Search

The literature suggests that the yield strain of cortical bone is invariant to its stiffness (elastic modulus) and strength (yield stress). However, data about intra-individual variations, e.g., the influence of different collagen/mineral organisations observed in bone aspects withstanding different habitual loads, are lacking. The hypothesis that the yield strain of human cortical bone tissue, retrieved from femoral diaphyseal quadrants subjected to different habitual loads, is invariant was tested. Four flat dumbbell-shaped specimens were machined from each quadrant of the proximal femoral diaphysis of five adult donors for a total of 80 specimens. Two extensometers attached to the narrow specimen region were used to measure deformation during monotonic tensile testing. The elastic modulus (linear part of the stress–strain curve) and yield strain/stress at a 0.2% offset were obtained. Elastic modulus and yield stress values were, respectively, in the range of 12.2–20.5 GPa and 75.9–136.6 MPa and exhibited a positive linear correlation. All yield strain values were in the narrow range of 0.77–0.87%, regardless of the stiffness and strength of the tissue and the anatomical quadrant. In summary, the results corroborate the hypothesis that tensile yield strain in cortical bone is invariant, irrespective also of the anatomical quadrant. The mean yield strain value found in this study is similar to what was reported by inter-species and evolution studies but slightly higher than previous reports in humans, possibly because of the younger age of our subjects. Further investigations are needed to elucidate a possible dependence of yield strain on age. [ABSTRACT FROM AUTHOR]

The literature suggests that the yield strain of cortical bone is invariant to its stiffness (elastic modulus) and strength (yield stress). However, data about intra-individual variations, e.g., the influence of different collagen/mineral organisations observed in bone aspects withstanding different habitual loads, are lacking. The hypothesis that the yield strain of human cortical bone tissue, retrieved from femoral diaphyseal quadrants subjected to different habitual loads, is invariant was tested. Four flat dumbbell-shaped specimens were machined from each quadrant of the proximal femoral diaphysis of five adult donors for a total of 80 specimens. Two extensometers attached to the narrow specimen region were used to measure deformation during monotonic tensile testing. The elastic modulus (linear part of the stress–strain curve) and yield strain/stress at a 0.2% offset were obtained. Elastic modulus and yield stress values were, respectively, in the range of 12.2–20.5 GPa and 75.9–136.6 MPa and exhibited a positive linear correlation. All yield strain values were in the narrow range of 0.77–0.87%, regardless of the stiffness and strength of the tissue and the anatomical quadrant. In summary, the results corroborate the hypothesis that tensile yield strain in cortical bone is invariant, irrespective also of the anatomical quadrant. The mean yield strain value found in this study is similar to what was reported by inter-species and evolution studies but slightly higher than previous reports in humans, possibly because of the younger age of our subjects. Further investigations are needed to elucidate a possible dependence of yield strain on age.

It is not conservative to directly use the strength tested under the laboratory loading rates to evaluate the long-term creep strength of polymers. A suitable strain rate-dependent constitutive model is crucial for accurately predicting the long-term strength and mechanical behavior of polymer pressure pipes. In this study, the Kondner hyperbolic constitutive model is considered the base model in deriving the rate-dependent constitutive model for PE100 pipe material, and the yield stress and initial tangent modulus are the two rate-dependent parameters of the model. Uniaxial tension tests are carried out under five specified strain rates ranging from 10−5 s−1 to 5 × 10−2 s−1 to obtain these two parameters. It is demonstrated that the strain rate dependence of the yield stress and the initial tangent modulus can be described by either a power or a logarithm law. The predictions from the two models are in good agreement with the experiments. In contrast, the power-law rate-dependent Kondner model is more suitable for describing the rate-dependent tensile behavior of PE100 pipe material than the logarithm-law rate-dependent Kondner model, especially for the cases of very low strain rates which relate to the polymer pressure pipe applications. [ABSTRACT FROM AUTHOR]

Effect of coating with calcium nitrate in three concentrations (0.0, 0.5, and 1.0 wt%) on chemical and mechanical properties, and impact behaviour of two apple cultivars (Golden Delicious (GD) and Red Delicious (RD)) during time (0, 2, and 4 months) was studied. Moisture content, pH, titratable acidity, °Brix, organoleptic properties, modulus of elasticity (E), yield stress, yield strain, and toughness were measured. The effect of impact loads was determined by measuring bruise volume (BV) and bruise susceptibility (BS). The results showed that pH and °Brix significantly increased, while titratable acidity, E, yield strain, toughness, and BV decreased during storage time. As Ca(NO3)2 concentration increased, titratable acidity, E, yield strain and yield stress increased and pH decreased (P < 0.05). Highest and lowest values for °Brix were observed in GD treated with 1.0% Ca(NO3)2 after four months (13.31) and GD treated with 0.5% Ca(NO3)2 at the first day (10.65), respectively. Maximum E was obtained in GD treated with 1.0% Ca(NO3)2 on the first day (2130 kPa) and this sample also showed the lowest BS after four months of storage (2.82 mL J−1), while the uncoated GD had the highest BS on the first day (7.11 mL J−1). [ABSTRACT FROM AUTHOR]

We report experimental microfluidic measurements and theoretical modeling of elastoviscoplastic materials under steady, planar elongation. Employing a theory that allows the solid state to deform, we predict the yielding and flow dynamics of such complex materials in pure extensional flows. We find a significant deviation of the ratio of the elongational to the shear yield stress from the standard value predicted by ideal viscoplastic theory, which is attributed to the normal stresses that develop in the solid state prior to yielding. Our results show that the yield strain of the material governs the transition dynamics from the solid state to the liquid state. Finally, given the difficulties of quantifying the stress field in such materials under elongational flow conditions, we identify a simple scaling law that enables the determination of the elongational yield stress from experimentally measured velocity fields. [ABSTRACT FROM AUTHOR]

Tension dynamics is key to graphene oxide (GO) when composited in flexible materials, and there is still lack of some dynamic pictures to show how it is affected by oxidation level. In this paper, uniaxial tension of GO with different oxygen-containing functional groups densities (R) are simulated by molecular dynamics. It is indicated that the elastic modulus and ultimate stress both decrease with increasing R, especially when R < 30%. The yield strain along AC-orientation falls after rises because of the R-depended fractural mechanisms: when R is small, cracks initiate from the distorted carbon bonds connecting to oxygen-containing groups and propagate along the ZZ-orientation, or else, cracks start from the point defects and expands by consolidating point defects; when loaded along the ZZ-orientation, however, fractures are edge dominated. Our research suggests that introducing oxygen-containing groups would be a feasible strategy to improve the deformability of graphene oxide. [ABSTRACT FROM AUTHOR]

In this paper, hysteresis of magnetorheological (MR) fluids is identified from experimental tests following the mechanism of rate-independence and further studied to explore the hysteresis mechanism. The theoretical analysis based on the dipole model is provided to reveal the hysteresis mechanism of MR fluids. Specifically, the performance tests of a self-developed double-rod MR damper under different excitations show that instead of the typical force-velocity plot, the relationship between the force and displacement meets the requirements of rate-independence of the hysteresis well. A critical concept of “yield displacement” is defined and analyzed in the force-displacement plot to illustrate the hysteresis characteristics. In addition, the relationship of the normalized restoring force vs. strain is derived for a single chain from the dipole model. Then a stress-strain curve is developed for the multi-chain structure with an assumption of the dynamic equilibrium between the rupture and reconstruction of the chains. Sequentially, the hysteresis mechanism is established based on the force-displacement characteristics under reciprocating excitations. The consistency between the yield displacement in experiment and yield strain in theory verifies the effectiveness of the hypothetical hysteresis mechanism. The analysis results provide a guideline for the structural design of MR devices to enhance/reduce the hysteresis effect. The hysteresis mechanism-based further extension for the stress-strain properties of MR elastomers and the response time of MR fluids are provided as well.

To investigate the brittle ductile transformation characteristics of mudstone under high temperature, the MTS810 electro mechanical hydraulic servo test system and matched high temperature furnace MTS652.02 are used to perform mechanical tests to study the influence of loading rate on the yield strain and ductility coefficient of the mudstone at high temperatures. [ABSTRACT FROM AUTHOR]

The current gold standard of identifying yield points from stress strain curves involves identifying a significant change in elastic modulus or using an arbitrary strain offset (0.1%, 0.2% or 2%) of the elastic modulus. The development of the offset method was due to the ambiguous definitions of yield point. The result is an arbitrary yield point which is prone to various human-related errors. This article presents a method to identify a unique yield point consistently using energy absorbed by the material up to first peak stress. This mathematical process idealises the stress strain curve for easy identification of the yield point. The method was tested on three possible types of stress strain curves with either a distinct yield point or without a distinct yield point (with peak stress closer to elastic region or closer to fracture). The yield points obtained by the proposed method are shown to be robust, consistent and unaffected by variations of the stress strain curves and data noises. [ABSTRACT FROM AUTHOR]

Sliding and scratching are fundamental tribological phenomena which affect the surface and surface-near zones of materials. To clarify ongoing tribological and microstructural mechanisms, a thorough analysis of three fcc materials (aluminium, austenitic steel and copper) was performed via nano-sliding and scratching at different load levels. Nanoindentation was used to evaluate the phases' mechanical properties, namely hardness H , Young's modulus E and the ratios H/E (yield strain) and H³/E 2 (resistance against plastic indentation), which proved to be good measures to understand the abrasive wear behaviour. Electron backscatter diffraction (EBSD) measurements and focused ion beam (FIB) cross-sections of the scratches provided deeper insight into the degree of deformation and deformation induced phase changes. Results show a distinct influence of the materials' mechanical parameters and phase changes on the deformation and wear mechanisms, and the thereby entailed apparent coefficient of friction (F T /F N). The mechanical properties were a key factor for a change in wear mechanism from sliding to ploughing to chipping. The thresholds were investigated for the three materials and increase from Aluminium to Copper to Austenite with H³/E 2 being a good descriptor of the necessary contact pressures entailing changes of the wear mechanism. • Evaluation of thresholds for wear mechanism changes on fcc metals via nanoscratching • Microstructural analyses focussed on ongoing mechanisms during abrasion. • Strong influence of the hardness H, the Young's modulus as well as H³/E2. • Dynamic recovery effects evaluated during beginning chip formation for Cu and Al. • Deformation induced martensite formed during abrasion of austenitic steel. [ABSTRACT FROM AUTHOR]

This work contributes to the theory of strain controlled large amplitude oscillatory shear (LAOS) as well as modelling the key properties of type III behavior of Hyun, the decreasing storage modulus and a loss modulus with considerable maximum. The latter two can be modelled with the help of the Prandtl element. Since it is a yield stress fluid, the use of LAOS is necessary to calculate the storage and loss modulus. Furthermore, a condition is presented which has to be met in order to avoid even harmonics. The storage and loss modulus as well as the higher harmonics of the Prandtl element are determined analytically in this work. They are given as mathematical functions which can be discussed conveniently. This allows the identification of characteristic points which are related to material parameters of the Prandtl element and enable a physically motivated material parameter identification. Beside this, it is observed that the yield strain do not coincide with the crossover G’(ŷ) = G’’(ŷ) but with the increasing of the loss modulus and the decreasing of the storage modulus. Thanks to the analytical calculations, it is also obvious that the stress response of yield stress fluids does not necessarily include even harmonics. In this work the steady state stress response of the Prandtl element is also presented as Lissajous plots and Pipkin diagrams to visualise the rheological fingerprint.

This paper is dedicated to providing a detailed plastic collapse load analysis for un-cracked and circumferential through-wall cracked pipe bends under torsion moment by three dimensional FE methods considering geometric nonlinearity. For un-cracked pipe bends results show that radius-to-thickness is the main factors affecting the plastic collapse load. For cracked pipe bends the weakening factor decreases with increasing crack length, and the decreasing rate exhibits three typical stages which performs a similar trend with that in bending case. Although the weakening factor in plastic collapse load shows the similar variation based on geometric nonlinearity with that based on geometric linearity change, the limit load solutions based on geometric linearity fail to be used in prediction for torsion load based on geometric nonlinearity. So estimating limit load solutions by FE method are proposed, which shows a better choice compared with the past solutions. Furthermore the effect of yield strain is considered with the normalized parameter proposed to represent this weakening effect of yield strain on torsion moment. Results show that pipe parameters bend radius-to-radius and crack length have little impact on the weakening parameter, however radius-to-thickness have an obvious impact on the weakening parameter, which increases with decreasing weakening parameter. Results also show that radius-to-thickness has a great impact on the ovality deformation, while bend radius-to-radius hasn't. Therefore geometry effect is significant for a high yield strain value and a high radius-to-thickness value. [ABSTRACT FROM AUTHOR]

In computational materials science, predicting the yield strain of crosslinked polymers remains a challenging task. A common approach is to identify yield as the first critical point of stress-strain curves simulated by molecular dynamics (MD). However, in such cases the underlying data can be excessively noisy, making it difficult to extract meaningful results. In this work, we propose an alternate method for identifying yield on the basis of deformation-recovery simulations. Notably, the corresponding raw data (i.e. residual strains) produce a sharper signal for yield via a transition in their global behavior. We analyze this transition by non-linear regression of computational data to a hyperbolic model. As part of this analysis, we also propose uncertainty quantification techniques for assessing when and to what extent the simulated data is informative of yield. Moreover, we show how the method directly tests for yield via the onset of permanent deformation and discuss recent experimental results, which compare favorably with our predictions. [ABSTRACT FROM AUTHOR]

It has been established that it is the peripheral solder joints that are the most vulnerable in the ball-grid-array (BGA) and column-grid-array (CGA) designs and most often fail. As far as the long-term reliability of a soldered microelectronics assembly as a whole is concerned, it makes a difference, if just one or more peripheral joints experience inelastic strains. It is clear that the low cycle fatigue lifetime of the solder system is inversely proportional to the number of joints that simultaneously experience inelastic strains. A simple and physically meaningful analytical expression (formula) is obtained for the prediction, at the design stage, of the number of such joints, if any, for the given effective thermal expansion (contraction) mismatch of the package and PCB; materials and geometrical characteristics of the package/PCB assembly; package size; and, of course, the level of the yield stress in the solder material. The suggested formula can be used to determine if the inelastic strains in the solder material could be avoided by the proper selection of the above characteristics and, if not, how many peripheral joints are expected to simultaneously experience inelastic strains. The general concept is illustrated by a numerical example carried out for a typical BGA package. The suggested analytical model (formula) is applicable to any soldered microelectronics assembly. The roles of other important factors, such as, e.g., solder material anisotropy, grain size, and their random orientation within a joint, are viewed in this analysis as less important factors than the level of the interfacial stress. The roles of these factors will be accounted for in future work and considered, in addition to the location of the joint, in a more complicated, more sophisticated, and more comprehensive reliability/fatigue model. [ABSTRACT FROM AUTHOR]

Obtaining the mechanical properties of soft tissues is critical in many medical fields, such as regenerative medicine and surgical simulation training. Although various tissue-characterization methods have been developed, such as AFM, indentation, and elastography, there remain some limitations on their accuracy and validity for measuring small and fragile soft tissues. This paper presents a tensile testing technique to measure the mechanical properties of soft tissues directly and accurately. Tensile testing was chosen as the primary method because of its simple procedure and ability to derive mechanical properties without requiring many assumptions or complicated models. However, tensile testing on soft tissues presents challenges related to gripping the tissue sample without affecting its inherent properties, applying minuscule forces to the sample, and measuring the cross-section area and strain of the sample. To solve these issues, this study presents a sub-micro scale tensile testing system that uses a flexure mechanism and a novel 3D-printed sample holder for gripping the tissue samples. The system also measures tested samples' cross-section area and strain using two high-resolution cameras. The system was validated by testing standard materials and used to characterize the elastic modulus, yield stress, and yield strain of lung tissue slices from six different mice. The results from the validation tests showed a less than 2.5% error for elastic modulus values measured using the tensile tester. At the same time, results from the mice lung tissue measurements revealed qualitative findings that closely matched those seen in the literature and displayed low coefficient of variation values, demonstrating the high repeatability of the system. [ABSTRACT FROM AUTHOR]

The ability to tolerate large strains during various degrees of deformation is a core issue in the development of flexible electronics. Commonly used strategies nowadays to enhance the strain tolerance of thin film devices focus on the optimization of the device architecture and the increase of bonding at the materials interface. In this paper, we propose a strategy, namely elasto-plastic design of an ultrathin interlayer, to boost the strain tolerance of flexible electronics. We demonstrate that insertion of an ultrathin, stiff (high Young's modulus) and elastic (high yield strain) interlayer between an upper rigid film/device and a soft substrate, regardless of the substrate thickness or the interfacial bonding, can significantly reduce the actual strain applied on the film/device when the substrate is bent. Being independent of existing strategies, the elasto-plastic design strategy offers an effective method to enhance the device flexibility without redesigning the device structure or altering the material interface.

Strength should be the most outstanding mechanical property for metallic glasses (MGs). Here we analyze the strengths of MGs with more than 300 compositions in ∼30 alloy systems covering nearly all strength levels, ranging from 0.3 GPa to 6 GPa. With these abundant experimental data available, we find that the yield strain is not always constant but depends on glass transition temperature, T g , ranging from 1% to 2.5% for normal strain and from 1.2% to 3.4% for shear strain. This can be well explained by assuming an equivalent energy barrier for yielding and glass transition. Relations derived based on this assumption show that MGs with high T g may yield with larger critical strain and higher strength, implying that high elasticity, high strength and high thermostability can be synchronously achieved for MGs. [ABSTRACT FROM AUTHOR]

Using finite element analysis, we compared the biomechanical performance of a CT scan-based three-part trochanteric fracture model (31-A2 in the AO classification) stabilized with a sliding hip screw for nine different positions of the lag screw (3 × 3 arrangement, from anterior to posterior and from inferior to superior). Our results showed that the volume of bone susceptible to yielding in the head and neck region is the lowest for inferior positions and increases as the lag screw is moved superiorly. Overall, for this specific subject, the models less likely to lead to cut-out are the ones corresponding to inferior middle and inferior posterior positions of the lag screw. In our study, the tip-apex distance (TAD) was anti-correlated with the risk of cut-out, as quantified by the volume of bone susceptible to yielding, which suggests that a TAD >25 mm cannot be considered to be an accurate predictor of lag screw cut-out. Further clinical studies investigating lag screw cut-out should attempt to find more reliable predictors of cut-out that should better reflect the biomechanics and subject-specificity of the femoral head. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31: 596-600, 2013 [ABSTRACT FROM AUTHOR]

The yielding and flow behaviour of plant suspensions are perhaps the most important rheological properties in process and product design for applications in paper, biofuel and food industries. Studies are reported here on the yield properties and flow behaviour of suspensions of plant particles with different shapes (clusters of cells, individual cells and cell fragments). Carrot and tomato were selected as model plant systems to prepare suspensions at particle dry mass concentrations ranging from 0.010 to 0.065. The flow behaviour was characterised by an apparent yield stress and shear thinning. The Herschel-Bulkley yield stress obtained from up and return flow curves was compared to the yield stress calculated from oscillatory measurements. The dependence of the yield stress values on particle dry mass concentration is approximately a power-law, with a fitted exponent of 3 ± 0.5 for all the suspensions, independently of the plant origin and particle shape. This same power-law behaviour was found for the elastic modulus G′, and in this case the exponent was 3 for carrot and 4 for the tomato suspensions. The yield strain, calculated from oscillatory measurements, decreased slightly with dry mass fraction, but did not follow a power-law. We discuss possible explanations for power law behaviour, and provide a model for G′ based on folded elastic sheets, which predicts an exponent of 3, similar to the values obtained for these suspensions. [ABSTRACT FROM AUTHOR]

Specimens of nanocrystalline pure gold were prepared by the gas deposition method. The formation of helium bubbles in the specimens and their annealing behavior were studied in order to confirm their effect on thermal stabilities of grain size and mechanical properties. The specimens with 10-25nm mean grain size were analyzed by transmission electron microscopy and X-ray diffraction methods. Spherical helium bubbles, about 5nm in diameter, were formed, the same as in the case of helium ion implantation. After annealing at 573K for 1h in vacuum, most of the bubbles had not disappeared and some were trapped at the grain boundaries. Larger numbers of bubbles were trapped at grain boundaries in the specimens with high thermal stability than for low thermal stability specimens. Helium bubbles trapped at grain boundaries can be considered as local barriers to grain growth and to contribute to thermal stability of mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract: The structural properties of Daqing gelled waxy crude oil were studied with a controlled-stress rheometer under oscillatory shear mode. Our results demonstrate that the gelled waxy crude oil shows viscoelastic properties. The linear viscoelastic region and yielding of crude oil can be determined not only by the critical linear shear stress (τ cl ) and yield stress (τ y ), but also by the critical linear shear strain (γ cl ) and yield strain (γ y ) respectively. With the decrease of test temperature, τ cl and τ y increased greatly while γ cl and γ y decreased gradually. The crude oil showed more elastic at lower temperatures. The frequency had little effect on the structure of crude oils in the measured range. [Copyright &y& Elsevier]

Magnetorheological (MR) fluid is used as the working medium in MR finishing. The viscosity of the MR fluid, which determines the shear acting on the workpiece surface stress, can be controlled by the intensity of the applied external magnetic field, and is thus an important design parameter in the finishing process. Most previous studies have used a shear stress value obtained experimentally under a limited set of conditions. Although a recent theoretical model that predicts the shear stress in an external vertical magnetic field has been developed, it treats the energy variation with respect to the strain and the intensity of the magnetic field only among the adjoining particles in a chain. Because that model assumes no multiparticle interactions, it is not well suited to a case in which the magnetic field is more than one dimension such as in MR finishing. In this study, a new three-dimensional model is proposed by expanding the one-dimensional model and considering multiparticle interactions. The proposed model assumes that each particle is surrounded by the 26 neighboring particles, and the total internal energy is estimated by calculating the magnetic dipole interactions among the particles. Therefore, the proposed model considers not only the particle-to-particle energy variations, but also the chain-to-chain energy variations. The behavior of MR fluid is evaluated using the proposed model in a two-dimensional skewed magnetic field. [ABSTRACT FROM AUTHOR]

Abstract: In this study the effect of cyclic loads on monotonic shear strength has been studied on torsional apparatus. Tests have been conducted on both reconstituted and undisturbed fine-grained hollow soil specimens. The plasticity index of soils is in the range from 2 to 33 for reconstituted specimens, prepared by dry pluviation, and from 5 to 13 for undisturbed soil specimens. The existence of a critical shear strain level, called yield shear strain, where softening starts, is determined from cyclic tests. The level of cyclic yield strain is ±0.75% for the reconstituted soil specimens and ±0.5% for the undisturbed soils. If soil undergoes a cyclic shear strain level below the cyclic yield strain, reduction of monotonic strength of reconstituted and undisturbed specimens is limited, but when cyclic shear strain level is larger than yield strain monotonic strength decreases down to 40% of its initial strength. [Copyright &y& Elsevier]

The properties that make plastic of direct interest to designers and engineers are its good strength to weight ratio, low manufacturing and installation costs and high durability. The strength of polymers is known to be sensitive to temperature and this generally limits their use under service temperatures lower than the glass transition temperature. The present work addresses the effect of temperatures ranging from -10 to 70°C on the tensile properties of high density polyethylene PE-100 pipe material. Tensile tests are performed on dog bone type ASTM standard specimens. Yield stress and modulus of elasticity are found to decrease linearly with temperature. The average yield strength decreased linearly from 32 to 9 MPa when the temperature is increased from - 10 to 70°C. The modulus of elasticity varied in the same fashion as the yield strength. The yield strain, however, showed a slight increase in this temperature range. Ductile fracture is observed to be the controlling failure mechanism at all the temperatures of interest. The deformation at room and high temperatures is accompanied by considerable necking. The temperature effect on the tensile properties of PE-100 pipe material is compared with that of CPVC and PVC pipe materials, used in comparable applications. In general, a similar effect was observed on yield stress, modulus of elasticity and yield strain in all these materials. [ABSTRACT FROM AUTHOR]

Abstract: Dimensional arguments suggest that the yield stress of aqueous foams and emulsions, for a given volume fraction of the dispersed phase, should scale as the ratio of surface tension and a length scale, such as the mean bubble radius. We show that yield stress data from the literature and from our experiments follow this scaling only in a very rough approximation. We present new experimental evidence that clarifies the role of shear banding in this context and we discuss the robustness of the yield stress with respect to changes of flow geometry and experimental technique. Finally, we show that scaling oscillatory yield stress data by the elastic shear modulus at small amplitude provides a master curve when plotted versus the volume fraction of the dispersed phase. [Copyright &y& Elsevier]

This article describes an experiment to study the yield strain behavior of polyethylene terephthalate (PET). Studies on the mechanical properties of polymers such as yield behavior have been keys to successful use of polymers in various mechanically functional purposes. The yield behavior of polymers has been investigated by using polymers with varying structure. Strain rate and temperature have been the experimental parameters in those studies, as polymeric molecules display temperature and rate dependent phenomena. On the nature of the yield behavior of polymers, there have been reported a variety of phenomenological descriptions and molecular interpretations. One is to correlate the yield behavior with secondary mechanical relaxation behavior. It is based on the general understanding that such relaxation mediate macroscopic mechanical properties. PET samples with varying orientation and crystallinity were produced by the high speed melt spinning of high molecular weight PET. PET was extruded at a constant mass flow rate and spun at a take-up velocity range of 2.5 to 5.5 kilometer per minute to have different degree of melt draw ratio. Oriented semicrystalline PET samples displayed a linear increase with logarithmic strain rate.

The ability to determine trabecular bone tissue elastic and failure properties has biological and clinical importance. To date, trabecular tissue yield strains remain unknown due to experimental difficulties, and elastic moduli studies have reported controversial results. We hypothesized that the elastic and tensile and compressive yield properties of trabecular tissue are similar to those of cortical tissue. Effective tissue modulus and yield strains were calibrated for cadaveric human femoral neck specimens taken from 11 donors, using a combination of apparent-level mechanical testing and specimen-specific, high-resolution, nonlinear finite element modeling. The trabecular tissue properties were then compared to measured elastic modulus and tensile yield strain of human femoral diaphyseal cortical bone specimens obtained from a similar cohort of 34 donors. Cortical tissue properties were obtained by statistically eliminating the effects of vascular porosity. Results indicated that mean elastic modulus was 10% lower (p<0.05) for the trabecular tissue (18.0±2.8 GPa) than for the cortical tissue (19.9±1.8 GPa), and the 0.2% offset tensile yield strain was 15% lower for the trabecular tissue (0.62±0.04% vs. 0.73±0.05%, p<0.001). The tensile–compressive yield strength asymmetry for the trabecular tissue, 0.62 on average, was similar to values reported in the literature for cortical bone. We conclude that while the elastic modulus and yield strains for trabecular tissue are just slightly lower than those of cortical tissue, because of the cumulative effect of these differences, tissue strength is about 25% greater for cortical bone. [Copyright &y& Elsevier]

The controlled rate vane method was used to evaluate the yield stress and apparent yield strain of ten cream cheeses at refrigeration (5 °C) and room temperature (22 °C). Plotting yield stress versus apparent yield strain produced a "texture map," showing a trend where a decrease in yield stress corresponded to an increase in yield strain. The map can be used as a tool for evaluating product spreadability in quality control and product development applications. Yield stress values for all cream cheeses ranged from approximately 1.3 kPa to 6.6 kPa, while yield strain values from 0.2 rad to 0.6 rad were found. [ABSTRACT FROM AUTHOR]

We have studied the oscillatory shear response of three thermotropic smectic-A liquid crystalline materials with no external aligning field (other than the necessary presence of rheometer plates). Two are polymers (one main-chain and one side-chain) and the other is a small molecule smectic. All three exhibit the classical linear response to oscillatory shear characteristic of a viscoelastic solid at sufficiently small strain amplitudes and frequencies. However, for strain amplitudes exceeding a small critical value, these materials exhibit a strongly nonlinear response to strain, which is characterized in detail. While the low-strain moduli and the critical strain of the three smectics are considerably different, the nonlinear response has some universal character which is presumably related to the low energy for the formation of defects in smectic liquid crystals. [ABSTRACT FROM AUTHOR]

Viscosity, modulus, and yield stress for 0-6 wt% aqueous solutions of Carbopol 941 were investigated using constant shear rate, constant shear stress, and dynamic oscillatory experiments. The microgel character of the polymer was evident from the solid-like behavior of the solutions above 1 wt%. Yield stress increased with concentration, but yield occurred at a critical shear strain of 40%, independent of concentration. The static stress-strain relationship became non-linear at ~ 25% strain, in fair agreement with the onset of non-linear response in the storage modulus at ~ 10% strain. Small strain moduli from static and low frequency measurements agreed rather well; modulus values obtained from the recoverable strain after yielding were 30-40% smaller. Solutions flowed at near-constant stress in the low shear rate regime; at higher rates the stress increases with shear rate more rapidly. The viscosity did not obey the Cox-Merz rule. Steady-state viscosity scaled with polymer concentration to the 3/4 power. Results were interpreted using a cellular, deformable sphere model for the polymer, in analogy to emulsions and foams. [ABSTRACT FROM AUTHOR]

Continuous-filament rayon yarns were subjected to an acid-catalyzed cross-linking treatment using dihydroxydi methylol ethyleneurea under pad-dry-cure conditions to two levels of add-on. The stress-strain curves of these yarns were measured at a constant 40%/min rate of extension in the dry (65% RH and 70°F) and wet states and in an "anhy drous" condition. In the dry state, cross-linking increases the elastic modulus, the stress at the yield point, and the stress at break, and decreases the extension at break and the energy to break. In the wet state, there is a disappearance of the primary yield point and the deformation process is plastic-like from the onset without an initial Hookean elastic region. Furthermore, in the wet state, the untreated yarns are weaker and more extensible than under dry conditions, but cross- linking again increases strength and decreases extensibility. Cross-linking brings about the reappearance of the primary yield point even in the wet state. This is interpreted to reflect a protective effect of the hydrogen-bond network in the cellulose structure.The recovery properties were measured as a function of load, strain, and energy of deformation over the entire possible range of values. In uncross-linked state, dry yarns are more resilient than wet yarns, when measured from given loads of deformation, whereas wet yarns are more resilient than dry yarns, when measured from given strains, except for strains below the primary yield point. At low energies of deformation, uncross-linked dry yarns are more resilient, whereas at higher energies of deformation the reverse is the case. These data clearly indicate that, in comparing the recovery prop erties of yarns with different stress-strain curves, an entirely different view of this important yarn characteristic is obtained, depending on whether recovery is measured from given loads, strains, or energies of deformation. Cross-linking significantly increases resilience both in the wet and dry states, particularly from higher levels of deformation. [ABSTRACT FROM PUBLISHER]

Hydrates and waxes are supposed to coexist in the deep-water pipelines under suitable conditions of low temperature and high pressure. Understanding the effect of precipitated wax crystals on hydrate formation and rheological properties of hydrate slurry is crucial to the flow assurance in offshore petroleum production. In this work, a stress-controlled rheometer was used to carry out the rheological experiments for investigating the impact of wax crystals on hydrate formation and yield property of hydrate slurry. The effects of wax content and water cut on cyclopentane (CP) hydrate nucleation and growth were investigated in terms of the measured viscosity data. Log-normal distribution could well fit the probability density histogram of CP hydrate critical time. The logarithmic mean values of CP hydrate critical time decreased with increasing water cut but increased with increasing wax content in water-in-oil (w/o) emulsions. Semi-empirical models were proposed to describe the inhibitory effect of wax crystals on CP hydrate nucleation kinetics by considering the inhibition of mass transfer based on the Freundlich and Langmuir adsorption functions, respectively. Hydrate slurry viscosity rate showed the two-stage characteristics in wax-free w/o emulsions, while four stages could be clearly observed in waxy w/o emulsions. The maximum values of hydrate slurry viscosity rate and calculated hydrate effective volume fraction decreased with increasing wax content. Hydrate growth time was gradually extended as wax content increased. Furthermore, the measured yield stress and yield strain increased with increasing wax content at different water cuts, which was associated with the multiple effect of capillary bridge between hydrate particles, spatial network of wax crystals and coalescence of water droplets. At last, compared to the stress ramp rate, the influence of annealing time on yield stress was more significant. [ABSTRACT FROM AUTHOR]

• The axial yield strain in all zeolite-cement grouted specimens is less than 1%. • The q (y) and c′y increase by increasing the Z in the grouted specimens up to 30%. • An increase of more than 30% in Z leads to a decrease in q (y) and c′y. • With increasing Z content, the φ′ y increases with a slight slope. Permeation grouting with cementitious materials is a widely used soil behavior improvement technique. Since the Portland cement production leads to environmental pollution and is also an energy-intensive process, replacing a part of the cement with cheaper and more environmentally friendly materials, such as zeolite, is very important. In the present study, a series of consolidated undrained triaxial tests were carried out on zeolite-cement grouted sand specimens to investigate the effect of cementation on the yield stress (q (y)) through shear loading. The results showed that the axial yield strain (ε (y)) in all zeolite-cement grouted sand specimens is less than 1%. Beyond the yield point (YP), a sudden increase in the strain occurs, and the stress–strain curve continues with a slight gradient. The effect of cementitious bonds is significant up to the YP and then gradually decreases. The effective stress path (ESP) of the grouted specimens rises approximately vertically up to the YP. Beyond the YP , the abrupt change of the curvature occurs and the ESP turns to the right. The q (y) and cohesion corresponding to the YP (c′y) increase by increasing the amount of cement replacement with zeolite (Z) in the grouted specimens up to 30%. An increase of more than 30% in Z leads to a decrease in q (y) and c′y. Therefore, the optimum Z to achieve the maximum q (y) and c′y is 30%. With increasing Z content, the effective internal friction angle corresponding to yield (φ′ y) always increases with a slight slope. [ABSTRACT FROM AUTHOR]

This paper is dedicated to providing a detailed limit load analysis for 180° pipe bends under bending moment using three dimensional finite element (FE) method considering geometric nonlinearity. Results show that FE results for 180° pipe bends are all lower compared to those for 90° pipe bends, especially for pipe bends with thin wall and small bend radius (R / r = 1.5, r / t = 50). However, for pipe bends with thick wall and large bend radius (R / r = 4, r / t = 5), results seem very close. New predicted equations are proposed based on the FE results. If the geometric nonlinearity effect is considered, when the material parameters of yield strain ε s = 0, results still obey the estimating solutions without geometric nonlinearity considered. But the geometry change should have some significant influence on the failure with the material's behavior changing. With the applied bending load increasing, the ovalization parameter C will also continue to increase. The change of the parameter C is significant for the thin pipe bends (r / t = 50), while is not obvious for thick pipe bends (r / t = 5). The influence of the bend radius on the parameter C is not significant. Geometric effect is significant for a high yield strain value that the pipes will have enough ability to be deformed. • Three-dimensional non-linear finite element method considering geometric nonlinearity is used. • Limit loads are analyzed for 180° pipe bends under bending moment. • Parameter r / t is the main factor affecting the limit load of the pipe bends. [ABSTRACT FROM AUTHOR]