A Level Physics Practice Exam

What is true of the stress-strain graph of a brittle material?

1. It has a distinct plastic region

2. It exhibits a high yield point

3. It has no plastic region

4. It shows extensive ductility

The correct answer is: It has no plastic region

The stress-strain graph of a brittle material is characterized by its lack of a plastic deformation region. Brittle materials, such as glass and ceramics, do not undergo significant deformation before they fail. Instead, they tend to fracture soon after they reach their elastic limit, which is represented on the graph by a steep slope reaching a maximum stress point, followed by a sudden drop to zero stress when fracture occurs. In contrast to ductile materials that can deform plastically, brittle materials exhibit elastic behavior until they reach their ultimate tensile strength and then fracture almost immediately. This means that once the material surpasses its elastic limit, there is no gradual plastic deformation that takes place; instead, it translates directly from elastic behavior to rupture. Hence, the absence of a plastic region in the stress-strain graph is a defining feature of brittle materials.