Hardness

A surface hardness measurement made with a handheld impressor that presses a sharp steel indenter into the material, standardised in ASTM D2583 and EN 59. In the composites industry it is widely used as a quick workshop or site check of laminate and gelcoat cure, since readings rise as the resin hardens.

The hardness of rubbers, elastomers and softer plastics measured with a durometer that presses a spring-loaded indenter into the surface, most commonly on the Shore A scale for elastomers and Shore D for harder materials. Methods are standardised in ASTM D2240 and related ISO standards.

The ability of a material to absorb energy and deform without fracturing, combining strength with ductility. Tough materials resist impact and flaw growth, whereas strong but brittle materials can fail suddenly.