Show Strain Hardening Research Articles

Acid-induced pea protein gels pretreated with media milling: Gelling properties and the formation mechanism

This study explored the effect of stirred media mill (SMM) processing on the acid-induced gelling properties of pea protein. Results showed that SMM treatment enhanced the gel strength from 75.06 g to 183.89 g and increased the water holding capacity from 46.64 % to 73.50 %. The minimum gelation concentration achieved for SMM-treated pea protein was 4 %, significantly lower than that of heat-pretreated pea protein (9 %). SMM decreased protein aggregate size from 104 μm to 180 nm. Microscopy analysis revealed that the small aggregates facilitated the formation of uniform gel networks with tight connections. Linear rheology indicated that small protein aggregates resulted in slower gelation rates with a higher Gʹ for the formed gels. The SMM-pretreated protein gel showed strain hardening, shear thinning behaviors, and satisfactory stability to withstand large-amplitude oscillatory shear. Overall, SMM emerges as a promising technology for producing protein gel products with strong mechanical attributes and customizable rheological properties.

In situ experimental investigation of fiber orientation kinetics during uniaxial extensional flow of polymer composites

The demand for fiber-filled polymers has witnessed a significant upswing in recent years. A comprehensive understanding of the local fiber orientation is imperative to accurately predict the mechanical properties of fiber-filled products. In this study, we experimentally investigated the fiber orientation kinetics in uniaxial extensional flows. For this, we equipped a rheometer with a Sentmanat extensional measurement device and with an optical train that allows us to measure the fiber orientation in situ during uniaxial extension using small angle light scattering. We investigated an experimental system with glass fibers for the suspended phase (L/D=8−15), and for the matrix either low density polyethylene, which shows strain hardening in extension, or linear low density polyethylene, which shows no strain hardening. For these two polymer matrices, the fiber orientation kinetics were investigated as a function of fiber volume fraction (ϕ=1%, 5%, and 10%) and Weissenberg number (by varying the Hencky strain rate, ϵ˙H=0.01−1s−1). We found that all these parameters did not influence the fiber orientation kinetics in uniaxial extension and that these kinetics can be described by a multiparticle model, based on Jeffery’s equation for single particles. Our results show that, in uniaxial extension, fiber orientation is solely determined by the applied strain and that, up to the concentrated regime (ϕ≈D/L), fiber-fiber interactions do not influence the fiber orientation. The extensional stress growth coefficient of these composites, which is measured simultaneously with the orientation, shows high agreement with Batchelor’s equation for rodlike suspensions.

Shear-induced crystallization of polypropylene/low-density polyethylene blend

Shear-induced crystallization behavior was studied using a phase-separated blend comprising a polypropylene continuous phase and a low-density polyethylene (LDPE) dispersion, which is known to show strain hardening in transient elongation viscosity. In this study, crystallization behavior was mainly evaluated by the light intensity transmitted through a transparent parallel-plate geometry. It was found that shear-induced crystallization was greatly accelerated by the addition of LDPE, resulting in a high crystallization temperature and a highly oriented structure. When the sample was cooled slowly, however, shear-induced crystallization was not accelerated by LDPE. Furthermore, extrusion was performed using a capillary rheometer. The molecular orientation in the strands collected after cooling in the air was found to be enhanced by the LDPE addition, suggesting that flow-induced crystallization was accelerated even at capillary extrusion.

Oil-water interfacial behavior of zein-soy protein composite nanoparticles in high internal phase Pickering emulsion

We investigated the interfacial properties of zein-soy protein isolate (SPI) composite particles (ZSCPs) at the oil-water (O/W) interface through pH-shift treatment, along with the preparation and stability of high internal phase Pickering emulsions (HIPPEs). Fourier transform infrared spectroscopy (FTIR), three-dimensional fluorescence, and scanning electron microscopy (SEM) revealed hydrogen bonds and hydrophobic interactions within ZSCPs, altering their structure based on mass ratios. Increasing SPI content in ZSCPs decreased particle size, dynamic interfacial tension (γ), and molecular entanglement, promoting diffusion, penetration, and rearrangement processes. Zein particles (ZPs) exhibited fast diffusion and penetration rates due to higher surface hydrophobicity (H0) and lower zeta potential, while rearrangement was hindered. ZSCPs formed viscoelastic films at the O/W interface, strengthened by SPI. Protein films displayed strain softening during extension in the dilatational measurement under relatively large amplitude (>20%). However, during compression at large amplitude, the protein particle with zein to SPI mass ratios of 10:0 and 7:3 interface films showed strain hardening, while 5:5, 3:7 and 0:10 strain softening. HIPPEs stabilized by ZSCPs showed enhanced interface performance, ensuring long-term stability (upto 30 days). These findings offer new prospects for ZSCP applications in food emulsions, while enhancing our understanding of protein particle adsorption at the O/W interface.

Mechanical and thermal properties of polyamide‐6 nanocomposites reinforced by graphene oxide with low loading by double extrusion method

AbstractThe high toughness, high abrasion resistance, and high water absorption capacity of polyamide‐6 (PA6), and the restacking of graphene oxide (GO) sheets make it quite challenging to get uniformly dispersed GO/PA6 nanocomposites. Herein, GO of different parts per hundred ratios (phr) was melt‐mixed with PA6 matrix by double extrusion using a twin‐screw compounder, followed by the micro twin‐screw extruder, and composites were prepared by injection molding method. The stress–strain curves from tensile measurements showed strain hardening in nanocomposites. The yield strength and Young's modulus increased by 11.3% and 16.7% respectively, for 0.1 phr GO loading. The crystallization and melting temperatures in differential scanning calorimetry (DSC) were increased by 4.7 and 9.6°C, respectively with 0.1 phr GO reinforcement. The Raman and XRD analysis showed continuous shifting in the intensity peaks with increasing reinforcements. Moreover, a double extrusion process imparts good mechanical and thermal stability to our composites. The significant improvement in mechanical and thermal performance of injection molded nanocomposites at very low reinforcements leads to their potential applications in automobiles, civil constructions, smart textiles, packaging, and sensors.

Soil particle size-dependent constitutive modeling of frozen soil under impact loading

In this study, the soil particle size dependence of the impact dynamic mechanical properties of frozen soil was investigated using a split Hopkinson pressure bar, and the meso-deformation mechanism of frozen soil was analyzed via electron microscopy. Under impact loading, the dynamic stress-strain curves of frozen soil showed strain hardening, strain softening, strain rate-temperature sensitivity, and soil particle size dependence, and the soil particle size dependence of frozen soil was considered to be significantly influenced by non-uniform meso-deformation, which primarily appeared in the form of microcracks surrounding the coarse particles. A constitutive model comprising a multiplicative hardening law was proposed, and soil particle size dependence was introduced through the equivalent strain gradient of the soil cell element. The impact compression process of frozen soil was simulated in ABAQUS/Explicit using the proposed model, and the mechanism of frozen soil deformation was summarized by the finite element analysis: the stress concentration around coarse particles induces the initiation of microcracks, the propagation of microcracks forms a crack network, eventually leading to the softening behavior of frozen soil.

Shear strength of municipal solid waste rejected from material recovery facilities in the city of São Paulo, Brazil

The mechanical behavior of municipal solid waste (MSW) is a critical issue in environmental geotechnics, given the pollution and public health risks associated with slope failures. In Brazil, waste composition is expected to change due to the hierarchy of sustainable practices established by the National Solid Waste Policy, which aims to improve the recovery of organic and recyclable materials. Not much progress has been made since the implementation of this law; thus, its effects on the design and operation of landfills are not fully clear. This study presents and discusses compaction and shear strength parameters of dry MSW after mechanical sorting of medium and large recyclable items and shredding. The maximum dry unit weight for the standard Proctor compaction test ranged from 6.6 to 10.0 kN/m3 and the optimum moisture content ranged from 20% to 42%. Stress-displacement curves of direct shear tests showed strain hardening and shear strength parameters of Mohr-Coulomb envelopes were displacement-dependent. The friction angle ranged from 3.2° to 42.9° and the cohesion intercept ranged from 1.3 to 31.3 kPa, at a displacement of 9 mm (15% of the specimen length). These results are in line with the literature, since a high content of waste materials that proved to affect geotechnical properties, such as plastic, paper, cardboard, textile, and glass, remained after pre-treatment.

Finite-strain elasticity theory and liquid-liquid phase separation in compressible gels.

The theory of finite-strain elasticity is applied to the phenomenon of cavitation observed in polymer gels following liquid-liquid phase separation of the solvent, which opens a fascinating window on the role of finite-strain elasticity theory in soft materials in general. We show that compressibility effects strongly enhance cavitation in simple materials that obey neo-Hookean elasticity. On the other hand, cavitation phenomena in gels of flexible polymers in a binary solvent that phase separates are surprisingly similar to those of incompressible materials. We find that, as a function of the interfacial energy between the two solvent components, there is a sharp transition between cavitation and classical nucleation and growth. Next, biopolymer gels are characterized by strain hardening and even very low levels of strain hardening turn out to suppress cavitation in polymer gels that obey Flory-Huggins theory in the absence of strain hardening. Our results indicate that cavitation is, in essence, not possible for polymer networks that show strain hardening.

Mechanical test and action mechanism of interface between gravel soil and concrete

The mechanical properties of the gravel soil-concrete structure interface are one of the important issues in academia and engineering. In this research, gravel soil samples were collected from the Three Gorges Reservoir region to carry out simple shear and direct shear tests of the gravel soil-structure interface. The shearing process was simulated with the numerical method. The strength and deformation characteristics of the interface, the applicability of the interface constitutive model, and the failure mechanism of the interface were analyzed. The results show that: 1) The direct shear test curve of the gravel soil-concrete interface shows strain softening with obvious stress peak, while the simple shear test curve shows strain hardening. The stress peak of the direct shear test is about 30% higher than that of the simple shear test. The shear contraction effect of the simple shear test is about 31% larger than that of the direct shear test. 2) The non-linear relationship of the gravel soil-concrete interface can be described by a hyperbola model, which has a good adaptability to the constitutive relationship of the interface in numerical analysis software. 3) The gravel soil-concrete interface gradually develops shear failure from the edge to the inside. The essence of soil-structure interaction is the movement of soil grains. The research results can provide a reference for the analysis of gravel soil-concrete interaction.

Study on the cohesive shear characteristics and intrinsic modelling of the root–tailing soil interface of Amorpha fruticosa

To study the soil consolidation effect of shrub plant roots on tailings soil and to explore the frictional characteristics of plant roots on tailings soil, three experimental conditions of the root–soil interface were established by using a modified indoor direct shear instrument with binders such as liquid sodium silicate and cyanoacrylate to conduct direct shear frictional tests at the root–soil interface using the roots of the typical slope protection plant Amorpha fruticosa. The Gompertz improved curve model was established by using the relationship between shear stress and shear displacement and the trend of the root–soil interface parameter index. The results were compared between the improved Gompertz curve model and the Clough–Duncan hyperbolic model, and a two-factor coupled improved Gompertz interfacial intrinsic structure model with normal stress and cohesive strength factor was established. The results showed that the interface shear stress and shear displacement showed strain hardening characteristics at different normal pressures for cohesive strength ratios of 1.5 and 1.7 at the root–tailing soil interface. At a cohesive strength ratio of 1.6, strain-softening was observed from 100 to 300 kPa and strain hardening was observed at 400 kPa. The improved Gompertz curve model predicts the shear stress and shear displacement curves at the root–soil interface with different cohesive strengths more reasonably than the Clough–Duncan hyperbolic model, and the maximum accuracy can be improved by nearly 40%. The two-factor coupled improved Gompertz curve model can fit the shear stress versus shear displacement relationship at the A. fruticosa root–tailing soil interface.

Experimental investigation and fuzzy TOPSIS optimisation of Ti6Al4V finish milling

ABSTRACT Ti6A14V is a well-known ‘Difficult to Cut’ material in the aerospace industry. Ti6Al4V shows strain hardening, poor thermal conductivity and chemical reactivity at elevated temperatures, which implies low machinability. This work presents an experimental investigation of 3D finish milling of Ti6Al4V material by Taguchi design of experiments, having L25 array. The considered process parameters are cutting speed, feed, depth of cut, tool type, coolant type and computer aided manufacturing strategy. The experimentation is conducted on the 3D finish milling process, and the performance in terms of tool life, tool wear and surface integrity were recorded. The fuzzy technique for order of preference by similarity to ideal solution, a multiple-criteria decision-making tool, was applied on experimental responses. The yielded optimum results are derived at minimum cutting speed, moderate depth of cut, feed rate per tooth and collaboration under high concentrated wet lubrication using a PVD-TiAlN cutting tool driven by streamline computer aided manufacturing strategy. In addition, analysis of variance confirms the influential process parameter contribution on the respective performance. Finally, optimised process parameters were applied for the gear bracket finish milling through streamline CAM strategy, which results in minimum flank and crater wear with an average surface roughness of 0.17 microns.

Finite element analysis to determine the role of porosity in dynamic localization and fragmentation: Application to porous microstructures obtained from additively manufactured materials

In this paper, we have performed a microstructurally-informed finite element analysis on the effect of porosity on the formation of multiple necks and fragments in ductile thin rings subjected to dynamic expansion. For that purpose, we have characterized by X-ray tomography the porous microstructure of 4 different additively manufactured materials (aluminium alloy AlSi10Mg, stainless steel 316L, titanium alloy Ti6Al4V and Inconel 718L) with initial void volume fractions ranging from ≈0.0007% to ≈ 2%, and pore sizes varying between ≈ 6 μm and ≈110 μm. Three-dimensional analysis of the tomograms has revealed that the voids generally have nearly spherical shape and quite homogeneous spatial distribution in the bulk of the four materials tested. The pore size distributions quantified from the tomograms have been characterized using a Log-normal statistical function, which has been used in conjunction with a Force Biased Algorithm that replicates the experimentally observed random spatial distribution of the voids, to generate ring expansion finite element models in ABAQUS/Explicit (2016) which include actual porous microstructures representative of the materials tested. We have modeled the materials behavior using von Mises plasticity, and we have carried out finite element calculations for both elastic perfectly-plastic materials, and materials which show strain hardening, strain rate hardening and temperature softening effects. Moreover, we have assumed that fracture occurs when a critical value of effective plastic strain is reached. The finite element calculations have been performed for expansion velocities ranging from 50 m/s to 500 m/s. A key point of this investigation is that we have established individualized correlations between the main features of the porous microstructure (i.e. initial void volume fraction, average void size and maximum void size) and the number of necks and fragments formed in the calculations. In addition, we have brought out the effect of the porous microstrucure and inertia on the distributions of neck and fragment sizes. To the authors’ knowledge, this is the first paper ever considering actual porous microstructures to investigate the role of material defects in multiple localization and dynamic fragmentation of ductile metallic materials.

Study on Mechanical Properties of Gravelly Sand under Different Stress Paths

To investigate the strength and deformation characteristics of gravelly sand on the Qinghai-Tibet Plateau under different stress paths, a series of triaxial shear tests was conducted under confining pressures of 50–400 kPa in four types of stress path conditions of conventional triaxial compression (CTC) (drained and undrained), triaxial compression (TC), and reduced triaxial compression (RTC). We can see from the test results that gravelly sand samples show strain hardening and shear contraction under the CTC (drained), TC, and RTC during the shearing process but exhibit strain softening under the CTC (undrained). To explore the microscopic deformation mechanism of gravelly sand, a characteristic angle θ was defined to reflect the relative movement of soil particles. The relationship between principal stress ratio σ1/σ3 and characteristic angle θ and that between void ratio e and characteristic angle θ were derived. Subsequently, the relationship expression of stress ratio η (q/p) and void ratio e was established, and the trend of void ratio e with the stress path was studied. To describe the strain hardening and strain softening characteristics of gravelly sand in different stress paths, a new dilatancy equation was obtained by introducing the characteristic state stress ratio Mc into the dilatancy equation of the modified Cam-Clay model based on the state-dependent dilatancy theory. Finally, an elastoplastic constitutive model of gravelly sand was established by applying a nonassociate flow rule. All model parameters can be determined by triaxial shear tests under different stress paths, and the comparison results show that the proposed model can well reflect the mechanical behaviors of gravelly sand under different stress paths.

Investigation on the mechanical properties of a calcareous sand: the role of the initial fabric

This study examines the effect of the initial fabric on the coefficient of the lateral earth pressure at rest K0, the undrained monotonic loading strength and the liquefaction resistance of a calcareous sand from a reclamation land in Persian Gulf. K0 consolidation, undrained compression and extension and cyclic undrained loading triaxial tests are performed on laboratory samples reconstituted by air and water pluviation, dry and moist tamping and dry funnel deposition methods. Test results show that the air pluviation and moist tamping samples own the highest and the lowest K0 respectively. All the samples at medium loose and medium dense states show strain hardening when subjected to undrained monotonic loading. The air pluviation samples are more contractive than the other samples at the phase transformation points and the moist tamping samples exhibit an over-consolidated behavior. In the cyclic loading tests, the air pluviation and the moist tamping samples exhibit the lowest and the highest liquefaction resistance. It is shown that the evaluation and comparison of the cyclic undrained strength of various sands should take the sample preparation method into consideration scrupulously. The test results also indicate that although the mechanical property of soil sample is influenced by the fabric differences induced by sample preparation method, other factors such as homogeneity and stress history should not be neglected.

Physical and mechanical properties of the overburden layer on gas hydrate-bearing sediments of the South China sea

Gas hydrate exploitation may trigger the destruction of the overburden structure and settlement of the overburden layer on the gas hydrate-bearing sediments. It is extremely urgent to explore the basic laws governing the physical and mechanical properties of the overburden layers before performing commercial exploitations of hydrates. However, relatively few studies have focused on the physical and mechanical properties of the overburden layer (uppermost ~10 m) on the gas hydrate-bearing sediments of the South China Sea. In this research, we studied the physical and mechanical properties of the overburden sediments from this area, including the particle size distribution, the specific surface area, the pore size distribution, the water content, the liquid/plastic limits, and the mineral and chemical compositions of the particles, as well as the strength and deformation characteristics. According to the results, we found that the overburden sediments of the Shenhu area are characterized as well-graded clayey silts and considered to be internally stable and self-filtering. The isothermal adsorption-desorption curve is a Type H3 hysteretic loop, indicating that the shape of the particles occurs primarily in a plate form, and most of the pores are slit-shaped. The plasticity index in this area is relatively lower than that in other areas, which suggests that there is a risk of overburden collapse during the production process of hydrates. The mineral composition of the overburden sediment particles is primarily quartz, plagioclase, calcite and some accessory clay minerals, which can provide guidance for remolding the overburden sediments in the laboratory. The sediments show strain hardening and shear contraction behavior upon shearing; in addition, the established strength criterion will contribute to the formulation of constitutive equations for the overburden sediments, which can be used as essential input parameters in gas hydrate production simulations.

Investigation on mechanical properties of artificially structured soils under different stress paths

Natural soils are structured in deposit process. This is the biggest difference between the remolded soils and natural soils. As one of the stress-dependent materials, different kinds of stress-path have great influences on the mechanical properties of structured soils. Based on the triaxial tests on different kinds of stress path, the mechanical properties of structured soils and remolded soils are discussed in the paper. The main conclusions are as follows: under conventional triaxial compression tests, the sample of structured soils shows strain softening and volume dilation when the confining pressure is lower (25kPa); when the confining pressure becomes large (100 kPa and 200 kPa), the sample shows strain hardening and volume contraction; while, the remolded soils behave stress hardening and volume strain contraction under all kinds of confining pressures. Under triaxial extension tests, the sample of structured soils shows strain softening and volume dilation in the loading process; the remolded soils have strain hardening and volume contraction. Under constant mean stress loading path, the sample of structured soils shows plastic flow and volume strain contraction, while the remolded soils perform strain hardening and volume contraction.

Effect of salt valency and concentration on shear and extensional rheology of aqueous polyelectrolyte solutions for enhanced oil recovery

The injection of polymer solutions into an oil basin can lead to enhanced oil recovery (EOR) by increasing the microscopic sweep of the reservoir, improving the water-oil motility ratio, and thus leading to greater yield from oil fields. In this contribution, we characterize both shear and extensional rheological response of aqueous solutions of partially hydrolyzed polyacrylamide (HPAM), the most commonly used polymer for EOR, for velocity gradients in both the flow direction (extensional) and perpendicular to flow (shear) arise in EOR applications. As HPAM is a charged polymer, to better emulate the environment in oil basins, the rheological response was investigated in presence of salt, sodium chloride, and calcium chloride, with concentrations 3.7 × 10−4 − 1.5 M, as a function of polymer molecular weight (2–10 million g/mol) and concentration (0.005–0.3 wt%). The extensional relaxation times and extensional viscosity are measured using dripping-onto-substrate (DoS) rheometry protocols, and a commercial shear rheometer was utilized for characterizing the shear rheology response. The polyelectrolyte solutions formed by HPAM exhibit shear thinning in steady shear, but show strain hardening in response to extensional flow. Even though an increase in monovalent salt concentration leads to a decrease in both shear viscosity and extensional relaxation times, an increase in divalent salt concentration leads to an increase in extensional viscosity and relaxation time, implying that ion coordination can play a role in the presence of multivalent ions.

Effect of Finite Extensibility on Nonlinear Extensional Rheology of Polymer Melts

We recently showed that two systems have the same nonlinear flow dynamics if they have (1) the same number of entanglements, Z, (2) the same number of Kuhn segments between entanglements, Ne, and (3) a single monomeric friction reduction between all species. Because differences in polymer chemistry result in different values of (1)–(3), these results show that the likelihood of two melts having the same nonlinear behavior is improbable. This work determines the dependence of the nonlinear extensional flow behavior on Ne for three polymer melts: polystyrene, poly(methyl methacrylate), and poly(tert-butylstyrene). We show that polymer melts with the same Z have almost identical scaled linear viscoelasticity. Extensional rheology at constant strain rate shows strain hardening depends strongly on the value of Ne. More specifically, our data suggest a power-law dependence of steady state stress on the Weissenberg number which increases with increasing Ne.

Experimental simple shear study of composite soil with cemented soil core

Cement soil mixing piles are an effective treatment method for marine soft clay. To investigate the static and dynamic characteristics of the composite soil with cemented soil core, a series of experiments are carried out by using the cyclic simple shear test. The result shows that, the static shear strain showed strain hardening, cemented soil core can improve static shear strength of composite soil, vertical stress can enlarge reinforcement of cemented soil core. The tendency of strain development of composite soil with different area replacement ratios under cyclic loading is the same as that of pure clay, existing critical cyclic stress ratios corresponding to different area replacement ratios. In addition, improving area replacement ratio can increase cyclic strength. At same time, adding of cemented soil core does not change shape of hysteresis curve compared with it for clay either. Moreover, cemented soil core can also obstruct stiffness softening. Through regression analysis of the experimental data, relationship between cyclic number and soil softening index is proved to be linear. The results can give a reference for the dynamic characters of the marine soft clay foundation with cement soil mixing piles.

Influence of processing on the flow properties of long‐chain branched polypropylene

Long‐chain branched polymers have high melt strength and show strain hardening in the elongational flow. These characteristics are important quantities for certain processing procedures, but are strongly affected by thermomechanical treatment. In this study, different rheological methods and material functions in shear and elongation are applied to determine the flow behavior that is affected by certain processing procedures. For this purpose, a series of blends of linear polypropylene (L‐PP) and long‐chain branched polypropylene (LCB‐PP) is prepared using different processing methods (mixing chamber with kneading elements, twin‐screw extruder, foaming) and varying processing parameters. The decrease of dynamic moduli and of flow activation energy depends on the number of processing stresses. Equilibrium states are created by solution treatment, and in this way process‐modification can be separated into reversible and irreversible parts. It is concluded that the irreversible process‐modification does not reduce the density of entanglements, but tears chains. POLYM. ENG. SCI., 58:1596–1603, 2018. © 2017 Society of Plastics Engineers