Stress
Stress is the force per unit area within a material.
- Normal stress acts perpendicular to an area
- Shear stress acts parallel to an area
Strain
Strain is the deformation produced by stress, expressed as a change in length divided by original length.
Stiffness
Stiffness is the resistance of a structure to deformation. On a load–deformation graph, it is represented by the slope of the curve.
Elasticity and plasticity
- Elastic deformation: the material returns to its original shape after the load is removed
- Plastic deformation: permanent deformation remains after removal of the load
Young modulus
Young modulus is a material property that describes the relationship between stress and strain in the elastic region. It reflects the intrinsic stiffness of the material itself.
Strength
Strength is the maximum stress a material can withstand before failure.
- Yield strength: stress at which permanent deformation begins
- Ultimate strength: maximum stress before failure
Toughness
Toughness is the ability to absorb energy before failure. It corresponds to the area under the stress–strain curve.
Ductility and brittleness
- Ductility is the ability to undergo plastic deformation before fracture
- Brittleness describes fracture with little plastic deformation
Fatigue
Fatigue failure results from repeated cyclic loading at stress levels below the ultimate strength.
Creep
Creep is progressive deformation with time under a constant load.
Diagram
