Edexcel AS Physics - Solid Materials

[vanibharutham]

Hi,

There is something that i can never seem to understand in a stress strain graph....
 the difference between the yield point and elastic limit

according to my teacher they are the same thing,

according to the edexcel book:

Yield Point = the point where a small change in stress causes a large change in strain
Elastic Limit = the point up to which a material is elastically deformed


along with that doubt, there seems to be a misconception with the definitions of the words STRENGTH and TOUGHNESS...

i did some reading, and found that toughness is the energy absorbed per unit volume, and stronger materials have a high ultimate tensile stress..

Now, once again resorting to edexcel definitions:

TOUGHNESS = the property of materials to resist plastic deformation. A large amount of force is needed to cause plastic deformation.
STRENGTH = property of materials to absorb large amounts of stress without failure...

those are a bit vague... any clarification would be great

[EVIL DOCTOR]

Strength of a material: is the the tensile stress at which a material breaks.
Toughness:is the ability for a material to resist or absorb a shock or stress without breaking (the opposite of brittle) like wood.
                its also calculated by  the area under the stress strain graph.

Yeild point is the point just beyond the elastic limit they r almost the same.
limit of proportionality is at the end of the linear line  then come the Elastic limit at the beginning of the curve the n comes the yeild point.                 
 

[7ooD]

actualy from wat i understood is that the yeild point is the point where the elastic limit has been exceeded and it is like a stage between elastic region and plastic region but to be specific the easy definition for it is point where the matrial crystal plans start slipping and there is a marked large increase in stress blah blah blah but for the difference between strength and toughness is a strong matrial would have little plastic region but a tough matrial would a large plastic region and if you want to make sure about that lets take steel it is strong and stiff and elastic in hooks law region which means that it doesnt have a plastic region whereas mild steel is tough and rubber tyres are tough and flexible which is opposite to stiffness therefore we conclude that a tough object go plastic but a strong object doesnt go plastic