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
