The ultimate fail point on a stress–strain curve refers to...

• A. Elastic limit
• B. Yield point
• C. Ultimate fail point
• D. Toe region

Answer: (C)

The main idea is the final point where the material actually fails and breaks under the applied load. On a stress–strain curve, after the material has yielded and undergone plastic deformation, it may neck and eventually fracture; the fracture point marks the ultimate fail point—the end of the curve where the specimen can no longer carry load. The elastic limit is where elastic behavior ends, the yield point is the onset of plastic deformation, and the toe region is the small initial nonlinear portion due to fibers straightening—none of these signify the final failure. Note that the maximum stress reached (ultimate tensile strength) occurs before fracture in many materials, but the ultimate fail point specifically refers to the fracture point itself.