ASTM D813-07(R2019) pdf free download

ASTM D813-07(R2019) pdf free download.Standard Test Method for Rubber Deterioration—Crack Growth
1. Scope
1.1 This test method covers the determination of crack growth of vulcanized rubber when subjected to repeated bending strain or flexing. It is particularly applicable to tests of synthetic rubber compounds which resist the initiation of cracking due to flexing when tested by Method B of Test Methods D430. Cracking initiated in these materials by small cuts or tears in service, may rapidly increase in size and progress to complete failure even though the material is extremely resistant to the original flexing-fatigue cracking. Because of this characteristic of synthetic compounds, particu- larly those of the SBR type, this test method in which the specimens are first artificially punctured in the flex area should be used in evaluating the fatigue-cracking properties of this class of material. 1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.4 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
6. Apparatus
6.1 DeMattia Flexing Machine—The essential features of the apparatus, one design of which is shown in Fig. 1, are as follows: 6.1.1 The machine has an adjustable stationary head or member provided with suitable grips for holding one end ofthe test specimens in a fixed position and a similar reciprocating member for holding the other end of each of the specimens. 6.1.2 The reciprocating member is so mounted that its motion is straight in the direction of and in the same plane as the center line between the grips. The travel of the moving member shall be adjustable and shall be obtained by means of a connecting rod and eccentric having a minimum length ratio of 10 to 1. 6.1.3 The eccentric shall be driven by a motor operating at constant speed under load and giving 5 6 0.1 Hz (300 6 10 cpm). Provision shall be made for a maximum travel of the moving grips of 100 mm (4 in.). 6.1.4 The machine may be designed so that all the speci- mens are mounted on a single bar and all are flexed at the same time. A double bar may also be used in which case those specimens mounted on one bar are being flexed while those on the other bar are being straightened. Such an arrangement improves the smoothness of operation. 6.2 Mold—A mold for curing individual test specimens is required, preferably of a multiple cavity design and having adequate overflow cavities. The cavity plate shall have a minimum thickness of about 20 mm (0.750 in.) and the cover plate a minimum thickness of 14.5 mm (0.575 in.). Refer to Practice D3182. N OTE 1—The curing ofwide samples from which specimens may be cut may be provided for by increasing the width ofthe cavity and maintaining all other dimensions. 6.3 Measuring Scale of suitable length, graduated in milli- metres (or 0.01 in.) for measuring the length of cut growth. 6.4 Micrometer, to measure the thickness of the test speci- men as specified in Practice D3767, Procedure A2.
9. Preparation of Specimens
9.1 Each test specimen shall be prepared by piercing the bottom of the groove at a point equidistant from the sides. The tool shall be maintained perpendicular to both the traverse and longitudinal axes and the cut accomplished by a single inser- tion and withdrawal ofthe tool. The dimension H (of Fig. 4) of the tool shall be parallel and centered with the longitudinal axis of the groove. The leading cutting edge of the tool shall completely penetrate the specimen and project through the specimen a minimum of 3.2 mm (0.125 in.). Lubrication with water containing a suitable wetting agent may be used. The piercing tool shall be a spear-type instrument conforming to the dimensions given in Fig. 4. It is imperative that the tool is sharp and maintained to the correct dimensions, or test results will be affected.