ASTM D790:17 pdf free download – Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials.
5.1 .K.3 Chant Modulus E1—The chord modulus is calculated from two discrete points on the load deflection curse. The selected points are to be chosen at two pre-specilied stress or strain points in accordance with the appropriate material specification or by customer contract. The chosen stress or strain points used for the determination of the chord modulus shall be reported. Calculate the chord modulus. L, using Eq 7 in 12.5.2.
5.2 Experience has shown that flexural properties vary with specimen depth. temperature. almosphenc conditions, and strain rate as specified in nedurcs A and B.
5.3 Before proceeding with these test methods, refer to the ASTM specification of the material being tested. Any test specimen preparation. conditioning, dimensions, or testing parameters. or combination thereof, covered in the ASTM material specification shall take precedence over those mentioned in these test methods. Table I in Classification System D3(X) lists the ASTM material specifications that currently exist for plastics.
6. Apparatus
6. I Tesling Machine—A testing machine capable of being operated at constant rates of crosshead motion over the range indicated and comprised of the follosing:
6. I. I lAkid Frume—The stillness of the testing machine shall be such that the total elastic deformation of the system does not exceed 1 % of the total deflection of the test specimen during testing. or appropnate corrections shall be made.
6.1. I. I Fixed Member—A fixed or essentially stationary member holding the specimen supports:
6.1.1.2 Movable Member—A movable member carrying the loading nose.
6.1.2 Noses and Supports—The loading nose and supports shall have cylindrical surfaces.
6.1.2. I The radii of the loading nose and supports shall be 5.0 ± 0.1 mm (0.197 ± 0.004 in.) unless otherwise specified in an ASTM material specification or as agreed upon between interested parties.
6. 1 .2.2 Other Radii for Loading Nises and Supports— Alternative loading noses and supports arc perniitted to be used in order to avoid excessive indentation or failure due to stress concentration directly under the loading nose or if required by an ASTM material specification. If alternative loading nose and support radii arc used, the dimensions of the loading nose and supports shall be clearly identified in the test report and reference shall be made to any applicable specifications.
(1) Alternative supports shall have a minimum radius of 3.2 mm (¼ in.) When testing specimens 3.2 mm or greater in depth. the radius of the loading nose and supports arc permitted to be up to 1.6 times the specimen depth.
(2) The arc of the loading nose in contact with the specimen shall be ufliciently large to prevent contact of the specimen with the sides of the nose.