Y1: Materials Flashcards
What is density
The mass per unit volume of a substance (kg m^-3)
What is the equation for density
ⲣ = m/v
What is Hooke’s Law
The extension of a stretched wire is proportional to the load force
F=kΔL
k: Spring constant (Nm^-1)
What is the total spring constant for springs in series
1/kT = 1/k1 + 1/k2 + 1/k3
What is the total spring constant for springs in parallel
kT = k1 + k2 + k3
What is the limit of proportionality
The point beyond which Hooke’s law no longer applies ( < Elastic limit)
Different for each spring
What is the elastic limit
The point beyond which plastic deformation occurs ( > Limit of proportionality)
What is an elastic stretch
When the material returns to its original length when the force is removed
What is shown by the area between the loading and unloading curve on a force-extension curve
The energy dissipated during the loading (eg. heat)
What is the equation for elastic strain energy
Ep = 1/2 (kΔL^2)
What is a plastic stretch
When the material is permanently stretched after the force is removed
- Atoms have moved relative to each other so don’t return to their original position
- Stretched past the elastic limit
What is tensile stress
The force per unit of surface area (Nm^-2)
What is the equation for tensile stress
σ = Force / Surface area
What is the breaking stress of a material
The force per unit of surface area great enough to break the material as the atoms are completely separated
Occurs after the breaking stress, as the material breaks after being deformed
What is the ultimate tensile stress of a material
The maximum stress a material can withstand
Occurs before the breaking stress, as the material will start to deform
What is strain
The extension per unit of length (dimensionless)
What is the equation for strain
ε = Extension / original length
What is the young modulus of a material
A measure of how stiff a material is
What is the equation for the young modulus
E = Stress / Strain = (F/A) / (ΔL/L)
∴ E = FL / AΔL
What is shown by the area under the proportional section of a stress-strain graph
The strain energy per unit volume
What is shown by the gradient of a stress-strain graph
The young modulus
What is the yield point on a stress-strain graph
Point at which a large amount of plastic deformation occurs with less load, as the material suddenly starts to stretch without increasing the load.
What is a brittle material
A material that fails under load by cracking, with little/no plastic deformation.
Occurs as the atoms are arranged in a rigid structure
What is a ductile material
A material that can be drawn into wires, as necking occurs when stretched
What is the strength of a material
The maximum stress a material can withstand before cracking
