ASTM D785 is a Rockwell indentation hardness test method used to quantify the hardness of plastics and related plastic electrical insulating materials using a Rockwell hardness tester.
If you are not sure which Rockwell scale, indenter, or load combination fits your material and thickness, talk with our team about matching the standard’s requirements to a practical lab setup.
ASTM D785 — Standard Test Method for Rockwell Hardness of Plastics and Electrical Insulating Materials
ASTM D785 describes how to measure indentation hardness on plastics using Rockwell hardness principles. The result is reported as a Rockwell hardness number on a defined Rockwell scale (the scale identifies the indenter, test forces, and dial scale used).
The standard includes two recognized procedures, which can matter for materials that show time-dependent deformation (creep and recovery) under load.
Quick Definition
Document type: Test method (indentation hardness).
What it measures: Rockwell indentation hardness of plastics and related plastic electrical insulating materials using a Rockwell hardness tester and specified ball indenters.
Key option: Two procedures are provided, which differ in how the indentation depth is taken relative to the load cycle.
What This Standard Covers
ASTM D785 covers Rockwell hardness testing for plastics and related plastic electrical insulating materials using a Rockwell hardness tester.
The standard is organized around two procedures for determining indentation hardness. It also recognizes that material specifications (if applicable) can override default preparation, conditioning, dimensions, or test parameters described in the method.
Why This Standard Matters in Testing
Rockwell hardness on plastics is commonly used for quick material comparison, incoming inspection, and process monitoring where an indentation hardness value is needed on a defined, repeatable scale.
Because some plastics are sensitive to time under load, the procedure choice and dwell timing can significantly influence results. ASTM D785 also notes that hardness values should not be treated as a direct measure of abrasion or wear resistance.
Common Materials, Product Types, or Applications Covered
Common materials: Rigid and semi-rigid plastics, and plastic electrical insulating materials where Rockwell indentation hardness is an appropriate acceptance or comparison metric.
Common applications: Material qualification and comparison, QC checks on molded or machined parts, and verification workflows where a drawing, datasheet, or procurement requirement calls out a Rockwell hardness value for a plastic component.
Common Test or Verification Workflow
Most ASTM D785 workflows follow a straightforward bench test sequence: choose the appropriate Rockwell scale for the material, verify the correct indenter and test forces, stabilize the specimen, and run the load cycle to obtain the Rockwell hardness reading per the selected procedure.
Practical workflow note: When a product specification exists for the material (or the part), its specimen requirements and test conditions generally take precedence over default guidance in the test method.
Equipment Commonly Used for This Standard
ASTM D785 points to standard Rockwell hardness testing equipment configured for plastics, using specified ball indenters and the required minor/major force application sequence for the selected scale and procedure.
Common equipment: Rockwell hardness tester (plastics-capable), appropriate ball indenter(s), anvil/supporting fixtures suitable for flat, stable support, and verification tools/accessories used to maintain repeatability for the chosen scale.
Quoting tip: The most important purchasing variables typically include the required Rockwell scales, force application capability, and whether your workflow needs Procedure A vs. Procedure B reporting. If you are comparing systems or configurations, you can request a detailed quote matched to your required scales and throughput.
How to Read This Designation or Revision
Designation format: ASTM D785 (often cited with a year suffix, such as ASTM D785-23).
What the suffix means: The two-digit year suffix indicates the year of the referenced edition. Test setup details, reporting expectations, and procedure language can vary by edition, so purchasing decisions and test plans should match the exact revision cited in a contract, drawing, or material specification.
Related Standards, Methods, or Frameworks
ASTM D785 is based on Rockwell hardness principles and references ASTM E18 for Rockwell hardness test methods (commonly used for metallic materials) as a foundational basis for the approach. ASTM D785 also notes equivalency alignment with ISO 2039-2 for Rockwell indentation hardness of plastics, with the two procedures corresponding to different parts of ISO 2039-2.
Need help selecting a Rockwell hardness tester for ASTM D785?
If you need to align a tester configuration to the exact ASTM D785 revision, required Rockwell scale(s), and your sample geometry, contact our team for practical guidance before you commit to equipment or fixtures.