Dead load hardness test

The standard briefly covers the significance of hardness in terms of its relation with modulus, and the practical use of hardness tests. The hardness tests for rubber that are standardized by ISO are introduced and the distinction between dead load and durometer type instruments is explained to help with selection of a test method for particular circumstances. The effect of test piece, use of standard hardness blocks and comparison of hardness scales is also outlined. 

The particular case of the hardness of rollers is covered by ISO 726734 36 which is in three parts dealing with the normal dead load method, Shore durometer and the Pusey Jones methods respectively. This last method is a very old hardness test which is now virtually never seen, although it is understood to still be popular in some circles for rollers. It is an amazing brass and chain contraption that uses a 3.175 mm indentor acting under a load of 1kg and without a surrounding foot. 

FIGURE 17. Comprehensive peel data for a natural-rubber-based surgical adhesive peeling from glass. Sigmoidal curves show soft-machine data at different crosshead speeds while error bars show hard-machine (vertical) and dead-load (horizontal) data. Only soft-machine tests reveal the lower bound and transition phenomena. 

Larger indentations were made with the floor mounted hardness-testing machine that had a 98 N capacity. This dead weight loading machine applied force via a dashpot controlled lever beam and was set in compliance with ASTM E 384 Microhardness of Materials and ASTM C 1326. The initial diamond clearance and contact time were set in accordance with the manufacturer s instructions, and produced an average indenter velocity of 0.025 mm/s. Dwell time was 15 s 20 s after which the machine automatically extracted the indenter. Indentations made with this floor mounted larger capacity machine were measured within 10 minutes with the tabletop machine in order to eliminate machine optics as a source of variability. There was one important difference in procedure, however, that initially caused us... 

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