++++ ++++ ++++ ++++ ++++ Concept Question ++++ ++++ ++++ ++++ ++++ Which of the following statements is correct? U 0 = U ? 0 for ALL elastic materials (1) U 0 = σ ij ? ij ?U ? 0 ONLY for linear elastic materials (2) 1 σ ij ? ij for a nonlinear elastic material 2 (3) U 0 = 1. ++++ Statements (1) and (3) 2. ++++ Statement (2) 3. ++++ Statement (2) and (3) 4. ++++ None of the above statements 5. ++++ DKDU The answer to this concept question is: (4) ++++ None of the above statements.