Evaluation on Stress Relaxation Properties of Geomembrane

2010 ◽  
Vol 168-170 ◽  
pp. 1572-1576
Author(s):  
Si Fa Xu ◽  
Yong Zhang ◽  
Zhe Wang
Keyword(s):  
Stress Relaxation ◽  
Tensile Force ◽  
High Stress ◽  
Elastic Model ◽  
Design Strength ◽  
Elapsed Time ◽  
Side Slope ◽  
Design Life ◽  
Liner System ◽  
Long Time

Geomembrane installed on the bottom and the side slope of a waste landfill as liner system is made of high density polyethylene or thermo plastic elastmer polyplopylene. Stress in the geotextile is caused by friction between the waste and the geotextile which is a result of the compression of the disposed waste, and the tensile force is transferred into the liner system by friction. With elapsed time, the stress relaxation will occur under certain strain conditions. If the stress of geomembrane is at high stress for a long period of time, the long time design strength of the geomembrane may be controlled by the creep at the end of the design life. So it is very important for design to determine the stress induced in the geomembrane. In this paper, the authors present a formula based three element visco-elastic model to evaluate the relation between the stress and elapsed time. Then the authors present some results of modeled tests conducted, it is shown that the relation between the material characteristic and temperature by indoor experiment.

Rate Dependent Constitutive Equations of Cyclic Softening

1985 ◽  
Vol 40 (7) ◽  
pp. 653-665
Author(s):  
J. S. Mshana ◽  
A. S. Krausz
Keyword(s):  
Stress Relaxation ◽  
Low Temperature ◽  
Constitutive Equations ◽  
Strain Softening ◽  
Structural Characteristics ◽  
High Stress ◽  
Cyclic Strain ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Stress Softening

Constitutive equations of cyclic strain and stress softening for materials with low internal stress levels are derived from the rate theory. The study shows that over the high stress and low temperature range where the description of plastic flow in cyclic softening can be approximated with activation over a single energy barrier, cyclic strain softening is well related to stress relaxation process while cyclic stress softening is related to creep process. The material structural characteristics for cyclic strain softening, cyclic stress softening and stress relaxation are identical. Subsequently, it is shown that cyclic stress and strain softening within the high stress and low temperature range can be evaluated from the constitutive equations using the material structural characteristics measured from a simple stress relaxation test.

scholarly journals Preparation and properties of hybrid materials for high-rise constructions

2018 ◽  
Vol 33 ◽  
pp. 02075 ◽  
Author(s):  
Tatyana Matseevich
Keyword(s):  
Stress Relaxation ◽  
Epoxy Resin ◽  
Relaxation Process ◽  
Hybrid Materials ◽  
Mechanical Performance ◽  
Mechanical Relaxation ◽  
Physical Parameters ◽  
Quasi Equilibrium ◽  
High Rise ◽  
Long Time

The theme of the research is important because it allows to use hybrid materials as finishing in the high-rise constructions. The aim of the study was the development of producing coloured hybrid materials based on liquid glass, a polyisocyanate, epoxy resin and 2.4-toluylenediisocyanate. The detailed study of the process of stress relaxation at different temperatures in the range of 20-100°C was provided. The study found that the obtained materials are subject to the simplified technology. The materials easy to turn different colors, and dyes (e.g. Sudan blue G) are the catalysts for the curing process of the polymeric precursors. The materials have improved mechanical relaxation properties, possess different color and presentable, can be easily combined with inorganic base (concrete, metal). The limit of compressive strength varies from 32 to 17.5 MPa at a temperature of 20 to 100°C. The values σ∞ are from 20.4 to 7.7 MPa within the temperature range from 20 to 100°C. The physical parameters of materials were evaluated basing on the data of stress relaxation: the initial stress σ0, which occurs at the end of the deformation to a predetermined value; quasi-equilibrium stress σ∞, which persists for a long time relaxation process. Obtained master curves provide prediction relaxation behavior for large durations of relaxation. The study obtained new results. So, the addition of epoxy resin in the composition of the precursor improves the properties of hybrid materials. By the method of IR spectroscopy identified chemical transformations in the course of obtaining the hybrid material. Evaluated mechanical performance of these materials is long-time. Applied modern physically-based memory functions, which perfectly describe the stress relaxation process.

Analysis on the Creep Mechanism of 12Cr-Mo-W-0.25V Steel Based on Long-Term Stress Relaxation Test Data

2016 ◽  
Vol 853 ◽  
pp. 158-162
Author(s):  
Jie Zhao ◽  
Tie Shan Cao ◽  
Cong Qian Cheng ◽  
Hui Fang Li
Keyword(s):  
Stress Relaxation ◽  
Test Data ◽  
Activation Volume ◽  
High Stress ◽  
Relaxation Curve ◽  
Relaxation Test ◽  
Dislocation Slip ◽  
Stress Relaxation Test ◽  
Steel Base

The current paper investigates on the creep behavior of 12Cr-Mo-W-0.25V heat resistant steel base on the long-term stress relaxation test data. It is shows that the stress relaxation curve can be divided into 2 stages: the high stress stage has higher apparent activation volume of 79~350 b3 and the low stress stage is 35~78 b3. Besides, the Helmholtz free energy at the high stress stage is 827~1034 kJ/mol which is higher than 210~252 kJ/mol of the low stress stage. Taking both apparent activation volume and activation energy into account, it is assumed that the high stress stage is mainly controlled by dislocation slip and the low stress stage is more related to diffusion.

scholarly journals DEVELOPMENT OF THE METAL RHEOLOGY MODEL OF HIGH-TEMPERATURE DEFORMATION FOR MODELING BY FINITE ELEMENT METHOD

2019 ◽  
Vol 2 ◽  
pp. 52-60 ◽  
Author(s):  
Oleg Markov ◽  
Oleksiy Gerasimenko ◽  
Leila Aliieva ◽  
Alexander Shapoval
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Stress Relaxation ◽  
Hot Deformation ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Software Systems ◽  
Elastic Model ◽  
Communication Model ◽  
Element Method

It is shown that when modeling the processes of forging and stamping, it is necessary to take into account not only the hardening of the material, but also softening, which occurs during hot processing. Otherwise, the power parameters of the deformation processes are precisely determined, which leads to the choice of more powerful equipment. Softening accounting (processes of stress relaxation) will allow to accurately determine the stress and strain state (SSS) of the workpiece, as well as the power parameters of the processes of deformation. This will expand the technological capabilities of these processes. Existing commercial software systems for modeling hot plastic deformations based on the finite element method (FEM) do not allow this. This is due to the absence in these software products of the communication model of the component deformation rates and stresses, which would take into account stress relaxation. As a result, on the basis of the Maxwell visco-elastic model, a relationship is established between deformation rates and stresses. The developed model allows to take into account the metal softening during a pause after hot deformation. The resulting mathematical model is tested by experiment on different steels at different temperatures of deformation. The process of steels softening is determined using plastometers. It is established experimentally that the model developed by 89 ... 93 % describes the rheology of the metal during hot deformation. The relationship between the components of the deformation rates and stresses is established, which allows to obtain a direct numerical solution of plastic deformation problems without FED iterative procedures, taking into account the real properties of the metal during deformation. As a result, the number of iterations and calculations has significantly decreased.

scholarly journals A sensory integration account for time perception

2020 ◽  
Author(s):  
Alessandro Toso ◽  
Arash Fassihi ◽  
Luciano Paz ◽  
Francesca Pulecchi ◽  
Mathew E. Diamond
Keyword(s):  
Time Perception ◽  
Time Constant ◽  
Sensory Integration ◽  
Neuronal Firing ◽  
Elapsed Time ◽  
Leaky Integrator ◽  
Long Time ◽  
Integrator Model ◽  
Short Time ◽  
Sense Of Touch

ABSTRACTThe connection between stimulus perception and time perception remains unknown. The present study combines human and rat psychophysics with sensory cortical neuronal firing to construct a computational model for the percept of elapsed time embedded within sense of touch. When subjects judged the duration of a vibration applied to the fingertip (human) or whiskers (rat), increasing stimulus mean speed led to increasing perceived duration. Symmetrically, increasing vibration duration led to increasing perceived intensity. We modeled spike trains from vibrissal somatosensory cortex as input to dual leaky integrators – an intensity integrator with short time constant and a duration integrator with long time constant – generating neurometric functions that replicated the actual psychophysical functions of rats. Returning to human psychophysics, we then confirmed specific predictions of the dual leaky integrator model. This study offers a framework, based on sensory coding and subsequent accumulation of sensory drive, to account for how a feeling of the passage of time accompanies the tactile sensory experience.

The Effect of Aging Conditions on the Stress Relaxation Behavior of 17-7PH Stainless Steel

2021 ◽  
Vol 1016 ◽  
pp. 1664-1669
Author(s):  
Shota Yamasaki ◽  
K. Takano
Keyword(s):  
Stainless Steel ◽  
Stress Relaxation ◽  
Dislocation Density ◽  
Cold Working ◽  
Relaxation Behavior ◽  
Age Hardening ◽  
Stress Relaxation Behavior ◽  
Long Time ◽  
Aging Conditions ◽  
High Age

17-7PH stainless steel is high age-hardening property due to precipitate NiAl intermetallics by aging heat treatment after the deformation induced martensitic transformation by cold working. In this study, the effect of aging conditions on stress relaxation behavior of 17-7PH stainless steel was investigated, and the mechanism of the stress relaxation was discussed. The 0.2% proof stress after aging at 753K for 180s-18ks is about 450MPa, and then decreases after 18ks. On the other hand, the stress relaxation ratio decreases by long time aging at 753K. The dislocation density of 17-7PH decreases by long time aging at 753K. The formation of NiAl clusters around 5nm by 3D-AP analysis is observed in 17-7PH aged at 753K for 1.8ks. It is suggested that the reduction of the stress relaxation ratio after long time aging at 753K is caused by NiAl clusters and decreasing mobile dislocation density.

A Continuum Theory and an Experiment for the Ion-Induced Swelling Behavior of Articular Cartilage

1984 ◽  
Vol 106 (2) ◽  
pp. 151-158 ◽  
Author(s):  
E. R. Myers ◽  
W. M. Lai ◽  
V. C. Mow
Keyword(s):  
Articular Cartilage ◽  
Stress Relaxation ◽  
Tensile Force ◽  
Continuum Theory ◽  
Swelling Behavior ◽  
Bovine Articular Cartilage ◽  
Free Swelling ◽  
Transient Force

Swelling of normal bovine articular cartilage equilibrated in NaCl solutions was dimensionally measured in thin strips of tissue. The ion-induced strains show that free swelling of articular cartilage is anisotropic and inhomogeneous. For the molar concentrations used, contraction increased linearly with concentration, defining a “coefficient of chemical contraction” (αc). Isometrically constrained specimens registered a rise in tensile force followed by stress relaxation. An extension of the biphasic theory incorporating this ion-induced strain is proposed. This theory can describe the equilibrium anisotropic swelling behavior of cartilage and explain the transient force history observed in the isometric experiment.

Reduced Variables and Integral Equations in Design of Plastics and Rubber Structures

1966 ◽  
Vol 39 (4) ◽  
pp. 1065-1080
Author(s):  
I. L. Hopkins ◽  
R. P. Wentz
Keyword(s):  
Integral Equation ◽  
Stress Relaxation ◽  
Numerical Solution ◽  
Integral Equations ◽  
Creep Behavior ◽  
Integral Relation ◽  
Storage Battery ◽  
Long Time

Abstract The long-time creep behavior of a hard rubber storage battery jar is analyzed by means of (a) reduced variables applied to stress relaxation in torsion, and (b) numerical solution of the integral equation connecting stress relaxation and creep. The validity of the integral relation is shown by calculation of creep in compression (ASTM D-621) from stress relaxation in torsion.

scholarly journals Stress Relaxation Properties and Microscopic Deformation Structure in Bending of the C7025 and C7035 Alloy

2018 ◽  
Author(s):  
Xiangpeng Xiao ◽  
Hai Xu ◽  
Jian Huang ◽  
Junfeng Wang ◽  
Jianbo Zhang
Keyword(s):  
Stress Relaxation ◽  
Structural Changes ◽  
Relaxation Curve ◽  
Relaxation Properties ◽  
Limit Value ◽  
The Matrix ◽  
Long Time ◽  
Microscopic Deformation ◽  
Cantilever Bending ◽  
Two Stages

Stress relaxation tests in cantilever bending were performed on the C7025 and C7035 alloys at 298K and 393K，respectively. The effect of stress-relief treatments on stress relaxation properties was investigated. The structural changes associated with the stress relaxation process were examined using transmission electron microscope. The stress relaxation curve fits well to empirical formula σ*=[Kˊln(t+α0)+C]-n for stress relaxation. The curves can be split into two stages. The stress relax quickly in the first stage, slows down in the second stage, and tends to be a certain limit value after a long time. The curve and microstructure reveals that the C7035 alloy has a lower rate of stress relaxation and a higher anti-stress relaxation capacity than the C7025. The first reason is that the movement of vacancies required by spinodal decomposition is inhibited, and the quantity of cobalt -containing vacancies decreases dramatically in the C7035 alloy. The other reason is that the precipitated phases became uniformly diffused in the C7035 alloy. The precipitate phase uniformly distributes in the grain boundaries and the matrix, during the relaxed condition, and thus the dislocations moving is blocked by the precipitates.

Robust Design Approach to 2 Inch and 3 Inch Thermal Tees on 14 Inch Pipework for Hot and Cold Fluid Turbulent Mixing at the Branch-Run Interface

2020 ◽  
Author(s):  
Phil Wallace
Keyword(s):  
Robust Design ◽  
Thermal Fatigue ◽  
Turbulent Mixing ◽  
High Stress ◽  
Internal Diameter ◽  
Geometric Features ◽  
Concept Design ◽  
Design Life ◽  
Cold Fluid ◽  
Computational Fluid Dynamics Analysis

Abstract This paper presents a concept design methodology to establish robust designs against thermal fatigue of 2″ and 3″ thermal tee branch sizes on 14″ pipework, which are subjected to relatively hot and cold fluid turbulent mixing, for use in Pressurised Water Reactor Plant. Thermal tees can be subjected to extremely demanding thermal fatigue conditions, e.g. high temperature fluctuations causing high stress ranges where hot and cold fluid mix at the tee position from different branches of the system, these conditions ultimately limiting design life. Prior to conducting a full design justification to the ASME Section III code [1], which for these components Rolls-Royce has justified by a section NB3200 approach using finite element analysis and computational fluid dynamics, analysis/iteration time can be saved, and the likelihood of a robust design being found increased, by understanding the effect and significance of geometric features of the tees. Fundamentally, establishing which features have a greater influence on the thermal fatigue performance of the tee and setting maximum and minimum values for these features. This paper presents an approach that can be used in the concept design phase to understand the influence of variables such as: branch throat internal diameter, run versus branch reinforcement, inclusion of integral orifices and branch fluid flow rate, and also of how they interact with each other in relation to providing a code compliant design. The approach is also used to size such features so that they are away from ‘cliff edges’ in performance, i.e. away from values that are likely to produce high stress levels and reduce design life. The paper covers: the variables chosen to be investigated, the methodology including the associated stress models to understand the effect of variable change and positioning in the ‘design landscape’, and identifies which geometric features should be maximised or minimised in size to maximise thermal fatigue life.

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