Shore Hardness / Durometer Hardness ASTM D2240 & ISO 48-4
ASTM D2240 and ISO 48-4 describe the test method for determination of the indentation hardness of rubber, elastomers and plastics with the use of a durometer (durometer hardness / Shore hardness).
Another method for determining the hardness of plastics and similar materials by measuring the indentation depth of a standardized specimen (Shore hardness) is described in ISO 868. ISO 48-4 replaces the withdrawn ISO 7619-1 standard.
Shore hardness testing definitionASTM D2240 vs. ISO 48-4Running a testVideoISO 868Shore methods Representation Shore hardness valueShore hardness testers DownloadsFAQs Request a consultation
Definition of Shore hardness testing according to ASTM D2240 & ISO 48-4
Shore hardness testing according to ASTM D2240 & ISO 48-4, as well as ISO 868 is a standardized static test method for measuring the hardness of rubber using a device known as a durometer. Shore hardness is therefore also commonly referred to as durometer hardness and has the following characteristics:
- the durometer method is used to determine hardness in the macro range with a test force of 3.924-50 N.
- Shore hardness is a depth measurement method. This means that in order to determine the hardness value of a specimen, the true indentation depth is measured, rather than the permanent impression made by the indenter.
- The indentation depth is measured by a spring-loaded indenter that penetrates the material or specimen. The indenter is a hardened steel pin, with different pin and steel ball designs depending on the Shore method. 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 best known scales are Shore A and D. Other scales such as Shore B, C, 0, 00, 000 and D0 are known for 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
ASTM D2240 vs. ISO 48-4
ISO 48-4 and ASTM D2240 are standards for measuring the hardness of rubber and similar materials using a durometer. ISO 48-4 focuses on vulcanized or thermoplastic rubber and defines four specific scales, while ASTM D2240 covers a broader range of materials and twelve scales. ASTM D2240 is widely used in North America and is more flexible in its application, while ISO 48-4 is more common on an international level and provides more specific guidelines for rubber. Both standards use similar measuring principles, but with slightly different instructions and areas of application.
| 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 |
Running a test according to ASTM D2240
For the Shore hardness test according to ASTM D2240, it must first be ensured that the contact surface of the durometer is parallel to the specimen table. The vertical distance between the contact surface of the durometer and the contact surface of the specimen is then set to 25.4 mm ± 2.5 mm. During the test procedure, the hardness tester is pressed against the specimen with the defined pressure until the surface is in full contact. The hardness value can be read one second after the contact surface has made firm contact with the specimen. Five measurements are taken at different points on the specimen and the average or median is calculated and documented.
Running at test according to ISO 48-4
For the Shore hardness test 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 Shore hardness 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 indentation depth is measured with the durometer 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 Test According to ISO 868
ISO 868 is an international standard that specifies the method for determining the indentation hardness of plastics and ebonite using the Shore hardness test method. In this method, a test probe is pressed onto the material with a defined force to measure the indentation depth. The hardness of the material is determined on the basis of this penetration depth and is presented on a scale from 0 (very soft) to 100 (very hard).
In particular, ISO 868 refers to the measurement of hardness according to the Shore A and Shore D scales, which are used for different material hardness values.
- A-scale for softer materials such as soft plastics, elastomers and rubber, which are measured with a truncated cone
- D-scale for harder materials such as hard plastics or stiffer elastomers, which are measured with a cone (needle with a rounded tip, R = 0.1 mm)
Shore hardness testing methods
The individual Shore hardness test methods differ from each other:
- 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 do you read and display Shore hardness?
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 tester for determining Shore hardness according to ISO 48-4, ASTM D2240 and ISO 868
- The measurement method for determining the Shore hardness of rubber, elastomers and plastics in accordance with ASTM D2240, ISO 48-4 and ISO 868 can be easily carried out with portable durometers. Hardness measurements according 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. 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 presented 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.
- Analog and digital Shore hardness testers/durometers
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.
Frequently asked questions about Shore hardness testing
Shore hardness indicates the hardness of a material by measuring its indentation resistance using a standardized specimen (pin). It is typically used for rubber, plastics and similar materials and is specified on different scales (e.g. Shore A, Shore D), which vary depending on the type of material. A higher Shore hardness value indicates a harder material, while a lower value represents a softer material.
ASTM D2240 describes a test method for determining the hardness of materials using a durometer. This standard covers twelve different types of durometers used to measure the indentation hardness of a wide range of materials, including thermoplastic elastomers, vulcanized rubber, elastomeric materials, cellular materials, gel-like materials and some plastics. It gives detailed instructions on how to carry out the hardness measurement, using different durometer types for different hardness ranges and material types.
The main difference between ASTM D2240 and ISO 48-4 lies in the applications and methods: ASTM D2240 covers a wider range of materials, including rubber, elastomers and plastics, and uses different hardness scales such as Shore A and Shore D. ISO 48-4, on the other hand, focuses specifically on determining the hardness of vulcanized or thermoplastic rubber and also uses microindentation methods. While both standards use durometers for hardness measurement, ISO 48-4 provides more detailed instructions for specific rubber types and thin specimens.
Shore A is used to measure the hardness of softer materials such as rubber and soft plastics, while Shore D is suitable for harder materials such as hard plastics and thermoplastics. A higher value on the respective scale indicates a greater hardness of the material.