What property does yield strength measure, and why is it important in design?

What property does yield strength measure, and why is it important in design?

• A. The stress at which a material yields plastically; it indicates the maximum stress before permanent deformation, guiding material selection.
• B. The rate at which a material cools.
• C. The hardness of a material.
• D. The modulus of elasticity.

Answer: (A)

Yield strength is the stress level at which a material begins to deform plastically, meaning permanent shape change starts when that stress is exceeded. This matters in design because you want service stresses to stay below this value so the part won’t deform permanently under normal loads. It guides material selection and the safety factors used in calculations. If you push past yield strength, the material won’t return to its original shape, which can lead to distortion or failure under repeated loading. The other options describe different properties: rate of cooling affects thermal history, hardness measures resistance to indentation, and the modulus of elasticity (Young’s modulus) describes stiffness in the elastic range, not when permanent deformation begins.

Yield strength is the stress level at which a material begins to deform plastically, meaning permanent shape change starts when that stress is exceeded. This matters in design because you want service stresses to stay below this value so the part won’t deform permanently under normal loads. It guides material selection and the safety factors used in calculations. If you push past yield strength, the material won’t return to its original shape, which can lead to distortion or failure under repeated loading. The other options describe different properties: rate of cooling affects thermal history, hardness measures resistance to indentation, and the modulus of elasticity (Young’s modulus) describes stiffness in the elastic range, not when permanent deformation begins.