Trig3IsoPMembraneStresses.m

%------------------------------------------------------------------
% Trig3IsoPMembraneStresses calculates the stresses for the tri3 elements
% nodeCoord: all node coordinates
% E young modulus matrix
% udisp: displacements of all the element nodes
% It returns sige:
% matrix with the element stress

function sige = Trig3IsoPMembraneStresses(nodeCoord,Emat,udisp)
    	x1 = nodeCoord{1,1}(1);
        y1 = nodeCoord{1,1}(2);
        x2 = nodeCoord{1,2}(1);
        y2 = nodeCoord{1,2}(2);
        x3 = nodeCoord{1,3}(1);
        y3 = nodeCoord{1,3}(2);
        %calculation of Triangle's Area
        A= ( x2*y3-x3*y2+(x3*y1-x1*y3)+(x1*y2-x2*y1) )/2;
        x21 = x2-x1;
        x32 = x3-x2;
        x13 = x1-x3;
        y12 = y1-y2;
        y23 = y2-y3;
        y31 = y3-y1;
        %calculating the Be, in which epsilon(x,y) = Be*e
        Be= 1/(2*A)*[ y23,0,y31,0,y12,0;...
                      0,x32,0,x13,0,x21;...
                      x32,y23,x13,y31,x21,y12;];
        sige{1,3} = {};
        % the stresses inside the triangle are constant
        sige{1,1} = Emat*Be*udisp;
        sige{1,2} = sige{1,1};
        sige{1,3} = sige{1,1};
end