11.4- MORE ABOUT STRESS AND STRAIN Flashcards
(21 cards)
Experiment to see how strength of material change as a result of being stretched?
tension in strip of material increased by increasing weight it supports in steps
at each step, extension of material measured
What is the loading + unloading curve for a metal wire like?
same, provided elastic limit not exceeded
What happens to loading + unloading curve of a wire when the elastic limit is exceeded?
unloading line parallel to loading line
Why is a metal slightly longer when unloaded after it has exceeded the elastic limit?
permanent extension
What is the change in length during unloading + loading for a rubber band like?
change of length during unloading greater than during loading for given change in tension
Although the rubber band returns to the same unstretched length, what is the unloading curve like?
unloading curve below loading curve except at zero + maximum extensions
What does the rubber band band remain as, as it regains its initial length?
remains elastic
What does the rubber band have a low of?
low limit of proportionality
What is the extension for loading + unloading of a polythene strip like?
extension during unloading greater than during loading
Does the polythene strip return to the same initial length when it’s completely unloaded?
no
What does the polythene strip have a low of?
low limit of proportionality
What does the polythene strip suffer?
plastic deformation
What is the are under a force-extension graph equal to?
equal to work done to stretch wire
What is strain energy?
work done to deform object
Provided the limit of proportionality is not exceeded, what is the equation for elastic energy stored in a stretched wire?
= 1/2TΔL
As the graph of tension against tension is the same for unloading as for loading, what happens to energy? (metal wire (or spring))
all energy stored in wire can be recovered when wire unloaded
What is the work done to stretch a rubber band represented by?
area under loading curve
What is the work done by rubber band when it’s unloaded represented by?
area under unloading curve
What does the area between the loading curve + unloading curve represent? (rubber band)
difference between energy stored in rubber band when it’s stretched + useful energy recovered from it when it’s unstretched
Why is there a difference between the energy stored in rubber band when it’s stretched + unstretched?
some of the energy stored in rubber band becomes internal energy of molecules when rubber band unstretches
What is the area between the loading + unloading curve as polythene does not regain its initial length?
area between loading + unloading curves represent work done to deform materials permanently, + internal energy retained by polythene when it unstretches
