Service-induced discontinuities can be the result of:

• A. Stress risers
• B. Vibration
• C. All of the above
• D. Corrosion

Answer: (C)

Service-induced discontinuities arise from damage mechanisms that operate during actual use. Stress risers, such as sharp corners, notches, or holes, focus local stresses and promote crack initiation and growth under service loads. Vibration subjects a part to repeated or fluctuating stresses, driving fatigue crack initiation and propagation over time. Corrosion weakens material and creates pits or surface flaws that act as initiation sites and, under load, can lead to cracks or corrosion fatigue. Because any of these processes can occur in service—and they can also interact (for example, pits near a notch can accelerate crack growth under cyclic loading)—the observed discontinuities can result from all of these mechanisms. Therefore, the best answer is that all of these factors can produce service-induced discontinuities.