Basic Concepts of Stress, Strain & Elasticity

Vocabulary flashcards review fundamental terms and definitions related to stress, strain, elasticity, and associated mechanical properties as presented in the lecture notes.

Stress (σ)

Internal resistance developed per unit cross-sectional area when a body is subjected to an external load (σ = P/A). Units: N/mm².

Strain (ε)

Ratio of change in dimension to the original dimension produced by stress (ε = ΔL/L₀). Dimensionless quantity.

Young’s Modulus / Modulus of Elasticity (E)

Constant ratio of normal (tensile or compressive) stress to corresponding normal strain within the elastic limit (E = σ/ε).

Modulus of Rigidity / Shear Modulus (G or C)

Ratio of shear stress to corresponding shear strain within the elastic limit (G = τ/φ).

Elastic Limit

Maximum stress up to which a material returns completely to its original shape and size on removal of the external load.

Hooke’s Law

Within the elastic limit, stress is directly proportional to strain (σ ∝ ε).

Factor of Safety (FoS)

Ratio of ultimate tensile stress to working (permissible) stress: FoS = σultimate / σworking.

Ultimate Stress

Maximum stress a material can withstand before failure.

Working (Permissible) Stress

Stress level adopted in design to ensure safety; equal to ultimate stress divided by the factor of safety.

Tensile Stress

Normal stress that tends to elongate a material; produced by axial pulling load.

Compressive Stress

Normal stress that tends to shorten or compress a material; produced by axial pushing load.

Shear Stress (τ)

Stress acting tangentially to a plane in the material, producing sliding between adjacent layers.

Shear Strain (φ)

Angular distortion produced by shear stress; measured as the tangent of the angle of deformation.

Volumetric Strain (ε_v)

Ratio of change in volume to the original volume when a body is subjected to uniform normal stresses.

Lateral Strain

Strain measured perpendicular to the direction of applied axial load; accompanies longitudinal strain.

Longitudinal (Linear) Strain

Axial deformation per unit original length in the direction of the applied load.

Load (P)

External force applied to a body that induces internal stresses.

Strength of Material

Property that describes the capacity of a material to resist deformation and failure under applied loads.

Normal Stress

Stress whose line of action is perpendicular to the cross-section being considered; includes tensile and compressive stresses.

Cross-Sectional Area (A)

Area of the material’s section perpendicular to the applied load; directly influences the magnitude of induced stress.

Axial Deformation (ΔL)

Change in length of a member along the line of action of an applied axial load.

Elastic Body

Material that regains its original shape and size completely after removal of the external force within the elastic limit.