I have replaced aluminum rims on a Tandem from cracks twice. I pulled three children in a two wheeled trailer with that Tandem. The cracks were easy to spot. The only carbon on my bicycle is in the Gates Belt. I read posts about carbon failures quite often. wheels, forks and handlebars. They also use carbon in some helicopter blades but there is a specific amount of operational hours before the blades are replaced. You most likely wont see a crack in carbon before a failure.