Rockwell M hardness

Tests for indention under load are performed basically like the ASTM measure the hardness of other materials, such as metals and ceramics. There are at least four popular hardness scales in use. Shore A and Shore D is for soft to relatively hard plastics and elastomers. Barcol is used from the mid-range of Shore D to above it as well as RPs. Rockwell M is used for very hard plastics (Chapter 5, MECHANICAL PROPERTY, Hardness),... 

Figure 3.6. Hardness examples of Rockwell M versus Shore D for some thermoplastics...

Figure 6. Effect of composition on hardness Measured on Rockwell M scale sample thickness, 0.317 cm...

The energy absorbed when an object strikes a surface is related to the hardness of the surface the harder the surface, the less the energy absorbed, and the greater the rebound height of the object after impact. Several methods have been developed to measure hardness in this way. The most common method uses a Shore scleroscope, in which the hardness is determined fi om the rebound height after the impact of a diamond cone dropped onto the surface of the test piece. Typical values of Scleroscope hardness together with the Rockwell M values (in parentheses) for some common plastics are as follows PMMA 99 (M 102), LDPE 45 (M 25), polystyrene 70 (M 83), and PVC 75 (M 60). 

Maximum continuous use temperature °C Coefficient of linear expansion cm/cmxlO °C Tensile strength, MPa % Elongation Flexural strength, MPa Compressive strength, MPa Notched Izod impact J/m Hardness Rockwell Specific gravity... 

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