BS/EN 17096-2018 pdf download.Geosynthetics – Test method for the determination of the strain hardening modulus of PE-HD geosynthetic barriers.
3.11
draw ratio
actual length per unit original length of the gauge
Note I to entry: Draw ratio at yield is expressed as a dimensionless ratio.
3.12
strain hardening modulus cGp>
slope of the Neo-Hookean constitutive model between a draw ratio of 8 and up to the point of maximum stress but not above 12
Note I to entry: Strain hardening modulus is expressed in MPa.
3.13
variation coefficient
standard deviation of the test results divided by the arithmetic mean of the test results multiplied by
100
Note I to entry: Variation coefficient is expressed as a percentage (%).
4 Principle
A stress-strain curve is measured at (80 ± 1) °C sufficiently beyond the natural draw ratio and the strain hardening modulus determined from the slope alter the natural draw ratio (see informative Annex A).
5 Apparatus
5.1 Tensile-testing machine
5.1.1 The machine shall comply with EN ISO 527-1. The tensile-testing machine shall be capable of maintaining a test speed of(lO ± 2) mm/mm.
5.1.2 Load cell, which shall comply with class 1 as defined in EN ISO 7500-1.
Due to measurement at elevated temperature of (80 ± 1) °C, the measured forces are low. Therefore, a load cell with a range of 250 N is recommended.
5.1.3 Non-contact extensometer, which shall comply with the same accuracy requirements as given for contact extensometers in EN ISO 9513. A non-contact extensometer shall be used because the test is performed at an elevated temperature of (80 ± 1) °C. The traverse displacement shall not be used as to measure strain.
5.1.4 Temperature chamber to control the temperature at (80 ± 1) °C.
A switch to enable closing and opening the clamps without opening the temperature chamber is recommended but not necessary, if the testing device is able to hold force of zero.
5.2 Devices for measuring the thickness and width of the test specimens
5.2.1 Thickness (ci) shall be measured according to EN ISO 9863-1:2016, Annex A.
5.2.2 Width (b) shall be measured with an optical device with an accuracy of 0,01 mm, according to EN 1849-2:2009, 5.4.3. Three additional specimens, which are not used for determination of strain hardening modulus but which are punched using the identical punch die tool as for the test specimens tested for strain hardening modulus shall be measured optically. A cutting of the cross section area perpendicular to the axis of the specimen within the gauge length of each of the three specimens shall be prepared. The widest width as well as the narrowest width of each specimen’s cutting shall be determined and recorded. The mean value of all six values regarding width (two measured values per specimen) will be applied for all test specimens tested for strain hardening modulus for calculation of stress.
The dimensions of the cross section area have a great influence on the value of strain hardening modulus. Due to the punching, the width of specimens might be conical shaped. The dimensions close to the bottom surface of the geosynthetic barrier and close to the top surface of the geosynthetic barrier might be significantly different. Mechanical measurement of width cannot take this into account. Therefore, special attention has to be payed to determination of width by performing optical measurements Instead of mechanical measurements.
5.3 Punch die tool
A punch die tool for the specimen geometry specified in 6.1 shall be used.
5.4 Device for application of the gauge marks
A suitable device for the application of the gauge marks for the non-contact extensometer shall be used. The gauge mark shall be suitable for the optical sensor system used.
6 Test specimen
6.1 Dimensions and figure of the test specimen
The specimen geometry as shown in Figure 1 shall be used.
6.2 Test specimen preparation
Five test specimens (each in CMD and MD) shall be punched from the sample (see 6.1). The punching procedure shall be carried out in such a way that no deformation, crazes or other irregularities are present on the test specimens.
The thickness of the test specimens shall be measured at three points of the parallel area of the specimen; the lowest measured value for thickness of these measurements shall be used for data treatment (see Clause 8).
Apply the gauge marks on each test specimen equidistant from the midpoint, keeping the gauge length
7 Test procedure
The measurement is described below:
— measurement of the width of three additional specimens as described in 5.2.2 for determination of the mean width (b) and measurement of thickness (d) as described in 5.2.1 of each individual test specimen;
— conditioning of the test specimens for at least 30 mm in the temperature chamber at a temperature of (80 ± 1) °C prior to starting the test;
— the test specimen shall be clamped on the upper side in a way that slippage in the clamps is prevented. The test specimens shall not be damaged by the clamps;
— the test specimen shall remain between the clamps for at least I mm before the load is applied and measurement starts;BS/EN 17096-2018 pdf download.