Which statement best describes the relationship between yield strength and ultimate tensile strength in design?

Which statement best describes the relationship between yield strength and ultimate tensile strength in design?

• A. They define the maximum loading without any deformation.
• B. They determine cost of production.
• C. Yield strength marks onset of plastic deformation; UTS is maximum stress before necking and failure; together they guide safety factors.
• D. They only apply to metallic materials.

Answer: (C)

Understanding how yield strength and ultimate tensile strength function in a design helps ensure parts don’t deform or fail under load. Yield strength is the stress at which plastic, permanent deformation begins; below that, deformations are elastic and reversible. Ultimate tensile strength is the highest stress a material can withstand in a tensile test, reached just before necking and eventual fracture. In design, these values set limits and, together, guide safety factors: you design service stresses to be safely below the yield strength to avoid permanent shape change, while the ultimate tensile strength provides a limit for the total load capacity and helps assess margin against failure. The statement that yields marks onset of plastic deformation and UTS is the maximum stress before necking and failure, and that they together guide safety factors, is the best description.

Understanding how yield strength and ultimate tensile strength function in a design helps ensure parts don’t deform or fail under load. Yield strength is the stress at which plastic, permanent deformation begins; below that, deformations are elastic and reversible. Ultimate tensile strength is the highest stress a material can withstand in a tensile test, reached just before necking and eventual fracture. In design, these values set limits and, together, guide safety factors: you design service stresses to be safely below the yield strength to avoid permanent shape change, while the ultimate tensile strength provides a limit for the total load capacity and helps assess margin against failure. The statement that yields marks onset of plastic deformation and UTS is the maximum stress before necking and failure, and that they together guide safety factors, is the best description.