3rd Class Power Engineering (3A1) Practice Exam

When a material is subjected to tensile stress and exceeds its yield point, it experiences plastic deformation. This means that the material will undergo a permanent change in shape or length. Initially, as stress is applied, the material deforms elastically, meaning it will return to its original shape once the stress is removed. However, once the yield point is reached, the material can no longer return to its original dimensions, and any further application of stress leads to a more significant and permanent increase in length.

This behavior is characterized by a region of necking, where localized deformation occurs, often resulting in a sudden increase in length. This is a typical characteristic of ductile materials, which can elongate significantly before eventually failing. Therefore, the statement regarding the material undergoing a sudden increase in length when forced beyond its yield point is accurate, as it represents the transition from elastic to plastic behavior in materials under tensile stress.