Hooke's Law and Young's Modulus and Poisson's Ratio
Robert Hook found that within the elastic limit, the stress is directly proportional to strain. Thus we have
Stress = K.strain
where k is the constant of proportionality called 'Elastic Modulus' of the material.
According to Hooke’s law, if strain increases the stress will increase and vice-versa.
Hooke’s law is applicable to all elastic substances.
It does not apply to plastic deformation.