ASTM D785-23

Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials

SIGNIFICANCE AND USE
4.1 A Rockwell hardness number is a number derived from the net increase in depth impression as the load on an indenter is increased from a fixed minor load to a major load and then returned to a minor load (Procedure A). A Rockwell alpha (α) hardness number represents the maximum possible remaining travel of a short-stroke machine from the net depth of impression, as the load on the indenter is increased from a fixed minor load to a major load (Procedure B). Indenters are round steel balls of specific diameters. Rockwell hardness numbers are always quoted with a scale symbol representing the indenter size, load, and dial scale used. This test method is based on Test Methods E18. Procedure A (Section 11) yields the indentation of the specimen remaining 15 s after a given major load is released to a standard 10-kg minor load. Procedure B (Section 12) yields the indentation of the indenter into the specimen after a 15-s application of the major load while the load is still applied. Each Rockwell scale division represents 0.002-mm (0.00008-in.) vertical movement of the indenter. In practice, the Rockwell hardness number is derived from the following relationship:  
     where:
  HR  =  the Rockwell hardness number, and   e  =  the depth of impression after removal of the major load, in units of 0.002 mm. This relation only holds for the E, M, L, R, and K scales.    
4.2 A Rockwell hardness number is directly related to the indentation hardness of a plastic material, with the higher the reading the harder the material. An α hardness number is equal to 150 minus the instrument reading. Due to a short overlap of Rockwell hardness scales by Procedure A, two different dial readings on different scales may be obtained on the same material, both of which may be technically correct.  
4.3 For certain types of materials having creep and recovery, the time factors involved in applications of major and minor loads have a considerable effect on the results of the measureme...
SCOPE
1.1 This test method covers two procedures for testing the indention hardness of plastics and related plastic electrical insulating materials by means of the Rockwell hardness tester.  
1.2 The values stated in SI units are to be regarded as 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 appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
Note 1: This test method and ISO 2039-2 are equivalent. Procedure A of this test method is equivalent to the test method in the main body of ISO 2039-2. Procedure B of this test method is equivalent to the test method in the integral annex part of ISO 2039-2.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 14-Mar-2023
• ICS: 29.035.20 - Plastics and rubber insulating materials
• Technical Committee: D20 - Plastics
• Drafting Committee: D20.10 - Mechanical Properties

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D785 − 23
Standard Test Method for
Rockwell Hardness of Plastics and Electrical Insulating
1
Materials
This standard is issued under the fixed designation D785; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* E18 Test Methods for Rockwell Hardness of Metallic Ma-
terials
1.1 This test method covers two procedures for testing the
E456 Terminology Relating to Quality and Statistics
indention hardness of plastics and related plastic electrical
E691 Practice for Conducting an Interlaboratory Study to
insulating materials by means of the Rockwell hardness tester.
Determine the Precision of a Test Method
1.2 The values stated in SI units are to be regarded as
E2935 Practice for Evaluating Equivalence of Two Testing
standard. The values given in parentheses are for information
Processes
only. 3
2.2 ISO Standards
1.3 This standard does not purport to address all of the
ISO 2039-2 Plastics—Determination of Hardness—Part 2:
safety concerns, if any, associated with its use. It is the
Rockwell Hardness
responsibility of the user of this standard to establish appro-
3. Terminology
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
3.1 Definitions used in this test method are in accordance
with Terminology D883.
NOTE 1—This test method and ISO 2039-2 are equivalent. Procedure A
of this test method is equivalent to the test method in the main body of ISO
3.2 For definitions of terms that appear in this practice
2039-2. Procedure B of this test method is equivalent to the test method
relating to quality and statistics (such as precision and bias),
in the integral annex part of ISO 2039-2.
refer to Terminology E456.
1.4 This international standard was developed in accor-
3.3 Definitions of Terms Specific to This Standard:
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the 3.3.1 indentation hardness—the resistance of a material to
surface penetration or plastic deformation.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
4. Significance and Use
Barriers to Trade (TBT) Committee.
4.1 A Rockwell hardness number is a number derived from
2. Referenced Documents
the net increase in depth impression as the load on an indenter
2
is increased from a fixed minor load to a major load and then
2.1 ASTM Standards:
returned to a minor load (Procedure A). A Rockwell alpha (α)
D618 Practice for Conditioning Plastics for Testing
hardness number represents the maximum possible remaining
D883 Terminology Relating to Plastics
travel of a short-stroke machine from the net depth of
D2240 Test Method for Rubber Property—Durometer Hard-
impression, as the load on the indenter is increased from a fixed
ness
minor load to a major load (Procedure B). Indenters are round
D4000 Classification System for Specifying Plastic Materi-
steel balls of specific diameters. Rockwell hardness numbers
als
are always quoted with a scale symbol representing the
indenter size, load, and dial scale used. This test method is
1 based on Test Methods E18. Procedure A (Section 11) yields
This method is under the jurisdiction of ASTM Committee D20 on Plastics and
is the direct responsibility of Subcommittee D20.10 on Mechanical Properties. the indentation of the specimen remaining 15 s after a given
Current edition approved March 15, 2023. Published April 2023. Originally
major load is released to a standard 10-kg minor load.
approved in 1944. Last previous edition approved in 2015 as D785 - 08(2015). DOI:
Procedure B (Section 12) yields the indentation of the indenter
10.1520/D0785-23.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
3
Standards volume information, refer to the standard’s Document Summary page on Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036, http://www.ansi.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

---------------------- Page: 1 ----------------------
D785 − 2
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D785 − 08 (Reapproved 2015) D785 − 23
Standard Test Method for
Rockwell Hardness of Plastics and Electrical Insulating
1
Materials
This standard is issued under the fixed designation D785; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope Scope*
1.1 This test method covers two procedures for testing the indention hardness of plastics and related plastic electrical insulating
materials by means of the Rockwell hardness tester.
1.2 The values stated in SI units are to be regarded as 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 appropriate safety and healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use.
NOTE 1—This test method and ISO 2039-2 are equivalent. Procedure A of this test method is equivalent to the test method in the main body of ISO 2039-2.
Procedure B of this test method is equivalent to the test method in the integral annex part of ISO 2039-2.
NOTE 1—This test method and ISO 2039-2 are equivalent. Procedure A of this test method is equivalent to the test method in the main body of ISO 2039-2.
Procedure B of this test method is equivalent to the test method in the integral annex part of ISO 2039-2.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2
2.1 ASTM Standards:
D618 Practice for Conditioning Plastics for Testing
D883 Terminology Relating to Plastics
D2240 Test Method for Rubber Property—Durometer Hardness
D4000 Classification System for Specifying Plastic Materials
E18 Test Methods for Rockwell Hardness of Metallic Materials
E456 Terminology Relating to Quality and Statistics
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
E2935 Practice for Evaluating Equivalence of Two Testing Processes
1
This method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.
Current edition approved Oct. 1, 2015March 15, 2023. Published October 2015April 2023. Originally approved in 1944. Last previous edition approved in 2008 as
D785 - 08. DOI: 10.1520/D0785-08R15.2015 as D785 - 08(2015). DOI: 10.1520/D0785-23.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

---------------------- Page: 1 ----------------------
D785 − 23
3
2.2 ISO Standards
ISO 2039-2 Plastics—Determination of Hardness—Part 2: Rockwell Hardness
3. Terminology
3.1 Definitions used in this test method are in accordance with Terminology D883.
3.2 For definitions of terms that appear in this practice relating to quality and statistics (such as precision and bias), refer to
Terminology E456.
3.3 Definitions of Terms Specific to This Standard:
3.3.1 indentation hardness—the resistance of a material to surface penetration or plastic deformation.
4. Significance and Use
4.1 A Rockwell hardness number is a number derived from the net increase in depth impression as the load on an indenter is
increased from a fixed minor load to a major load and then returned to a minor load (Procedure A). A Rockwell alpha (α) hardness
number represents the maximum possible remaining travel of a short-stroke machine from the net depth of impression, as the load
on the indenter is increased from a fixed minor load to a major load (Procedure B). Indenters are round steel balls of specific
diameters. Rockwell hardness numbers a
...