Beginner
Stress & Strain
How materials resist being pulled, pushed and deformed.
STEP 1 · CONCEPT
Stress is internal force per unit area. Strain is how much the material stretches relative to its original length.
STEP 2 · HOOKE'S LAW
In the elastic region, stress is proportional to strain. The constant is Young's modulus (E).
STEP 3 · WHY IT MATTERS
Designers keep stress below the material's yield strength with a factor of safety.
WORKED EXAMPLE
A 10 mm² steel wire carries 2,000 N. Stress = 2000 / 10 = 200 N/mm² = 200 MPa.
Formulas
Normal stress
σ = F / A
F force, A cross-section area
Strain
ε = ΔL / L
ΔL change in length, L original length
Hooke's law
σ = E · ε
E Young's modulus
Practice questions
Q1.SI unit of stress is…
Stress & Strain · Easy
Q2.Strain has units of…
Stress & Strain · Easy
Q3.Steel E = 200 GPa, stress = 100 MPa. Strain?
Stress & Strain · Hard