Aha a question for which my expertise is called! A lightsaber is a beam of ionized plasma contained in a force field. We have seen shardplate block energy attacks(Adolin on the shattered plains). This indicates that plate can resist the kind of damage that a saber can do and so most likely would be able to survive a number of hits before cracking. Against a shardblade would actually be much more dangerous as neither party could parry the other. Shardblades can go directly through what is in state of matter closer to a liquid but the saber would not be damaged by the event.