Question: I know that the American Society for Testing and Materials (ASTM) approves several handles (the requirement is that they be "flat") to conform to ASTM D4632 and ASTM D5034.

For woven geotextiles, we use a hard, smooth rubber surface and for nonwoven geotextiles, we use a slightly ridged surface. One of our customers uses a smooth metal surface.

I'm trying to understand what effect a tongue and geo fabric groove surface can have on the test results for a woven material. Can you give me a quick explanation or direct me to some literature to read to better understand this?

FIGURE 1 Correct grip surfaces for a pull grip. Photo courtesy of GSI.

Answer: Figure 1 shows the three grip surfaces that can be used for the ASTM D4632 and ASTM D5034 test methods. However, the grip surfaces in Figure 2 are not acceptable.

They are not "flat" as required by Section 6.2 of ASTM D4632. Such grips have two effects on the geotextile before testing. The first effect is that it pre-charges the sample. So the modulus and elongation values ​​will be off (the elongation will be less and the modulus will be higher).

Second, tongue-and-groove faces consume much more than 2 inches (50 mm) of material in the longitudinal direction of the mounts compared to flat faces. This leads to the fact that the strength is up to 10% higher, depending on the demands of the profile and the type of material tested.