Basic properties — definition of strength Which statement correctly defines the mechanical property “strength” for engineering materials?

Introduction / Context:
Strength is one of the most frequently cited mechanical properties in design. It determines the maximum stress a material can withstand before yielding or fracturing, guiding the sizing of components and choice of safety factors in mechanical, civil, and aerospace engineering.

Given Data / Assumptions:

• Strength is evaluated relative to specific modes: tensile, compressive, shear, bearing, etc.
• Yield strength and ultimate strength are the most common metrics.
• Loading is within the intended service environment and rate.

Concept / Approach:
Strength relates to resistance to failure under load. When stress exceeds yield strength, permanent deformation occurs; when it exceeds ultimate strength, fracture can occur. The correct definition emphasizes withstanding external forces without breakdown (fracture) or yielding (permanent deformation). This differs from stiffness (resistance to elastic deformation) and toughness (energy absorption to fracture).

Step-by-Step Solution:
Identify terminology: “breakdown or yielding” covers both fracture and plastic flow.Map to standard measures: yield strength (e.g., 0.2% offset) and ultimate tensile strength.Exclude other properties: stiffness belongs to elasticity modulus; toughness to impact energy; elasticity to shape recovery.Thus, choose the statement that best captures failure resistance under force.

Verification / Alternative check:
Design codes specify allowable stresses using fractions of yield or ultimate strengths, confirming that “strength” is fundamentally about limits before yielding or breaking.

Why Other Options Are Wrong:
(a) defines stiffness; (c) defines toughness; (e) defines elasticity; (d) is invalid since a correct definition is provided.

Common Pitfalls:
Using high strength materials where stiffness controls deflection; strength does not guarantee low deflection. Also, conflating hardness with strength—related but distinct.

Final Answer:
Ability to resist externally applied forces without breakdown or yielding