combined with the exponential growth of cracks in structure has led to the development of non-destructive testing methods which allow inspectors to look for very tiny cracks which are often invisible to the naked eye. Examples of this technology include eddy current, ultrasonic, dye penetrant, and X-ray inspections. By catching structural cracks when they are very small, and growing slowly, these non-destructive inspections can reduce the amount of maintenance checks, and allow damage to be caught when it is small, and still inexpensive to repair. As an example, such repair can be achieved by drilling a small hole at the crack tip, thus effectively turning the crack into a keyhole-notch. References Further reading Aerospace engineering Fracture mechanics Mechanical failure Mechanical failure modes