At 18 Feb 05, 05:19 PM, Pierre Abbat wrote: >On Friday 18 February 2005 14:53, Pat Naughtin wrote: >> This area looks to be screaming out for the standards writers to come to >> their rescue by writing a uniform standard using an SI unit such as a >> pascal (newton per square metre) in one or several of its many forms from >> millipascal to megapascal. > >I think what's happening is they're conflating several quantities and calling >them "hardness". There are the moduli, such as Young's modulus, which are the >ratio of stress to strain, that is, the amount of pressure needed to deform >it elastically by a certain amount. Then there's the elastic limit, which is >the stress beyond which it is permanently deformed.
According to some of the websites I've visited, "hardness" may be related to things like modulus of elasticity, tensile strength, etc., but not in any direct fashion. And, of course, "hardness" varies based on other things such as temperature, %elongation or %compression, moisture content, etc. >My father had a set of variously colored plastic disks about 3 cm in diameter, >each of a different hardness, held together with a ball chain passing through >the hole in the middle. I thought he was the only person who had one of >those, until I met an Israelite named David who had one too. Any idea where >to get them? My mechanical designer has several of these: thermoplastics, nonporous gasket material, porous gasket material, texture samples, and so on. They are sets of samples made by the companies that sell the various materials, and are intended to help designers and engineers choose the right materials for their designs. Jim
