Intrinsic Shear Research Articles

Synthesis of Polyacrylamide with Superb Salt-Thickening Performance

Vinyl glycoside (GnR) was prepared and reacted with acrylamide (AM) to synthesize a novel AM copolymer (AM/GnR) through redox free-radical polymerization in aqueous solution. Fourier transform infrared spectroscopy, 1H NMR spectroscopy, and scanning electron microscopy were applied to characterize the polymer. Several performance evaluations such as intrinsic viscosity, temperature resistance, salt tolerance, and shear resistance were also conducted. Experiment results demonstrated that the introduced GnR could endow the copolymer with excellent salt tolerance capability and shear resistance ability. The superior salt tolerance performance of AM/GnR provided some clues to the synthesis of salt resistant polymer.

Laboratory measurements of ‘porosity‐free’ intrinsic Vp and Vs in an olivine gabbro of the Oman ophiolite: Implication for interpretation of the seismic structure of lower oceanic crust

AbstractIn order to determine ‘porosity‐free’ intrinsic ultrasonic compressional (Vp) and shear wave (Vs) velocities and Vp/Vs of an olivine gabbro from the Oman ophiolite, we developed a new experimental system using a piston‐cylinder type high‐pressure apparatus. The new system allowed us to measure velocities at pressures ranging from 0.20 to 1.00 GPa and at temperatures up to 300°C for Vp and 400°C for Vs. At room temperature, the Vp and Vp/Vs increase rapidly with pressure up to 0.40 GPa, while between 0.45 and 1.00 GPa the increase is more gradual. The change in increasing rate is attributed to closure of porosity at pressures above 0.45 GPa. Based on the linear regression of data obtained at higher pressures (0.45–1.00 GPa) and extrapolation to the lower pressures, combined with temperature derivatives of velocities of the sample measured at 1.00 GPa, we determined the intrinsic Vp and Vs of the sample as a function of pressure (P, in GPa) and temperature (T, in °C). The intrinsic velocities can be expressed as Vp (km/s) = 7.004 + 0.096 × P − 0.00015 × T, and Vs (km/s) = 3.827 + 0.007 × P − 0.00008 × T. We evaluated the intrinsic Vp and Vs of the olivine gabbro at oceanic crustal conditions and compared them with a velocity depth‐profile of the borehole seismic observatory WP‐2 area in the northwestern Pacific Basin. Although the intrinsic Vp (∼7.0 km/s) and Vs (∼3.8 km/s) for the olivine gabbro studied are comparable to those of seismic layer 3 in the WP‐2 area, the estimated vertical gradients of intrinsic velocities are significantly smaller than those reported from layer 3. These results suggest that velocity profiles of layer 3 in the WP‐2 area may reflect the presence of a minor porosity in lower oceanic crust, which closes with increasing depth and/or continuous changes in mineralogy of layer 3 rocks.

Viscoelastic shear properties of porcine temporomandibular joint disc.

To investigate the intrinsic viscoelastic shear properties in porcine TMJ discs. Twelve fresh porcine TMJ discs from young adult pigs (6-8months) were used. Cylindrical samples (5mm diameter) with uniform thickness (~1.2mm) were prepared from five regions of the TMJ disc. Torsional shear tests were performed under 10% compressive strain. Dynamic shear was applied in two methods: 1) a frequency sweep test over the frequency range of 0.1-10rad/s with a constant shear strain amplitude of 0.05rad and 2) a strain sweep test over the range of 0.005-0.15rad at a constant frequency of 10rad/s. Transient stress relaxation tests were also performed to determine the equilibrium shear properties. As the frequency increased in the frequency sweep test, the dynamic shear complex modulus increased, with values ranging from 7 to 17kPa. The phase angle, ranging from 11 to 15 degrees, displayed no pattern of regional variation as the frequency increased. The dynamic shear modulus decreased as the shear strain increased. The equilibrium shear modulus had values ranging from 2.6 to 4kPa. The posterior region had significantly higher values for dynamic shear modulus than those in the anterior region, while no significant regional difference was found for equilibrium shear modulus. Our results suggest that the intrinsic region-dependent viscoelastic shear characteristics of TMJ disc may play a crucial role in determining the local strain of the TMJ disc under mechanical loading.

Elasticity dominates strength and failure in metallic glasses

Two distinct deformation mechanisms of shearing and volume dilatation are quantitatively analyzed in metallic glasses (MGs) from the fundamental thermodynamics. Their competition is deduced to intrinsically dominate the strength and failure behaviors of MGs. Both the intrinsic shear and normal strengths give rise to the critical mechanical energies to activate destabilization of amorphous structures, under pure shearing and volume dilatation, respectively, and can be determined in terms of elastic constants. By adopting an ellipse failure criterion, the strength and failure behaviors of MGs can be precisely described just according to their shear modulus and Poisson's ratio without mechanical testing. Quantitative relations are established systematically and verified by experimental results. Accordingly, the real-sense non-destructive failure prediction can be achieved in various MGs. By highlighting the broad key significance of elasticity, a “composition-elasticity-property” scheme is further outlined for better understanding and controlling the mechanical properties of MGs and other glassy materials from the elastic perspectives.

Elasticity of the Heart, Problems and Potentials

The biomechanical integrity of the human heart is critically important, with various diseases affecting the active or passive stiffness of the myocardium. Although manual palpation is an integral part of many diagnostic procedures and is of undisputed clinical value, its applicability is limited to superficial regions. Furthermore, it remains a qualitative not quantitative method. These limits, however, may be overcome with elastography, an exciting new imaging modality that enables noninvasive assessment of biomechanical properties deep inside the body. The general concept is based on the intertwined relationship between the local propagation properties of shear waves and the underlying, intrinsic mechanical shear parameters. Elasticity imaging already has demonstrated very promising results in breast cancer, liver fibrosis staging, and neurodegenerative diseases. However, its application to the cardiovascular system is rather novel, and its challenges include data acquisition and mechanical parameter reconstruction. This article discusses the requirements for performing quantitative elastography of the heart, as well as current developments and future perspectives.

Estimation of microstructure of titania particulate dispersion through viscosity measurement

Aggregate structure and its variation with shear rate are investigated using viscosity data of titania (TiO2) dispersion consisting of anatase titania particles of 200nm in diameter and ethylene glycol. The particle volume fraction ϕ ranges from 0.01 to 0.1 and the viscosity measurement is performed at shear rates 1–201s−1. The viscosity data exhibit that the dispersion is shear-thinning and titania particles exist in the form of aggregates in the dispersion. The Krieger–Dougherty equation is used to obtain the intrinsic viscosity which is related with the aggregate structure and size. It is found that the intrinsic viscosity for ϕ ≤0.04 is different from that for ϕ ≥0.05 where gel-like behavior is observed in sedimentation test. A scaling relation is applied to correlate the intrinsic viscosity at low ϕ with the aggregate structure characterized by fractal dimension df and exponent for shear dependence of aggregate size m. Logarithmic linearity between the intrinsic viscosity and shear rate indicates that the aggregates are rigid and thus m is close to 1/3. Therefore, df is 1.9813. Yield stress as a function of ϕ also provides information on m and df at the shear rate just above yield point. The fractal dimension df from the yield stress data is 1.9818 when m=1/3, which is nearly equal to 1.9813 from the intrinsic viscosity data.

Rotator Cuff Tears in the Throwing Athlete

Tears of the rotator cuff, both partial, and less commonly, full thickness, are relatively common in the throwing athlete. The rotator cuff is subjected to enormous stresses during repetitive overhead activity. The supraphysiological strains, especially when combined with pathology elsewhere in the kinetic chain, can lead to compromise of the cuff fabric, most commonly on the undersurface where tensile overload occurs. Exacerbation by a tight posterior capsular, anterior instability, and internal impingement render the cuff progressively compromised, with intrinsic shear stresses and undersurface fiber failure. Advances in imaging technology, including contrast magnetic resonance imaging, dynamic ultrasound, and arthroscopic visualization have enhanced our understanding of cuff pathology in this athletic population. Unfortunately, this has not yet translated into how to best approach these athletes to return them to their previous level of activity. Nonoperative management remains the mainstay for most throwers, with arthroscopic debridement an effective surgical option for those with refractory symptoms. Despite technological advances in cuff repair in the general population, comparable outcomes have not been achieved in high-level throwers. Widespread appreciation that securing the cuff operatively will likely end an athletes' throwing career has led to adopting a surgical approach that emphasizes debridement over repair for nearly all partial and full-thickness tears. Whether advances in surgical technique will ultimately permit definitive and lasting repairs that allow overhead throwers to return to their previous level of sports remains unknown at this time.

First-principles study on the structure, elastic properties, hardness and electronic structure of TMB4 (TM=Cr, Re, Ru and Os) compounds

The structural formation, elastic properties, hardness and electronic structure of TM B 4 ( TM =Cr, Re, Ru and Os) compounds are investigated using first-principles approach. The value of C 22 for these compounds is almost two times bigger than the C 11 and C 33 . The intrinsic hardness, shear modulus and Young's modulus are calculated to be in a sequence of CrB 4 >ReB 4 >RuB 4 >OsB 4 , and the Poisson's ratio and B / G ratio of TM B 4 follow the order of CrB 4 <ReB 4 <RuB 4 <OsB 4 . The intrinsic hardness of CrB 4 and ReB 4 by LDA is bigger than 40 GPa. The high hardness of TM B 4 compounds is derived from the feature of B–B bonds cage and higher C 22 value. The B–B covalent bonds as bonds cage enhances the resistance to shear deformation and improve the hardness. We predict that the TM B 4 compounds with CrB 4 -type are the potential superhard materials. The first-principles calculations show that the intrinsic hardness of CrB 4 and ReB 4 are bigger than 40 GPa, which are the potential superhard materials due to the B–B bonds cage structure. • The intrinsic hardness of CrB 4 and ReB 4 is bigger than 40 GPa. • The hardness of TM B 4 is calculated to be in a sequence of CrB 4 >ReB 4 >RuB 4 >OsB 4 . • The trend of hardness for TM B 4 is consistent with the variation of elastic modulus. • The C 22 value of TM B 4 is bigger than that of C 11 and C 33 . • The high hardness of TM B 4 is originated from the B–B bonds cage.

Mass to light ratio of galaxies and gravitational lensing

We investigate the potential of constraining the mass to light ratio of field galaxies using weak lensing shear and flexions. A suite of Monte Carlo simulations are used to generate weak lensing observations with different noise models. Using mock data, we find that the inclusion of flexions can improve the estimate of foreground halo parameters, but the details are strongly dependent on noise in the model. In the intrinsic noise limit, both shear and flexions are promising tools to study the mass to light ratio of galaxies. However, if the noise model of flexions follows the form described by Rowe et al., there is only ∼5% improvement in the constraints even with next generation lensing observations.

Temperature-induced ductile-to-brittle transition of bulk metallic glasses

Uniaxial tensile and uniaxial compressive tests for Zr-based bulk metallic glasses (BMGs) were conducted at room and cryogenic temperatures, respectively. It was observed that both the change of macroscopic fracture mode from ductile shear fracture to brittle normal tensile fracture and microscopic fracture feature from micron-scaled vein patterns to nano-scaled dimples with decreasing test temperatures were identified, indicating a significant ductile-to-brittle transition (DBT) behavior. The mechanism of DBT behavior was revealed by the competition between the intrinsic critical shear strength τ0 and critical tensile strength σ0 at different temperatures.

Low-dimensional intrinsic material functions for nonlinear viscoelasticity

Rheological material functions are used to form our conceptual understanding of a material response. For a nonlinear rheological response, the possible deformation protocols and material measures span a high-dimensional space. Here, we use asymptotic expansions to outline low-dimensional measures for describing leading-order nonlinear responses in large amplitude oscillatory shear (LAOS). This amplitude-intrinsic regime is sometimes called medium amplitude oscillatory shear (MAOS). These intrinsic nonlinear material functions are only a function of oscillatory frequency, and not amplitude. Such measures have been suggested in the past, but here, we clarify what measures exist and give physically meaningful interpretations. Both shear strain control (LAOStrain) and shear stress control (LAOStress) protocols are considered, and nomenclature is introduced to encode the physical interpretations. We report the first experimental measurement of all four intrinsic shear nonlinearities of LAOStrain. For the polymeric hydrogel (polyvinyl alcohol - Borax) we observe typical integer power function asymptotics. The magnitudes and signs of the intrinsic nonlinear fingerprints are used to conceptually model the mechanical response and to infer molecular and microscale features of the material.

Density sensitivity of intrinsic rotation profiles in ion cyclotron range of frequency-heated L-mode plasmas

The physical mechanisms that cause tokamak plasmas to rotate toroidally without external momentum input are of considerable interest to the plasma physics community. This paper documents a substantial change in both the magnitude of the core-rotation frequency, −1 < ω(r/a = 0) < +10 kHz, and the sign of rotation shear at mid-radius, u′ = −R2 dω/dr/vth,i, which varies in the range −0.6 < u′ < +0.8 in response to very small changes in the electron density. In 0.8 MA, 5.4 T Alcator C-Mod L-mode plasmas using 1.2 MW of on-axis ion-cyclotron resonance heating, plasmas with line-averaged densities in the range exhibit a transition from a peaked intrinsic rotation profile to one that is hollow. Gradient scale lengths of the temperature and density profiles, the drive for plasma turbulence thought to play a role in intrinsic rotation, are indistinguishable within experimental uncertainties between the plasmas, and linear stability analysis using GYRO shows the plasmas to be in the ion temperature gradient-dominated turbulence regime. The impact of changes in the rotation profile in response to minor changes under target plasma conditions is discussed in relation to established analysis techniques and cross-machine rotation scaling studies, with comparisons made with existing ASDEX-Upgrade work on intrinsic rotation shear.

Shear-induced Reynolds stress at the edge of L-mode tokamak plasmas

The turbulent flux of momentum—or Reynolds stress—is a mechanism responsible for the generation of sheared flow by turbulence. The structure of the flux-surface-averaged stress is investigated in the edge region of an L-mode tokamak plasma. The stress induced by the perpendicular tilting of ballooning modes is considered. In addition to the tilting by the E × B flow shear, which is a negative viscosity effect, a magnetic-shear-induced Reynolds stress—called -residual stress—arises as a consequence of a residual spatial tilting of ballooning modes by the magnetic shear in a poloidally up–down asymmetric magnetic geometry. A model is derived in the weak flow shear regime under the approximation of circular flux surfaces. The amplitude of this residual stress is of the order of the square of the radial velocity fluctuations in the scrape-off layer (SOL), and in the immediate radial vicinity of the separatrix if an X-point exists. Its amplitude drops rapidly to zero towards the plasma core, thus appearing as a source of transverse rotation at the interface. Its non-linear dependence on the electric shear is discussed in the context of the weak electric shear effect on the poloidal shape of the ballooning envelope. The local -residual stress is non-uniform poloidally and changes sign according to the up/down position of SOL end-plates with respect to the ∇B × B direction. The electric- and magnetic-shear-induced stresses are then included in a flux-surface-averaged 1D model of mean flow conservation at the plasma edge, including the SOL volume. In L-mode weak shear regimes, it is shown that changing the plasma geometry from ∇B × B away from the divertor to ∇B × B towards the divertor approximately doubles the electric shear strength inside the separatrix, as reported in experiments. This shear-induced stress also enters the toroidal momentum balance, where it appears as a significant source of momentum in the immediate vicinity of the separatrix. Balanced by the toroidal viscosity only, it can sustain toroidal flow gradients of the order of a km s−1 cm−1 at the separatrix, with a sign also dependent on the plasma geometry. These momentum sources arising from symmetry breaking at the boundary of the confined region may explain why low to high mode power thresholds are lower in favourable than unfavourable configurations, and may be important for the issue of optimal plasma shapes with respect to edge intrinsic shear.

Acoustic attenuation due to transformation twins in CaCl2: Analogue behaviour for stishovite

CaCl2 undergoes a tetragonal (P42/mnm) to orthorhombic (Pnnm) transition as a function of temperature which is essentially the same as occurs in stishovite at high pressures. It can therefore be used as a convenient analogue material for experimental studies. In order to investigate variations in elastic properties associated with the transition and possible anelastic loss behaviour related to the mobility of ferroelastic twin walls in the orthorhombic phase, the transition in polycrystalline CaCl2 has been examined using resonant ultrasound spectroscopy (RUS) at high frequencies (0.1–1.5MHz) in the temperature interval 7–626K, and dynamic mechanical analysis (DMA) at low frequencies (0.1–50Hz) in the temperature interval 378–771K. RUS data show steep softening of the shear modulus as the transition temperature is approached from above and substantial acoustic dissipation in the stability field of the orthorhombic structure. DMA data show softening of the storage modulus, which continues through to a minimum ∼20K below the transition point and is followed by stiffening with further lowering of temperature. There is no obvious acoustic dissipation associated with the transition, as measured by tanδ, however. The elastic softening and stiffening matches the pattern expected for a pseudoproper ferroelastic transition as predicted elsewhere. Acoustic loss behaviour at high frequencies fits with the pattern of behaviour expected for a twin wall loss mechanism but with relaxation times in the vicinity of ∼10−6s. With such short relaxation times, the shear modulus of CaCl2 at frequencies corresponding to seismic frequencies would include relaxations of the twin walls and is therefore likely to be significantly lower than the intrinsic shear modulus. If these characteristics apply also to twin wall mobility in stishovite, the seismic signature of the orthorhombic phase should be an unusually soft shear modulus but with no increase in attenuation.

High resolution residual stress measurement on amorphous and crystalline plasma-sprayed single-splats

Residual stress was measured on plasma sprayed crystalline NiAl, Al2O3 and amorphous Al2O3TiO2ZrO2CeO2 single splats, by using an incremental focused ion beam (FIB) micron-scale ring-core method (IμRCM).Tensile residual stress exists in polycrystalline NiAl splats, where the quenching stress is only partially relaxed by edge curling and through-thickness yielding. Significant compressive stress was observed for the amorphous Al2O3TiO2ZrO2CeO2 splats, where viscous flow above the glass transition temperature completely relaxed the quenching stresses without micro-cracking. Comparatively lower compressive stress was measured on crystalline Al2O3 splats, where, in spite of extensive micro-cracking, not all of the tensile quenching stress was relaxed. Using stress data and micro-crack geometry, the intrinsic shear adhesion strength of Al2O3 splats was calculated, giving insights into the role of (sub)micron-scale phenomena on adhesion/cohesion of thermally sprayed coatings. The proposed stress build-up mechanisms and relaxation phenomena are supported by a TEM microstructural analysis of the splats.The experimental methodology developed provided a unique way for the study of the residual stress build-up mechanisms in amorphous and crystalline single splats obtained by plasma spraying, and gave further insights into the actual micro-scale phenomena that give rise to adhesion and nano-mechanical behavior of thermally sprayed coatings.The proposed approach is also expected to find a wide range of applications in materials science and engineering, as it allows for the residual stress measurement even on amorphous materials with micrometer spatial resolution.

Macroscopic tensile plasticity of bulk metallic glass through designed artificial defects

Catastrophic fracture with nearly zero tensile elongation at room temperature in bulk metallic glasses (BMGs) makes their future application as structural materials seem bleak. The instable localized shear banding with work softening under unconfined uniaxial tension should be responsible for the zero elongation. Here we show how to control the shear band and make it contribute to the macroscopic tensile plasticity of BMGs through designed artificial defects. By promoting the initiation of shear bands and hindering their instable propagation through introducing artificial defects, appreciable macroscopic tensile plasticity was successfully achieved in a conventional Zr-based BMG. Moreover, by designing the distribution of the defects to inhibit the intrinsic shear fracture, the nominal tensile strength and elongation of the BMG have been enhanced simultaneously. The principles for toughening BMG through designed artificial defects are proposed; accordingly, some strategies for designing future porous BMG materials with high mechanical performance were presented. (C) 2011 Elsevier B.V. All rights reserved.

Novel method to measure the shear strength of exfoliated montmorillonite/polymer nanocomposite films

AbstractShear fracture of exfoliated montmorillonite/poly(methyl acrylate‐co‐methyl methacrylate) (MMT/P(MA‐co‐MMA)) nanocomposite films fabricated via soap‐free emulsion polymerization was studied using a unique test fixture that is capable of controlling the inclined angle between the loading axis and the shear fracture plane. It was found that fracture of the films depended on both shear and normal stresses and could be described by the Mohr–Coulomb criterion. The effects of MMT content on the intrinsic shear strength (i.e. the shear strength at zero normal stress) τs were also examined. The obtained τs increased from 1.66 to 2.78 MPa as 1 wt% MMT was incorporated into P(MA‐co‐MMA) and then increased almost linearly to 5.32 MPa when the content of MMT increased to 15 wt%. Also, the fracture‐surface morphology of the composite film depended on both the MMT content and the inclined angle (and hence the normal‐to‐shear stress ratio). For low MMT contents and low normal‐to‐shear stress ratios, striations normal to the shear direction appeared on the fracture surface. As the MMT content or the stress ratio increased, the fracture surface became rough accompanied by the presence of interfacial micro‐cracking between MMT nanoplatelets and the matrix. With further increase in MMT content and high stress ratio, the MMT nanoplatelets were compressed into large flakes on the fracture surface. Copyright © 2011 Society of Chemical Industry

Adhesion of thermoplastic polyurethane elastomer to galvanized steel

When a thermoplastic polyurethane elastomer (TPU) is co-molded with galvanized steel, the subsequent adhesion and its durability are very sensitive to the chemical bonds created at the interface. Silane coupling primers are known for enhancing adhesion between inorganic substrates and several polymers and this study addresses their efficiency at the TPU–metal interface. γ-APS aminosilane was deposited with different parameters, including pH and solvents. Several other surface treatments were studied for comparison: degreasing, corona discharge, acidic etching, gas flame, and a zinc phosphate conversion coating. The adhesion was characterized with a single wire pull-out test derived from the microbond test geometry, after different aging conditions. Results confirmed that γ-APS worked as a coupling agent in between TPU and the inorganic substrate, outperforming all other surface treatments tested in term of strength and durability, but the silane required the appropriate deposition parameters to be really efficient. In parallel, a finite element approach was proposed for the modeling of fiber reinforced thermoplastic elastomer composites accounting for the non-linear viscoelastic material properties and its results compared to an analytical elastic shear-lag interpretation of the single filament pull-out test. The analytic interpretation was found to be sufficiently accurate for stress analysis but not for fracture mechanics. The FEM analysis offered an evaluation of the internal stresses developed within the entire system, which helped the interpretation of results. The model, compared to experimental results, also revealed that it is important to account for internal stresses, mostly for treatments leading to low intrinsic interfacial shear strength values.

Effect of Bondline Thickness on the Static Strength of Structural Adhesives Under Nearly-Homogeneous Shear Stresses

An usual experimental observation retrieved in the technical literature is that the strength of an adhesive joint decreases by increasing the adhesive layer thickness. This well-known behaviour is still not completely understood. All works found in the literature consider a complex stress state in the adhesive with mode mixing, stress concentrations on the midplane, and stress singularities at the interface occurring at the same time. This paper aims at estimating the effect of the adhesive thickness on its intrinsic static shear strength and evaluate whether this strength can explain the behaviour of a real bonded joint. A nearly uniform shear stress distribution is obtained through an ad-hoc tubular butt joint subject to pure torsion. A standard single lap joint is considered as a benchmark, due to its complex and singular stress field into the adhesive. The experimental campaign is focused on two brittle adhesives: a modified methacrylate and high-strength epoxy. Four levels and three levels of the adhesive thickness were considered in the tubular butt joint and in the single lap joint, respectively, all in the range between 0.05 and 0.4 mm. The effect of the adhesive thickness on the static strength of the adhesive is investigated by considering the type of failure and by comparing the structural stresses in the tubular butt joint with the ones on the midplane of the adhesive layer in the single lap joint. Moreover, the stress intensity factor in the single lap joint is calculated.

Freezing behavior of argon layers confined in mesopores

Adsorbed layers of argon in mesoporous Vycor glass exhibit a peculiar phase behavior. We have studied their liquid-solid transition in pores with a mean pore diameter of 8 nm via ultrasonic measurements. An effective medium analysis reveals that during isothermal filling at low temperatures ($T&lt;{T}_{\mathrm{fr},\mathrm{bulk}}$) frozen layers form on top of liquidlike surface layers. These frozen layers are bulklike (i.e., ${G}_{\mathrm{Ar},\mathrm{SL}}\ensuremath{\approx}{G}_{\mathrm{Ar},\mathrm{bulk}}$ holds for their intrinsic shear modulus). We detect that both the first and the second layer undergo a continuous phase transition in a broad temperature range of at least 40 K. A complete freezing is only achieved at very low temperatures of approximately 20 K (i.e., far below the bulk freezing temperature). Whereas those two adsorbed layers remain stable during cooling, the third one becomes unstable around 66 K, rearranges, and solid capillary condensate is formed (delayering transition).