Red Seal Machinist Practice Exam

What effect does surface finish have on the fatigue strength of a part?

1. It lengthens expected lifespan

2. It has no effect

3. It reduces expected lifespan

4. It decreases production costs

The correct answer is: It lengthens expected lifespan

The effect of surface finish on the fatigue strength of a part is significant. A better surface finish typically leads to an increase in fatigue strength, which can consequently lengthen the expected lifespan of a component. This relationship arises because a smoother surface has fewer imperfections and stress concentrators that can act as initiation points for fatigue cracks. By reducing these flaws, the likelihood of crack propagation under cyclic loading is diminished, resulting in improved performance and durability over time. When considering other aspects such as production costs, a rough surface may be cheaper and easier to produce but may lead to a reduced lifespan due to fatigue failure, which contradicts the benefits of a well-finished surface. Therefore, the answer aligns with the understanding that enhanced surface finishes contribute positively by increasing fatigue strength and prolonging part functional life.