++++ ++++ ++++ ++++ ++++ Concept Question ++++ ++++ ++++ ++++ ++++ The following stress-strain curves were obtained for dif- ferent materials subjecting the specimen to the loading path (a,b,c,d). Which one(s) of them correspond to elas- tic material(s)? b c d d b c d b c d σ ε σ ε σ ε σ εa a a a (1) (2) (3) (4) b c 1. ++++ (1) and (2) 2. ++++ (3) 3. ++++ (2) and (4) 4. ++++ None of the above 5. ++++ DKDU ++++ ++++ ++++ ++++ ++++ Answer ++++ ++++ ++++ ++++ ++++ The correct answer to the concept question is: 2. ++++ .