i am getting this error "Brace indexing is not supported for variables of this type" at line which contains (S_bar{i}=​R{i}*T_1{i​}*R_1{i}*S​{i}*T{i});​.

sigma1=0.002;
sigma2=-0.003;
tau_12=0.004;
E1=181;
E2=10.3;
mu_12=0.28;
G12=7.17;
tetha=0:90;

c=cosd(tetha);
s=sind(tetha);
Stress_12=[sigma1; sigma2; tau_12];
%S matrix calculation
S=[1/E1 -mu_12/E1 0;-mu_12/E1 1/E2 0;0 0 1/G12];
%Q matrix calculation
Q=inv(S);
%Strain Vector calculation
Strain_12=S*Stress_12;
for i=1:numel(tetha)
    %Transformation matrix calculation
    T{i}=[c(i).^2 s(i).^2 2.*s(i).*c(i); s(i).^2 c(i).^2 -2.*s(i).*c(i); -s(i).*c(i) s(i).*c(i) (c(i).^2)-(s(i).^2)];
    %Inverse of the transformation matrix
    T_1{i}=inv(T{i});
            
    %R matrix
    R{i}=[1 0 0; 0 1 0; 0 0 2];
        
    R_1{i}=inv(R{i});
    
    %S bar matrix calculation
    S_bar{i}=R{i}*T_1{i}*R_1{i}*S{i}*T{i};
end

Answer 1

[KSSV]

IN this line:

S_bar{i}=R{i}*T_1{i}*R_1{i}*S{i}*T{i};

S is a matrix not a cell. So replace it by:

S_bar{i}=R{i}*T_1{i}*R_1{i}*S*T{i};

Also try initializing R, T_1, R_1 etc. Note that you can also intialize them as 3D matrix.

R = zeros(3,3,numel(tetha)) ;

[Mahmoud Chawki]

thank you,

it worked ,

why would i initiaalize them i don't understand

[KSSV]

?You have orange colored undeline in the code right? Those are warning, place the cursor there and see what MATLAB suggesting you.

Answer 2

[John D'Errico]

Is S a regular matrix?

S=[1/E1 -mu_12/E1 0;-mu_12/E1 1/E2 0;0 0 1/G12];

Yes. You then you assume it is a cell array for some reason.

S_bar{i}=R{i}*T_1{i}*R_1{i}*S{i}*T{i};
                            ____

Did MATLAB tell you there was a problem on that line?