause the highest tensile and shear strains to occur near the surface, and that these may be a main reason for TDFC in the state. The simulated stresses and strains under high temperature gradients also indicate they may be conducive to delamination problems related to large horizontal shear strains generated near the surface and combined with nearly vertical but small tensile strains at the layer interface. The observation that cracking suddenly and consistently stops under overpass bridges and immediately resumes after them provides strong evidence consistent with the findings of the stress/strain distributions generated from profiles with high surface temperature and high temperature gradients potentially causing TDFC. The paper provides recommendations for further study.

Natural rubber bearing incorporated with high toughness steel ring dampers

The behavior of natural rubber bearing incorporated with high toughness steel ring dampers (NRB-HTSRDs) is presented. These dampers are made of several steel rings, which are connected by weld in different configurations around the rubber bearing. The operational characteristics of this system including effective horizontal stiffness, secondary hardening, system stability, energy dissipation, equivalent viscous damping, and residual deformation were studied. The results showed that the energy dissipation in these dampers; is mainly revealed as yielding due to flexural deformation of the rings. All specimens of NRB-HTSRDs system; overally enhance the behavior and are considerably better than natural rubber bearing (NRB) or high damping rubber bearing (HDRB). The arrangement of HTSRD2, HTSRD4 and HTSRD6 have better behavior rather than HTSRD1, HTSRD3 and HTSRD5 due to modest initial stiffness at lower shear strains to control small lateral loads of the structure and undesirable effects on the flexibility of rubber bearing, and higher secondary hardening in larger shear strains that increases the energy dissipation and stability of the structure. Also, the specimens in which the rings have larger diameter and are only connected to the top and bottom plates, dissipate energy better than other specimens.

Fabric evolution of granular soils under multidirectional cyclic loading

Cyclic behavior of granular soils under multidirectional shaking is significantly different from that under unidirectional loading. In this study, a series of undrained simple shear simulations were conducted using a discrete-element method (DEM) under unidirectional and multidirectional loading conditions. Although the excess pore water pressure within a sample cannot reach the initial confining pressure, large shear strains of a similar amplitude still develop in samples under multidirectional loading. The simulation results further illustrate that granular soils have vastly different liquefaction resistance under different loading conditions. Evolution of soil fabric is also quantitatively studied in terms of inter-particle contacts and particle-void distribution. The same “stable state” of soil fabric will be reached under different multidirectional loading paths, which corresponds to that of a post-failure hardening state under unidirectional loading. The DEM study provides a new perspective in terms of microstructure evolution of granular soils under a variety of loading conditions.

Present-day crustal deformation revealed active tectonics in Yogyakarta, Indonesia inferred from GPS observations

We investigated the active crustal structure in Yogyakarta, Indonesia, using new and denser Global Positioning System (GPS) data. Deformation rate estimated from five years (2013–2018) of observations on 22 campaign might record broad deformation after the 2006 Mw7.8 Java tsunami earthquake and postseismic transient due to the 2006 Mw6.3 Yogyakarta earthquake. We conducted a decomposition method to obtain a short wavelength feature by removing those postseismic deformations from the observation data. The short wavelength pattern revealed active tectonics indicating a combination of E–W dip-slip motion and N–S left-lateral structure. A large maximum shear strain rate (>0.1 microstrain/yr) was estimated along the Opak fault while a large dilatation rate (<-0.1 microstrain/yr) was estimated around the Bantul Graben. The analysis result indicates important implications for crustal dynamics and assessing future seismic hazards potential in the Yogyakarta region.

Anisotropic yield surfaces after large shear deformations in pearlitic steel

Rolling contact fatigue often initiates in the highly deformed surface layer of railway rails. However, the behavior of pearlitic rail steels, subjected to such large shear strains, is not well known. Due to buckling, it is not possible to obtain the large shear deformation with tubular test bars. We have, therefore, developed a novel experimental methodology. Large shear strains (up to 1.13) were obtained by twisting cylindrical solid test bars under a compressive axial load. After that, these bars were re-machined into thin-walled tubular test bars. The re-machined bars were then used to characterize the behavior of the deformed material. Changes in both the elastic and plastic responses are observed, quantified, and discussed. We evaluate the ability of different yield criteria to model the experimentally measured yield surfaces. Three anisotropic yield criteria are considered: Hill (1948), Barlat's yld2004-18p, and Karafillis and Boyce (1993). The accuracies of these criteria are evaluated and compared to the estimated experimental uncertainty. Furthermore, cross-validation is used to investigate the predictive abilities of the yield criteria. It turns out that the Hill yield criterion fits and predicts the experimental data very well. Finally, the evolution of yield surfaces is found to be strongly dependent on the amount of plastic deformation defining the yield limit.

Transport of coexisting Ni-Cu sulfide liquid and silicate melt in partially molten peridotite

Transport of coexisting sulfide and silicate melts in partially molten peridotite contributes to the redistribution of chalcophile elements within the upper mantle as well as the genesis of magmatic Ni-Cu sulfide deposits, but has not been investigated systematically. Using laboratory experiments, theoretical calculations, and X-ray synchrotron microtomography, this study documents the topology and considers controls on the extraction of two immiscible liquids during partial melting of mantle peridotite. Under hydrostatic conditions, the measured dihedral angle at silicate melt-mineral-mineral junctions is 13.7–21.3°. Silicate melt is distributed along grain edges forming incompletely interconnected melt channels that disconnected by some dead ends at melt fractions ∼7–9 vol%. Application of theoretically predicted permeability (k∼10−14–10−16 m2) permits estimation of the extraction velocity of silicate melt of 0.7-11.1 μm/day within a single interconnected melt channel. In the absence of silicate melt, isolated sulfide droplets (3.77 vol%) show a sulfide-olivine-olivine dihedral angle of 91.5–101.3°. However, in the presence of silicate melt, sulfide droplets (average size ∼2.53 ± 2.14 μm, 1σ) are partially surrounded by silicate melt and stranded in triple junctions or melt pockets due to the limitation of the smallest dimension (0.3 μm) of melt channels. Thus, the extraction of sulfide liquid is highly restricted by these dead ends and the smallest dimension of melt channels during porous flow of silicate melt. In contrast, during large-strain shear deformation (strain ∼1.6–2.5), initially stranded sulfide droplets were elongated and extracted with silicate melt into liquid-rich sheets with a length of several hundred microns, constantly oriented at 14.3 ± 4.5° to the shear plane and antithetic to the shear direction. The angle is lower than that (18–30°) of those sheets containing sulfide liquid only, indicating that silicate melt dominates liquid-rich sheets. Driven by stress, silicate melt-dominated liquid-rich sheets open the appropriately oriented grain boundaries between silicate minerals, thus providing an efficient pathway for the extraction of sulfide liquid during deformation. When such sheet-like channels remain open, sulfide droplets (> millimeter-scale) can be potentially mobile through high strain domains of the upper mantle, contributing to the addition of chalcophile elements and the fertilization of the lithospheric mantle.

Study on effects of strong shear strain on recrystallized grain size of pure iron and microstructure control method

The effects of severe plastic deformation by orthogonal cutting on static recrystallization is discussed, and a simpler microstructure control method by using metal cutting and heat treatment is proposed. Pure iron was used as a test material. Large shear strain of 6.60 and 5.04 was induced by orthogonal cutting. Chips were straightened by skin-pass rolling to produce thin metal specimens. After rolling, the specimens were subjected to heat treatment under argon gas atmosphere at 500 °C and 600 °C for 1 min. Microstructure was analyzed by the SEM-EBSD method and mechanical properties were measured by a tensile test. Ultrafine grained sheets with average grain diameter of 0.2 µm were produced by cutting. It was observed that different recrystallized grain structure in different heat treatment temperature. The mechanical properties of the specimen could be controlled by heat treatment conditions. The proposed method is useful to produce an ultrafine grained sheet and to control mechanical properties.

Cartilage and collagen mechanics under large-strain shear within in vivo and at supraphysiogical temperatures

Human joints, particularly those of extremities, experience a significant range of temperatures in vivo. Joint temperature influences the mechanics of both joint and cartilage, and the mechanics of cartilage can affect the temperature of both joint and cartilage. Thermal treatments and tissue repairs, such as thermal chondroplasty, and ex vivo tissue engineering may also expose cartilage to supraphysiological temperatures. Furthermore, although cartilage undergoes principally compressive loads in vivo, shear strain plays a significant role at larger compressive strains. Thus, we aimed to determine whether and how the bulk mechanical responses of cartilage undergoing large-strain shear change (1) within the range of temperatures relevant in vivo, and (2) both during and after supraphysiological thermal treatments. We completed large-strain shear tests (10 and 15%) at four thermal conditions: 24∘C and 40∘C to span the in vivo range, and 70∘C and 24∘C repeated after 70∘C to explore mechanics during and after potential treatments. We calculated the bulk mechanical responses (strain-energy dissipation densities, peak-to-peak shear stresses, and peak-effective shear moduli) as of function of temperature and used statistical methods to probe significant differences. To probe the mechanisms underlying differences we assessed specimens, principally the type II collagen, with imaging (second harmonic generation and transmission electron microscopies, and histology) and assessed the temperature-dependent mechanics of type II collagen molecules within cartilage using steered molecular dynamics simulations. Our results suggest that the bulk mechanical responses of cartilage depend significantly on temperature both within the in vivo range and at supraphysiological temperatures, showing significant reductions in all mechanical measures with increasing temperature. Using imaging and simulations we determined that one underlying mechanism explaining our results may be changes in the molecular deformation profiles of collagen molecules versus temperature, likely compounded at larger length scales. These new insights into the mechanics of cartilage and collagen may suggest new treatment targets for damaged or osteoarthritic cartilage.

Modeling cyclic shearing of sands in the semifluidized state

SummaryLiquefaction is associated with the loss of mean effective stress and increase of the pore water pressure in saturated granular materials due to their contractive tendency under cyclic shear loading. The loss of mean effective stress is linked to loss of grain contacts, bringing the granular material to a “semifluidized state” and leading to development and accumulation of large cyclic shear strains. Constitutive modeling of the cyclic stress‐strain response in earthquake‐induced liquefaction and post‐liquefaction is complex and yet very important for stress‐deformation and performance‐based analysis of sand deposits. A new state internal variable named strain liquefaction factor is introduced that evolves at low mean effective stresses, and its constitutive role is to reduce the plastic shear stiffness and dilatancy while maintaining the same plastic volumetric strain rate in the semifluidized state. This new constitutive ingredient is added to an existing critical state compatible, bounding surface plasticity reference model, that is well established for constitutive modeling of cyclic response of sands in the pre‐liquefaction state. The roles of the key components of the proposed formulation are examined in a series of sensitivity analyses. Their combined effects in improving the performance of the reference model are examined by simulating undrained cyclic simple shear tests on Ottawa sand, with focus on reproducing the increasing shear strain amplitude as well as its saturation in the post‐liquefaction response.

Dynamic properties of EPS-sand mixtures using cyclic triaxial and bender element tests

In this study, a series of strain-controlled cyclic triaxial as well as bender element tests are carried out, so that the dynamic properties of mixtures of sand and expanded polystyrene (EPS) beads can be assessed under large and small-scale shear strains, respectively. The effect of various parameters such as shear strain amplitude, confining pressure (25 kPa, 50 kPa and 100 kPa) and EPS weight content (up to 2% by weight) on the small strain shear modulus, secant shear modulus and damping ratio is investigated. Laboratory results indicated that the values of shear velocity and shear modulus obtained from the bender element tests decrease with increasing EPS content. The results also revealed that the damping and shear modulus of the samples are highly dependent on the weight percentage of EPS, such that the increase in EPS content results in the increase of damping ratio up to 100% or even more under constant confining pressure. On the contrary, for all the values of confining pressure, the shear modulus of the mixture undergoes a significant reduction with increasing EPS content. Moreover, it is shown that the confining pressure has a important impact on both the soil damping ratio and shear modulus.

Effects of small and large shear histories on multiple liquefaction properties of sand with initial static shear

It has been reported that soils belonging to slope grounds show different types of liquefaction behavior than those belonging to horizontal grounds. Some research has also revealed that liquefaction histories can significantly affect the shear behavior of sandy soils. However, the combined effects of the slope angle and the magnitude of past shear histories on the liquefaction properties of soils have not been studied comprehensively. Based on this background, several multiple liquefaction tests with initial static shear were conducted on Toyoura sand. In each of these tests, a single specimen was sheared several times up to small or large double amplitude shear strain under a constant volume condition using a specially designed stacked-ring shear apparatus. The behavior of the Toyoura sand observed in these tests was discussed considering various perspectives, such as the increase in relative density, the induced anisotropy, the change in liquefaction resistance, and the shear strain accumulation. The findings of this study established that shear histories of smaller magnitude had relatively less influence on densification and induced anisotropy than those of larger magnitude. Moreover, shear histories of smaller magnitude also resulted in the relatively higher liquefaction resistance of sand specimens against the next cyclic shear, while the opposite trend was observed in the case of specimens subjected to shear histories of larger magnitude. Finally, shear strain accumulated less easily in tests with small shear histories than in those with large shear histories.

Methods for measuring large shear strains in in-plane torsion tests

The in-plane torsion test achieves true strains far beyond 1.0 for sheet metals, especially using specimens with circular grooves. The accurate measurement of these high strains is a challenge for the conventional digital image correlation (DIC). Thus, the determination of flow curves is limited and fracture strains for very ductile materials cannot be measured. A new grooved specimen is introduced to avoid strain localization. Shear stress and shear strain along a defined area in the groove are constant so that strains can be measured independently of the DIC system setting without error due to strain localization. Furthermore, three methods for the measurement of very high shear strains in the in-plane torsion test are presented: Firstly, the limit of the optical strain measurement is extended by multiple renewal of the digital image correlation (DIC) pattern on the samples. Secondly, the shear strain for the planar specimen is calculated exactly from the rotation angle curve. Lastly, a new incremental method is presented. This method enables to determine shear strains for plane and grooved specimen exactly by only measuring the torque and the angle of rotation. All methods were applied for three steel sheet materials namely DP1000, CP1000 and DC04. The equivalent strain in a grooved in-plane torsion test of sheet steel DC04 was determined as 3.3 with the new incremental method. Such high strains far exceed conventional methods for determining the flow curve.

Ovine Vocal Fold Tissue Fatigue Response to Accumulated, Large-Amplitude Vibration Exposure at Phonatory Frequencies.

Purpose The contribution of tissue mechanical response to vocal fatigue is poorly understood. This study investigated the fatigue response of vocal fold tissues to large-amplitude vibration exposure at phonatory frequencies, using an ex vivo ovine model. Method Twelve sheep vocal fold mucosal specimens were subjected to sinusoidal, simple-shear deformation for prolonged cycles, under a large but physiological shear strain (46%) in a frequency range of 100-230 Hz. The duration of shear varied from a critical vibration exposure limit of 1,040 s to 4 times the limit (4,160 s). Tissue viscoelastic response was quantified by the elastic shear modulus (G'), viscous shear modulus (G″), and damping ratio (G″/G'). Results Distinct response patterns were observed at different frequencies. G' and G″ generally decreased with vibration exposure at 100 Hz, whereas they generally increased with vibration exposure at 200 and 230 Hz. Statistically significant differences were found for G″ increasing with vibration exposure at 200 Hz and damping ratio decreasing with vibration exposure at 200 Hz. Significant increases with frequency were also found for all viscoelastic functions. Results suggested that the contribution of tissue viscoelastic response to vocal fatigue could be highly frequency dependent. In particular, increases in G″ with vibration exposure could lead to high phonation threshold pressures and difficulty sustaining phonation at higher frequencies following prolonged vocalization. Conclusion These preliminary findings may help us better understand vocal fatigue and recovery and should be corroborated by studies with human vocal fold tissues.

Three-Dimensional Analysis of Fragmentation Process of Al3Ti Platelet Particles in Al–Al3Ti Multiphase Alloy Deformed by Asymmetric Rolling

Asymmetric rolling (ASR) can introduce larger shear strains than symmetric rolling (SR). Therefore, application of ASR to metal-based multiphase alloy containing platelet particles will yield different particle distributions compared with SR. In this study, differences in the fragmentation behavior of Al3Ti platelet particles in Al–Al3Ti multiphase alloy after SR or ASR were investigated in three dimensions. The size of the Al3Ti platelet particles in the ASR-treated multiphase alloy was smaller than that in the SR-treated multiphase alloy. The platelet shape of the Al3Ti particles in the multiphase alloy deformed by rolling was retained because deformation by rolling occurs via plane strain. The results show that both SR and ASR can be used to modify the distribution of Al3Ti platelet particles in Al–Al3Ti multiphase alloy, but that ASR can change it more severely.

Smooth Flow in Diamond: Atomistic Ductility and Electronic Conductivity.

Diamond is the quintessential superhard material widely known for its stiff and brittle nature and large electronic band gap. In stark contrast to these established benchmarks, our first-principles studies unveil surprising intrinsic structural ductility and electronic conductivity in diamond under coexisting large shear and compressive strains. These complex loading conditions impede brittle fracture modes and promote atomistic ductility, triggering rare smooth plastic flow in the normally rigid diamond crystal. This extraordinary structural change induces a concomitant band gap closure, enabling smooth charge flow in deformation created conducting channels. These startling soft-and-conducting modes reveal unprecedented fundamental characteristics of diamond, with profound implications for elucidating and predicting diamond's anomalous behaviors at extreme conditions.

Assessment the Engineering Characteristics of the Smear Zone around PVDs Using Laboratory Tests

Smear zone is usually formed around the prefabricated vertical drains (PVD’s) due to mandrel driving. The geotechnical properties of the soil in this zone exhibit significant changes that affect the performance of the PVD’s. The most relevant property in this respect is the coefficient of permeability. So far, no serious attention is paid to investigate the effects of shearing under large shear strains on the geotechnical properties of the soft soil in Fao region. In this study, an extensive laboratory testing program was conducted to assess the characteristics of the smear zone with an emphasis on the permeability coefficient of Fao soft soil. The results show that the permeability of the smear zone is about 70% of the horizontal permeability of the intact soil. An attempt was made to estimate the extension of the shearing zone in the direct shear test. The analysis results indicate that thickness of the shearing zone is about (2.4) cm.&#x0D;