Visual Testing (VT) Practice Exam

What term describes the localized reduction in an area of a bolt that is under overload conditions?

1. sizing

2. necking down

3. erosion

4. elongation

The correct answer is: necking down

The correct term for the localized reduction in an area of a bolt under overload conditions is "necking down." This phenomenon occurs when a material is subjected to stress that exceeds its yield strength, leading to an area of localized deformation. As the bolt undergoes tension, it begins to stretch and narrow at its weakest point, creating a "neck." This necking is a critical indicator of the material's failure process, as it reflects the transition from elastic deformation to plastic deformation. In understanding this concept, it's valuable to recognize that necking typically occurs along with elongation, but elongation refers to the overall lengthening of the material under load, while necking specifically denotes the localized reduction in cross-sectional area. Thus, while elongation signifies the material's overall stretching behavior, necking down is what directly describes the reduction in the diameter or width at the point of maximum stress.