Analysis of stress relaxation behaviour with the use of Li-curves

Ek, C. G.; Kubát, J.; Rigdahl, Mikael

doi:10.1007/bf01418456

Cited by 9 publications

(3 citation statements)

References 18 publications

(28 reference statements)

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“…This is in agreement with Equation 1 which requires that fi = 0.27 (= e/10) when calculating the slope from plots based on exp (kttJ). Experimentally, as a rule, such plots cannot be distinguished from G(log t) diagrams when the constants are properly adjusted [27]. Despite the rather limited experimental material available, it has been possible to demonstrate that the wood samples used here fit the general pattern of relaxational behaviour found with other solids and manifesting itself in the form of Equation 1.…”

Section: Discussionmentioning

confidence: 95%

Stress relaxation in wood (Scots pine veneer)

Kubát¹,

Samuelsson²,

Klason³

1989

J Mater Sci

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The kinetics of the stress relaxation process in Scots pine veneer with regard to the relation between the slope of the stress (In time) curves and the initial effective stress, o-* (applied minus internal stress) are analysed. The data obtained provide further support for the validity of the relation F ~ 0.1 o-~, with F denoting the above slope. This relation has been found to appUy to a large variety of different materials, including metals, polymers, and others. The relaxation process was linear with regard to the initial stress. There was an increase in F in the final stage of the relaxation curves, apparently due to a different mechanism. This had to be taken into account when checking the validity of the above relationship between F and o-~. The measurements relate to radially cut veneer samples at 50% relative humidity.

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Section: Discussionmentioning

confidence: 95%

Stress relaxation in wood (Scots pine veneer)

Kubát¹,

Samuelsson²,

Klason³

1989

J Mater Sci

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“…However, the Williams-Watts function does not predict a curve shape which agrees very well with experimental results. This has been pointed out earlier [23].…”

Section: Prediction Of the Ageing Behaviour Using Other Time Functionsmentioning

confidence: 86%

A model for the effect of physical ageing on the stress relaxation behavior of high density polyethylene

Kubát¹,

Maurer

Rigdahl

et al. 1989

Rheol Acta

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Abstract:The stress relaxation behavior of high density polyethylene (HDPE) can be affected by ageing processes; e.g., with increasing storage time at a low temperature following a quench from a high temperature (close to the melting point) the relaxation curves change shape. More specifically, the stress level approached after very long loading times in a stress relaxation experiment increases with the ageing time. Here this stress level is denoted "the internal stress" a i. Struik has pointed out that physical ageing may also occur in semicrystalline polymers like HDPE. The physical ageing should then be associated with that part of the amorphous phase which is closest to the surfaces of the crystallites. This part of the amorphous phase of HDPE can be assumed to have a restricted mobility at room temperature and may have a partially "glassy" character. In this paper a model for explaining the increase in a; for HDPE with increasing ageing time is proposed and discussed. It is based on the separation of the amorphous phase into two parts as suggested by Struik. The glassy part of the amorphous phase ages in a way similar to that of an entirely amorphous polymer quenched to a temperature below its glass transition, while the more rubbery phase is assumed not to undergo any physical ageing.

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“…The tests of the validities of the models are almost always comparisons with experimental results, and although they have extensive similarities, different materials show slightly different characteristics (Kubät 1965, Ek et al 1987 and the result is a number of competing models of the phenomena with little indication of which model should be applicable to what material. These characteristics can often be modelled using relatively simple mathematical expressions in which some of the terms can be given physical meanings.…”

Section: Introductionmentioning

confidence: 99%

Boson Mediated Relaxation in Solids

McQueen¹,

Kubát²

2000

Journal of the Mechanical Behavior of Materials

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Dielectric and mechanical relaxation in solids, characterised by non-exponential, extended relaxation spectra, is analysed taking the interaction of the phonon (boson) field with the relaxing elements in the solid explicitly into account. Combination of Einstein's rate equations with Bothe's analysis of boson clustering results in a second order non-linear rate equation for the relaxing elements.The character of the solutions of this equation is governed by the strength and frequency dependence of the interaction of the phonons with the relaxing elements. The upper frequency limit is the Debye cutoff frequency while the lower frequency limit is determined by grain boundaries or the like.Relaxations extending over four decades of time are obtained using physically realistic parameters.Fourier transformation produces a 1/f spectrum over a correspondingly wide frequency range. These results are compatible with experimental results concerning stress relaxation in solids and with the "universal dielectric response" of dipoles in condensed matter.Brought to you by | Purdue University Libraries Authenticated Download Date | 5/27/15 2:19 PM well illustrated in Li plots. This is a consequence of the fact that the phonon spectra of the solids can vary somewhat as well as can the details of how the applied mechanical stress moves the relaxing elements to their excited states.Finally, we have shown that the results obtained here are compatible with results obtained by Ngai, Jonscher and Kubät, among others.

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Analysis of stress relaxation behaviour with the use of Li-curves

Cited by 9 publications

References 18 publications

Stress relaxation in wood (Scots pine veneer)

Stress relaxation in wood (Scots pine veneer)

A model for the effect of physical ageing on the stress relaxation behavior of high density polyethylene

Boson Mediated Relaxation in Solids

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