Creep Measurements Research Articles

Viscoelastic Behavior of Crude Oil-Gum Emulsions in Enhanced Oil Recovery.

The experimental study of the Creep-recovery examination is necessary to understand the viscoelastic behavior of crude oil-Xanthan gum emulsions. The experimental measurements and analysis of these tests were completed using RheoStress RS100 under controlled stress CS-mode. Rheometers with CS-mode allow for a useful and direct technique for the experimental measurements of creep and recovery stages. This investigation covers a wide range of crude oil concentration of 0–75% by volume, Xanthan concentration range of 0–104 ppm, and two types of Xanthan gums are used and investigated. The creep-recovery measurements of crude oil-Xanthan gums emulsions were extensively investigated. It was important to find the linear viscoelastic range for the examined crude oil-Xanthan gum emulsions. The experimental measurements and analysis of the creep-recovery examinations showed that the linear viscoelastic range was up to 1 Pa. The experimental investigation showed that the higher the concentration of the used gum and crude oil, the lower the compliance of the emulsions. For the Xanthan concentrations of less than 103 ppm, the crude oil-gum emulsion exhibited viscous behavior. However, for the Xanthan concentration of higher than 103, the examined emulsions displayed viscoelastic behavior.

Interface creep behavior of tensioned GFRP tendons embedded in cemented soils

This paper presents an experimental investigation and modeling of interface creep behavior of glass fiber-reinforced polymer (GRFP) tendons embedded in cemented soils. Rapid and creep pullout tests were carried out on GRFP tendons embedded in cemented soils using a specially developed pullout setup. Interface creep displacement responses for specimens with two different water–cement ratios were derived under various interface shear stress conditions. A modified Burgers model was developed to characterize the interface creep behavior by incorporating a time-dependent viscosity coefficient. This viscosity coefficient was calibrated using creep rate variation obtained experimentally. Regression fittings on a part of interface creep measurements were conducted to determine the value of the parameters of the interface creep model. Additional interface creep measurements were used to validate the applicability of the presented creep testing protocol and the effectiveness of the rheological modeling was validated.

The effect of aspect ratio on the mechanical behavior of Li metal in solid-state cells

The Li metal anode is necessary for solid-state batteries to dramatically exceed the energy density of state-of-the-art conventional Li-ion batteries. To enable the Li metal anode, the mechanical properties of Li metal under compression in a commercially relevant cell configuration must be determined. This work examines the compression creep behavior of Li metal coupled with a relevant model solid-state electrolyte (Li 6.5 La 3 Ta 0.5 Zr 1.5 O 12 ) and current collector (Ni) as a function of applied stress (1–10 MPa) and Li foil thickness (100–700 μm). At 1 MPa applied stress, the strain rate of all Li foil thicknesses under compression was almost four orders of magnitude lower than what is predicted from tensile creep tests. Steady-state creep behavior was observed for Li foil ≥350 μm at 5 MPa and ≥250 μm at 10 MPa. Conversely, sustained creep deformation was not observed for 100 and 150 μm Li foils at any applied stress. It is suggested that friction at the Li/LLZO and Li/Ni interfaces leads to the formation of hydrostatic stress that controls Li deformation at low aspect ratios. These results have implications for battery pack stack pressure requirements, particularly relating to void formation during stripping and Li metal filament penetration during plating. • Compressive creep measurements of Li metal foils in solid-state cell configuration. • Strain and strain rate decreased with decreasing Li foil thickness. • The strain rate of Li measured in compression was lower than predicted from tension. • Friction at Li interfaces prevents substantial creep deformation for thin Li foils.

Yielding to stress in Pickering emulsions at dilute and intermediate volume fractions

Emulsions yield and flow (or lose their shape) when sufficient stress is applied to force the drops to move past each other. The drops in emulsions stabilised by nanoparticles do not move all at once, unlike in emulsions stabilised by surfactants. This is because particles that are not attached to the oil-water interface can aggregate into networks in the continuous phase. The networks around the drops must be disrupted before the drops can move. We used a combination of steady and oscillatory shear, and creep measurements to probe Pickering emulsion yielding behaviour at different drop volume fractions. We characterised the heterogeneous structure of the emulsions on the micro- and nano-scale using confocal fluorescence and electron microscopy techniques. A key finding is that two processes occur during the transition from solid to fluid flow in Pickering emulsions. This is best revealed by oscillatory measurements. We also found evidence of structure recovery in emulsions while they were being sheared. These results have implications for designing Pickering emulsions which retain their shape, rather than slumping.

Mechanical Performances of Isolated Cuticles Along Tomato Fruit Growth and Ripening.

The cuticle is the most external layer that protects fruits from the environment and constitutes the first shield against physical impacts. The preservation of its mechanical integrity is essential to avoid the access to epidermal cell walls and to prevent mass loss and damage that affect the commercial quality of fruits. The rheology of the cuticle is also very important to respond to the size modification along fruit growth and to regulate the diffusion of molecules from and toward the atmosphere. The mechanical performance of cuticles is regulated by the amount and assembly of its components (mainly cutin, polysaccharides, and waxes). In tomato fruit cuticles, phenolics, a minor cuticle component, have been found to have a strong influence on their mechanical behavior. To fully characterize the biomechanics of tomato fruit cuticle, transient creep, uniaxial tests, and multi strain dynamic mechanical analysis (DMA) measurements have been carried out. Two well-differentiated stages have been identified. At early stages of growth, characterized by a low phenolic content, the cuticle displays a soft elastic behavior. Upon increased phenolic accumulation during ripening, a progressive stiffening is observed. The increment of viscoelasticity in ripe fruit cuticles has also been associated with the presence of these compounds. The transition from the soft elastic to the more rigid viscoelastic regime can be explained by the cooperative association of phenolics with both the cutin and the polysaccharide fractions.

Microstructure evolution and deformation mechanism of a [111]-oriented nickel-based single-crystal superalloy during high-temperature creep

Through creep measurement and microstructure observation, the microstructure evolution and deformation mechanism of a [111]-oriented nickel-based single-crystal superalloy at 980 °C/186 MPa were studied. The results show that the [111]-oriented single-crystal superalloy after full heat treatment featured cubic γ' phases coherently embedded in the γ phases and regularly arranged along the <100> direction. During the creep, the cubic γ' phases were interconnected, phase thickening and coarsening occurred, and the phase transformed into a lamellar rafted structure that grew staggered in three-dimensional space. The deformation characteristics of the [111]-oriented nickel-based single-crystal superalloy during creep under experimental conditions were that the dislocations slipped, propagated, and climbed over the γ' phases in the matrix, and then cut into the γ' phase and cross-slipped from the {111} plane to the {100} plane to form Kear–Wilsdorf (K–W) locks. Finally, the dislocations cut the γ' phase in the form of dislocation pairs, causing the γ' phase to lose its creep resistance, resulting in creep fracture.

Finite element modeling of creep deformation in dendritic alloys

Finite element modeling is used to simulate the secondary creep rate of alloys with an inhomogeneous distribution of nano-precipitates, located within colonies of long, parallel dendrites, due to elemental segregation during directional solidification. Three-dimensional, periodic unit cells are created to approximate the aligned dendritic microstructure, with cylindrical dendrites (with high creep resistance due to nanoprecipitates) embedded within a precipitate-free matrix (with low creep resistance). Using creep power-laws for the precipitate-free matrix and the precipitation-strengthened dendrites, the creep rate of a dendritic aluminum alloy is computed for various dendrite geometry and volume fraction. When stress is applied parallel to the dendrite long axis, calculated creep rates are in reasonable agreement with creep measurements, at 300 °C, of a dendritic Al-0.07Sc-0.05Zr (at.%) alloy consisting of a pure Al matrix containing 50–60 vol% dendrites strengthened with L12-Al3(Sc,Zr) nanoprecipitates. Calculations for cases where aligned, cylindrical dendrites are ridged (emulating dendritic stubs) or bridged (emulating secondary arms) predict that these dendritic geometries, at constant volume fraction and parallel loading, strengthen less efficiently the matrix as compared to uniform cylindrical dendrites, reflecting a less effective load transfer between the two phases. When stress is applied perpendicular to the dendrites, the creep response becomes dominated by the matrix which shows higher stresses than under parallel loading, leading to much higher alloy creep rates. Alloys with bridged dendrites show the lowest perpendicular strain rate due to the alignment of the secondary arms (bridges) with the applied load, increasing load transfer to the precipitation-strengthened dendrites.

Experimental Study of Blended Binders with Metakaolin

Three metakaolins are evaluated for use as supplementary cementitious materials in cement-based systems. The metakaolins vary in mineralogical composition and in fabrication (traditional and flash calcination), but are quite similar in their surface area (16–19 m2/g), but are quite similar in mineralogical composition. Performance of metakaolin mixtures will be compared to two control mixtures (standard concrete for foundation C40/50 and high performance concrete C60/75). In this study, the properties of fresh concrete and the mechanical and durability properties of hardened concrete will be examined. The rheological behaviour are aimed to determine the effect of metakaolin on mixture workability. Compressive, tensile and flexural strength and elastic modulus will be measured at various concrete ages. The influence of metakaolin on durability is assessed through rapid chloride migration and carbonation measurements. For high performance concrete mixtures, drying and autogenous shrinkage will be monitored and creep measurements are performed and compared.

Elevated-temperature Deformation Mechanisms in a CrMnFeCoNi High-Entropy Alloy

Stress reduction creep experiments were performed on a CrMnFeCoNi high-entropy alloy at 1073 K to characterize the steady-state and transient creep properties of this material. From measurements of constant-structure creep, the activation area for deformation of CrMnFeCoNi was determined to be ∼100 b2 and to decrease with increasing applied stress, indicating the presence of both concentrated solid solution and forest dislocation control of high temperature plastic deformation. With the aid of a recent solid solution theory for high entropy alloys, quantitative separation of the two mechanisms was carried out using a Haasen plot and the results show that creep in CrMnFeCoNi relies heavily on thermal activation with the majority of creep strength coming from solid solution hardening, especially at low applied stresses. The overall analysis conducted in this study reveals that steady-state creep deformation of CrMnFeCoNi at 1073 K can be adequately described by existing concentrated solid solution hardening models and forest dislocation hardening models. This observation suggests it may be possible to develop a unified treatment of the dislocation glide kinetics for this alloy from cryogenic to elevated temperatures.

Volume Change during Creep and Micromechanical Deformation Processes in PLA-PBSA Binary Blends.

In this paper, creep measurements were carried out on poly(lactic acid) (PLA) and its blends with poly(butylene succinate-adipate) (PBSA) to investigate the specific micromechanical behavior of these materials, which are promising for replacing fossil-based plastics in several applications. Two different PBSA contents at 15 and 20 wt.% were investigated, and the binary blends were named 85-15 and 80-20, respectively. Measurements of the volume strain, using an optical extensometer, were carried out with a universal testing machine in creep configuration to determine, accompanied by SEM images, the deformation processes occurring in a biopolymeric blend. With the aim of correlating the creep and the dilatation variation, analytical models were applied for the first time in biopolymeric binary blends. By using an Eyring plot, a significant change in the curves was found, and it coincided with the onset of the cavitation/debonding mechanism. Furthermore, starting from the data of the pure PLA matrix, using the Eyring relationship, an apparent stress concentration factor was calculated for PLA-PBSA systems. From this study, it emerged that the introduction of PBSA particles causes an increment in the apparent stress intensity factor, and this can be ascribed to the lower adhesion between the two biopolymers. Furthermore, as also confirmed by SEM analysis, it was found that debonding was the main micromechanical mechanism responsible for the volume variation under creep configuration; it was found that debonding starts earlier (at a lower stress level) for the 85-15 blend.

Creep on the Sargent Fault over the Past 50 Yr from Alignment Arrays with Implications for Slip Transfer between the Calaveras and San Andreas Faults, California

ABSTRACT The 55-km-long Sargent fault connects the creeping Calaveras fault with the locked San Andreas fault through the Santa Cruz Mountains west of Gilroy, California. The position of the Sargent fault between these two faults may have implications for slip transfer and strain accumulation between a creeping and locked fault. The detection and measurement of creep on the Sargent fault would indicate where interseismic strain is accumulating adjacent to these neighboring faults. In 1969, two alignment arrays separated by 3.7 km were installed across the central section of the Sargent fault to investigate potential creep. These arrays were measured in 1970 and 1975, and comparison of these measurements yielded a creep rate of 3.4 ± 0.6 mm/yr across two fault strands in the northern array; results from the southern array were never published. In 2019 and 2020, we resurveyed both arrays using a total station and analyzed the results to determine accumulated fault creep. Our results show that between 1970 and 2020, a period of 49.3 yr, the northern array was dextrally offset 164 ± 25 mm across the same two fault strands that were active in the 1970s, yielding an average creep rate of 3.3 ± 1.3 mm/yr. Thus, it appears that the 5 and 50 yr creep rates at this site are similar. The southern array, which may not span the entire fault zone, was dextrally offset 84 ± 13 mm across two fault strands between 1970 and 2019, yielding an average creep rate of 1.7 ± 0.8 mm/yr over 48.9 yr. These recent surveys document continued creep on the Sargent fault, which may reduce seismic strain accumulation and therefore seismic hazard. However, continued aseismic slip on this fault may result in the redistribution of stress and strain to adjacent faults and should be an area of continued study.

Influences of elasticity on the measurement of power law creep parameters by nanoindentation

Indentation testing is a well-known method to measure the rate dependence of the strength of materials at small scales through a variety of different testing methodologies. In many cases, a power-law creep constitutive relationship relating the indentation strain rate to the hardness, or the mean pressure applied to the material by the indenter, is assumed. However, this method of analysis does not explicitly include elastic effects, which for some testing methods may be significant. In this work, a new method of analysis that explicitly considers the elastic effects is presented. The conditions and materials for which the elastic contribution is non-negligible are identified, and simple closed-form analytical expressions are developed to account for the elastic effects. This leads to improvements in the measurement of power law creep parameters such as the stress exponent and creep coefficient. Experimental assessment of the new analysis procedures is presented for amorphous selenium (Se) and calcium fluoride (CaF2). After accounting for the elastic effects, an equivalence of different indentation creep testing methods is observed for Se due to the fact that this material has a very nearly history independent plastic response and no indentation size effect (ISE). On the other hand, significant differences are observed in the case of CaF2 because of indentation size effects. The findings of this work have important implications for several widely used indentation creep measurement methods such as the constant strain rate method (CSR) and the strain rate jump test (SRJ). Based on the results, guidelines for performing indentation creep tests with improved precision and accuracy are presented.

Aeolian creep transport: A review

This paper reviews the literature on the nature of aeolian creep, the field and wind tunnel methods used to measure creep transport, the relative contribution of creep transport to total transport, and creep models. We discuss the dynamics of fluid- and impact-driven creep, potential sources of error in creep measurement or estimation, and the variability of the relative contribution of creep to total transport. We compare and discuss creep transport studies conducted in wind tunnels and in the field and demonstrate the disparity of results between different studies. Regression analysis of creep data indicates no significant relationship between the proportion of sand flux moved as creep and the magnitude of wind forcing. Individual studies are shown to produce contradictory results for the relationship between the proportion of total transport moved as creep and wind forcing. These findings point to the importance of better empiricism, especially, to elucidate the role of creep in wind-blown sand systems.

An extension-dominant 9-km-long ground failure along a buried geological fault on the eastern Beijing Plain, China

In the northern Beijing Plain (BPN), ground failures associated with land subsidence have occurred and rapidly progressed, damaging hundreds of buildings and roads in recent years. In 2016, an 8.7-km-long ground failure, named the Songzhuang (SZ) ground failure, was discovered in the eastern part of the Beijing Plain. Geological surveys, mapping, creep measurements, trenching, drilling, and geophysical exploration indicate that the SZ ground failure has geometric structural features and surface deformation that differ from those of other ground failures in the BPN: First, the SZ ground failure consists of one main fissure and many secondary fissures. Second, the SZ failure shows tensile deformation with negligible vertical dislocation. Third, in the profile, the SZ ground failure shows extensional cracks with limited extension depths that close gradually with depth. Based on the relationships between ground failures and influencing factors, including a pre-existing fault, earthquakes, and groundwater pumping, we conclude that this failure took shape after the earthquake, and was enlarged under the action of groundwater pumping. The pre-existing fault, which is a subsidiary fault of the northern section of the Nanyuan-Tongxian (NTN) fault, determined the area in which the SZ ground failure first formed.

A time-shift correction for extraction of viscoelastic parameters from ramp-hold AFM experiments

The stress relaxation and creep measurements are commonly implemented in AFM indentation experiments to analyze the viscoelastic properties of a sample in the time domain. The assumption of an instantaneous step load is often applied which can lead to erroneous estimation of viscoelastic parameters from the experimental data. A viscoelastic solution for the ramp-hold indentation profile might be used but requires higher computational costs. Here, we employed simulations for the ramp-hold indentations for the power-law rheology (PLR) and standard linear solid models. The error coming from the instantaneous load assumption was analyzed and a simple empirical correction for the finite ramp time was employed as a time shift of the hold region. The correction was tested in experiments on cells, in which the data from stress relaxation, creep, and force volume experiments were compared. The correction showed good applicability for the extraction of the PLR viscoelastic parameters.

Effect of Bi Content on the Microstructure and Mechanical Performance of Sn-1Ag-0.5Cu Solder Alloy

The purpose of this work is to explore the impact of 0.5, 1.5, 2.5 and 3.5 wt.% Bi additions on the microstructure and mechanical performance of Sn-1Ag-0.5Cu solder alloy. Scanning electron microscope (SEM) and X-ray diffraction (XRD) were utilized to examine the microstructure of the present solders. Creep measurements have been used for the preliminary assessment of mechanical properties. The steady-state creep rate, έst, diminished as the Bi’s concentration increased and reached 2.5 wt.%, with this trend altering above this point. Furthermore, increasing the aging or testing temperature caused the έst values to increment for all the investigated solders. έst variations with different Bi content and aging temperature were observed by examining the Sn-Ag-Cu solders’ structural evolutions. The mean value of the activation energy of all investigated solder alloys was found to be ∼52 kJ/mol. This value is appropriate to that quoted for the dislocation climb through the core diffusion as the dominant operating mechanism. The XRD findings supported the microstructure and lattice parameters variations with both aging temperatures and bismuth concentrations.

Effect of Fenugreek fiber on Rheological and chapati making quality of whole wheat flour.

Increase in awareness of consumers and demand has led to the development of various fibre rich food products from different fiber source. In the present work novel roller milled fenugreek fiber rich fraction (FFRF) rich in galactomannans was used for the development of high fiber chapati. Farinograph water absorption and dough stability increased with increase in the addition of FFRF in blends. The creep measurement results showed reduction in the maximum creep compliance and viscoelastic compliance while the zero shear viscosity showed the increasing trend with the increase in the addition of FFRF. The pliability of chapatis significantly decreased on addition of FFRF. The sensory evaluation concluded that the chapati with 10% FFRF is acceptable. The shear force value of chapatis prepared from the control and WWF-FFRF blends were decreased as the storage time increased showing brittleness in the chapatis. The micrographs of an outer layer of chapati (crust) showed partially gelatinized starch. The crumb micrographs of the WWF-FFRF blends chapatis showed large and small starch granules coated with galactomannans gums, and this coating increased with increased addition of FFRF. The composition of 10% fenugreek fiber chapati contained higher amount of minerals, insoluble and soluble dietary fiber compared to that of control sample. The in vitro starch digestibility of formulated chapati showed significant decrease in the values.

Stabilization of Nanocrystalline Copper by Tantalum Grain Boundary Segregation

Nanocrystalline Cu-Ta alloy films were deposited on glass slides by magnetron sputtering. Microstructure characterization proved that most of the tantalum atoms are segregated in the grain boundaries. Nanoindentation creep measurements were performed on it to uncover the stability mechanism of grain boundary segregation on nanocrystalline materials. It is found that segregation can effectively slow down the creep strain rate and the grain boundary activities. The suppressed grain boundary activities endow the alloy with a stable microstructure during plastic deformation and annealing.

Automation in Measurement of Inverse Creep in Textile Yarns

From decades Creep has been known and studied for textile materials. In comparison, a newly observed phenomenon of inverse creep seems not to have received much attention. A new instrument has been fabricated to measure creep and inverse creep in textile materials particularly yarns. Creep and Inverse creep measurements of few of the textile yarns like nylon multifilament yarn, Polyester multifilament yarn, Cotton and wool yarn at different levels of stress have been studied, using the new instrument along with Transreceiver, embedded system and Personal computer the automation is achieved and results are reported in the present paper.

Comprehensive investigation of the viscoelastic properties of PMMA by nanoindentation

Instrumented nanoindentation (NI) was used to examine the viscoelastic properties of poly(methyl methacrylate) (PMMA) as an amorphous polymer model. An evaluation combining adhesive contact and empiric spring–dashpot models has been applied to obtain the instantaneous elastic modulus E0 and the infinitely elastic modulus E∞ from nanoindentation creep curves. The value of E0 has been compared to moduli obtained with atomic force microscopy-based nanoindentation (AFM-NI) and compression tests. Furthermore, the elastic modulus has been evaluated by the method introduced by Oliver and Pharr (O&P) for the NI and AFM-NI results. Comparison of the elastic modulus E0 from the creep measurements of NI and AFM-NI to compression tests reveals good agreement of the results. However, only the O&P based AFM-NI results yield to lower values.