1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The difference between strain and strain_y

  1. Sep 25, 2013 #1
    1. The problem statement, all variables and given/known data

    I am doing a lab. My textbook defines strain as ε= lf-lo and E = σ/ε. In my lab, E= σyy. εy = ΔLy/lo

    I do not understand how they can both = ε as lf-lo is completely different from ΔLy/lo. ΔLy is "elongation at yeild" according to my lab. Why are they both labelled E if they are different? The y subscript, according to the lab, has to do with the yield point. I was under the impression that there was only 1 elastic modulus as after the yield point, stress and strain are no longer proportional and plastic deformation occurs.

    2. Relevant equations

    See above.

    3. The attempt at a solution

    I can only conclude I am either missing something or the equations mean the same thing, somehow.
  2. jcsd
  3. Sep 26, 2013 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    that is elongation, not strain... Did you copy this down incorrectly?
    correct. Lf -Lo = ΔL = elongation, and ΔL/Lo = ε = σ/E
    correct the definition for strain in your text. The y subscripts then refer to specific values of stress and strain etc at yield. Without the subscripts, these are the general equations within the proportional limit.
  4. Sep 26, 2013 #3
    Thank you, I understand now.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted