18. The load-elongation curve represents results of a tensile test of a cylindrical specimen (initial diameter is 4 mm, gauge length is 25 mm). Estimate the yield strength 0.2. (3 points) 3 Load (kN) 2.5 2 1.5 1 0.5 0 0 0.025 0.05 0.075 0.1 0.125 0.15 0.175 0.2 Elongation (mm) 19. How does the material strength (S) change as a function of a distance (C) between defects that impede the motion of dislocations? (1 point) (a) S is proportional to C (b) S is inversely proportional to C (c) S is proportional to C (d) S is inversely proportional to C 21. The stress tensor (left) was transformed to principal axes resulting in the new tensor (right). Is this a proper transformation? (1 points) 0 0 0 0 ' = 0 0 200 0 200 0 = 0 200 0 0 0 200 (a) True (b) False 22. Precipitate hardening is associated with... (1 point) (a) particles of a secondary phase. (b) solid particles in a liquid alloy phase. (c) solid solution of atoms that share the same crystal lattice. (d) atoms that are small enough to crowd into interstitial sites.