Could Warriors SPLIT Helmets? - How Well Did Medieval Armor Really Work?

We have some paintings from the Middle Ages depicting battle scenes that show swords cutting into helmets. Of course we have to take everything with a grain of salt... many of those images contain accurate, realistic portrayals of arms and armor, but some have mythical creatures and manhunting killer bunnies...

So how plausible is this armor slicing trope? Are some helmets more susceptible to damage from blades than others? Let's take a closer look!