Topic 4 - Materials 2 Flashcards
What’s energy density?
It’s the work done in stretching a specimen per unit volume of the sample
= 1/2 x stress x strain
If a material can absorb a lot of energy before it’s fracture what does this mean?
It’s a tough material
Little plastic deformation means what about a material?
It’s brittle
What’s the hysteresis loop?
On a stress-strain graph it represents the energy per unit volume transferred to internal energy for each cycle
How do you calculate the extension?
New length - original length = extension
If you want to compare 2 different materials what do you use force-extension or stress-strain?
Stress-strain
If a force stretches a material it’s called …
Tensile
If a force squashed a material it’s called?
Compressive
Compressive forces tend to be?
Negative
What’s breaking stress?
When the stress becomes too much the atoms separate completely and the material breaks
What comes first on a stress-strain graph the UTS or the breaking stress?
UTS
Name one thing that can effect UTS and breaking stress?
Temperature
What does the area under a force extension graph represent?
Elastic energy strain
What’s the equation for elastic strain energy?
Elastic strain energy = 1/2 x spring constant x extension*2
What’s the equation for work done?
Work done = 1/2 x force x extension
Up to the ………. …… ………… the stress and strain of a material are proportional. After this point you can no longer use the equation to calculate the young modulus
Limit of proportionality
From a stress-strain graph how would you calculate the energy per unit volume?
Energy per unit volume = 1/2 x stress x strain
What are the different point on a stress-strain graph?
- limit of proportionality
- Elastic limit
- Yield point
The stronger a material the higher the ………. ……. on the stress-strain graph
Breaking stress
Stiff materials have a large ………. ……… . And for a given stress a stiff material will have a lower ……….. than a less stiff material
Young’s modulus
Strain
What’s the difference between stress-strain & force-extension?
- F-E are specific for the tested object and depend on its dimensions
- S-S describes the general behaviour of a material, they’re independent of the dimensions
What’s on which axis of the stress-strain graph?
Y axis - stress
X axis - strain
What does it mean if a material is elastic?
Regains original dimensions when the deforming force is removed
-example rubber
