BS ISO 5893:2019 pdf download – Rubber and plastics test equipment — Tensile, flexural and compression types (constant rate of traverse) — Specification
The test piece shall be held in such a manner that slip relative to the grips is prevented. When an adhesion test piece is made from different adherends, then grips of a different design might be required for each adherend.
5.4 Drive characteristics The moving crosshead of the machine shall be driven smoothly at all test speeds, and the drive shall be without any significant backlash.
5.5 Jigs for use in compression, shear and flexure testing Such jigs or fixtures shall conform with the requirements of the relevant method of test or material specification. They shall not significantly affect the accuracy of the machine by the introduction of friction, backlash or misalignment.
6 Types of force-measuring system In all cases, a continuous indication of the force applied to the test piece, preferably recorded automatically with a permanent indication of the maximum force, shall be provided. Machines with low-inertia force-measuring systems are preferred. NOTE Pendulum-type machines might have levels of friction and inertia which will significantly affect their dynamic response and decrease their accuracy.
7 Steady-state machine accuracy For each force scale, an accuracy class of 0,5, 1, 2 or 3 is specified (see Clause 4). The designation of each scale of a machine depends upon the values of relative errors of accuracy, repeatability and reversibility found when the machine is verified in accordance with ISO 7500-1. When separate scales for use in compression or other modes of operation are provided, these shall be verified separately.
8 Dynamic machine accuracy Tensile-testing machines fitted with electronic force-measuring devices may be regarded as sufficiently free of inertia at the test speeds given in Clause 10. This does not necessarily apply to the electronic recorders normally used with them, and in many cases the dynamic inaccuracy of these recorders considerably exceeds their steady-state inaccuracy.
All electromechanical recorders suffer from dynamic errors which are usually made up of acceleration errors, stemming from the inertia of the device, and pen-lag errors due to mechanical and electrostatic friction effects. Measurement of dynamic recorder accuracy is best achieved by recording the error- signal level during the test. This can be done without affecting instrument performance, but it is usually technically difficult. It is therefore not considered practicable at present to specify limits and a calibration procedure for dynamic accuracy in this document. Consequently, the user is advised to obtain from the test-machine manufacturer dynamic-accuracy figures for the recorder with which he/she can calculate the probable measurement error, and assess whether or not it is significant. In cases where it is, either the test speed can be reduced, or the full-scale reading of the output device can be increased, in order to reduce the acceleration and velocity levels. As a guide to recorder requirements, the response time for full-scale travel should be considerably less than the rise time of the force, if the dynamic errors are to be comparable with the steady force with the steady-state inaccuracy. It is recommended therefore that the maximum demanded pen velocity v D should be less than the maximum possible pen velocity v max by a factor dependent on the machine class as follows:v v D max ≤ 10 for class 0,5 and 1 machines
9 Measurement of elongation (deflection)
The elongation (deflection) of rubber and plastics test pieces may be measured by methods of test utilizing
a) grip separation;
b) extensometers attached to the test piece;
c) optical or other remote (non-attached) extensometers.
When elongation is measured, a continuous indication of the elongation (deflection), preferably recorded autographically in the form of a force/elongation (deflection) curve, and a permanent indication of the maximum elongation (deflection) shall be given. For some purposes, particularly the elongation of ring test pieces and for tests in flexure, shear or compression, the measurement of grip separation is the most convenient method. In such cases, it is essential that there be no play in the elongation (deflection) measuring system, nor any slippage between the grips and the test piece, which will significantly affect the accuracy of the test results.