First, if anyone is trying this and not getting failures, make sure you aren't doing it too close to the pivot, or else the inertia of the blade and leverage will greatly reduce the pressure that actualkly ends up testing the lock.
Second, an impact like this can put far more stress on something than a huge strong person trying to bend it by hand. If you stab into something and accidentally hit something fairly solid (bone, wood, etc, depending on the intended target), especially if doing it with great strength, you could get this type of impact. Someone might say "look, our knife held up 150 pounds in our test," but the instant force cause by crashing into a solid object can be more than that.
