ASTM D412:2006 pdf free download – Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers- Tension.
10. Apparatus
10.1 Die—The shape and dimensions of the die for preparing dumbbell specimens shall conform with those shown in Fig. 2. The inside faces in the reduced section shall he perpendicular to the plane formed by the cutting edges and polished for a distance of at least 5 mm (0.2 in.) from the cutting edge. The die shall at all limes be sharp and free of nicks (see 9.2).
Note 4—The condition of the die may be determined by investigating the rupture point on any series of broken (ruptured) specimens. Remove such specimens from the grips of the testing machine, stack the joined- together specimens on top of each other, and note if there is any tendency for tensile breaks to occur at the same position on each of the specimens. Rupture consistently at the same place indicates that the die may be dull. nicked, or bent at that location.
10.2 Bench Marker—The two marks placed on the specimen and used to measure elongation or strain are called ‘hench marks” (see Note 5). The bench marker shall consist of a base plate containing two raised parallel projections. i’he surfaces of the raised projections (parallel to the plane of the base plate) are ground smooth in the same plane. The raised projection marking surfaces shall he between 0.05 and 0.08 mm (0.002 and 0.003 in.) wide and at least 15 mm (0.6 in.) long. The angles between the parallel marking surfaces and the sides of the projections shall be at least 75°. The distance between the centers of the two parallel projections or marking surfaces shall be within I % of the required or target bench mark distance. A handle attached to the back or top of the bench marker base plate is normally a part of the bench markcr.
Nom 5—If a contact extensometer is used to measure elongation. bench marks are nut necessary.
10.3 Ink Applicator—A flat unyielding surface (hardwood, metal, or plastic) shall be used to apply either ink or powder to the bench marker. The ink or powder shall adhere to the specimen, have no deteriorating effect on the specimen and be of contrasting color to that of the specimen.
10.4 Grips—The testing machine shall have two grips, one of which shall be connected to the dynamometer.
10.4.1 Grips for testing dumbbell specimens shall tighten automatically and exert a uniform pressure across the gripping surfaces, increasing as the tension increases in order to prevent slippage and to favor failure of the specimen in the straight reduced section. Constant pressure pneumatic type grips also are satisfactory. At the end of each grip a positioning device is recommended for inserting specimens to the same depth in the grip and for alignment with the direction of pull.
10.4.2 Grips for testing straight specimens shall be constant pressure pneumatic, wedged, or toggle type designed to transmit the applied gripping force over the entire width of the gripped specimen.
11. Specimens
11.1 Dumbbell Specimens—Whenever possible, the test specimens shall he injection molded or cut from a flat sheet not less than 1.3 mm (0.05 in.) nor more than 3.3 mm (0.13 in.)