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**1. Homework Statement**

I have a lab report where I have to plot a stress-strain diagram for 2 beams. We apply an increasing load at midspan and record the deflection. I have to find the strain so I can plot the diagram. Also, the diagram willl be use to find the modulus of elasticity so I can use the stress = Ee

**2. Homework Equations**

I cannot use stress = Ee since the modulus need to be find. I know that strain = (l-lo)/lo but since it is not en elongation but a bending I don't know what's the relation between strain and deflection

**3. The Attempt at a Solution**

I was thinking about using trigonometry to find the change in length but I wouldn't be accurate and the error on the length will be to big to use. It's a lab report so usually it shouldn't be to complicated. I look on the internet, in all my books and didn't not find any relation between strain and deflection.

Thank you

Alex B.