What was the realistic strength of platemail armor eg what weapons were able to penetrate it and what would it be albe to protect against?

Answer 1

A platemail armour was very effective against slashing weapons (swords and other blades). It would be as effective as to be behind a sheet of metal when such weapons struck and would, in most cases, drift off the attack by deflecting the hit. Hammer picks, maces, mauls and other heavy crushing weapons were more effective against such type of armor damaging it severely with each blow. Later developments in Fencing blades were thin enough and flexible enough to pierce through the weak points in the joints without breaking. Nonetheless plate armour was very expensive, and only the richest knights had enough money to purchase high quality plate. Poor warriors used what they looted which imho should be quite uncomfortable because it was made for someone else. Heavy crossbows had enough strength to pierce through most shields and plate armour but were considered as dishonorable as most ranged weapons.