Comparison of the elongational behaviour of a polyethylene melt at constant stress and constant strain rate

1976 ◽  
Vol 15 (10) ◽  
pp. 517-524 ◽  
Author(s):  
H. M. Laun ◽  
H. M�nstedt
Keyword(s):  
Strain Rate ◽  
Constant Strain Rate ◽  
Constant Stress ◽  
Polyethylene Melt

scholarly journals Primary, secondary and tertiary creep of ice modelled as a viscoelastic fluid

2009 ◽  
Vol 55 (189) ◽  
pp. 170-178 ◽  
Author(s):  
L. W. Morland
Keyword(s):  
Strain Rate ◽  
Viscoelastic Fluid ◽  
Ice Sheet ◽  
Constant Strain Rate ◽  
Constant Stress ◽  
Constitutive Law ◽  
Asymptotic Limit ◽  
Tertiary Creep ◽  
Secondary Creep ◽  
Viscous Behaviour

AbstractAs an ice sheet evolves, there are ice elements near the surface only recently subjected to stress following deposition, and others that have been subjected to stress over many ranges of time. The constant stress and constant strain-rate responses of ice in uniaxial compressive stress exhibit non-viscous behaviour, that is, the strain rate is not fixed by the stress (and conversely) but both vary with time. At constant stress the initial primary strain rate decreases with time to a minimum, described as secondary creep. It then increases and approaches an asymptotic limit, described as tertiary creep. Analogously, at constant strain rate the initial stress increases to a maximum then decreases to an asymptotic limit. These responses are used to construct a simple viscoelastic fluid constitutive law of differential type. Such a time-dependent law, with timescales changing widely with temperature, can be expected to yield a flow field in an ice sheet that is very different from that obtained from the viscous law. Only comparison solutions for both constitutive laws can determine the differences and significance of the non-viscous behaviour, and the simple law constructed would be a candidate for such comparisons.

A Rate-Dependent Stress-Strain Relationship for Sea Ice

1983 ◽  
Vol 105 (1) ◽  
pp. 2-5 ◽  
Author(s):  
Y. S. Wang
Keyword(s):  
Sea Ice ◽  
Strain Rate ◽  
Nonlinear Models ◽  
Constant Strain Rate ◽  
Relative Difference ◽  
Constant Stress ◽  
Stress Rate ◽  
Loading Conditions ◽  
Stress Strain ◽  
Strain Relationship

A one-dimensional rate-sensitive stress-strain relationship is developed to describe the uniaxial mechanical behavior in compression for sea ice. It is a one-term, nonlinear model and is simpler in form than the nonlinear models proposed by other investigators. It contains four independent constants that are determined by experimental data. This model can describe the behavior of sea ice very well under constant strain rate loading, constant stress rate loading and creep loading conditions. In particular, it describes the following features of sea behavior: 1 the increase in ice strength with strain rate and with stress rate; 2 the increase in strain-softening effects with strain rate; 3 the relative difference between the strengths obtained by constant stress rate and constant strain rate tests; 4 the rate dependence of ice stiffness; 5 primary, secondary, and tertiary creep, where the duration and rate depend on the applied stress level. This paper presents the proposed rate-sensitive stress-strain relationship and discusses its behavior under various loading conditions. A set of coefficients has been selected to compare with test results under constant strain rates. Agreement between predicted and observed stress-strain behaviors is very good. Predicted behavior under constant stress rate and creep are also presented.

Ultimate Tensile Properties of Elastomers. I. Characterization by a Time and Temperature Independent Failure Envelope

1964 ◽  
Vol 37 (4) ◽  
pp. 777-791 ◽  
Author(s):  
Thor L. Smith
Keyword(s):  
Strain Rate ◽  
Tensile Properties ◽  
Elevated Temperatures ◽  
Constant Strain Rate ◽  
Test Methods ◽  
Constant Stress ◽  
Test Method ◽  
Failure Envelope ◽  
Polymeric Network ◽  
Time To Rupture

Abstract The tensile stress at break (σb) and the associated ultimate strain (εb) of an elastomer depend on (1) the chemical and topological characteristics of the polymeric network, and (2) the test conditions under which rupture is observed. To separate these effects, the ultimate tensile properties can often be characterized by a “failure envelope” defined by values of σb and εb determined at various strain rates over a wide temperature range. Provided time—temperature superposition is applicable, such data superpose on a plot of log σbT0/T versus log εb, where T is the test temperature (absolute) and T0 is an arbitrarily selected reference temperature. The resulting failure envelope is independent of time (strain rate) and temperature and thus it depends only on basic characteristics of the polymeric network. To illustrate the characterization method, data on two styrene-butadiene gum vulcanizates, SBR-I and SBR-II, were analyzed. For SBR-I, values of σb and εb obtained over extensive ranges of strain rate and temperature superposed to give a failure envelope. Data at elevated temperatures also gave a reliable value for the equilibrium modulus. For SBR-II, data obtained at various temperatures under conditions of constant strain and constant strain rate yielded identical failure envelopes; this strongly suggests that the failure envelope is independent of the test method. A theoretical consideration of the time-to-rupture associated with different test methods showed that for given values of σb and εb the time-to-rupture from the following types of tests should increase in the order: constant strain < constant stress < constant strain rate < constant stress rate.

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