Most of the tire studs available today have a stem made from steel or aluminum and a head made from tungsten to ensure they last as long as possible.
All these materials are highly durable, so if you find that they're breaking off, it's more than likely because they've been overused.
In this case, they should be replaced as soon as possible to avoid motor accidents.
It could also indicate that they've been used on the wrong surfaces such as dry asphalt.
Keep in mind that they're meant primarily for icy roads and anything else that sacrifices control could put the driver and passengers in danger.