Define the words Load Force Stress Strain by using them in the same sentence.
A load is applied to a material which exerts a force on the material which produces a stress within a material and
associated strain
What are the units for Load?
Kilograms (Kg)
What are the units for Force?
Newton (N)
Name 3 types of forces
- Uniaxial (single axis)
- Biaxial (2 perpendicular axis)
- Triaxial (equal in all directions)
Name 3 uniaxial forces
- Tensile
- Compressive
- Shear
What are the units for stress?
Pa
What are the units for strain?
No units
What is the measure of stiffness
Young’s modulus (E)
State Hooke’s Law
Stress (σ) is proportional to strain (ε)
What is compliance a measure of?
- Softness
- 1/E (reciprocal to stiffness)
What is the proportional limit on an stress-strain curve?
The limit when even if the load is removed the material is permanently damaged
What is the ultimate tensile strength on an stress-strain curve?
The fracture point where the material breaks apart
What is the yield point on an stress-strain curve?
The point above which strain will increase even with no further increase in stress
What is the elastic region on an stress-strain curve?
Region where, if stress is removed the original shape is recoverable
What is the plastic region on an stress-strain curve?
Region where, if stress is removed the material is permanently deformed
Define resilience
Energy absorbed without permanent deformation
Define toughness
Total energy absorbed up to fracture
Equation for Poisson’s ratio
Lateral strain / Axial strain
Equation for Shear modulus
Shear stress / Shear strain
Equation for Bulk modulus (liquids)
Hydrostatic pressure / Shear strain
What is a brittle fracture?
- Occurs with little or no plastic deformation
- Low energy absorption
What is a ductile fracture?
- Occurs after significant plastic deformation
- High energy absorption
What are the 2 steps in a fracture?
- Crack formation (slow)
- Crack propagation (fast)
How is direct tensile strength measured?
By gauges and extensometers
