Drawing a parallel line to the straight portion of the curve

[svishal03]

I have a curve of this form (as attached) drawn in excel.

Now, the point P upto which the red curve is (almost) a straight line is called the proportional limit.

OK. Now, I need to find the proportional limit as hown by the point p on the curve.

It is given in literature that;

As a convention, to determine the yield point and proportional limit (yield point is the point corresponding to σy on the curve) a straight line is constructed parallel to the elastic portion of the curve (elastic portion means the portion that remains a straight line) corresponding to the value of strain 0.002 as shown in the figure above.

My question is:

How to construct this parallel line to the elastic portion of the curve ?? I need to do it in excel (preferable or even Matlab if you say)- how to do it? That is; how to construct a straight line parallel to the elastic (staright) portion of the red curve above??

Please help

 

[pbuk]

Fit a straight line to the curve between O and P and measure its slope.

 

[Number Nine]

As MrAnchovy said, you have two points of the curve (O and P), which you can use to calculate the slope. Use the slope to derive the equation of the line.

 

[Integral]

A easy way to do this in Excell is to select a few points on the line and select a linear trend line. Choose to show the equation and you will have your line.