Hardness Testing

Determination of Shore hardness to ISO 7619-1, ISO 868 and ASTM D2240 is a test method that can be easily performed with a portable hardness tester. The method is used widely in quality control and belongs to the macroscopic group of methods. Use of the instrument in combination with a test stand is recommended for laboratory tests.

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 indenter load. The test loads are 10 N for Shore A and 50 N for Shore D.

A range of different Shore scales have been established due to the 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. This application area ranges from soft elastomers (Shore A) to thermoplastics (Shore D).

ZwickRoell offers hardness testers to Shore with analog or digital displays and PC connection options.

Ball indentation hardness to ISO 2039-1 is used widely in European laboratories. A spherical indenter with a diameter of 5 mm is pressed into the plastic specimen at a constant test load. The indention depth under load is the determining variable for the hardness value. The standard defines a selection of test loads so that the indention depth is limited to a range of 0.15 mm to 0.35 mm.

The high test loads and the deep indention allow for measurement across a large test surface and thus, a strong average of the measured value. This method is suitable for measuring both filled and unfilled plastics.

ISO 2039-2 and ASTM D785 define various Rockwell hardness scales for plastics testing. In contrast to ball indention hardness, in which the indention depth is measured under load, with the Rockwell method, the indention depth is measured at a defined preload. There are a variety of indenters available that correspond to the Rockwell scale.

Hardness test methods based on continuous recording of the entire force-penetration behavior are known as instrumented hardness testing methods.

In addition to multipoint data in the form of a single hardness value, these methods generate complete curve sequences that demonstrate other interesting material characteristics. Instrumented, recorded hardness measurement is an extension of conventional hardness measurement.

In general, instrumented hardness measurement methods can be used in the nano, micro, or macro range. Indenters can have different geometries, for example, spherical, conical, four-sided pyramid shape (Vickers), or a three-sided pyramid shape (Berkovic).

Submicron-structured materials, their structures from a few nanometers to one micrometer can be measured with micro hardness methods. Filled or reinforced polymers and polymer blends are measured with macro methods, meaning a high load is applied. This prevents the matrix behavior or the fiber or filler from dominating the hardness value, producing data scatter that is too large.

Such a method has been standardized for metals as defined in ISO 14577-1. An initial draft of the standard to ISO 19278 exists for plastics