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Physics question - new spec - HELP!

This is taken from last years unit 2 paper:
Why is the yield point at B and not C? Isn't the yield point the stress or force at which a large amount of plastic deformation takes place with constant or reduced load? On the graph, extension increases for a decrease in force at C, so why is B the yield point?

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(edited 6 years ago)
C is the Ultimate Tensile Stress. - strongest point of wire.
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Original post by anissabir95
C is the Ultimate Tensile Stress. - strongest point of wire.


But doesn't C also meet the criteria to be the yield point?
And what makes B the yield point?
B is the yield point, C is the UTS, you get some molecular rearrangement after yield point which lowers youngs modulus at that point but after UTS material is breaking so also some molecular reshuffle there. In general the little hump after the elastic limit is the yield point
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Original post by glad-he-ate-her
B is the yield point, C is the UTS, you get some molecular rearrangement after yield point which lowers youngs modulus at that point but after UTS material is breaking so also some molecular reshuffle there. In general the little hump after the elastic limit is the yield point


what from the graph made you identify B as the yield point? Just the fact that it comes after the elastic limit? Is that the only indication from the graph?
Original post by exams292
what from the graph made you identify B as the yield point? Just the fact that it comes after the elastic limit? Is that the only indication from the graph?


That the gradient of the graph has a slight dip add to that the fact that it's not the maximum of the graph suggests it must be the yield point
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Original post by glad-he-ate-her
That the gradient of the graph has a slight dip add to that the fact that it's not the maximum of the graph suggests it must be the yield point


Thanks! One last thing. Can the yield point and UTS point ever coincide?
Original post by exams292
Thanks! One last thing. Can the yield point and UTS point ever coincide?


No-as far as I know
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Original post by glad-he-ate-her
No-as far as I know


Ok, thanks, good luck on Wednesday
Original post by exams292
Ok, thanks, good luck on Wednesday


Thank you

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