Chapter 12: Properties Of Materials Flashcards
What is density?
The mass per unit volume of a material
ρ=mass/volume
Mass in kg, volume in m^3
What is Hooke’s Law in words?
The extension of an elastic object is directly proportional to the force applied to it up to the object’s limit of proportionality
F=ke
What is Hooke’s Law?
F=ke
Force in Newtons
Extension in metres
Spring constant in N/m
What is a spring constant?
A measure of how hard it is to bend or stretch a spring.
It defines the stiffness of a spring as the force required for a unit extension of the spring (N/m).
A large k means the spring is stiff.
What are compressive forces?
Forces that tend to squeeze an object and reduce its size in the direction that the forces are applied.
What are tensile forces?
Forces that act to pull or stretch an object.
What is extension?
The length a material has stretched when a load is added.
extension= stretched length - original length
What is the limit of proportionality?
The endpoint of the linear section of a force extension graph after which extension is no longer proportional to the load.
What is the elastic limit?
The force above which a material is permanently deformed (plastically deformed).
… and below which the material will return to its original length when the load is removed.
What is elastic deformation?
When a material will return to its original shape once the applied forces are removed
What is plastic/inelastic deformation?
When a material does not return to its original shape once the applied forces are removed. It is permanently deformed.
What is ductility?
The ability of a material to be formed into wires by stretching them. It is an example of plastic deformation.
How does a brittle material act?
Shows little or no plastic deformation before breaking (once the elastic limit is exceeded), eg glass.
How do ductile materials fracture?
The material will elongate and ‘neck’ before breaking (plastic region on graph).
How does a brittle material fracture?
No change of shape as it does not plastically deform; straight break in the material.
What is elastic strain energy?
Energy stored in a material that is equivalent to the work done in stretching the material.
How do you calculate elastic strain energy?
Area under a force extension graph
Energy stored= (Fe)/2
How does strain energy differ when a rubber band is loaded and unloaded?
Strain energy stored is greater when it’s being loaded than when unloaded (it becomes warmer as it stretches and relaxed).
What happens to extension when two springs are connected in series and in parallel?
Series: extension doubles
Parallel: extension halves
What is tensile stress?
A measurement of the force applied over cross-sectional area of a material.
tensile stress=force/cross-sectional area
σ= F/A
Force in Newtons, Area in m^2, σ in Pa
What is tensile strain?
The ratio of extension to original length of a material
tensile strain= extension/original length
Ɛ=x/l
Extension (x) in m, length in m, Ɛ dimensionless
What is Young Modulus?
A measure of stiffness of an elastic material and it does not depend on the dimensions of the sample being tested. Measured in Pa or N/m^2
What is the equation for Young modulus?
Young modulus = stress/ strain
E= σ/Ɛ
Young modulus= Fl/Ax
How is the Young Modulus found using a stress strain graph?
Gradient of the straight line part of the graph (up to LoP).
What is the ultimate tensile stress/strength of a material?
The greatest stress a material can withstand before breaking.
What is creep?
A property some metals have in which extension increases over time even though stress applied is not increased.
