ASTM D785-08 (R2015) PDF Download

ASTM D785-08 (R2015) is a standard test method that provides procedures for measuring the Rockwell hardness of plastics and electrical insulating materials using a Rockwell hardness tester. The test involves applying a fixed minor load to an indenter, increasing the load to a major load, and then returning to the minor load to measure the net increase in depth impression. There are two procedures: Procedure A measures the indentation of the specimen 15 seconds after the major load is released, while Procedure B measures the indentation while the load is still applied.

The Rockwell hardness number obtained from the test is a measure of the indentation hardness of the material, with higher numbers indicating harder materials. The hardness number is derived from the depth of impression after removal of the major load. The standard specifies the relationship between the Rockwell hardness number and the depth of impression for the E, M, L, R, and K scales.

The standard emphasizes that Rockwell hardness numbers should not be used as a measure of abrasion or wear resistance of the plastic materials. It also mentions that time factors, such as the application of major and minor loads, can affect the results for materials with creep and recovery properties. The test method is useful for indicating the cure of thermosetting materials at room temperature, as uncured specimens generally have lower hardness readings.

The standard includes a table of Rockwell hardness scales, which are extensions of each other, with some overlap between adjacent scales. However, there is no guarantee that readings on one material will correspond to readings on another due to differences in elasticity, creep, and shear characteristics.

Before conducting the test, it is recommended to refer to the material specification to determine any specific specimen preparation, conditioning, dimensions, or testing parameters that may take precedence over the standard procedure. If there are no specific material specifications, the default conditions outlined in the standard should be followed. ASTM D785-08 (R2015) is considered equivalent to ISO 2039-2, with Procedure A corresponding to the main body of ISO 2039-2 and Procedure B corresponding to the integral annex part of ISO 2039-2.