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    I know that necking causes a stress strain graph to start to curve but I don't understand how. If stress is force/area and area is the same and force is increasing by 100 grams each time then the stress shouldn't cause it to curve. strain is change in length/length so it should carry on being proportional as the length it stretches increases when more weight is added rather than the extension getting less?
    can someone explain what Im getting so confused about?

    Thanks
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    Different materials have different stress strain graphs. Concrete has a linear stress strain graph because it only undergoes elastic deformation. Something like copper wires has a linear section when it undergoes elastic deformation, but also has a curved section where it undergoes plastic deformation.
    Elastic deformation mean that after it has been extended it can return to it original length
    Plastic deformation means that after it has been extended it CANNOT return to its original length
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    (Original post by jonnypdot)
    Different materials have different stress strain graphs. Concrete has a linear stress strain graph because it only undergoes elastic deformation. Something like copper wires has a linear section when it undergoes elastic deformation, but also has a curved section where it undergoes plastic deformation.
    Elastic deformation mean that after it has been extended it can return to it original length
    Plastic deformation means that after it has been extended it CANNOT return to its original length
    Oh right thanks.
    So when the copper wire undergoes plastic deformation does the change in length increase more than when its undergoing elastic deformation?
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    (Original post by dont)
    Oh right thanks.
    So when the copper wire undergoes plastic deformation does the change in length increase more than when its undergoing elastic deformation?
    yes
 
 
 
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