A grab test is used for woven and nonwoven textile fabrics, while a modified grab test is mainly for woven textile fabrics. The grab test is a tensile test where the central part of the specimen's width is tested in the grips. It uses 100 mm x 150 mm (at least) long specimens with a line drawn parallel to the long direction and located in from the edge of one side of the specimen. The modified grab test is similar with lateral slits cut into the sides of each specimen, except for the center 25 mm (specifications are different for testing of wet fabrics). In all tests, the specimen is pulled to break at 300 mm/min (12 in/min). Test results are the breaking strength (maximum load) and elongation.
While manual action grips with smooth flat faces or rubber faces will work, many of our customers prefer the pneumatic action grips for ease of use, productivity, and better repeatability. Pneumatic action grips allow the user to set a clamping pressure, while manually operated grips depend on the operator's strength (which may not be so repeatable). Grab tests specify 25 mm x 25 mm (or 50 mm sizes) faces (while suggesting larger faces for the lower grip) while modified grab tests require one set of 25 mm x 50 mm AND 50 x 50 mm faces.
We find that gripping pressure and specimen alignment are very important in these tests. Too much gripping pressure can produce premature breaks, while not enough gripping pressure can lead to specimen slippage or breaks at or near the jaws. Software will help tremendously in these tests since it can correct for preload or pretension once the grips close, or for slack if the specimen is held too loosely in the grips at the start of the test.