Creep of hollow concentric tubes

1968 ◽  
Vol 3 (3) ◽  
pp. 163-169
Author(s):  
W S Blackburn
Keyword(s):  
Yield Stress ◽  
Axial Load ◽  
Axial Strain ◽  
Outer Tube ◽  
Material Parameters ◽  
Constant Rate ◽  
Swelling Rate

For a thin outer tube of non-linearly creeping material with a sharp yield stress surrounding a thick inner tube of linearly creeping material with a sharp yield stress which is swelling at a constant rate, the conditions in which each tube is plastic and in which each tube creeps have been determined for the conditions of zero axial load and zero axial strain. Equations yielding the ratios of the axial and circumferential creep rates of the outer tube to the swelling rate of the inner have been determined in terms of the material parameters for each of the above conditions and have been solved on the assumption that these ratios are small.

scholarly journals A simulation-based approach to evaluate objective material parameters from concrete rheometer measurements

2019 ◽  
Vol 29 (1) ◽  
pp. 130-140 ◽  
Author(s):  
Florian Gerland ◽  
Alexander Wetzel ◽  
Thomas Schomberg ◽  
Olaf Wünsch ◽  
Bernhard Middendorf
Keyword(s):  
Yield Stress ◽  
High Performance ◽  
Evaluation Method ◽  
High Performance Concrete ◽  
Direct Determination ◽  
Plastic Viscosity ◽  
Flow Properties ◽  
Fresh Sample ◽  
Material Parameters ◽  
Simulation Based

Abstract Modern concretes such as ultra-high performance concrete (UHPC) show excellent strength properties combined with favorable flow properties. However, the flow properties depend strongly on process parameters during production (temperature, humidity etc.), but also change sensitively even with slight variations in the mixture. In order to ensure desired processing of the fluidlike material and consistent process quality, the flow properties of the concrete must be evaluated quantitatively and objectively. The usual evaluation of measurements from concrete rheometers, for example of the ball probe system type, does not allow the direct determination of the objective material parameters yield stress and plastic viscosity of the sample. We developed a simulation-based method for the evaluation of rheometric measurements of fine grained high performance concretes like self-compacting concrete (SCC) and UHPC. The method is based on a dimensional analysis for ball measuring systems. Through numerical parameter studies we were able to describe the identified relationship between measuring quantities and material parameters quantitatively for two devices of this type. The evaluation method is based on the Bingham model. With this method it is possible to measure both the yield stress and the plastic viscosity of the fresh sample simultaneously. Device independence of the evaluation process is proven and an application to fiber-reinforced UHPC is presented.

Constitutive Relations and Parameter Estimation for Finite Deformations of Viscoelastic Adhesives

2015 ◽  
Vol 82 (2) ◽  
Author(s):  
G. O. Antoine ◽  
R. C. Batra
Keyword(s):  
Constitutive Relation ◽  
Axial Strain ◽  
Constitutive Relations ◽  
Finite Deformations ◽  
Low Velocity Impact ◽  
Uniaxial Tensile ◽  
Strain Rates ◽  
Cauchy Stress ◽  
Peak Strain ◽  
Material Parameters

We propose a constitutive relation for finite deformations of nearly incompressible isotropic viscoelastic rubbery adhesives assuming that the Cauchy stress tensor can be written as the sum of elastic and viscoelastic parts. The former is derived from a stored energy function and the latter from a hereditary type integral. Using Ogden’s expression for the strain energy density and the Prony series for the viscoelastic shear modulus, values of material parameters are estimated by using experimental data for uniaxial tensile and compressive cyclic deformations at different constant engineering axial strain rates. It is found that values of material parameters using the loading part of the first cycle, the complete first cycle, and the complete two loading cycles are quite different. Furthermore, the constitutive relation with values of material parameters determined from the monotonic loading during the first cycle of deformations cannot well predict even deformations during the unloading portion of the first cycle. The developed constitutive relation is used to study low-velocity impact of polymethylmethacrylate (PMMA)/adhesive/polycarbonate (PC) laminate. The three sets of values of material parameters for the adhesive seem to have a negligible effect on the overall deformations of the laminate. It is attributed to the fact that peak strain rates in the severely deforming regions are large, and the corresponding stresses are essentially unaffected by the long time response of the adhesive.

Yield stress evaluation of Finnish clays based on analytical piezocone penetration test (CPTu) models

2020 ◽  
Vol 57 (11) ◽  
pp. 1623-1638 ◽  
Author(s):  
Bruno Di Buò ◽  
Marco D’Ignazio ◽  
Juha Selänpää ◽  
Tim Länsivaara ◽  
Paul W. Mayne
Keyword(s):  
Yield Stress ◽  
Soil Mechanics ◽  
Friction Angle ◽  
Coefficient Of Determination ◽  
Soil Conditions ◽  
Piezocone Penetration Test ◽  
Bias Factor ◽  
Constant Rate ◽  
Target Values ◽  
Spherical Cavity Expansion

A well-established analytical model based on spherical cavity expansion and critical state soil mechanics theories is applied to piezocone soundings for profiling the yield stress and overconsolidation ratio of five soft sensitive test sites located in Finland. Yield stress is related to three piezocone parameters: net cone resistance, excess porewater pressure, and effective cone resistances. Input geoparameters include the effective stress friction angle, defined at both peak strength and at maximum obliquity, and the model directly provides the operational value of the undrained rigidity index. The piezocone-evaluated profiles compare favorably with results from laboratory constant-rate-of-strain consolidation tests for all the investigated sites. Based on the obtained experimental results, simplified correlations valid for Finnish soil conditions are derived. Their validity is assessed based on the bias factor, coefficient of variation, and coefficient of determination, showing a fairly good agreement between the predicted and the target values.

Plastic Coupling and Stress Relaxation During Nonproportional Axial-Shear Strain-Controlled Loading

2000 ◽  
Vol 123 (1) ◽  
pp. 81-87
Author(s):  
Cliff J. Lissenden ◽  
Steven M. Arnold ◽  
Atef F. Saleeb
Keyword(s):  
Stress Relaxation ◽  
Shear Strain ◽  
Stress Reduction ◽  
Large Range ◽  
Axial Stress ◽  
Axial Strain ◽  
Time Dependent ◽  
Load Path ◽  
Percent Reduction ◽  
Material Parameters

A nonproportional strain-controlled load path consisting of two segments was applied to the cobalt-based alloy Haynes 188 at 650°C. The first segment was purely axial; the axial strain was then held constant while the shear strain was increased during the second segment. The alloy exhibited about a 95-percent reduction in axial stress (298 to 15 MPa) during shear straining. This reduction was due primarily to plastic coupling, but time-dependent stress relaxation also occurred. A rate-independent plasticity model approximated the stress reduction due to plastic coupling reasonably well, but as expected was unable to account for time-dependent stress relaxation. A viscoplasticity model capable of predicting the interaction between stress relaxation and plastic coupling also predicted the plastic coupling reasonably well. The accuracy of the viscoplastic model is shown to depend greatly upon the set of nonunique material parameters, which must be characterized from a sufficiently large range of load histories.

Small-strain behavior of frozen sand in triaxial compression

1995 ◽  
Vol 32 (3) ◽  
pp. 428-451 ◽  
Author(s):  
Glen R. Andersen ◽  
Christopher W. Swan ◽  
Charles C. Ladd ◽  
John T. Germaine
Keyword(s):  
High Pressure ◽  
Strain Rate ◽  
Yield Stress ◽  
Axial Strain ◽  
Triaxial Compression ◽  
Strain Curve ◽  
Confining Pressure ◽  
Stress Strain ◽  
Strain Behavior ◽  
Frozen Sand

The stress–strain behavior of frozen Manchester fine sand has been measured in a high-pressure low-temperature triaxial compression testing system developed for this purpose. This system incorporates DC servomotor technology, lubricated end platens, and on-specimen axial strain devices. A parametric study has investigated the effects of changes in strain rate, confining pressure, sand density, and temperature on behavior for very small strains (0.001%) to very large (> 20%) axial strains. This paper presents constitutive behavior for strain levels up to 1%. On-specimen axial strain measurements enabled the identification of a distinct upper yield stress (knee on the stress–strain curve) and a study of the behavior in this region with a degree of precision not previously reported in the literature. The Young's modulus is independent of strain rate and temperature, increases slightly with sand density in a manner consistent with Counto's model for composite materials, and decreases slightly with confining pressure. In contrast, the upper yield stress is independent of sand density, slightly dependent on confining pressure (considered a second order effect), but is strongly dependent on strain rate and temperature in a fashion similar to that for polycrystalline ice. Key words : frozen sand, high-pressure triaxial compression, strain rate, temperature, modulus, yield stress.

Simulation of Circumferential Pull-off Failure of Composite Foam Sandwich Tube under Axial Load

2014 ◽  
Vol 501-504 ◽  
pp. 649-652
Author(s):  
Feng Li ◽  
Hong Bing Liu ◽  
Kang Xu ◽  
Yan Mei Luo
Keyword(s):  
Finite Element ◽  
Axial Load ◽  
Axial Strain ◽  
Circumferential Direction ◽  
Test Results ◽  
Hoop Strain ◽  
Composite Foam ◽  
Composite Tube ◽  
Finite Element Software ◽  
Model Variation

Horizontal fibers of the outer layers of composite foam sandwich tube affected the compressive capacity of the tube under axial load. In order to clarify the strain distributions when the horizontal fibers of the outer layers were pulled off, dynamics finite element software LS-DYNA was used to simulate the model. Variation of hoop strain and axial strain of elements were observed. The simulation showed that the hoop strain of the composite tube increased gradually from the bottom and became the maximum in the middle of the member, which caused the pull-off damage and agreed with the test results. Strain along the circumferential direction of same height on the tube was average, and the same to the axial strain.

Sensitivity Analysis of Material Parameters on Spring-Back of NC Bending of High-Strength TA18 Tube

2012 ◽  
Vol 472-475 ◽  
pp. 1003-1008 ◽  
Author(s):  
Pei Pei Zhang ◽  
Mei Zhan ◽  
Tao Huang ◽  
He Yang
Keyword(s):  
Elastic Modulus ◽  
Strain Hardening ◽  
Yield Stress ◽  
Strain Hardening Exponent ◽  
Spring Back ◽  
Initial Yield Stress ◽  
Material Parameters ◽  
Strength Coefficient ◽  
Initial Yield ◽  
Nc Bending

Spring-back is one of the key factors affecting the forming quality of the NC bending of high-strength TA18 tubes (TA18-HS tubes). Since material parameters have a direct influence on stress and strain fields during the bending and after unloading, the springback of TA18-HS tubes after NC bending depends on material properties to a great degree. In order to study the effect of material parameters, the sensitivity of material parameters on spring-back of TA18-HS tubes is analyzed in this study, using the numerical simulation and the multi-parameters sensitivity analysis method. The results show the following: (1) The springback angle has a positive correlation with the strength coefficient and initial yield stress, and has a negative correlation with the elastic modulus and strain hardening exponent. Besides, with the increase of elastic modulus, the fluctuation of springback goes gently; with the increase of the strength coefficient and initial yield stress, the fluctuation of springback goes abruptly; but with the variation of the strain hardening exponent, the springback fluctuates slightly; (2) The elastic modulus is the most sensitive material parameter on spring-back, the strength coefficient and initial yield stress rank the second and third, respectively, and the strain hardening exponent is the last. The achievement of the study is valuable to eliminate the non-sensitivity parameters, simplify the optimization project, and improve the spring-back prediction capability.

Identification of viscoplastic material parameters from spherical indentation data: Part II. Experimental validation of the method

2006 ◽  
Vol 21 (3) ◽  
pp. 677-684 ◽  
Author(s):  
D. Klötzer ◽  
Ch. Ullner ◽  
E. Tyulyukovskiy ◽  
N. Huber
Keyword(s):  
Yield Stress ◽  
Young’S Modulus ◽  
Experimental Validation ◽  
Young's Modulus ◽  
Surface Preparation ◽  
Small Variation ◽  
Application Rate ◽  
Spherical Indentation ◽  
Viscoplastic Material ◽  
Material Parameters

A neural network-based analysis method for the identification of a viscoplasticity model from spherical indentation data, developed in the first part of this work [J. Mater. Res.21, 664 (2006)], was applied for different metallic materials. Besides the comparison of typical parameters like Young’s modulus and yield stress with values from tensile experiments, the uncertainties in the identified material parameters representing modulus, hardening behavior, and viscosity were investigated in relation to different sources. Variations in the indentation position, tip radius, force application rate, and surface preparation were considered. The extensive experimental validation showed that the applied neural networks are very robust and show small variation coefficients, especially regarding the important parameters of Young’s modulus and yield stress. On the other hand, important requirements were quantified, which included a very good spherical indenter geometry and good surface preparation to obtain reliable results.

The Yielded Compound Cylinder in Generalized Plane Strain

1961 ◽  
Vol 83 (4) ◽  
pp. 441-448 ◽  
Author(s):  
S. J. Becker
Keyword(s):  
Plane Strain ◽  
Axial Load ◽  
Axial Strain ◽  
Complete Solution ◽  
Yield Condition ◽  
Compound Cylinder ◽  
Elastic Zone ◽  
Tresca Yield Condition ◽  
Internal Pressures ◽  
Generalized Plane Strain

The theory of a previous paper [1], which was designed for plane strain of a compound cylinder, is extended to generalized plane strain, where the axial strain is a constant nonzero value for every radius and depends only on the external and internal pressures and any extraneous axial load. The method is limited to incompressible elastic material and is found to be completely solvable only if an elastic zone exists in each component. The assumed Tresca yield condition is verified in the process of obtaining the complete solution.

Calculation Strategy for the Determination of Plasticity Correction Factors

2016 ◽  
Vol 725 ◽  
pp. 345-350
Author(s):  
Juan Du ◽  
Xue Jiao Shao ◽  
Qian Hua Kan ◽  
Ying Zhang ◽  
Xiao Long Fu
Keyword(s):  
Titanium Alloy ◽  
Yield Stress ◽  
Thermal Loading ◽  
Elastic Stress ◽  
Correction Factors ◽  
Material Parameters ◽  
Linear Elastic ◽  
New Material ◽  
General Material

This paper presents an investigation about the plasticity correction factor, Ke, proposed in the RCCM code, for correction of the elastic stress ranges exceeding twice the yield stress, resulting from both mechanical and thermal loading. The plasticity correction factors are analyzed using a calculation strategy based on a comparison between results from linear elastic and elastoplastic analyses. The RCC-M code provides the codified expressions of Ke and material parameters for general materials of nuclear components, but there are no expressions and material parameters for the new material. Several elastoplastic models, geometries and loading types are considered in the study based on the general material listed in RCCM code to determine the calculation strategy for the determination of Ke for new material. Based on the results, the determination of Ke expressions and parameters for Titanium Alloy is discussed. The proposed Ke factor of Titanium Alloy has been determined and delivered the same sufficiently conservative results. An exemplary verification calculation of general materials that have been performed and the conservative allowance is obtained.

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