Are bonded stainless pans safe to use if they make knocking sounds? We were gifted a set of Cuisanart stainless steel (impact bonded) pots and pans last Winter and use them fairly heavily for cooking at home.
We just started to notice however that a few of the smaller pieces are pinging/popping/knocking when they get put on the burner. The noises return when we cool the piece down, and occasionally if you tap it on the counter. From my experience designing and fabricating parts it seems like the different metals in the bonded billet are separating from the pan in some fashion and the noises are a result of that happening.
Fortunately they're under warranty, and Cuisanart has already put new ones in the mail saying we can toss the old ones if we want. However, I'm wondering whether they would be safe to keep and use instead, if it's just sounds.
Are they safe? Sure. I think you might be thinking of thermal stress in something like a glass casserole dish, where a temperature gradient can cause the thing to violently fracture, exploding in all directions. (Trip report: It was surprising, and terrifying in retrospect!) That can't happen with a metal pan, which will deform rather than fracturing.
Moreover, the stress on your partially separated pan is less than it would be on a non-busted pan. The sounds you're hearing are the sounds of stress being released little by little, rather than being stored up.
A bonded pan bottom comes off bit by bit over a large number of heating cycles, and in my experience never comes off completely (unless pulled off). But once the separation starts, thermal conduction goes way down in the separated areas, leaving uneven hot and cold spots. So these pans aren't going to kill you... but they're likely to disappoint you.