Materials Flashcards
What is the density of water?
1gcm^3, 1000kgm^3
Define density
The mass per unit volume of a substance; its ‘compactness’
What does Hooke’s Law state
Extension of a stretched object is proportional to force (F=kΔl, where k is the stiffness constant)
What is an elastic stretch
When a material returns to its original shape and size once load is removed (atoms remain relative to their equilibrium)
What is a plastic stretch
When a material is permanently stretched, as the atoms do not return to their original positions
Define tensile stress
Force applied divided by the cross-sectional area
Define tensile strain
Ratio of change in length divided by the original length
What is the difference between tensile and compressive forces
Forces are tensile if they stretch a material and compressive if they squash it
What is the ultimate tensile stress
The maximum stress a material can withstand before its atoms separate
Energy stored in a stretched wire =
1/2 force x extension
1/2kΔL^2
Young Modulus equation and units
E = tensile stress/tensile strain, Nm^-2 or Pa
What is the Young Modulus
A measure of the stiffness of a material
How can you find Young’s Modulus from a stress-strain graph
Gradient of the graph
How to calculate energy per unit volume from a stress-strain graph
1/2 x stress x strain
What is the yield point on a stress-strain graph
Where the material begins to stretch without any extra load
What is the different between the elastic limit and the limit of proportionality
The elastic limit is the point where the material starts to behave plastically (will not return to its original position). The limit of proportionality is where the material stops obeying Hooke’s Law, yet would still return to its original shape once the stress was removed
