Development of a simplified relationship between uniaxial creep, stress relaxation, and constant strain-rate results for viscoelastic polymeric materials

2001 ◽  
Vol 82 (3) ◽  
pp. 527-540 ◽  
Author(s):  
Richard D. Sudduth
Keyword(s):  
Stress Relaxation ◽  
Strain Rate ◽  
Constant Strain Rate ◽  
Polymeric Materials ◽  
Creep Stress ◽  
Uniaxial Creep

Some Implications of a Nonlinear Viscoelastic Constitutive Theory Regarding Interrelationships Between Creep and Strength Behavior of Ice at Failure

1989 ◽  
Vol 111 (2) ◽  
pp. 144-148 ◽  
Author(s):  
B. D. Harper
Keyword(s):  
Strain Rate ◽  
Constant Strain Rate ◽  
Nonlinear Viscoelastic ◽  
Uniaxial Creep ◽  
Strength Behavior ◽  
Minimum Strain Rate ◽  
Strength Constant ◽  
Viscoelastic Constitutive Model ◽  
Stress And Strain Rate ◽  
Special Case

This study explores several possibilities for a correspondence in the behavior of ice at failure during uniaxial creep (constant stress) and strength (constant strain rate) experiments. The usual notion of failure in ice is employed (i.e., the occurrence of a minimum strain rate during a creep test and a peak or maximum stress during a strength test), and the behavior at failure is discussed in terms of a recently proposed nonlinear viscoelastic constitutive model for ice. It is demonstrated that no correspondence between creep and strength data can be expected in general; however, several approximate interrelationships do occur for the experimentally motivated special case of a constant (independent of stress and strain rate) failure strain.

Effect of Fiber Orientation and Strain Rate on the Nonlinear Uniaxial Tensile Material Properties of Tendon

2003 ◽  
Vol 125 (5) ◽  
pp. 726-731 ◽  
Author(s):  
Heather Anne Lynch ◽  
Wade Johannessen ◽  
Jeffrey P. Wu ◽  
Andrew Jawa ◽  
Dawn M. Elliott
Keyword(s):  
Stress Relaxation ◽  
Strain Rate ◽  
Material Properties ◽  
Poisson’S Ratio ◽  
Constant Strain Rate ◽  
Tensile Tests ◽  
Poisson's Ratio ◽  
Fiber Direction ◽  
Linear Region ◽  
Rate Dependent

Tendons are exposed to complex loading scenarios that can only be quantified by mathematical models, requiring a full knowledge of tendon mechanical properties. This study measured the anisotropic, nonlinear, elastic material properties of tendon. Previous studies have primarily used constant strain-rate tensile tests to determine elastic modulus in the fiber direction. Data for Poisson’s ratio aligned with the fiber direction and all material properties transverse to the fiber direction are sparse. Additionally, it is not known whether quasi-static constant strain-rate tests represent equilibrium elastic tissue behavior. Incremental stress-relaxation and constant strain-rate tensile tests were performed on sheep flexor tendon samples aligned with the tendon fiber direction or transverse to the fiber direction to determine the anisotropic properties of toe-region modulus E0, linear-region modulus (E), and Poisson’s ratio (ν). Among the modulus values calculated, only fiber-aligned linear-region modulus E1 was found to be strain-rate dependent. The E1 calculated from the constant strain-rate tests were significantly greater than the value calculated from incremental stress-relaxation testing. Fiber-aligned toe-region modulus E10=10.5±4.7 MPa and linear-region modulus E1=34.0±15.5 MPa were consistently 2 orders of magnitude greater than transverse moduli (E20=0.055±0.044 MPa,E2=0.157±0.154 MPa). Poisson’s ratio values were not found to be rate-dependent in either the fiber-aligned (ν12=2.98±2.59, n=24) or transverse (ν21=0.488±0.653, n=22) directions, and average Poisson’s ratio values in the fiber-aligned direction were six times greater than in the transverse direction. The lack of strain-rate dependence of transverse properties demonstrates that slow constant strain-rate tests represent elastic properties in the transverse direction. However, the strain-rate dependence demonstrated by the fiber-aligned linear-region modulus suggests that incremental stress-relaxation tests are necessary to determine the equilibrium elastic properties of tendon, and may be more appropriate for determining the properties to be used in elastic mathematical models.

Viscoelastic Characterization of an Epoxy-Based Molding Compound

1995 ◽  
Vol 390 ◽  
Author(s):  
V. H. Kenner ◽  
M. R. Julian ◽  
C. H. Popelar ◽  
M. K. Chengalva
Keyword(s):  
Stress Relaxation ◽  
Strain Rate ◽  
Constant Strain Rate ◽  
Viscoelastic Behavior ◽  
Tensile Tests ◽  
Prony Series ◽  
Master Curves ◽  
Molding Compound ◽  
Relaxation Curves

ABSTRACTThis paper describes the viscoelastic characterization of a highly filled epoxy molding compound commonly used in electronic packaging applications. Both stress relaxation tests and constant strain rate tensile tests were conducted. The material was found to be nonlinear in its viscoelastic behavior and to be amenable to horizontal shifting to form master curves. A representation of the master stress relaxation curves in terms of a Prony series is given, and the use of this representation illustrated in the context of both linear and nonlinear representations of the viscoelastic behavior to predict the results of the constant strain rate experiments.

Prediction of Inelastic High Temperature Materials Behavior by Strain-Rate Approach

1974 ◽  
Vol 96 (2) ◽  
pp. 104-108 ◽  
Author(s):  
A. Berkovits
Keyword(s):  
Experimental Study ◽  
High Temperature ◽  
Stress Relaxation ◽  
Strain Rate ◽  
Material Flow ◽  
Flow Behavior ◽  
Creep Stress ◽  
High Temperature Materials ◽  
Materials Behavior ◽  
Unique Relationship

An experimental study of the influence of strain rate on the inelastic properties of well-aged Udimet 700 at 925 C shows a unique relationship between strain rate, strain and stress for this material. This relationship, which is presented graphically as strain rate as a function of strain, is used to compute material flow behavior under loading histories including stress-strain, creep, stress relaxation, and creep under varying stress. Results obtained compare well with predicted behavior.

scholarly journals On the identification of power-law creep parameters from conical indentation

2021 ◽  
Vol 477 (2252) ◽  
pp. 20210233
Author(s):  
Yupeng Zhang ◽  
Alan Needleman
Keyword(s):  
Stress Relaxation ◽  
Stress Exponent ◽  
Power Law ◽  
Exponential Factor ◽  
Creep Stress ◽  
Uniaxial Creep ◽  
Creep Stress Exponent ◽  
Power Law Creep ◽  
Good Agreement ◽  
Conical Indentation

Load and hold conical indentation responses calculated for materials having creep stress exponents of 1.15, 3.59 and 6.60 are regarded as input ‘experimental’ responses. A Bayesian-type statistical approach (Zhang et al. 2019 J. Appl. Mech. 86 , 011002 ( doi:10.1115/1.4041352 )) is used to infer power-law creep parameters, the creep exponent and the associated pre-exponential factor, from noise-free as well as noise-contaminated indentation data. A database for the Bayesian-type analysis is created using finite-element calculations for a coarse set of parameter values with interpolation used to create the refined database used for parameter identification. Uniaxial creep and stress relaxation responses using the identified creep parameters provide a very good approximation to those of the ‘experimental’ materials with stress exponents of 1.15 and 3.59. The sensitivity to noise increases with increasing stress exponent. The uniaxial creep response is more sensitive to the accuracy of the predictions than the uniaxial stress relaxation response. Good agreement with the indentation response does not guarantee good agreement with the uniaxial response. If the noise level is sufficiently small, the model of Bower et al. (1993 Proc. R. Soc. Lond. A 441 , 97–124 ()) provides a good fit to the ‘experimental’ data for all values of creep stress exponent considered, while the model of Ginder et al. (2018 J. Mech. Phys. Solids 112 , 552–562 ()) provides a good fit for a creep stress exponent of 1.15.

scholarly journals Plastic Behavior of Predeformed Ice Crystals

1978 ◽  
Vol 21 (85) ◽  
pp. 700-701
Author(s):  
D. M. Joncich ◽  
J. Holder ◽  
A. V. Granato
Keyword(s):  
Stress Relaxation ◽  
Strain Rate ◽  
Constant Strain Rate ◽  
Dislocation Model ◽  
Stress And Strain ◽  
Strain Rates ◽  
Restoring Force ◽  
Dislocation Densities ◽  
After Effect ◽  
Stress Dependent

AbstractConventional studies of plastic deformation have been complicated by the simultaneous variation of dislocation velocity and dislocation density during the tests. In the present study this difficulty was avoided by carrying out deformation tests at low stress levels on samples which had been predeformed to relatively higher stresses prior to the measurements. Creep, mechanical after effect, constant strain-rate, and stress relaxation tests were carried out as a function of measurement stress or strain-rate, temperature, and predeformation level. The results were analysed in terms of a linear stress-dependent dislocation velocity in order to determine whether that simple behavior is able to account for the macroscopic deformation behavior of ice crystals. This report is a brief summary of the results; a complete discussion is to be published elsewhere. The principal results of the study are as follows: 1.The observed behavior was particularly simple for predeformed samples. The creep strain showed a nearly linear increase with time, without the large positive curvature characteristic of conventional tests. No stress maxima were observed in the constant strain-rate tests as have been found in previous studies of non-predeformed samples. The (complete) stress relaxation curve was virtually identical in shape to the inverted constant strain-rate curve.2.The steady-state creep and constant strain-rate behavior could be described to good approximation in terms of the motion of a constant density of dislocations moving with the same linear stress-dependent velocities as have been observed directly by others. The strain-rates were linear in stress and the estimated dislocation densities (4 to 16 × 10 cm-2) varied with the magnitude of the predeformation level in a manner consistent with previous observa-tions. The strain-rates or stress levels are exponential in 1/T with an activation energy of 0.6 eV, which is approximately equal to the activation energy reported for the motion of dislocations and for the mechanical relaxation time in internal friction studies.3.A small transient creep behavior, and a small but measurable mechanical after-effect with the same (≈ 3 min) time constant were present. These effects, as well as the non-exponential behavior of the constant strain-rate and stress-relaxation stress—strain results, could be accounted for by including a second, anelastic, component in a deformation model corresponding to a restoring force in addition to the linear viscous drag force on dislocations. This leads to a differential equation which is linear in stress and strain, but involves both first-and second-order time derivatives.4.The solutions of this differential equation describe the observed mechanical response well, and provide a general internal consistency check for the model.5.A quantitative fit of the experimental test results to the dislocation model gives values of 3-4 for the ratios of total dislocation density to the recoverable component and values of 7-8 dyn/cm2 for the restoring force constant for the recoverable dislocations. The restoring force constants and recoverable dislocation densities were, within experimental error, found to be independent of temperature, measurement stress and strain-rate, and predeformation level. Values found for the parameters for creep and mechanical after-effect tests were equal within experimental error to the values found from constant strain-rate and stress-relaxation tests carried out on the same sample. If the recoverable dislocation component is identified as bowed-out dislocation segments whose ends are fixed, the restoring force could be accounted for by the elastic line tension of dislocation segments of lengths of about 8 × 10-3 cm.No feature of the experimental results was inconsistent with this dislocation model, and the results of the study are all in agreement with the theory proposed by Weertman in which the dislocation drag force is very large because of the stress-induced ordering of water molecules in the stress field of the moving dislocation. This paper is to be submitted for publication in full in another journal.

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