Question: If it hardens when it is disturbed, does it mean that it hardens if the wearer runs, for example? This would mean you still can't properly armor joints...
500+MPH impacts are vary different than simple joint movements. Think of it like this, if you slowly move your hand though water you don't feel any resistance, jump off a bridge and hit it at 100MPH and the stuff might as well be concrete.
I think the more force (or acceleration?) it undergoes the more it hardens. So hopefully running wouldn't affect it, but a fast moving projectile would.
Have a good day.
Shear thickening fluids have a non-linear relationship between shear rate and shear stress. Schematically, it's the green line in this graph [1]. By choosing your material carefully, you can minimize shear stress at 'running' speeds, and then sharply ramp it up to protect against faster projectiles.