The Relation Between Mindlin's Strain Gradient and Eringen's Nonlocal Linear Elasticity Theories
Here are some definitions which I have in my mind about the hierarchy of field theories of any kind. Please read them and correct me if there is any misunderstanding. Then I shall raise two questions based on this model of thought about the Mindlin's strain gradient and Eringen's nonlocal linear elasticity theories.
Definition 1. Two field theories are the same if and only if the field equations of one can be obtained from the other.