Fracture strength point is the stress at which the material begins to fracture.

• A. Yield stress
• B. Proportional limit stress
• C. Maximum strength before necking
• D. Onset of fracture

Answer: (D)

In tensile behavior, several key stress levels describe different milestones in how a material responds under load. The phrase “begins to fracture” points to the moment when cracks first form and start to propagate—the start of the fracture process. That moment is what is meant by the onset of fracture, and it aligns with the idea of fracture strength as the stress at which fracture begins.

This is distinct from yield stress, where permanent plastic deformation starts, and from the proportional limit, where the response ceases to be perfectly linear elastic. It’s also different from the maximum strength before necking (the ultimate tensile strength), which is the highest engineering stress reached prior to substantial necking and prior to final fracture; the actual fracture occurs after further crack growth. Therefore, the stress at which fracture onset occurs best fits the description of the fracture strength in this context.