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BS ISO 20965:2021 pdf free

BS ISO 20965:2021 pdf free.Plastics一Determination of the transient extensional viscosity of polymer melts.
This document specifies the general principles of a method for determining the transient extensional viscosity of polymer melts. The procedure details the measurement of polymer melt specimens stretched uniaxially under conditions of constant strain rate and constant temperature.
The method is capable of measuring the transient extensional viscosity of polymer melts at l-Iencky strain rates typically in the range 0,01 s-1 to 1 s, at Hencky strains up to approximately 4 and at temperatures up to approximately 250 °C (see NOTEs I and 2). It is suitable for measuring transient extensional viscosity values typically in the range from approximately l0 Pas to io Pas (see NOTE 3).
NOTE 1 Hencky strains and strain rates are used (see Clause 3).
NOTE 2 Values of strain, strain rate and temperature outside these limiting values can be attained.
NOTE 3 The operating limit of an instrument, in terms of the lowest transient extensional viscosity values that can be measured, is due to a combination of factors, including the ability of the specimen to maintain its shape during testing and the resolution of the instrument.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applics. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 472, Plastics — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 472 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.orgJobp
— IEC Electropedia: available at http://www.electropedia.org/
4 General principles
In contrast to shear flow where reference is normally made only to steady shear flow behaviour, extensional flow behaviour is best described as being transient. In describing the transient behaviour of materials in extension at constant strain rate, they may exhibit either an unbounded stress growth behaviour in which the stress continually increases with increasing strain until the material fails, or the stress reaches a steady value with increasing strain thus yielding a tensile or equilibrium extensional viscosity. The latter occurs typically at large strains. An equilibrium extensional viscosity is thus dependent on strain rate but not on strain or time. Normally, the extensional viscosity varies as a function of both strain and strain rate as well as temperature.
In describing and modelling plastics processing, the use of Hencky strain is preferred. The rate of I-lencky strain of an element of fluid within a flow is independent of its original length and is determined only from the velocity field of that element. It is thus a more suitable characteristic of the flow. Strain and strain rate are taken by default herein to be Hencky values.
Stretching flow methods can be used to generate quantitatively accurate data on the extensional viscoelasticity of polymer melts. In carrying out extensional flow measurements, there are four types of measurement that are normally made: constant strain rate, constant stress, constant force and constant speed. This document describes the first of these: constant strain rate. In this method, the strain rate is uniform throughout the specimen and is held constant with time.
The basic principle behind stretching flow measurements is to subject a specimen to a tensile stretching deformation. By measurement of the force and deformation of the specimen, the stresses and strains and hence strain rate can be determined.
5 Apparatus
5.1 General description
The measuring apparatus shall consist of one of the following types, shown in Eiguri. to Figure 4. These types define the various instrument configurations. The notation Lised in these figures is defined in Li.
Type A: Two rotating clamps. Each clamp shall consist of either a single rotating element or a pair of rotating elements — only the pair arrangement is shown. The force exerted on the specimen can be measured at the fixed or rotating end.
NOTE It is likely that the force will be easier to measure, and will be measured with greater accuracy, on a fixed clamp rather than on a moving clamp as there will be fewer complications due, for example, to vibration and the inertia of the clamp which can introduce noise and errors into the force signal.BS ISO 20965 pdf download.

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