What is the best approach to make quasi-hard materials like metals from vellum cloth. I am successful with tweaking stretch and bend plasticity values but the grid still feels quite flappy. Help on how to take the soft, cloth like feel out of it to make it feel like a hard metal sheet. I am looking at this as alternative to the RBD approach to creating dent or bending in car crash situation or even metal pillars. Help would be very much appreciated

Have you tried throwing crazy numbers at the constraint iterations? Try changing it from the default of 100 to 4,000.

Good hint.
… and also increase the Substeps, the default 1 is very low. Try 10 or if you have time/fast machine, even more.
If you can access the actual 3D Artist mag check my tutorial which is partially about pseudo rigid bodies with Vellum, how to use helper constraints (with the limits of printed media…), but your metal sheet stuff is the most difficult to achieve properly.
Additionally you can add thickness (Game Tools/Thicken is the best) to the surface and threat it as Strut Softbody. The Thickness in the constraint node is a bit strange, higher values can significantly slow down the simulation.

I hooked up substeps and constraint iterations quite good. Got results that would look ok in a mid or far shot. But for a close shot, I got a perfectly stable result using the bullet soft constraint. I'd spend some more time on stable approach with vellum though. Thanks for the response

wow vellum is awesome!!! this works a treat. now i just need to work out tearing and how to make it active after my leading up animation with a sop solver and I'm sorted

Nice tips .. .This advice worked great for me .