What technique can be used to control crack propagation effectively?

Drilling stop holes is an effective technique for controlling crack propagation because it directly interrupts the crack's ability to extend further. By creating a hole at the terminus of a crack, the stress concentration at the crack tip is alleviated, which reduces the driving force that would allow the crack to grow. This method is commonly used in materials and structures to prevent cracks from spreading, especially in metal components where stress concentrations can lead to catastrophic failure.

Other options, while they may influence the material properties or appearance, do not directly target crack propagation in the same manner. For instance, heat treatment can alter the overall mechanical properties of a material, potentially making it more ductile or tougher, but it does not specifically address the existing cracks. Grinding edges can improve surface finish and remove surface defects but does not prevent a crack from growing once it has formed. Applying fillers may help restore material at a crack site, but it does not stop the crack from propagating if the underlying stress is still present. Therefore, drilling stop holes is the most targeted and effective method to control crack propagation.