It has been awhile since I looked at my materials books, but I'd like to add a couple of points here. 1. Hardness Hardness testing requires getting a statistical sample of the specimen. This means that standards exist for how many indentations are made in a sample and how the readings are weighted. Also, hardness readings can be affected by surface treatments and characteristics, which is why those who do extensive structural analysis try to utilize other means of characterizing the material. 2. Toughness As described on http://www.mse.cornell.edu/courses/mse265/...properties.html Basically, toughness is the parameter used to determine failure through crack propagation. I recall thinking of it as the ability of the material to distribute a stress around a stress concentration. Joanne - who loves this stuff and probably should have decided to study it even more instead of acoustics, grr, grr, grr.