3.4 Matierals Flashcards
Define brittle
The material distorts very little even when subject to a large stress and does not exhibit much plastic deformation
Define compression
The result of two coplanar forces acting into an object. Compression usually results in a reduction in the length of the objects shape
Define compressive deformation
The changing of an objects shape due to compressive forces
Define ductile
A material is ductile if it can undergo very large extensions without failure. Ductile materials can be stretched into wires.
Define Elastic deformation
If a material deforms with elastic behaviour, it will return to its original shape when the load is removed. The object will not be permanently deformed
Define Elastic potiental energy
The energy stored in an object when it is stretched.
How can you find the elastic potienal emergy from a force-extension graph?
The area under the graph
Define extension
The increase in an objects length
What is hookes law?
The extension of an elastic object will be directly proportional to the force applied to it up to the objects limit of proportionality.
What is the equation for the extension of a spring?
Force = spring constant x extension
F=kx
What is the equation for stress?
Stress = force/ area
ó = F/A
What is the equation for strain?
Strain = extension / length
E=x/L
What is the equation for youngs modulus?
young modulus = stress / strain
E=ó/E
What are the 2 equations for elastic potential energy?
Energy = 0.5 x force x extension
E = 0.5 x F x X
Energy = 0.5 x spring constant x extension^2
E = 0.5 x k x X^2
What is ultimate tensile strength?
The maximum stress a material can withstand before fracture
What is the elastic limit?
The value of stress or force beyond which elastic deformation becomes plastic deformation; the material will not return to its original shape and size when the stress or force is removed
What is the plastic region on a stress / strain graph?
Removal of the stress or force will not return the object to its original shape; the change in shape of the material is irrecoverable
What is the limit of proportionalityin regards to a stress/strain graph?
The value of the stress beyond which the stress is no longer proportional to the strain
What is the elastic region on a stress/ strain graph?
Removal of stress or force will return the object to its original shape
What is the yield point?
Yield Point—the point beyond which the material extends rapidly for a small change in stress
Why can ductile materials be drawn into a wire?
Materials that have a large plastic region and can therefore be drawn into a wire
What is a polymeric material?
A material comprised of long chain molecules, for example, rubber, which may show large strains
Define tough
Needs a large energy to break and create a new fracture surface
Define stiff
The extent to which a material under stress experiences a strain
Define hard
A measure of the difficulty of scratching or denting a material
Define strong
The extent to which a material resists breaking under stress; it has a high Ultimate Tensile Strength and a high breaking stress
What is the area of a hysteresis loop equal to?
The energy transferred per unit volume
