13. A body which break down just after crossing the elastic limit, is known as:

The body which breaks down just after crossing the elastic limit is known as a brittle material.

Here are the steps to understand this:

1. Elastic Limit: This is the maximum stress that a material can withstand without being permanently deformed. When a material is subjected to stress, it deforms (changes shape). If the stress is removed and the material returns to its original shape, it is said to be within the elastic limit.

2. Brittle Material: A brittle material is one that breaks or shatters easily. It is characterized by little to no deformation before failure. When the stress on a brittle material exceeds its elastic limit, it fails by breaking or cracking.

3. Therefore, a body that breaks down just after crossing the elastic limit is known as a brittle material because it cannot withstand stress beyond its elastic limit and breaks down instead of deforming.