Some new operational modes and parameters of stress relaxation for the viscoelastic characterization of solid polymers. I. The ""virtual modulus"" mode

Kytopoulos, VN; Bourkas, GD; Sideridis, E

dc.contributor.author	Kytopoulos, VN	en
dc.contributor.author	Bourkas, GD	en
dc.contributor.author	Sideridis, E	en
dc.date.accessioned	2014-03-01T01:52:00Z
dc.date.available	2014-03-01T01:52:00Z
dc.date.issued	2002	en
dc.identifier.issn	00218995	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/26526
dc.subject	Modeling	en
dc.subject	Modulus	en
dc.subject	Poly(propylene) (PP)	en
dc.subject	Relaxation	en
dc.subject	Viscoelastic properties	en
dc.subject.other	Differential equations	en
dc.subject.other	Integral equations	en
dc.subject.other	Stress relaxation	en
dc.subject.other	Viscoelasticity	en
dc.subject.other	Finite loading time	en
dc.subject.other	Propylene	en
dc.subject.other	polypropylene	en
dc.subject.other	relaxing	en
dc.subject.other	stress	en
dc.subject.other	viscoelasticity	en
dc.title	Some new operational modes and parameters of stress relaxation for the viscoelastic characterization of solid polymers. I. The ""virtual modulus"" mode	en
heal.type	journalArticle	en
heal.identifier.primary	10.1002/app.11165	en
heal.identifier.secondary	http://dx.doi.org/10.1002/app.11165	en
heal.publicationDate	2002	en
heal.abstract	A new operational (functional) parameter, the so-called virtual modulus, E(t), is introduced. By this, an attempt was made for the approximation of the function of the real modulus E(t), which, as known, is valid only for instantaneous loading, namely, for zero loading times. Thus, through a simple theoretical modeling and an algorithmic approach, the determination of E(t), from E(t), sets sail, at the end, to the solution of a Volterra integral equation of the second type, which, in turn, sets sail to the solution of a differential equation. By the aid of numerical integration and also of some experimental evidence, it seems that this solution is valid only for loading times approximately above 0.2 s, thus obtaining, in fact, a ""pseudomodulus"" of relaxation. To assess the validity of this pseudomodulus, the well-known Kohlrausch-Williams-Watt (KWW) and the power-law models were used as some crude ""criteria."" By means of best fit, it appeared, at the first instance, that the so-calculated pseudomodulus better obeys the power-law model than it does the KWW model. This is a certain contradiction with the so-called apparent modulus, which was obtained from experiment with a finite loading time superior to 1 s. Two other criteria that were used have shown a satisfactory proof of the validity of this modeling. © 2002 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 87.	en
heal.journalName	Journal of Applied Polymer Science	en
dc.identifier.doi	10.1002/app.11165	en
dc.identifier.volume	87	en
dc.identifier.issue	2	en
dc.identifier.spage	121	en
dc.identifier.epage	137	en