Standard Test Method for Grab Breaking Load and Elongation of Geotextiles

ASTM D4632 Vise Grip – Universal Grip Data Sheet (PDF)

Theory:

ASTM D4632 describes a test procedure for measuring the breaking load and elongation of geotextiles. The test is a "grab test" which means that the grip "grabs" the fabric in the middle of the specimen. It is the geotextile version of ASTM D5034, the grab test for ordinary textiles. D4632 applies to most geotextiles, both woven and nonwoven; it is not recommended for knitted geotextiles. Grab strength is a core property in AASHTO M288 and most DOT geotextile specifications, so this test is run on almost every separation, stabilization and filtration fabric. 

Geometry:

Specimens are 100 × 200 mm (4 × 8 in), with the 200 mm length in the direction being tested. Cut separate sets in the machine and cross-machine directions, keep them away from the roll edges, and sample the lot according to ASTM D4354. Condition specimens in the standard atmosphere for testing geotextiles (21 ± 2 °C and 50–70% RH, as defined in ASTM D4439). Wet testing is an option when a specification calls for it.

Solution:

A benchtop tensile testing machine is used to pull the geotextile at a constant-rate-of-extension (CRE). The grips and grip jaw inserts are extremely important for conformity to this test method. Each front jaw face measures 25.4 × 50.8 mm (1 × 2 in), with the 50.8 mm side parallel to the direction of pull, so only the center 25 mm of the 100 mm wide specimen is gripped. Set the jaws 75 mm (3 in) apart and pull at 300 ± 10 mm/min (12 ± 0.5 in/min). A universal joint adapter can be used to align the axial tension, however this is not always necessary. 

Analysis:

The grab breaking load is the peak force reached during the test, reported in N or lbf. Apparent elongation at break is the extension at peak divided by the 75 mm initial jaw separation, given as a percentage. The system can also measure elongation using either the crosshead position or the Galdabini MICRON balanced extensometer. 

Similar Specifications:

ASTM D5034 - Textile Grab Test

ASTM D4595 - Geotextile Tensile Testing

 

 

ASTM D4632 FAQ

What is the test speed for ASTM D4632?

300 ± 10 mm/min (12 ± 0.5 in/min), with the jaws set 75 mm (3 in) apart at the start of the test.

What size are ASTM D4632 specimens and jaws?

Specimens are 100 × 200 mm (4 × 8 in). The front jaw faces are 25.4 × 50.8 mm (1 × 2 in), so the clamps grip only the center 25 mm of the specimen width.

Does ASTM D4632 apply to nonwoven geotextiles?

Yes. D4632 is used for both woven and nonwoven geotextiles. It is not recommended for knitted fabrics.

What is the difference between ASTM D4632 and ASTM D4595?

D4632 is a grab test on a 100 mm wide specimen that gives a quick index value used in specifications such as AASHTO M288. D4595 is a wide-width strip test on a 200 mm wide specimen that gives tensile strength per unit width for design.

For the related grab and strip tests on ordinary fabrics, read our guide to textile testing on a universal testing machine.