I have plotted the stress strain graph from the tensile experiment and now I want to find the young's modulus of elasticity,yield point and yield stress

could you please help I want to write a code in such a way that we do not have to pick the points rather every time for finding the slope instead it should automatically pick the linear part of the graph and gives us the Young's Modulus of elasticity,Yield Stress and Yield Point and the offset line at 20% .I am attaching the matlab file and data also. thanks.

Answer 1

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T=readmatrix('tensile1_270_23.txt');
D=T(:,1);
F=T(:,2)*1000;
B=25;
A=(12.6*4.1);
strain=(D/B)+3.1710e-05;
stress=F/A+1.78295;
[idx val] = max(stress); % max value of stress in data
Thresh = val; % chose it as threshold
[TF S] = ischange(stress,'linear','Threshold',Thresh); % extract first occurance of abrupt change in data
idx = find(TF);
E = stress(idx(1))./strain(idx(1))  % Elastic (youngs) modulus

E = 1.0111e+03

Yield_sig = stress(idx(1))  % yield stress MPa

Yield_sig = 36.4346

Offset = strain(idx(1))*0.2 % offset distance @ 20% strain

Offset = 0.0072

plot(strain,stress,'LineWidth',2)
hold on
plot(strain(1:idx(1))+Offset,stress(1:idx(1)),'r--')
grid on
x=xlabel('strain, \epsilon');
y=ylabel('stress, \sigma (MPa)');

you can try this approach