A Thermoelastic-Viscoplastic Model With a Rate-Dependent Yield Strength

General nonlinear constitutive equations for a thermoelastic-viscoplastic material that exhibits a rate-dependent yield strength are developed by assuming that the yield function depends explicitly on the total strain rate and temperature rate. Following recent developments in continuum thermodynamics restrictions on the constitutive response functions are imposed to ensure that the moment of momentum and energy equations are identically satisfied and that various statements of the second law of thermodynamics are satisfied for all thermodynamical processes. A particular constitutive equation for a thermoelastic-viscoplastic material is proposed, and an analytical example is considered that examines the rate-dependent plastic response to a deformation history that includes segments of loading, unloading, and reloading, each occurring at varying strain rates.

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Fracture investigation in starch-based foods

Interface Focus ◽

10.1098/rsfs.2016.0005 ◽

2016 ◽

Vol 6 (3) ◽

pp. 20160005 ◽

Cited By ~ 13

Author(s):

C. G. Skamniotis ◽

Y. Patel ◽

M. N. Charalambides ◽

M. Elliott

Keyword(s):

Material Model ◽

Tensile Tests ◽

Viscoplastic Material ◽

Rate Dependent ◽

Highly Nonlinear ◽

Constitutive Response ◽

Average Crack ◽

Damage Law ◽

Blade Cutting ◽

Work Of Fracture

The study of oral processing and specifically cutting of the food piece during mastication can lead towards optimization of products for humans or animals. Food materials are complex biocomposites with a highly nonlinear constitutive response. Their fracture properties have not been largely investigated, while the need for models capable of predicting food breakdown increases. In this study, the blade cutting and the essential work of fracture (EWF) methodologies assessed the fracture behaviour of starch-based pet food. Tensile tests revealed rate-dependent stiffness and stress softening effects, attributed to viscoplasticity and micro-cracking, respectively. Cutting data were collected for 5, 10 and 30 mm s −1 sample feed rates, whereas the EWF tests were conducted at 1.7, 3.3 and 8.3 mm s −1 crosshead speeds corresponding to average crack speeds of 4, 7 and 15 mm s −1 , respectively. A reasonable agreement was achieved between cutting and EWF, reporting 1.26, 1.78, 1.76 kJ m −2 and 1.52, 1.37, 1.45 kJ m −2 values, respectively, for the corresponding crack speeds. These toughness data were used in a novel numerical model simulating the ‘first’ bite mastication process. A viscoplastic material model is adopted for the food piece, combined with a damage law that enabled predicting fracture patterns in the product.

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The Thermo-Mechanics Coupled Model of Polycrystalline Aggregates Based on Plastic Slip System in Crystals and their Interfaces

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.295-297.397 ◽

2011 ◽

Vol 295-297 ◽

pp. 397-405 ◽

Cited By ~ 1

Author(s):

Yun Chen ◽

Jun Zhi Cui ◽

Yu Feng Nie ◽

Xiao Fei Guan

Keyword(s):

Bending Strength ◽

Coupled Model ◽

Constitutive Relationship ◽

Plastic Slip ◽

Rate Dependent ◽

Polycrystalline Aggregates ◽

The Moment ◽

Energy Equations ◽

Crystal Interfaces ◽

Bending Loading

This paper presents the thermal-mechanical coupled model of polycrystalline aggregates based on plastic slip theory inside crystals and on the interfaces of crystals. It involves the mechanics and heat conduction behaviors caused by both force loads and temperature changing in the polycrystalline aggregates. At first, the constitutive relationship inside single crystal, and the moment equations and energy equations are derived by means of rate-dependent plastic deformation theory and the formulas of elastic-plastic tangent modulus depended on temperature. And those on crystal interfaces are also given. Based on the ABAQUS software [1], the subroutines to calculate the tension, torsion and bending strength of polycrystalline copper are coded. The numerical simulation results show that breakages occurred more easily on the interfaces than other areas of the polycrystalline aggregates, especially for bending loading and torsion loading, and that’s consistent with results by molecular dynamics but their computing cost are less and less than MD simulation.

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Constitutive Response of Passivated Copper Films: Experiments and Analyses

MRS Proceedings ◽

10.1557/proc-695-l6.8.1 ◽

2001 ◽

Vol 695 ◽

Author(s):

Y.-L. Shen ◽

U. Ramamurty

Keyword(s):

Thermal Loading ◽

Silicon Oxide ◽

Kinematic Hardening ◽

Copper Film ◽

Temperature Response ◽

Copper Interconnects ◽

Constitutive Law ◽

Copper Films ◽

Rate Dependent ◽

Constitutive Response

ABSTRACTThe constitutive behavior of passivated copper films is studied. Stresses in copper films of thickness ranging from 1000 nm to 40 nm, passivated with silicon oxide on a quartz or silicon substrate, were measured using the curvature method. The thermal cycling spans a temperature range from - 196 to 600°C. It is seen that the strong relaxation at high temperatures normally found in unpassivated films is nonexistent for passivated films. The copper film did not show any rate-dependent effect over a range of heating/cooling rate from 5 to 25°C/min. Further analyses showed that significant strain hardening exists during the course of thermal loading. In particular, the measured stress- temperature response can only be fitted with a kinematic hardening model, if a simple constitutive law within the continuum plasticity framework is to be used. The analytic procedures for extracting the film properties are presented. Implications to stress modeling of copper interconnects in actual devices are discussed.

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Beating Carnot efficiency with periodically driven chiral conductors

10.21203/rs.3.rs-468139/v1 ◽

2021 ◽

Author(s):

sungguen ryu ◽

Rosa Lopez ◽

L Serra ◽

David Sanchez

Keyword(s):

Entropy Production ◽

Second Law Of Thermodynamics ◽

Second Law ◽

Fundamental Limits ◽

Periodically Driven ◽

Power Injection ◽

Recent Developments ◽

Proper Definition ◽

Excitation Processes ◽

Absence Of Power

Abstract Classically, the power generated by an ideal thermal machine cannot be larger than the Carnot limit. This profound result is rooted in the second law of thermodynamics. A hot question is whether this bound is still valid for microengines operating far from equilibrium. Here, we demonstrate that a quantum chiral conductor driven by AC voltage can indeed work with efficiencies much larger than the Carnot bound. The system also extracts work from common temperature baths, violating Kelvin-Planck statement. Nonetheless, with the proper definition, entropy production is always positive and the second law is preserved. The crucial ingredients to obtain efficiencies beyond the Carnot limit are: i) irreversible entropy production by the photoassisted excitation processes due to the AC field and ii) absence of power injection thanks to chirality. Our results are relevant in view of recent developments that use small conductors to test the fundamental limits of thermodynamic engines.

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Cell-Based Regeneration and Treatment of Liver Diseases

International Journal of Molecular Sciences ◽

10.3390/ijms221910276 ◽

2021 ◽

Vol 22 (19) ◽

pp. 10276

Author(s):

Julia Hofmann ◽

Verena Hackl ◽

Hannah Esser ◽

Andras T. Meszaros ◽

Margot Fodor ◽

...

Keyword(s):

Liver Diseases ◽

Ex Vivo ◽

Organ Shortage ◽

Clinical Implementation ◽

Organ Function ◽

Novel Technologies ◽

Recent Developments ◽

Underlying Mechanisms ◽

The Moment ◽

End Stage

The liver, in combination with a functional biliary system, is responsible for maintaining a great number of vital body functions. However, acute and chronic liver diseases may lead to irreversible liver damage and, ultimately, liver failure. At the moment, the best curative option for patients suffering from end-stage liver disease is liver transplantation. However, the number of donor livers required by far surpasses the supply, leading to a significant organ shortage. Cellular therapies play an increasing role in the restoration of organ function and can be integrated into organ transplantation protocols. Different types and sources of stem cells are considered for this purpose, but highly specific immune cells are also the focus of attention when developing individualized therapies. In-depth knowledge of the underlying mechanisms governing cell differentiation and engraftment is crucial for clinical implementation. Additionally, novel technologies such as ex vivo machine perfusion and recent developments in tissue engineering may hold promising potential for the implementation of cell-based therapies to restore proper organ function.

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Relaxation creep model of impending earthquake

Annals of Geophysics ◽

10.4401/ag-3603 ◽

2001 ◽

Vol 44 (2) ◽

Author(s):

V. A. Morgounov

Keyword(s):

Strain Rate ◽

Signal To Noise Ratio ◽

Electromagnetic Emission ◽

Creep Model ◽

Current Status ◽

Alternative View ◽

Rate Dependent ◽

Tectonic Earthquakes ◽

Prediction Reliability ◽

The Moment

The alternative view of the current status and perspective of seismic prediction studies is discussed. In the problem of ascertainment of the uncertainty relation Cognoscibility-Unpredictability of Earthquakes, priorities of works on short-term earthquake prediction are defined due to the advantage that the final stage of nucleation of earthquake is characterized by a substantial activation of the process while its strain rate increases by the orders of magnitude and considerably increased signal-to-noise ratio. Based on the creep phenomenon under stress relaxation conditions, a model is proposed to explain different images of precursors of impending tectonic earthquakes. The onset of tertiary creep appears to correspond to the onset of instability and inevitably fails unless it is unloaded. At this stage, the process acquires the self-regulating character and to the greatest extent the property of irreversibility, one of the important components of prediction reliability. Data in situ suggest a principal possibility to diagnose the process of preparation by ground measurements of strain-rate-dependent parameters, like electromagnetic emission, etc. Laboratory tests of the measurements of acoustic and electromagnetic emission in the rocks under constant strain in the condition of self-relaxed stress until the moment of fracture are discussed in context. It was obtained that electromagnetic emission precedes but does not accompany the phase of macrocrack development.

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