STANDARD TEST METHOD FOR TEARING RESISTANCE AND ELONGATION OF TEXTILE FABRICS (Grip Test)
This test method covers grip and modified grip testing procedures to determine the breaking strength and elongation of most textile fabrics.
The grip test procedure is applicable to woven, non-woven, and felted fabrics, while the modified grip test procedure is mainly used for woven fabrics.
This test method is not recommended for fiberglass fabrics, or for knitted fabrics and other textile fabrics that have high elasticity (more than 11%).
This test method describes the procedures for carrying out fabric grip tensile testing using two types of specimens and three alternative types of testing machines.
-Tensile testing machine in accordance with D76/D76M:
CRE: Constant Spreading Speed
CRL: Constant Loading Speed
CRT: Constant Travel Speed
-Clamps.
-Gags.
PROCEDURE
CONDITIONING: according to D1776/D1776M
SAMPLE PREPARATION
-Batch Sample: Take a batch sample as indicated in the applicable material specification. In the absence of such a specification, randomly take the rolls or pieces constituting the sample batch as directed by this standard
-Cut at least one lab sample to the full width of the fabric and 1 m (1 yd) along the selvage of each roll/piece.
-Test Specimens: From each laboratory specimen, take five specimens from the warp direction (machine) and eight from the weft direction (transverse) (if tested) for each test condition.
-Cut each specimen from 100 ± 1 mm (4 ± 0.05 in.) wide by at least 150 mm (6 in.) long with the long dimension parallel to the direction of the test and the application of force.
-Draw a line on the specimen that is parallel to the long direction (and along a thread of woven fabric) and located 37 ± 1 mm (1.5 ± 0.02 in.) from the edge of one side of the specimen.
-For fabrics with high strength, the samples should be at least 400 mm (16.0 in) long and marked in the same way as the usual specimens.
-Make cuts on the sides of the sample, approximately halfway and perpendicular to the thread to be tested.
-When the number of threads per inch is less than 25, the nearest whole number of threads, immediately below the amount covered by 25 mm, shall be left uncut and the results shall be adjusted to that measurement.
-Mount the specimen on the clamping jaws with the previously drawn parallel line adjacent to the side of the upper and lower front jaws, or top, which is closest to this edge, and with approximately the same length of fabric extending beyond the jaw at each end. The parallel line serves as a guide to ensure that the same longitudinal threads of woven fabrics are gripped in both clamps and that the application of force does not form an appreciable angle to the test direction of the nonwovens. The stress on the specimen should be uniform over the entire width of the clamp.
-For stretch or heavy-duty fabrics where the specimen cannot be satisfactorily clamped down, place each specimen around the pins and between the jaws, using jaw pads if necessary.
-Elongation depends on the initial length of the specimen which is affected by any previous stress applied when mounting the specimen on the testing machine. If measuring the elongation of the specimen is required, mount the specimen to the upper clamp of the machine and apply a uniform pretension, not exceeding 0.5% of the full-scale load, to the lower end of the specimen before clamping the specimen in the lower clamp.
-Mark the specimen on the leading inner edge of each jaw to check if the specimen slides. When a slip occurs, the mark will move away from the edge of the jaw.
-Read the breaking force, and the elongation if required
-Record warp and weft direction results separately.
-If a specimen slips in the jaws, or breaks on the edge or in the jaws, or if for some reason the result falls noticeably below the average of the specimen set, discard the result and take another specimen
CALCULATIONS
-Breaking force: For each laboratory specimen and test condition, calculate the average of the observed breaking force for all acceptable specimens, i.e., the maximum force exerted on the specimen as read directly from the indicator mechanism of the testing machine.
-Measurement of apparent elongation. Unless some other force is specified, measure the apparent elongation of samples acceptable to the breaking force. Measure the increase in length from the beginning of the force-extension curve to a point corresponding to the breaking force or other specified force, as shown in the autographic record.
-Calculate apparent elongation as the percentage increase in length based on the calibrated length (initial nominal sample test length).
