Line interception in stress strain graph

Hello,

I have plotted stress vs strain and would like to get the yield stress at 0,2%strain. So I have calculated the slope from the linear part in the beginning of my plot and I plot a line that starts from 0,2 on my x-axis. This line intercepts the initial plot and I would like to know the value of the y-axis at this intercept.

Is there a graphical tool for this or what should I do?

Thank you.

Answer 1

[Star Strider]

We don’t have your data, so I can only outline the approach I would take.

If you calculated the line from the same x and y values of the stress-strain curve, subtract the y value of the line from the y value of the stress strain curve for the x values common to both. The y value of the line corresponding to the x coordinate of the ‘last positive’ value of that vector is the one you want.

This illustrates the approach:

x = 0:0.1:2;                        % Create Data
y = -(x-5).^2 + 25;                 % Create Data
b = polyfit(x(1:15),y(1:15),1);     % Fit Line
yf = polyval(b,x);                  % Evaluate Line
dif = y-yf;                         % Subtract Data From Line
xn = find(dif > 0, 1, 'last');      % Find Index Of Last +ve

figure(1)
plot(x,y)                           % Plot Data
hold on
plot(x,yf)                          % Plot Line
plot(x(xn),y(xn),'+r')              % Plot Point
hold off
grid