how many times i burned a flash disk
What exactly do you mean by that? Is it that the device just stops working? Can you see it in your hardware? Do you get any messages when you attempt to access it?

Does they die after connection to the PC, the Apple, or about even?

I do hope you are mounting/dismounting them in accordance with the instructions. Just pulling it out without going through the dismounting procedure is a good way to kill them. You can be lucky for a while then......................