5 Assume you accidentally hit the rear window of your car an

5. Assume you accidentally hit the rear window of your car and produced some cracks. It is suggested that if you drill a hole on the crack tip, you can actually prevent cracks from propagating. Does that make sense? Why or why not?

Solution

The cracks are formed along the lines of maximum stresses and once started they are the weakest zones. A small crack with not a big area of its tip can be stopped from propagating by creating a circular hole, because a circular hole does not have any straight edges, and therefore any load is distributed to a large area. This reduces the stress intensity and therefore the crack does not propagate.