What is the relationship between stress and strain in materials under mechanical deformation?

The relationship between stress and strain in materials under mechanical deformation is described by Hooke's Law, which states that stress is directly proportional to strain. This means that as a material is subjected to a force (stress), it will deform (strain) in a predictable and linear manner. The relationship between stress and strain helps engineers and scientists understand how materials behave under different conditions and can be used to predict their mechanical properties.