For annealed copper, the relation between true stress σ and true strain ε in the plastic region is σ = Kεⁿ with K = 530 MPa and n = 0.44. Which value is closest to the true stress at a true strain of 0.10?

Answer: C. About 192 MPa

σ = 530 × 0.10^0.44. Since 0.10^0.44 = 10^(−0.44) ≈ 0.363, σ ≈ 530 × 0.363 ≈ 192 MPa. About 53 MPa forgets the exponent and uses K × ε = 530 × 0.10. About 1460 MPa substitutes the strain as the percentage 10 (530 × 10^0.44); that it exceeds the strength coefficient K is itself a sign that something is wrong. n is called the strain-hardening exponent; the larger it is, the more readily the material strengthens as it deforms and the larger the uniform elongation before necking. Under constant volume, necking can be estimated to begin when the true strain equals n (0.44 in this example). FCC copper and austenitic stainless steels are typical examples with large n.