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Convert true stress - plastic strain to nominal stress - strain

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Convert true stress - plastic strain to nominal stress - strain

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This codes helps to check the input and output material property from FE programs such as Abaqus

ConvertTrueToNominal.m
% Converting true stress - plastic strain to true stress - true strain and to nominal/engineering stress - strain
% by: Ashkan Shahbazian (July 2013)
% (For steel, also could be modified for concrete)

% this code is great for checking output and input material property in Abaqus
% export von mises vs PEEQ from Abaqus and create "plastic" file/matrix, then
% run the code
%% input
E=205000; % steel young's modulus

%plastic file/matrix
% column #1 plastic strain (PEEQ) 
% column#2 true stress (von mises)

%plastic=[PEEQ mises]
%% calculating true strain
[pi pii]=size(plastic);
for si=1:1:pi;
    true(si,1)=plastic(si,1)+(plastic(si,2)/E);
end
true_strain=true;
%% calculating nominal strain
[ai aii]=size(true);
for ni=1:1:ai;
    syms noms;
    trues=true(ni,1);
    EQ=-trues+log(1+noms);
    noms=solve(EQ);
    nom1=double(noms);
    nom(ni,1)=nom1;
    clear EQ trues noms nom1
end
nom_strain=nom;
%% calculating nominal stress
for sii=1:1:pi;
    nom_stress(sii,1)=(plastic(sii,2)/(1+nom(sii,1)));
end
nom_material=[nom_strain nom_stress];

% now compare the input stress-strain curve with the output one.

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