Industry Terms Mechanical Elongation Set The extension remaining after a specimen has been stretched and allowed to retract, expressed as a percentage of original length. Two points are marked before elongation. After elongation, measure the distance between the benchmarks and calculate the set.(ASTM D-412) Tear Strength The specimen is clamped in the jaws of a testing machine and the jaws then separated at a speed of 20" per minute. After rupture of the specimen, the breaking force in pounds is noted. The resistance to tear is calculated from the force and the median thickness of the specimen. Values are given in pounds per inch for tearing a specimen of one inch in thickness. D-624 specifies that results be normalized to thickness, that is expressed as force to tear divided by thickness. (ASTM D-624) Tear Resistance Tear resistance is a measure of stress needed to continue rupturing a sheet of plastic, usually after an initiating cut. (ASTM D-624) Abrasion Resistance This is one of the properties of thermoplastic that is difficult to measure. The term refers to the resistance of a thermoplastic to wear and is usually measured by the loss of material when a part is brought into contact with a moving abrasive surface. It is specified as percent of volume loss of sample as compared with a standard. It is almost impossible to correlate these relative values to life expectancy. (ASTM D-1044) Compression Set This is the permanent creep that remains after the plastic has been held at either constant strain or stress and in compression for a given time. Constant strain is most generally employed, and is reported as a percentage of the permanent creep divided by the amount of original strain. A strain of 25 percent is most common. (ASTM D-395) Elongation Ultimate The fractional increase in length of a material stressed in tension. Flexural Yield & Flex Modulus Flexural properties of plastic can be compared to bending a steel beam between two supports. It measures the resistance to bending under load. A higher flexural strength in a material having little ductility usually indicates a higher tensile strength. (ASTM D-790)