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    Hey, when I looked at a stress/strain graph for two ductile metals (copper and gold) I noticed a dip where the elastic limit is exceeded and plastic deformation begins. Can somebody explain why this dip occurs? Thanks
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    (Original post by Horro421)
    Hey, when I looked at a stress/strain graph for two ductile metals (copper and gold) I noticed a dip where the elastic limit is exceeded and plastic deformation begins. Can somebody explain why this dip occurs? Thanks
    After the elastic limit is exceeded, as you said, plastic deformation occurs. Hence there's a much larger increase in strain for a smaller increase in stress. Understand?
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    you give a tiny force and get a much larger increase in extenstion!
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    I think that the question is more about why the graphs start to "go down" again - that is, why the extension continues to increase when the loading force is decreased. For materials like this, once the elastic limit has been passed, they can behave like this; removing part of the loading force and then gently putting the wire under the remaining loading force can still cause the wire to extend. It's worth doing this for yourself if possible; once you've experienced it with a copper wire, for example, it's easier to believe! (Doubt that you'll have the chance to do it with gold...)
 
 
 
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