# How to find yield point and plot strain hardening part?

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ans on 18 Oct 2021
Answered: KSSV on 18 Oct 2021 test = table2array(M)
strain = test(:,1);
stress = test(:,2);
p=plot(strain,stress,'ko-',"LineWidth", 2)
xlabel('\epsilon')
ylabel('\sigma (MPa)')
xlim([0 0.5]);
ylim([0 700]);
ultimate_strength = max(stress);
elongation = max(strain);
I have true_stress vs strain curve ploted in MATLAB. I want to find yeild stress from this curve and plot just strain hardening part (e.g, from yield point stress to ultimate stress). Please let me know what I should do and which code and function I should use, since I am quit new to MATLAB.

KSSV on 18 Oct 2021
x = T.X ; y = T.Y ;
% Ultimate strength
[val,idx] = max(y) ;
xmax = x(idx) ; ymax = val ;
% Get linear part
threshold = 550;
[TF,Sl,Ic] = ischange(y, 'linear','Threshold',threshold);
idx = find(TF);
xlinear = x(1:idx(2)) ;
ylinear = y(1:idx(2)) ;
figure
hold on
plot(x,y,'r')
plot(xmax,ymax,'*r')
plot(xlinear,ylinear,'*-b') 