Which of the following is an effect of poor surface finish in metal structures?

Poor surface finish in metal structures can lead to lower fatigue resistance. This is primarily because a rough or improperly treated surface can act as a stress concentration point. Such surface irregularities introduce micro-cracks and other imperfections that are more vulnerable to fatigue. When metals undergo cyclic loading, these flaws can initiate crack propagation, ultimately leading to premature failure. A smooth and properly finished surface, on the other hand, helps distribute stress more evenly and reduces the likelihood of failure due to fatigue over time.

In contrast, the other options do not align with the effects of poor surface finish. Poor surface quality does not lead to reduced weight or increased material strength; in fact, subpar finishing can negatively affect overall mechanical properties. Enhanced visual appeal is also not a result of poor surface finish, as it typically refers to a polished or well-maintained surface, which would be the opposite of poor finishing. Therefore, the correct choice clearly highlights a significant engineering concern related to the integrity and longevity of metal structures.