ASTM D 6693/D6693M : 2020

Note 1:This test method is not intended to precisely measure physical properties of a geomembrane for design purposes. This is an “index test” intended to be used for quality control and specification conformance purposes. The constant rate of crosshead movement of this test lacks accuracy from a theoretical standpoint, since crosshead movement as opposed to actual strain is used. A wide difference may exist between the rate of crosshead movement and the rate of strain in particular areas of the specimen since the specimen does not have a uniform width or cross-sectional area. This may disguise important effects or characteristics of these materials in the plastic state. Use of an extensometer, not included in this test, would more accurately measure strain and strain rate but would still have limitations for some geomembranes. Further, it is realized that variations in the thicknesses of test specimens, as permitted by this test method, produce variations in the surface-volume ratios of such specimens, and that these variations may influence the test results. Hence, where directly comparable results are desired, all samples should be of equal thickness. Special additional tests should be used where more precise physical data are needed. Test Method D4885 is a suitable performance test for many applications.