BS 4618-1 1 3-1974 Recommendations for the presentation of plastics design data - Mechanical properties - Creep lateral contraction ratio (Poissons ratio)《塑料设计数据表示方法推荐规程 第1部分 机械特性 .pdf

1、BRITISH STANDARD BS 4618-1.1.3: 1974 Recommendations for The presentation of plastics design data Part 1: Mechanical properties Subsection 1.1.3: Creep lateral contraction ratio (Poissons ratio) IMPORTANT NOTE. Before reading this subsection it is essential to read the General Introduction to this s

2、eries of Reccommendations, issued separately and also Section 1.1 and Subsection 1.1.1. UDC 001.8:678.5/.8:539.434BS4618-1.1.3:1974 BSI 07-1999 ISBN 0 580 07738 1 A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for

3、 their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 3 and a back cover. This standard has been updated (see copyright date) a

4、nd may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date CommentsBS4618-1.1.3:1974 BSI 07-1999 i Contents Page Introduction 1 1 Apparatus and test specimen 1 2 Test conditions 1 3 Recommended e

5、xperimental programmes 2 4 Form of presentation 2 Figure 1.1.3/1 Creep lateral contraction ratio log time curves 3 Figure 1.1.3/2 Isochronous creep lateral contraction ratio stress curve 3ii blankBS4618-1.1.3:1974 BSI 07-1999 1 Introduction The creep lateral contraction ratio (Poissons ratio) is one

6、 of the four fundamental parameters used to describe the deformation behaviour of an isotropic linear viscoelastic material. As only two of these four parameters are independent, the measurement of creep lateral contraction ratio and creep modulus during uniaxial tensile (or compressive) creep enabl

7、es such deformation behaviour to be characterized, using one basic type of apparatus. It is apparent that the measurements necessary for the determination of the creep lateral contraction ratio also enable the creep modulus to be calculated if the creep stress is known. Furthermore, both the creep m

8、odulus and creep lateral contraction ratio experiments are ideal for the study of non-linear viscoelasticity, as the stress is uniform across the specimen cross section NOTEThe following BSI references relate to work on this Recommendation: Committee reference PLC/36/1Draftforcomment 72/50117 DC 1 A

9、pparatus and test specimen 1.1 It is necessary for the basic creep machine and the method of measurement of the longitudinal strain to conform to the requirements laid down in clause 1 of Subsection 1.1.1. 1.2 The method of measurement of the lateral strain should be such that a) any axial force ass

10、ociated with the mass of the extensometer 1)is very low; b) any frictional or other constraints on the specimen as it deforms are negligible; c) any indentation of the specimen by the device does not change significantly with time. 1.3 Although there are obvious advantages if the lateral and axial s

11、trains are measured simultaneously on one specimen, there is no fundamental objection to the measurement of each strain on separate specimens, provided that they, and the test conditions, are identical except for the placing of the extensometers. The inter-specimen variability should be commensurate

12、 with the required accuracy. 1.4 The sensitivity requirements for the extensometers and the necessary degree of axiality of the creep machine depend on the type of material and the end use of the data. High precision may be required for both the longitudinal and the lateral strain when calculating u

13、nknown parameters (e.g.shear creep modulus from tensile creep modulus and creep lateral contraction ratio) However, for critical engineering applications, precise measurement of the longitudinal strain (forcreep modulus) with a lower precision for the lateral strain (and hence creep lateral contract

14、ion ratio) will usually be acceptable. Following the procedure laid down for the longitudinal strain measurement (1.5 of Subsection1.1.1) the three test classifications for the measurement sensitivity of the lateral strain are as follows A minimum detectable increment0.002%strain. B minimum detectab

15、le increment0.008%strain C minimum detectable increment0.02%strain. 1.5 High precision machines, as defined in 1.6 of Subsection 1.1.1, are essential for work within classification A and may also be required for some lateral strain devices working within classificationB. For work within classificati

16、on C, lower precision machines are adequate. 1.6 There is no objection to the use of extensometers working within different classifications on the same creep machine. In such cases the classification of the creep lateral contraction ratio will be given as, for example, AB if the longitudinal device

17、operates within classification A and the lateral device operates within classification B. This mixed classification is only meaningful if the precision of the creep machine matches that required for the higher classification. 1.7 Specimens should be prepared to an accuracy commensurate with the axia

18、lity specification and test machine accuracy. The degree of flatness and parallelism of the specimen surfaces monitored by the lateral strain-measuring device should also be commensurate with the test classification of that device. 2 Test conditions The test conditions should be identical to those g

19、iven in clause 2 of Subsection 1.1.1. 1) For the purposes of this subsection, the term “extensometer” applies to any acceptable strain measuring device.BS4618-1.1.3:1974 2 BSI 07-1999 3 Recommended experimental programmes 3.1 Experimental programmes should follow the pattern outlined in clause 5 of

20、Section 1.1. 3.2 When creep modulus and lateral contraction ratio are obtained simultaneously on a single creep machine, the programmes for the measurement of creep modulus, detailed in clause 3 of Subsection1.1.1, will also be suitable for the measurement of creep lateral contraction ratio. However

21、, such a comprehensive programme is not normally necessary for the characterization of creep lateral contraction ratio, the possible range of values being smaller, and acceptable error usually larger, when compared with the creep modulus. If appropriate, the test programme for the determination of c

22、reep lateral contraction ratio may be abbreviated as follows. a) At any chosen temperature, creep tests at two stress levels should suffice, unless extreme non-linearity is encountered. (The lower stress level should be such that the longitudinal strain does not exceed approximately 0.5 %. The highe

23、r stress level should be below that at which non-uniform deformation develops.) b) Creep tests at one other temperature apart from that selected in a) above should be chosen because of the relevance to particular service requirements. 4 Form of presentation 4.1 The primary data should be presented a

24、s curves showing creep lateral contraction ratio against logarithmic time at different stress levels. (SeeFigure 1.1.3/1.) 4.2 Isochronous creep lateral contraction ratio/stress curves (see Figure 1.1.3/2) are obtained either by constructing sections of constant time on the creep curves (if the numb

25、er of stress levels is sufficient) or by the method described in 4.2 of Section 1.1. The times should be chosen from the following: 60 s, 100 s, 1 h, 24 h, 100 h, 1 000 h, 1 year, 10years, 50 years. 4.3 These graphs (see 4.1) cannot normally be used to interpolate for intermediate stresses. Lateral

26、strain/log time graphs may be interpolated in the same way as longitudinal strain data. Interpolated lateral and longitudinal strain data can be used to give creep lateral contraction ratio data. 4.4 The effect of temperature can be displayed by fixing the values of two variables. For instance, a co

27、nvenient method is to stipulate time and longitudinal strain (or stress) and to plot creep lateral contraction ratio/temperature curves. 4.5 Recovery data may be presented as fractional recovered strain/reduced time curves for the individual strains. (See 6.7 of Section 1.1.) The duration of the cre

28、ep period and the maximum strain reached should be stated. 4.6 The creep data, presented in graphical form, should be accompanied by the information indicated in 6.8 of Section 1.1.BS4618-1.1.3:1974 BSI 07-1999 3 Figure 1.1.3/1 Creep lateral contraction ratio log time curves Figure 1.1.3/2 Isochrono

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