Large Strain Amplitudes Research Articles

Pure elastic stiffness of sand represented by response envelopes derived from cyclic triaxial tests with local strain measurements

The elastic stiffness of a fine sand at small to moderate strains ( $$\varepsilon \le 2 \times 10^{-4}$$ ) has been studied based on cyclic triaxial tests on cube-shaped samples with local strain measurements. Three samples with different densities (between very loose and very dense) were tested at up to 21 average stresses in succession (variation of mean pressure and stress ratio). At each average stress cycles were applied in six different directions, as a result of a simultaneous sinusoidal oscillation of the axial and lateral effective stress. Ten preconditioning cycles with larger strain amplitudes $$\varepsilon ^{\mathrm{ampl}}= 3 \times 10^{-4}$$ per polarization were intended to induce a shakedown. An almost purely elastic response was then observed during the 5 subsequent cycles per polarization with lower strain amplitudes $$\varepsilon ^{\mathrm{ampl}}= 2 \times 10^{-4}$$ . The stress and strain paths measured during the latter ones were used to derive the components of the incremental elastic stiffness tensor $${\mathsf{E}}= \{E_{PP}, E_{PQ}, E_{QP}, E_{QQ}\}$$ at a given average stress. The analysis of $${\mathsf{E}}$$ is based on all 60 reversal points and the corresponding stress and strain points lying in a certain distance $$\Delta \varepsilon$$ (e.g. $$10^{-4}$$ ) from the reversals. A graphical presentation of $${\mathsf{E}}$$ by means of response envelopes is shown. They are used to calibrate the hyperelastic stiffness incorporated into a new hypoplastic constitutive model.

The first normal stress difference of non-Brownian hard-sphere suspensions in the oscillatory shear flow near the liquid and crystal coexistence region.

We carry out a numerical study to investigate the dynamics of non-Brownian hard-sphere suspensions near the liquid and crystal coexistence region in small to large amplitude oscillatory shear flow. The first normal stress difference (N1) and related rheological functions are carefully analyzed, focusing on the strain stiffening phenomenon, which occurs in the large strain amplitude region. Under oscillatory shear, we observe several unique behaviors of N1. A negative nonzero mean value of N1 (N1,0) is observed for the applied strain amplitudes. The change of the sign, from negative to positive, at the maximum value of N1 (N1,max) is observed at a specific point, which is not consistent with the critical strain amplitude (γ0,c) at which the modulus begins to deviate from linear viscoelasticity. The behavior of N1 in the oscillatory shear flow is different from that of N1 in steady shear flow, that is, the characteristics of N1 in strain stiffening and shear thickening are quite distinguished from each other. We also perform structural analysis to confirm the relationship between the rheological properties and microstructure of the suspension. A strong correlation is observed between the global bond order parameter (Ψ6) and the distortions in both nonlinear shear and normal stresses. The most noticeable characteristic is captured through the maximum of the global bond order parameter (Ψ6,max). The strain amplitude at the slope change of Ψ6,max corresponds to the point where a unique behavior of N1 is observed, i.e. the change of the sign in N1,max, but a strong correlation is not captured at γ0,c. This demonstrates that the normal stress responds to particle ordering more sensitively than other rheological functions based on shear stress like dynamic moduli. As far as we are concerned, the behavior of N1 has rarely been fully explored and related with the strain stiffening of non-Brownian suspensions so far. Therefore, this study has significance as the first report to strictly analyze strain stiffening along with the first normal stress difference N1.

Reinforcement and Payne effect of hydrophobic silica filled natural rubber nanocomposites

Nanoparticles significantly reinforce rubber and enhance nonlinear rheological behaviors while the underlining mechanisms are not yet clear. Herein a time-concentration superposition (TCS) principle is employed for constructing master curves of high-frequency linear rheology of hydrophobic silica filled natural rubber compounds with reference to the matrix. The effect of dynamics retardation of the matrix disclosed by the TCS principle is explained by the time-dependent diffusion double reptation model that predicts linear rheology well covers the TCS mater curves in the nonterminal region. With aid of the convective constrain release model, the Payne effect of the compounds is shown to originate mainly from the filler-promoted disentanglement of chains in the matrix whose local strain amplitude is amplified by the filler. Furthermore, the filler is shown to be able to enhance both the elastic and viscous nonlinearities of compounds under large strain amplitudes.

Effect of hydrothermal treatment on linear and nonlinear rheological properties of highland barley gels

Highland barley gels were subjected to hydrothermal treatment, and the rheological properties of both small and large strain amplitude oscillation shear (SAOS/LAOS) were investigated in this study. The results showed that untreated highland barley gels formed a wider linear viscoelastic region (LVE) than hydrothermal-treated gels, and the storage moduli (G′) & loss moduli (G″) decrease as the hydrothermal treatment time increased. In particular, the LAOS behavior of highland barley gels in strain sweep was changed from Type Ⅳ strong strain overshoot to Type Ⅰ strain thinning by hydrothermal treatment. The frequency dependence of the viscoelastic moduli (G'∝ω0.41−0.74 and G''∝·ω0.41−0.77) for hydrothermal gels was classified as an entangled network. The creep behavior fitted well with a four-element Burgers model (R2>0.93). Moreover, after 10 min treatment, hydrothermal treatment had changed the gels from elastic-dominated to viscous-dominated, and the strain-stiffening/shear-thinning properties of highland barley gels also increased.

Influence of strain histories on liquefaction resistance of sand

The liquefaction resistance of sand increases with cyclic pre-shearing and pre-shaking as a result of earthquakes if the strain level in the pre-shearing is small. When larger shear strains are imposed, liquefaction resistance decreases. These complicated effects of pre-shearing histories on the liquefaction resistance are investigated in this study through a series of cyclic triaxial tests. Various combinations of cyclic stress amplitude and number of cycles of pre-shearing are examined. The tested sand is Toyoura Sand at 45% relative density, under a confining pressure of 50 kPa. Test results indicate that for the range of shear strain amplitude in pre-shearing smaller than 0.35%, the liquefaction resistance increases with pre-shearing. The increase in the liquefaction resistance depends strongly on the volumetric strain in the pre-shearing, and several effects of the shear stress amplitude and number of cycles can be negligible. Small volumetric strain of the order of 1% doubled the liquefaction resistance. Meanwhile, in the range of shear strain amplitude larger than 0.6%, the liquefaction resistance decreases. The liquefaction resistance decreases as the shear strain amplitude increases. Shear strain amplitude is one of the factors dominating this degrading effect, and the volumetric strain exerts beneficial effects to a certain extent. In this study, another series of tests are conducted to investigate the combined effects of small and large strain amplitude pre-shearing. It is observed that small shear strain pre-shearing cycles subsequent to large shear strain cycles erased the degrading effect of the latter. However, a large shear strain pre-shearing after small strain cycles degrades the beneficial effect of the small shear strain pre-shearing cycles previously applied to the specimens; however, the effects of the former small strain pre-shearing remains.

Evolution of Payne effect of silica-filled natural rubber in curing process

Vulcanisation is the key process for determining the final properties of elastomers due to the relationship between curing condition and viscoelastic behaviour. This study focuses on the variations in the dynamic behaviour of silica-filled natural rubber caused by crosslinking. The rubber samples with different degrees of curing (DOC) are prepared by thermal quenching during the crosslinking process. The strain sweep mode is used to study the Payne effect. The Kraus model is used to fit the test data. The relationship between the parameters of Kraus model and DOC is obtained at small strain (< 10%). The storage modulus at small strain amplitudes (usually < 0.01%) $$ G^{\prime}_{ 0} $$ is proportional to DOC; however, the storage modulus at large strain amplitudes $$ G^{\prime}_{\infty } $$ has small changes with DOC. The characteristic value of the strain amplitude $$ \gamma_{\text{C}} $$ shifts to large strain and the maximum loss modulus $$ G^{\prime\prime}_{\text{m}} $$ decreases with the increase of DOC. In addition, a deviation between Kraus model and experiment is observed when the strain is larger than 10%, and the loss modulus increases with the increase of strain amplitude. The deviation decreases when DOC increases. The mechanism for this deviation is discussed and the interaction between silica filler and rubber chain might be responsible for the observed deviation.

EFFECT OF IONIC LIQUID MODIFIED MWCNT ON THE RHEOLOGICAL AND MICROSTRUCTURAL DEVELOPMENTS IN STYRENE BUTADIENE RUBBER NANOCOMPOSITES

ABSTRACT Ionic liquid modified multiwalled carbon nanotube (MWCNT) based styrene–butadiene rubber (SBR) nanocomposites were prepared with the two-roll mill mixing method, and the rheological measurements were used to study the dispersion of MWCNTs on a microscopic scale and its compatibility with the SBR matrix. Viscous liquid-like rheological behavior at low MWCNT loadings and pseudo-solid-like rheological response at high MWCNT loadings were observed, showing the gradual transformation from individual structures of MWCNTs to polymer bridged MWCNT networks. A decrease in the mobility of SBR macromolecular chains by the geometric confinement of three-dimensional networks of MWCNTs further confirms the interdeveloped pseudo-solid behavior of filled composites. Dynamic viscoelasticity data have been compared with the theoretical Carreau–Yasuda equation. Transmission electron microscopy of the samples reveals that MWCNTs are randomly dispersed in the rubber matrix. Finally the nature of the filler association and its role in the nonlinear viscoelastic properties at large strain amplitudes were investigated.

A novel high-entropy alloy with excellent damping property toward a large strain amplitude environment

A new Fe60Mn20Co5Cr15 high-entropy alloy with excellent damping performance was synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). During SPS, the supersaturated solid solution produced in MA was transformed into a stable microstructure consisting of body-centered cubic (BCC) phase, face-centered cubic (FCC) phase and small amount of σ phase. The effects of different annealing temperature on phase evolution, microstructure, mechanical properties and damping behavior were investigated. The results of compressive properties indicated a reduction in strength but an increase in plastic strain when the alloy was annealed at high temperature. Compared with the SPSed bulk, the damping properties were improved significantly by the annealing process, which was related to the number of defects and the morphology of magnetic domains. For the samples annealed at 900 °C, a maximum of internal friction (IF) Q−1 = 0.076 was achieved and the corresponding strain amplitude was approximately 6×10−4, overwhelming the conventional damping alloys. Besides, a high damping capability of the alloy can be achieved in a wider strain range, which means that it can act as a promising candidate toward a larger strain amplitude environment.

Asymmetric cyclic response of tensile pre-deformed Cu with highly oriented nanoscale twins

History-independent, stable and symmetric cyclic response has been detected in as-deposited bulk polycrystalline Cu with highly oriented nanotwins [Nature 551 (2017) 214–217]. In this study, to deepen the understanding of cyclic deformation in nanotwinned (NT) structures, small levels of tensile pre-strains were applied on NT-Cu, followed by strain-controlled symmetric tension-compression cyclic tests. Distinct from the symmetric cyclic response of as-deposited NT-Cu, the magnitude of the maximum stress in tension is much larger than that of the minimum stress in compression, indicating that the cyclic response of tensile pre-deformed NT-Cu is highly asymmetric. The degree of its cyclic asymmetry gradually decays as the number of cycles or the plastic strain amplitude is increased. The tensile pre-deformed NT-Cu recovers to its symmetric cyclic response after cyclic deformation at sufficiently large plastic strain amplitude, analogous to that detected in as-deposited NT counterparts. Molecular dynamics simulations and microstructural observations revealed that the observed asymmetric cyclic response is mainly related to the activation and movement of threading dislocations with extended misfit dislocation tails lying on the twin boundaries (TBs) during tensile pre-deformation. During cyclic deformation, threading dislocations in adjacent twin interiors tend to link their long tails with one another to form correlated necklace dislocations (CNDs) with a symmetric structure. The CNDs move back-and-forth along the twin boundaries without directional slip resistance, contributing to the transition from asymmetric to symmetric cyclic response of NT-Cu.

Non-linear rheological (LAOS) behavior of sourdough-based dough

During processing, wheat dough is known to undergo large deformation led by mixing and fermentation processes. This deformation is much more pronounced when sourdough is used in the recipe of wheat dough whose gluten is considerably hydrolyzed during sourdough fermentation. This causes deeper effects on rheological properties and shelf life of bakery products. Traditional small amplitude oscillatory tests do not enable us to comprehend the viscoelasticity under large deformations. In this respect, large amplitude oscillatory shear (LAOS) tests are useful for accurate characterization of the non-linear mechanical response. This study, therefore, is undertaken to investigate the non-linear mechanical response of dough prepared with different amounts of sourdough (0, 10, 20 30 and 40%) in a strain values ranging from 0.005 to 200% (frequency at 10 rad/s). As a result, sourdough was determined to have considerable effects on the non-linear viscoelastic response of dough. Strain-stiffening and shear-thinning behaviors were considerably influenced by sourdough incorporation and the dough started to show strain-softening and lowered shear-thinning behavior after giving a peak around at 100% strain due to the onset of the breakdown of the gluten network and suspension of starch matrix as consequence of the metabolic activity of the starter culture (Lactobacillus brevis E25) used in the preparation of sourdough. The physicochemical (pH and TTA), microbiological properties (LAB count) and extensographic properties were also shown to support the LAOS results. LAOS tests could be effectively and clearly used to reveal the effect of processing conditions (sourdough content and deformation by large strain amplitude) on the non-linear mechanical response of wheat dough.

Fatigue resistance of dual-phase NiTi wires at different maximum strain amplitudes

Known by their functional shape memory and superelastic properties, aligned with an excellent biocompatibility, near equiatomic NiTi alloys are vastly used as biomaterials. In various applications, such as endodontic files and cardiovascular stents, NiTi components are subjected to aggressive fatigue conditions, making fatigue resistance and mechanisms relevant to the materiaĺs development. In this context, heat treatments can be a powerful tool to improve the fatigue life and efforts have been made to understand and predict the fatigue behavior of these alloys in different conditions. In this work, initially superelastic near equiatomic Ni-rich wires were heat-treated at 400 °C and 450 °C and the ε × Nf curve was obtained. Rotating-bending strain-controlled fatigue tests were performed at maximum strains varying from 1% to 5% at 37 °C. The results showed that both samples exhibited large fatigue resistance and similar fatigue behavior through the different maximum strains, and thus, treatments within the range of temperature from 400 °C to 450 °C are recommended to obtain NiTi components with high fatigue life for large maximum strain amplitudes.

Influence of Depositional Method on Dynamic Properties of Granular Soil

The behaviour of granular soil is mainly dependent upon the nature and arrangement of particles, which in turn affect fabric anisotropy. It has been known for many years that depositional method plays an important role in the results of laboratory testing of granular soils. Despite extensive studies on the dynamic properties of granular soil, previous research has lacked a quantitative study of the effects of depositional methods on the dynamic properties of the granular soil. The primary objective of the current study was to evaluate the effect of fabric anisotropy on the dynamic properties of granular soil for practical applications. The influence of depositional method, mean effective consolidation stress, shear strain amplitude and relative density on the maximum shear modulus (Gmax), shear modulus curve (G-γ), normalized modulus curve (G/Gmax-γ) and damping curve (D-γ) of pure sand, pure gravel and sand-gravel mixtures is investigated. The results of the tests indicate that depositional method has a significant effect on Gmax that this effect was more pronounced for the pure sand specimens than for the pure gravel or sand-gravel mixture specimens. However, the depositional method had no significant effect on the shear modulus at large shear strain amplitudes. The effects of depositional method on the G/Gmax-γ and D-γ curves are dependent on effective confining pressure and relative density.

Superior Stretchable Conductors by Electroless Plating of Copper on Knitted Fabrics

Stretchability is critical to wearable devices to afford a large amplitude strain. Herein, a uniformly nanoscale copper layer was successfully deposited onto the surface of a knitted fabric by a fa...

Insight into the weak strain overshoot of carbon black filled natural rubber

Weak strain overshoot (WSO) of loss modulus accompanying with strain softening under large amplitude oscillatory shear deformation is a common phenomenon that occurs in many systems but is still far from being clarified. Study about WSO has a strong practical significance, for it is directly related to sharp increase of energy dissipation of elastomer nanocomposites experiencing dynamic deformation of large strain amplitudes. Herein a systematical investigation was performed on WSO of uncured natural rubber (NR) and its low-loading carbon black compounds and a frequency-temperature-volume fraction diagram for the onset of WSO is firstly proposed to shed light on the mechanisms. A comparison of rheology behaviors of uncured polyisoprene rubber and NR and cured polyisoprene rubber suggests that WSO in NR originates from the non-isoprene fraction. Fourier-transform infrared spectroscopy measurement suggests the dissociation of hydrogen bonding at high temperatures, which accelerates the stress relaxation.

Simplified simulation of the installation of vibro-piles in water saturated soil

This paper presents a novel and simplified approach to simulate the effects of the vibro-pile installation on the deformation of deep excavation shoring walls at high ground water levels. Although commonly-used finite element simulations provide acceptable predictions of the wall displacements caused by underwater excavations, anchor installation, or pit dewatering processes, they could not explain the unexpected large wall movements measured in different excavations during the vibro-pile installation stage. Previous dynamic finite element simulations of the vibro-installation of a single pile showed that after few cycles the effective stress in the soil surrounding the pile reduces almost near to zero. The soil region affected was called “the liquefaction zone”. Due to the waves emanating from the pile, the soil beyond the liquefaction zone is subjected to a (high-) cyclic loading, i.e. a large number of strain cycles with small amplitude. When the soil behavior is modeled with hypoplasticity or elastoplasticity, its response to these small strain amplitudes is nearly (hypo)elastic resulting in an erroneous accumulation of stress or strains, see Osinov (2017) [1]. Based on this observation, Osinov et al. (2015) [2,3] suggested that the accumulation effects caused by many cycles of small strain amplitude could explain the large wall displacements observed during the pile installation. Following this idea, in this paper we model the soil behavior with a combination of hypoplasticity (which can be applied to cycles of large strain amplitudes and monotonic paths) and the high cyclic accumulation (HCA) model, which is able to extrapolate the accumulation of stress/strain caused by a large number of cycles of small strain amplitude (ϵampl<10−3). The pile installation is not explicitly modeled, but its effects are incorporated in the numeric model by applying a field of cyclic strain amplitudes around each pile. Using this combined constitutive model and simulation technique, the behavior of the shoring of an excavation pit in Potsdamer Platz, in Berlin was simulated under quasi-static conditions in a finite element program. The obtained simulation results are in good agreement with the horizontal displacement of the diaphragm wall measured during the entire construction stages, including the underwater excavation and the pile installation.

The influence of periodic shear on structural relaxation and pore redistribution in binary glasses

The evolution of porous structure and local density, and associated changes of potential energy in binary glasses under oscillatory shear deformation, are investigated using molecular dynamics simulations. The porous glasses were initially prepared via a rapid thermal quench from the liquid state across the glass transition temperature and allowed to phase separate and solidify at constant volume, thus producing an extended porous network in an amorphous solid material. We find that under periodic shear, the potential energy decreases over consecutive cycles due to gradual rearrangement of the glassy material, and the minimum of the potential energy after thousands of shear cycles is lower at larger strain amplitudes. Moreover, with increasing cycle number, the pore size distributions become more skewed toward larger length scales, where a distinct peak is developed and the peak intensity is enhanced at larger strain amplitudes. The numerical analysis of the local density distribution functions demonstrates that cyclic loading leads to formation of higher density solid domains and homogenization of the regions with reduced density.

An ultrafast symmetry switch in a Weyl semimetal.

Topological quantum materials exhibit fascinating properties1-3, with important applications for dissipationless electronics and fault-tolerant quantum computers4,5. Manipulating the topological invariants in these materials would allow the development of topological switching applications analogous to switching of transistors6. Lattice strain provides the most natural means of tuning these topological invariants because it directly modifies the electron-ion interactions and potentially alters the underlying crystalline symmetry on which the topological properties depend7-9. However, conventional means of applying strain through heteroepitaxial lattice mismatch10 and dislocations11 are not extendable to controllable time-varying protocols, which are required in transistors. Integration into a functional device requires the ability to go beyond the robust, topologically protected properties of materials and to manipulate the topology at high speeds. Here we use crystallographic measurements by relativistic electron diffraction to demonstrate that terahertz light pulses can be used to induce terahertz-frequency interlayer shear strain with large strain amplitude in the Weyl semimetal WTe2, leading to a topologically distinct metastable phase. Separate nonlinear optical measurements indicate that this transition is associated with a symmetry change to a centrosymmetric, topologically trivial phase. We further show that such shear strain provides an ultrafast, energy-efficient way of inducing robust, well separated Weyl points or of annihilating all Weyl points of opposite chirality. This work demonstrates possibilities for ultrafast manipulation of the topological properties of solids and for the development of a topological switch operating at terahertz frequencies.

Simulation and Experimental Test in Tensile Behaviour of Austenitic Stainless Steels

In the systems of fuel cell (FC) and nuclear safety (NS) components many liners of ultra-high pressure tanks and pipes are directly exposed to hydrogen. Austenitic stainless steels are used as material for FC and NS components because of their high resistance to hydrogen intrusion. It is reported that hydrogen degrades mechanical properties of metals significantly. In the hydrogen-charged specimen of SUS 304, a desired model would be able to capture the mechanisms found in experimental testing like large strain elasticity, rate dependence, amplitude dependence, creep and damage. Thus, a prediction of material failure/fracture, including its behavior at large plastic deformations is of importance. To validate existing failure models, the finite element (FE) simulations are used in terms of dependence on length scale and strain state. Restrictions made the selection limited to, in Abaqus, already existing models. Axisymmetric simulations are performed in Abaqus to verify the material model required in order to capture the necking phenomenon in tensile testing. The elasto-plastic modeling in the FE simulations is directed ultimately to initiation and propagation of tension processes. Furthermore, numerical simulation results using the sub-models of crack-tip meshes are discussed. In our experiments, the tensile test system MTS at a crosshead speed of 1 mm/s are conducted, which enabled accurate monitoring of displacements on the specimen surfaces. When a material reached the limit of its capacity to carry further loading, deformations localize into necking and became highly dependent on the length over which the strain evaluation is performed the length scale.

Relations between static and dynamic moduli of sedimentary rocks

ABSTRACTStatic moduli of rocks are usually different from the corresponding dynamic moduli. The ratio between them is generally complex and depends on several conditions, including stress state and stress history. Different drainage conditions, dispersion (often associated with pore fluid effects), heterogeneities and strain amplitude, are all potential reasons for this discrepancy. Moreover, comparison of static and dynamic moduli is often hampered and maybe mistaken due to insufficient characterization of anisotropy.This paper gives a review of the various mechanisms causing differences between static and dynamic moduli. By careful arrangements of test conditions, it is possible to isolate the mechanisms so that they can be studied separately. Non‐elastic deformation induced by the large static strain amplitudes is particularly challenging, however a linear relationship between non‐elastic compliance and stress makes it possible to eliminate also this effect by extrapolation to zero strain amplitude.To a large extent, each mechanism can be expressed mathematically with reasonable precision, thus quantitative relations between the moduli can be established. This provides useful tools for analyses and prediction of rock behaviour. For instance, such relations may be used to predict static stiffness and even strength based on dynamic measurements. This is particularly useful in field situations where only dynamic data are available. Further, by utilizing the possibility for extrapolation of static measurements to zero strain amplitude, dispersion in the range from seismic to ultrasonic frequencies may be studied by a combination of static and dynamic measurements.

Stretching PEO–PPO Type of Star Block Copolymer Gels: Rheology and Small-Angle Scattering

Cross-linked Tetronic star block copolymer gels, based on poly(ethylene oxide) and poly(propylene oxide), behave quite regular with respect to mechanical properties, but exhibits unusual absence of structural response to strain. The elastic response is linear up to more than 100% strain, with a steady-state modulus of the order of 0.01 MPa after an initial stress relaxation. Neutron and X-ray scattering experiments show a consistent but unexpected response to uniaxial strain, with no changes in characteristic molecular dimensions. Upon strain beyond about 100%, that is, when the stress-strain curve is no longer linear, structural texture appears and becomes even more pronounced upon further strain, thus, indicating alignment of the self-assembled hexagonally ordered cylindrical micelles with the cylinder-axis perpendicular to the strain. It is proposed that the main structural response to large-amplitude strain is related to a layer-dominated structure of cross-linked star molecules.