Ballpoint pens can be dangerous – just ask Steve Hall, a technician at UL’s Softline lab in Bentonville, Ark. Small objects, such as a ballpoint pen, have been known to poke holes through a shirt or pant pocket. The next thing you know, the contents of your pocket have escaped, and you’re left with nothing but a ruined item of clothing and a bad attitude about writing instruments.
The ability to resist stress is one of the most widely measured properties needed by designers to create durable articles of clothing like pants, shirts and jackets. Many labels build a brand by choosing quality fabrics that can stand up to the wear and tear of daily events, like ballpoint pens or playground antics.
That’s one of the reasons UL technicians around the world routinely test specific types of fabric. Two tests are performed to determine the strength of a fabric sample: the tensile test and the burst test.
The tensile test measures a samples ability to resist breaking under stress. For the test, the technician determines the grain of a 4”x 6” sample, then marks and centers the sample in the jaws of the testing machine. The technician clamps both ends of the sample in the jaw of the machine. The upper jaw moves upward, applying equal stress to the sample as it elongates or stretches. When the sample “snaps,” the breaking strength of the fabric is reported in pounds.
The burst test is used to measure the strength of the fabric by providing stress on the material from all directions equally at the same time. The test is widely used for fabrics such as knitted materials, lace, parachute fabrics, etc. For the burst test, a fabric sample is clamped over a rubber diaphragm and secured by a clamping ring. Continuous pressure is applied, using blown air, from the underside of the diaphragm until the sample bursts.
Knowing the strength of a particular fabric helps product designers make decisions that help improve product durability – from pockets capable of withstanding pens to parachute fabric that delivers a safe trip down to the ground.
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