scholarly journals Experimental investigation on the nanoindentation viscoelastic constitutive model of quartz and kaolinite in mudstone

2021 ◽  
Author(s):  
Changlun Sun ◽  
Guichen Li ◽  
Mohamed Elgharib Gomah ◽  
Jiahui Xu ◽  
Haoyu Rong
Keyword(s):  
Peak Load ◽  
Viscoelastic Model ◽  
Model Fitting ◽  
Underlying Mechanism ◽  
Time Dependent ◽  
Underground Engineering ◽  
Engineering Structures ◽  
Sandstone Sample ◽  
Soft Rocks ◽  
Viscoelastic Constitutive Model

AbstractThe creep behaviors in deep underground engineering structures, especially in soft rocks, have a remarkable impact on the long-term stability of the excavations, which finally leads to the high risk and failure of it. Accordingly, it is essential to recognize the time-dependent deformation through the investigation of this phenomenon. In this study, the creep behaviors of soft rocks were examined to help understand the underlying mechanism of the extended time-dependent deformation. Due to the limited results about the time-dependent properties of the constituents of the rock that reveal their heterogeneity, the targeting nanoindentation technique (TNIT), was adopted to investigate the viscoelastic characteristics of kaolinite and quartz in a two-constituent mudstone sample. The TNIT consists of identifications of mineralogical ingredients in mudstone and nanoindentation experiments on each identified constituent. After conducting experiments, the unloading stages of the typical indentation curves were analyzed to calculate the hardness and elastic modulus of both elements in mudstone. Additionally, the 180 s load-holding stages with the peak load of 50 mN were transformed into the typical creep strain–time curves for fitting analysis by using the Kelvin model, the standard viscoelastic model, and the extended viscoelastic model. Fitting results show that the standard viscoelastic model not only can perfectly express the nanoindentation creep behaviors of both kaolinite and quartz but also can produce suitable constants used to measure their creep parameters. The creep parameters of kaolinite are much smaller than that of quartz, which causes the considerable time-dependent deformation of the soft mudstone. Eventually, the standard viscoelastic model was also verified on the quartz in a sandstone sample.

scholarly journals Experimental investigation on the nanoindentation viscoelastic constitutive model of quartz and kaolinite in mudstone

2020 ◽  
Author(s):  
Changlun Sun ◽  
Guichen Li ◽  
Gomah Mohamed Elgharib ◽  
Jiahui Xu ◽  
Haoyu Rong
Keyword(s):  
Peak Load ◽  
Viscoelastic Model ◽  
Model Fitting ◽  
Underlying Mechanism ◽  
Time Dependent ◽  
Underground Engineering ◽  
Engineering Structures ◽  
Sandstone Sample ◽  
Soft Rocks ◽  
Viscoelastic Constitutive Model

Abstract The creep behaviors in deep underground engineering structures, especially in soft rocks, have a remarkable impact on the long-term stability of the excavations, which finally leads to the high risk and failure of it. Accordingly, it is essential to recognize the time-dependent deformation through the investigation of this phenomenon. In this study, the creep behaviors of soft rocks have been widely examined to help understand the underlying mechanism of the extended time-dependent deformation. Due to the limited results about the time-dependent properties of the constituents of the rock that reveal their heterogeneity, the targeting nanoindentation technique (TNIT), was adopted to investigate the viscoelastic characteristics of kaolinite and quartz in a two-constituent mudstone sample. The TNIT consists of identifications of mineralogical ingredients in mudstone with nanoindentation experiments on each identified constituent. After conducting experiments, the unloading stages of the typical indentation curves were analyzed to calculate the hardness and elastic modulus of both elements in mudstone. Additionally, the 180 s load-holding stages with the peak load of 50 mN were transformed into the typical creep strain-time curves for fitting analysis by using the Kelvin model, the standard viscoelastic model, and the extended viscoelastic model. Fitting results show that the standard viscoelastic model not only can perfectly express the nanoindentation creep behaviors of both kaolinite and quartz but also can produce suitable constants used to measure their creep parameters. Furthermore, the creep parameters of kaolinite are much smaller than that of quartz, which causes the considerable time-dependent deformation of the soft mudstone. Eventually, the standard viscoelastic model was also verified on the quartz in a sandstone sample.

scholarly journals Experimental Investigation on the Viscoelastic Properties of Constituents in Mudstone

2020 ◽  
Author(s):  
Changlun Sun ◽  
Guichen Li ◽  
Gomah Mohamed Elgharib ◽  
Jiahui Xu ◽  
Haoyu Rong
Keyword(s):  
Large Deformation ◽  
Viscoelastic Model ◽  
Model Fitting ◽  
Maximum Load ◽  
Time Dependent ◽  
Underground Engineering ◽  
Engineering Structures ◽  
Sandstone Sample ◽  
Deformation And Failure ◽  
Deep Underground

Abstract In deep underground engineering, the creep behaviors of soft rocks have been widely investigated to help understand the mechanism of the time-dependent large deformation and failure of underground engineering structures. However, rocks were used to be regarded as homogeneous materials and there are limited studying results about the time-dependent properties of constituents in them to reveal their creep mechanism. In this context, the targeting nanoindentation technique (TNIT) was adopted to investigate the viscoelastic characteristics of kaolinite and quartz in a two-constituent mudstone sample. The TNIT consists of identifications of mineralogical constituents in mudstone and nanoindentation experiments on identified constituents. After conducting experiments, the unloading stages of the typical indentation curves were analyzed to calculate the hardness and elastic modulus of constituents in mudstone. And the 180 s load-holding stages with the maximum load of 50 mN were transformed to the typical creep strain-time curves for fitting analysis by using the Kelvin model, the standard viscoelastic model and the extended viscoelastic model. Fitting results show that the standard viscoelastic model can perfectly express the nanoindentation creep behaviors of both kaolinite and quartz and fitting constants are suitable to be used to calculate their creep parameters. The creep parameters of kaolinite are much smaller than that of quartz, which drives the time-dependent large deformation of the soft mudstone. At last, the standard viscoelastic model was verified on a sandstone sample.

Application of a Viscoelastic Model for Polyester Mooring

2010 ◽  
Author(s):  
J. W. Kim ◽  
J. H. Kyoung ◽  
A. Sablok
Keyword(s):  
Material Properties ◽  
Viscoelastic Model ◽  
Practical Method ◽  
Time Dependent ◽  
Mooring Line ◽  
New Model ◽  
Global Performance ◽  
Excitation Period ◽  
Linear Viscoelastic ◽  
Floating Platforms

A new practical method to simulate time-dependent material properties of polyester mooring line is proposed. The time-dependent material properties of polyester rope are modeled with a standard linear solid (SLS) model, which is one of the simplest forms of a linear viscoelastic model. The viscoelastic model simulates most of the mechanical properties of polyester rope such as creep, strain-stress hysteresis and excitation period-dependent stiffness. The strain rate-stress relation of the SLS model has been re-formulated to a stretch-tension relation, which is more suitable for implementation into global performance and mooring analyses tools for floating platforms. The new model has been implemented to a time-domain global performance analysis software and applied to simulate motion of a spar platform with chain-polyester-chain mooring system. The new model provides accurate platform offset without any approximation on the mean environmental load and can simulate the transient effect due to the loss of a mooring line during storm conditions, which has not been possible to simulate using existing dual-stiffness models.

scholarly journals Transition to Periodic Behaviour of Flow Past a Circular Cylinder under the Action of Fluidic Actuation in the Transitional Regime

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 5069
Author(s):  
Wasim Sarwar ◽  
Fernando Mellibovsky ◽  
Md. Mahbub Alam ◽  
Farhan Zafar
Keyword(s):  
Circular Cylinder ◽  
Period Doubling ◽  
Underlying Mechanism ◽  
Time Dependent ◽  
Cylinder Wake ◽  
Transitional Regime ◽  
Periodic Behaviour ◽  
Vortex Shedding Frequency ◽  
Fluidic Actuation ◽  
Periodic Dynamics

This study focuses on the numerical investigation of the underlying mechanism of transition from chaotic to periodic dynamics of circular cylinder wake under the action of time-dependent fluidic actuation at the Reynolds number = 2000. The forcing is realized by blowing and suction from the slits located at ±90∘ on the top and bottom surfaces of the cylinder. The inverse period-doubling cascade is the underlying physical mechanism underpinning the wake transition from mild chaos to perfectly periodic dynamics in the spanwise-independent, time-dependent forcing at twice the natural vortex-shedding frequency.

scholarly journals Approach for Optimisation of Tunnel Lining Design

2020 ◽  
Vol 10 (19) ◽  
pp. 6705
Author(s):  
Marek Mohyla ◽  
Karel Vojtasik ◽  
Eva Hrubesova ◽  
Martin Stolarik ◽  
Jan Nedoma ◽  
...  
Keyword(s):  
Rock Mass ◽  
Numerical Models ◽  
Tunnel Lining ◽  
Time Dependent ◽  
Design Element ◽  
Heterogeneous Structure ◽  
Underground Engineering ◽  
Software Application ◽  
Tunnel Lining Design ◽  
Dependent Property

This paper presents an approach that enables the specific characteristics of a primary tunnel lining implemented using numerical modelling to be taken into account during its design. According to the fundamental principles of the New Austrian Tunnelling Method, the primary lining undergoes time-dependent deformation, which is determined by its design. The main design element is shotcrete, which, shortly after its application, interacts with the surrounding rock mass and steel arch frame. The primary lining ensures the equilibrium stress–strain state of “rock mass–tunnel lining” during excavation. The structural interaction varies depending on the hardening of the shotcrete, the rheological properties of the rock mass, and other factors. The proposed approach uses the Homogenisation software application, which was developed by the Faculty of Civil Engineering at the Department of Geotechnics and Underground Engineering of the VSB—Technical University of Ostrava. This software allows the heterogeneous structure of the lining to be considered by replacing it with a homogenous structure. The parameters of the homogeneous primary lining, which take into account the steel reinforcement elements and the time-dependent property of the shotcrete, are included in numerical models.

scholarly journals Delayed electromechanical instability of a viscoelastic dielectric elastomer balloon

2019 ◽  
Vol 475 (2229) ◽  
pp. 20190316 ◽  
Author(s):  
Xiongfei Lv ◽  
Liwu Liu ◽  
Jinsong Leng ◽  
Yanju Liu ◽  
Shengqiang Cai
Keyword(s):  
Hoop Stress ◽  
Mechanical Load ◽  
Viscoelastic Model ◽  
Dielectric Elastomer ◽  
Time Dependent ◽  
Convex Shape ◽  
Nonlinear Viscoelastic ◽  
Electromechanical Instability ◽  
Electromechanical Loading ◽  
Nonlinear Viscoelastic Model

When a dielectric elastomer (DE) balloon is subjected to electromechanical loading, instability may happen. In recent experiments, it has been shown that the instability configuration of a DE balloon under electromechanical loading can be very different from that only subjected to mechanical load. It has also been observed in the experiments that the electromechanical instability phenomena of a DE balloon can be highly time-dependent. In this article, we adopt a nonlinear viscoelastic model for the DE membrane to investigate the time-dependent electromechanical instability of a DE balloon. Using the model, we show that under a constant electromechanical loading, a DE balloon may gradually evolve from a convex shape to a non-convex shape with bulging out in the centre, and compressive hoop stress can also gradually develop the balloon, resulting in wrinkles as observed in the experiments. We have further shown that the snap-through instability phenomenon of the DE balloon also greatly depends on the ramping rate of the applied voltage.

Creep and Creep Recovery of 304 Stainless Steel Under Combined Stress With a Representation by a Viscous-Viscoelastic Model

1980 ◽  
Vol 47 (4) ◽  
pp. 755-761 ◽  
Author(s):  
U. W. Cho ◽  
W. N. Findley
Keyword(s):  
Stainless Steel ◽  
Viscoelastic Model ◽  
Multiple Integral ◽  
Time Dependent ◽  
304 Stainless Steel ◽  
Creep Recovery ◽  
Strain Component ◽  
Stress Dependence ◽  
Nonlinear Stress ◽  
Stress States

Creep and creep-recovery data of 304 stainless steel are reported for experiments under constant combined tension and torsion at 593°C (1100°F). The data were represented by a viscous-viscoelastic model in which the strain was resolved into five components—elastic, plastic (time-independent), viscoelastic (time-dependent recoverable), and viscous (time-dependent nonrecoverable) which has separate positive and negative components. The data are well represented by a power function of time for each time-dependent strain. By applying superposition to the creep-recovery data, the recoverable creep strain was separated from the nonrecoverable. The form of stress-dependence associated with a third-order multiple integral representation was employed for each strain component. The time-dependent recoverable and nonrecoverable strains had different nonlinear stress dependence; but, the time-independent plastic strain and time-dependent nonrecoverable strain had similar stress-dependence. A limiting stress below which creep was very small or negligible was found for both recoverable and nonrecoverable components as well as a yield limit. The limit for recoverable creep was substantially less than the limits for nonrecoverable creep and yielding. The results showed that the model and equations used in the analysis described quite well the creep and creep-recovery under the stress states tested.

scholarly journals Effect of Preservation Period on the Viscoelastic Material Properties of Soft Tissues With Implications for Liver Transplantation

2010 ◽  
Vol 132 (10) ◽  
Author(s):  
Sina Ocal ◽  
M. Umut Ozcan ◽  
Ipek Basdogan ◽  
Cagatay Basdogan
Keyword(s):  
Liver Transplantation ◽  
Viscoelastic Material ◽  
Material Properties ◽  
Soft Tissues ◽  
Excitation Frequency ◽  
Viscoelastic Model ◽  
Relaxation Modulus ◽  
Bovine Liver ◽  
Dynamic Responses ◽  
Time Dependent

The liver harvested from a donor must be preserved and transported to a suitable recipient immediately for a successful liver transplantation. In this process, the preservation period is the most critical, since it is the longest and most tissue damage occurs during this period due to the reduced blood supply to the harvested liver and the change in its temperature. We investigate the effect of preservation period on the dynamic material properties of bovine liver using a viscoelastic model derived from both impact and ramp and hold experiments. First, we measure the storage and loss moduli of bovine liver as a function of excitation frequency using an impact hammer. Second, its time-dependent relaxation modulus is measured separately through ramp and hold experiments performed by a compression device. Third, a Maxwell solid model that successfully imitates the frequency- and time-dependent dynamic responses of bovine liver is developed to estimate the optimum viscoelastic material coefficients by minimizing the error between the experimental data and the corresponding values generated by the model. Finally, the variation in the viscoelastic material coefficients of bovine liver are investigated as a function of preservation period for the liver samples tested 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 36 h, and 48 h after harvesting. The results of our experiments performed with three animals show that the liver tissue becomes stiffer and more viscous as it spends more time in the preservation cycle.

scholarly journals Time-dependent potentiation of the beta-cell is a Ca2+-independent phenomenon

2002 ◽  
Vol 172 (2) ◽  
pp. 345-354 ◽  
Author(s):  
S Yamada ◽  
M Komatsu ◽  
T Aizawa ◽  
Y Sato ◽  
H Yajima ◽  
...  
Keyword(s):  
Protein Kinase C ◽  
Glucose Metabolism ◽  
Underlying Mechanism ◽  
Subsequent Treatment ◽  
Time Dependent ◽  
Kinase C ◽  
High K ◽  
Camp Levels ◽  
Protein Acylation ◽  
Isolated Rat

When isolated rat pancreatic islets are treated with 16.7 mM glucose, a time-dependent potentiation (TDP) of insulin release occurs that can be detected by subsequent treatment with 50 mM KCl. It has been thought that TDP by glucose is a Ca2+-dependent phenomenon and only occurs when exposure to glucose is carried out in the presence of Ca2+. In contrast to this, we now demonstrate TDP under stringent Ca2+-free conditions (Ca2+-free buffer containing 1 mM EGTA). In fact, under these Ca2+-free conditions glucose caused an even stronger TDP than in the presence of Ca2+. TDP induced by glucose in the absence of extracellular Ca2+ was unaffected by inhibitors of protein kinase C (PKC). However, cerulenin or tunicamycin, two inhibitors of protein acylation, eradicated TDP without affecting glucose metabolism. The TDP by glucose was not associated with an increase in the cytosolic free Ca2+ concentration ([Ca2+]i) during subsequent treatment with high K+. Exposure of islets to forskolin under Ca(2+)-free conditions did not cause TDP despite a large increase in the cellular cAMP levels. In conclusion, glucose alone induces TDP under stringent Ca2+-free conditions when [Ca2+]i was significantly lowered. Protein acylation is implicated in the underlying mechanism of TDP.

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