Definition of Shore hardness testing
The hardness of rubber and elastomers according to Shore is determined using test procedures standardized in compliance with ISO 48-4 or ASTM D2240.
In the Shore hardness test, the indentation depth is measured using a spring-loaded indenter made of hardened steel to indent the material/specimen. The indentation depth is a measurement for Shore hardness, that is determined on a scale of 0 Shore (2.5 millimeter indentation depth) to 100 Shore (0 millimeter indentation depth). A range of different Shore scales have been established based on a variation in indenter forms and spring characteristics. The most well-known scales are Shore A and D. Other scales, such a Shore B, C, 0, 00, 000, and D0 apply to specific applications.
Shore scales and application examples:
- Shore A: Soft rubber, elastomers and natural rubber
- Shore D: Harder elastomers, plastics and rigid thermoplastics
- Shore 0: Soft elastomers and textile fabrics
- Shore 00: Expanded rubber, sponge rubber and cellular rubber
- Shore B: Harder elastomers than Shore A
- Shore C: Medium hard elastomers
VLRH (IRHD supersoft)
Shore 00
Shore A/B
Shore A/B
Shore D/C/D0
Micro Shore
Difference between Shore hardness testing to ISO 48-4 and ASTM D2240
| Standard | ISO 48-4 | ASTM D2240 |
| Specimen thickness | 6 mm | 6 mm |
| Layers | Yes (3 layers) | Yes |
| Measurements | 5 | 5 |
| Measuring distance | 6 mm | 6 mm |
| Test time | 3 s for vulcanized rubber 15 s TPE | Less than 1 s |
| Load | 1 kg Shore A 5 kg Shore D | 1 kg |
| Hardness specification | 54 Shore A 3 s 54 Shore A 15 s | A / 54 / 1 A / 54 / 15 |
Shore hardness test procedure
For the Shore hardness test method to ISO 48-4, the following parameters must be considered in advance:
- To determine the hardness of the material, the standard states that five measurements must be taken from which the median value is then calculated.
- The test time is 15 s; if other test times are used, this must be indicated in the hardness value.
- The material to be tested should be stored at room temperature of +23 °C ± 2°C for at least one hour.
In the first step of the test, the indenter is pressed into the specimen with a spring force of 1.11-44.5 N. Then the indenter is pressed onto the specimen with a contact force of 3.92-50 N for 15 seconds. The indentation depth in the specimen is between 0-2.5 mm. This penetration depth is measured with the hardness tester and the hardness value is derived from it. The indenter should act on the specimen with the full contact force and a duration of 15 seconds. If the duration of the applied force is exceeded or is not met, this must be indicated in the hardness value. The longer the duration, the lower the Shore hardness value will be.
The minimum distance of the test points must be maintained according to the standard. The center distance between the indentations should be ≥ 5mm and ≥ 12mm to the specimen edge.
Shore hardness testing methods
The individual methods are differentiated by:
- The shape of the indenter (see image)
- The magnitude of the spring force F
- The magnitude of the contact force FA
The different resulting test methods use seven different indenters and four different levels of contact force. More specific information on the differences between the individual methods can be found in the table below.
Method | Spring force F [N] | Contact force FA [N] | Indenters | Measurement travel t [mm] | Specimen thickness [mm] | Measurement range |
Shore A | 8.050 N | 9.81 N | Truncated cone, 35° cone angle | 2.5 | ≥6 | 10 … 90 <20 Shore D |
Shore A0 or Shore E | 8.050 N | 9.81 N | Ball, Ø 2.5 mm | 2.5 | ≥6 | <20 Shore A |
Shore AM or Shore M | 0.764 N | 9.81 N | Cone with 30° angle | 1.25 | ≥1.25 | 10 … 90 |
Shore B | 8.065 N | 9.81 N | Cone with 30° angle | 2.5 | ≥6 | 10 … 90 |
Shore C | 44.5 N | 49.0 N | Truncated cone, 35° cone angle, truncated cone dia. 0.79 mm | 2.5 | ≥6 | 10 … 90 |
Shore D | 44.5 N | 49.0 N | Cone with 30° angle | 2.5 | ≥6 | 30 … 90 >90 Shore A |
Shore D0 | 44.5 N | 49.0 N | Ball, Ø 3/32“ | 2.5 | ≥6 | 10 … 90 |
Shore 0 | 8.05 N | 9.81 N | Ball, Ø 3/32“ | 2.5 | ≥6 | 10 … 90 |
How is the hardness value read and represented?
The Shore test hardness value consists of three main components:
- 1. A numerical hardness value;
- 2. The word Shore, to indicate Shore hardness
- 3. The designation of the Shore method that defines the indenter and the associated parameters
If the dwell time deviates from the standard, a time is indicated as a suffixed fourth component.
Example of how to represent and read a hardness value:
| 75 Shore A 10 | |
|---|---|
| 75 | ... Hardness value |
| Shore | ... According to shore |
| A | ... Shore method truncated cone with cone angle 35°, spring force 8.065 N and contact force 12.5 N |
| 10 | ... Dwell time of the contact force outside the recommended duration, in this case 10 seconds |
Shore hardness ISO 868, ASTM D2240, ISO 48-1 and -4, ASTM D2240
- Shore hardness is measured on plastics according to ISO 868 or ASTM D2240. The measurement procedure is simple and can be easily carried out with portable instruments. Hardness measurements to Shore are widely used for quality control purposes and belong to the macroscopic methods. For laboratory tests, we recommend using the instrument in combination with a test stand. Calibration of these instruments is described in ISO 21509.
- The shore hardness on rubber and elastomers is measured according to ISO 48-1, ISO 48-4, ISO 48-7 or ASTM D2240. ISO 48-9 describes the instrument calibration. The main difference within the ISO standards compared to the measurement on plastics is the exposure time of the indenter.
- In both cases, the test measures the indention depth of the indenter in the material. The indenter is loaded by a spring with defined characteristics. The greater the hardness of the material to be tested, the smaller the indention depth, but the higher the load of the indenter. Shore hardness is shown on a scale from 0 to 100 Shore. The contact force of the contact foot of the instrument on the surface of the specimen determines the zero position. Depending on the standard this force is approximately 10 N for Shore A and approximately 50 N for Shore D.
- A range of different Shore scales have been established due to different indenter forms and spring characteristics. The most common scales are Shore A and D. Other scales, such a Shore B, C, 0, 00, 000, and D0 were developed for specific applications. The range of applications starts with soft elastomers (Shore A) and ends with harder thermoplastics (Shore D).
- Analog and digital Shore hardness tester
ZwickRoell offers Shore hardness testers with analog or digital displays and PC connection options. The testing instruments are equipped with backlash-free linear ball bearings and operate with virtually no friction. The spring rate can be precisely adjusted during calibration to maintain the forces specified in the standards for every Shore value. In this way, the tolerances specified by the standards are adhered to exactly and high repeatability of the results is made possible.
More information on Shore hardness tests
