- Average Shore A or Shore D value with reading-time designation
- Individual readings (minimum five) with median and standard deviation
- Scale selection rationale (A vs D)
- Specimen dimensions, conditioning record, and instrument calibration record
- ASTM D2240 / ISO 868 compliance statement
ASTM D2240 Shore Durometer Hardness Testing for Rubbers & Plastics
ASTM D2240 test method is utilized to evaluate Durometer Hardness or Shore Hardness of polymeric and plastic materials. The Shore Hardness value is used as a quality control parameter for polymers, elastomers, plastics, and rubbers to be used in various applications.
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- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
ASTM D2240 Testing Overview
ASTM D2240 measures the indentation hardness of rubbers, thermoplastic elastomers, soft thermoplastics, and rigid plastics using a spring-loaded durometer. The instrument’s indenter is pressed into the specimen, and the depth of penetration is converted to a Shore hardness number on a 0–100 scale. The test is a static indentation method, not an impact test, and is the most widely specified hardness method for rubbers and elastomers worldwide. ASTM D2240 is the US standard; ISO 868 is the direct international equivalent and produces directly comparable results when the same scale, specimen thickness, and reading protocol are used.
Two scales dominate plastic and rubber testing: Shore A for soft rubbers, elastomers, and flexible plastics, and Shore D for rigid rubbers, hard plastics, and hard thermoplastic elastomers. Shore A uses a truncated-cone indenter and an 822 gf spring force; Shore D uses a sharp 30° cone indenter and a 10 N (≈1,020 gf) spring force. As a rule of thumb, if a Shore A reading exceeds 90, switch to Shore D; if a Shore D reading falls below 20, switch back to Shore A. Higher values on either scale indicate greater resistance to indentation.
Scope, Applications, and Benefits
Scope
ASTM D2240 defines procedures for measuring hardness using Shore durometers across different material hardness ranges. The standard applies to materials that can be tested by indentation hardness methods.
The scope includes:
Measurement of hardness using Shore scales such as Shore A, Shore D, and others
Testing of rubber, elastomers, and soft to rigid plastics
Evaluation of hardness for quality control and material comparison
Testing of molded parts, sheets, and finished products
Procedures for hand-held or stand-mounted durometers
Applications
- Automotive seals, gaskets, and weather-strips — Shore A spec compliance
- O-ring material qualification — NBR, FKM, EPDM, silicone (Shore A 40–90)
- Footwear outsoles, midsoles, and grips — Shore A 55–80
- Industrial hoses, conveyor belts, and rubber rollers
- Flexible packaging films and thermoplastic elastomer films
- Sporting goods — grips, mouthguards, padding, sole inserts
- Electrical insulation — flexible cable jackets and connector boots
- Rigid plastic enclosures and housings — Shore D verification
- 3D-printed elastomer parts — TPU, TPE, and flexible photopolymers
- Failure analysis — hardness comparison of aged or field-returned parts against virgin spec
Benefits
- Fast, repeatable readings — full result in seconds
- Portable hand-held durometers enable field and in-process QC
- Minimal sample preparation; non-destructive at the part level
- Covers the full rubber and plastic range using A and D scales
- ISO 868 / ASTM D2240 dual compliance for global supply contracts
ASTM D2240 Test Process
Specimen Preparation
Samples must have a flat, smooth surface with sufficient thickness for accurate hardness measurement.
1Instrument Setup
The Shore durometer is calibrated, and the appropriate hardness scale is selected based on the material.
2Hardness Measurement
The durometer indenter is pressed onto the specimen surface with controlled force.
3Reading and Recording Results
The hardness value is read directly from the durometer scale and recorded as the Shore hardness value.
4ASTM D2240 Technical Specifications
| Parameter | Details |
|---|---|
| Standards | ASTM D2240, ISO 868 |
| Hardness Scales | Shore A, Shore D, Shore OO, Shore O, and others |
| Applicable Materials | Soft rubbers, elastomers, TPEs, flexible plastics (Shore A); hard rubbers, rigid plastics (Shore D) |
| Shore A Indenter | Truncated cone, 35° angle, 0.79 mm flat tip |
| Shore A Spring Force | 822 gf (≈ 8.064 N) |
| Shore D Indenter | Sharp 30° cone, 0.1 mm tip radius |
| Shore D Spring Force | 10 N (≈ 1,020 gf) |
| Hardness Scale Range | 0 to 100 (both scales) |
| Minimum Specimen Thickness | 6 mm |
| Reading Time | Instantaneous or 1-second delayed (must be reported) |
| Minimum Readings | 5 per specimen |
| Conditioning | 23 °C / 50 % RH, 40 h minimum |
| Reported Output | Shore A or Shore D value with reading-time designation |
Instrumentation Used for Testing
- Shore A durometer (analog or digital) compliant with ASTM D2240 calibration
- Shore D durometer (analog or digital) compliant with ASTM D2240 calibration
- Calibrated reference blocks for Shore A and Shore D verification
- Constant-pressure operating stand for repeatable foot loading (recommended)
- Specimen support fixture for thin or curved parts
- Conditioning chamber maintaining 23 °C / 50 % RH
Results and Deliverables
Frequently Asked Questions
ASTM D2240 determines hardness by measuring the resistance of rubber, elastomers, and certain plastics to indentation using a durometer instrument, providing hardness values on specific Shore scales depending on material stiffness.
Common scales include Shore A for soft elastomers and rubber materials, and Shore D for harder plastics and rigid polymers, with other specialized scales used for very soft or extremely hard materials.
ASTM D2240 is widely used for testing rubber, thermoplastic elastomers, soft plastics, and other flexible polymer materials used in seals, gaskets, footwear, automotive components, and consumer products.
Shore hardness testing helps verify material consistency, ensure compliance with product specifications, and evaluate elasticity and stiffness, which are critical for product performance and durability.
Test results may be influenced by specimen thickness, surface smoothness, temperature conditions, and the specific durometer scale used during measurement.
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