ASTM D4632 Geotextile Grab Test
This grab test is used for geotextile fabrics to determine the breaking load (grab strength) and elongation (grab elongation). The grab test is a tensile test where the central part of the specimen's width is tested in the grips, establishing the “effective strength” of the fabric. The effective strength is the strength of the material in a specific width, together with the additional strength of adjacent material.
The specimens are cut to 101.6 mm x 203.2 mm (4 in x 8 in), with attention to the fabrication machine direction. The specimen is loaded into the grips leaving a 75 mm (3 in) separation between the jaw faces, and jaw faces must be 25.4 mm x 50.8 mm (1 in x 2 in) with the longer dimension being parallel to the direction of the load. The test speed is 300 mm/min (12 in/min). The required test results are load at break and total elongation.
Geotextile materials tend to have coatings that may make it difficult to test without slippage or jaw breaks. Instron’s pneumatic side acting grips provide an easy, repeatable, high throughput gripping solution. Pneumatic grips allow the user to adjust grip clamping pressure, while the performance of manually operated grips will vary depending on the operator.
The challenges of testing to this standard are:
- Rapid data capture rate
- Jaw breaks
- Specimen slippage
- Rapid data capture rate in Bluehill® software allows data peaks and valleys to be captured accurately
- Instron pneumatic side acting grips enable rapid adjustment of the grip pressure and easy grip face changes for testing different types of specimens, all while maintaining high throughput
It is important to review ASTM D4632/D4632M-15 in order to fully understand the test setup, procedure, and results requirements.
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