Problem 3 (15 points): t+1 1 Consider the creep functions D(t) = + (1-e), unit is in MPa-. 600 600 a) Determine the corresponding strain output at time 20 seconds. b) Will the strain eventually drop to zero after 50 seconds? Explain! (It is not necessary to numerically solve the problem.) Stress (MPa) 20 10 20 Time (sec) 10 40 50