ASTM D4632 土工布的抓样法断裂强力及伸长率
Written by Charlie Pryor
How is the Test Performed?
The grab test is a tensile test where the central part of the specimen's width is tested to establish the "effective strength" of the fabric. The effective strength is the strength of the material at a specific width when combined with the additional strength of adjacent material. Test specimens are cut in both the machine direction and cross-machine direction, but are expected to have their results calculated separately. Specimens are cut to 101.6 mm x 203.2 mm (4 in x 8 in), with attention to the direction of the fabric.
The specimen is loaded into the grips leaving a 75 mm (3 in) separation between the jaw faces. ASTM D4632 calls for jaw faces that are at least 25.4 mm x 50.8 mm (1 in x 2 in). However, it allows for each grip to include one jaw face that is larger than the other (a modified grab test), which can be helpful in reducing the effects of specimen/jaw face alignment. The test is conducted at a speed of 300 mm/min (12 in/min) with the required results being load at break and total elongation.
Testing System
Geotextile testing requires a test system with a data rate capture high enough to measure the failure of individual fabric fibers. Because of this, Instron recommends a high tier 6800 Series test frame, which provides a data acquisition rate of up to 5 kHz and captures data peaks and valleys accurately at up to 2500 or 5000 points per second, respectively. For most geotextiles testing to ASTM D4632, a single column frame such as Instron's 68SC-5 is appropriate, as the loads rarely climb higher than 5 kN. The rapid data capture rate in Bluehill Universal software allows data peaks and valleys to be captured accurately.
