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Ex982.m
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Ex982.m
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%----------------------------------------------------------------------------
% Example 9.8.2
% plane stress analysis of a cantilever beam using isoparametric
% four-node elements
% (see Fig. 9.8.2 for the finite element mesh)
%
% Variable descriptions
% k = element matrix
% f = element vector
% kk = system matrix
% ff = system vector
% disp = system nodal displacement vector
% eldisp = element nodal displacement vector
% stress = matrix containing stresses
% strain = matrix containing strains
% gcoord = coordinate values of each node
% nodes = nodal connectivity of each element
% index = a vector containing system dofs associated with each element
% point2 = matrix containing sampling points
% weight2 = matrix containing weighting coefficients
% bcdof = a vector containing dofs associated with boundary conditions
% bcval = a vector containing boundary condition values associated with
% the dofs in 'bcdof'
%----------------------------------------------------------------------------
%------------------------------------
% input data for control parameters
%------------------------------------
clear
nel=8; % number of elements
nnel=4; % number of nodes per element
ndof=2; % number of dofs per node
nnode=18; % total number of nodes in system
sdof=nnode*ndof; % total system dofs
edof=nnel*ndof; % degrees of freedom per element
emodule=1e6; % elastic modulus
poisson=0.3; % Poisson's ratio
nglx=2; ngly=2; % 2x2 Gauss-Legendre quadrature
nglxy=nglx*ngly; % number of sampling points per element
%---------------------------------------------
% input data for nodal coordinate values
% gcoord(i,j) where i->node no. and j->x or y
%---------------------------------------------
gcoord=[0.0 0.0; 0.0 1.0; 0.5 0.0; 0.5 1.0; 1.0 0.0;
1.0 1.0; 1.5 0.0; 1.5 1.0; 2.0 0.0; 2.0 1.0;
2.5 0.0; 2.5 1.0; 3.0 0.0; 3.0 1.0; 3.5 0.0;
3.5 1.0; 4.0 0.0; 4.0 1.0];
%---------------------------------------------------------
% input data for nodal connectivity for each element
% nodes(i,j) where i-> element no. and j-> connected nodes
%---------------------------------------------------------
nodes=[1 3 4 2; 3 5 6 4; 5 7 8 6; 7 9 10 8;
9 11 12 10; 11 13 14 12; 13 15 16 14; 15 17 18 16];
%-------------------------------------
% input data for boundary conditions
%-------------------------------------
bcdof=[1 2 3 4]; % first four dofs are constrained
bcval=[0 0 0 0]; % whose described values are 0
%-----------------------------------------
% initialization of matrices and vectors
%-----------------------------------------
ff=zeros(sdof,1); % system force vector
kk=zeros(sdof,sdof); % system matrix
disp=zeros(sdof,1); % system displacement vector
eldisp=zeros(edof,1); % element displacement vector
stress=zeros(nglxy,3); % matrix containing stress components
strain=zeros(nglxy,3); % matrix containing strain components
index=zeros(edof,1); % index vector
kinmtx2=zeros(3,edof); % kinematic matrix
matmtx=zeros(3,3); % constitutive matrix
%----------------------------
% force vector
%----------------------------
ff(34)=500; % force applied at node 17 in y-axis
ff(36)=500; % force applied at node 18 in y-axis
%-----------------------------------------------------------------
% computation of element matrices and vectors and their assembly
%-----------------------------------------------------------------
[point2,weight2]=feglqd2(nglx,ngly); % sampling points & weights
matmtx=fematiso(1,emodule,poisson); % compute constitutive matrix
for iel=1:nel % loop for the total number of elements
for i=1:nnel
nd(i)=nodes(iel,i); % extract connected node for (iel)-th element
xcoord(i)=gcoord(nd(i),1); % extract x value of the node
ycoord(i)=gcoord(nd(i),2); % extract y value of the node
end
k=zeros(edof,edof); % initialization of element matrix to zero
%--------------------------------
% numerical integration
%--------------------------------
for intx=1:nglx
x=point2(intx,1); % sampling point in x-axis
wtx=weight2(intx,1); % weight in x-axis
for inty=1:ngly
y=point2(inty,2); % sampling point in y-axis
wty=weight2(inty,2) ; % weight in y-axis
[shape,dhdr,dhds]=feisoq4(x,y); % compute shape functions and
% derivatives at sampling point
jacob2=fejacob2(nnel,dhdr,dhds,xcoord,ycoord); % compute Jacobian
detjacob=det(jacob2); % determinant of Jacobian
invjacob=inv(jacob2); % inverse of Jacobian matrix
[dhdx,dhdy]=federiv2(nnel,dhdr,dhds,invjacob); % derivatives w.r.t.
% physical coordinate
kinmtx2=fekine2d(nnel,dhdx,dhdy); % compute kinematic matrix
%------------------------------
% compute element matrix
%------------------------------
k=k+kinmtx2'*matmtx*kinmtx2*wtx*wty*detjacob; % element matrix
end
end % end of numerical integration loop
index=feeldof(nd,nnel,ndof);% extract system dofs associated with element
kk=feasmbl1(kk,k,index); % assemble element matrices
end
%-----------------------------
% apply boundary conditions
%-----------------------------
[kk,ff]=feaplyc2(kk,ff,bcdof,bcval);
%----------------------------
% solve the matrix equation
%----------------------------
disp=kk\ff;
num=1:1:sdof;
displace=[num' disp] % print nodal displacements
%---------------------------------------
% element stress computation
%---------------------------------------
for ielp=1:nel % loop for the total number of elements
for i=1:nnel
nd(i)=nodes(ielp,i); % extract connected node for (iel)-th element
xcoord(i)=gcoord(nd(i),1); % extract x value of the node
ycoord(i)=gcoord(nd(i),2); % extract y value of the node
end
%--------------------------------
% numerical integration
%--------------------------------
intp=0;
for intx=1:nglx
x=point2(intx,1); % sampling point in x-axis
wtx=weight2(intx,1); % weight in x-axis
for inty=1:ngly
y=point2(inty,2); % sampling point in y-axis
wty=weight2(inty,2) ; % weight in y-axis
intp=intp+1;
[shape,dhdr,dhds]=feisoq4(x,y); % compute shape functions and
% derivatives at sampling point
jacob2=fejacob2(nnel,dhdr,dhds,xcoord,ycoord); % compute Jacobian
detjacob=det(jacob2); % determinant of Jacobian
invjacob=inv(jacob2); % inverse of Jacobian matrix
[dhdx,dhdy]=federiv2(nnel,dhdr,dhds,invjacob); % derivatives w.r.t.
% physical coordinate
kinmtx2=fekine2d(nnel,dhdx,dhdy); % kinematic matrix
index=feeldof(nd,nnel,ndof);% extract system dofs for the element
%-------------------------------------------------------
% extract element displacement vector
%-------------------------------------------------------
for i=1:edof
eldisp(i)=disp(index(i));
end
kinmtx2=fekine2d(nnel,dhdx,dhdy); % compute kinematic matrix
estrain=kinmtx2*eldisp; % compute strains
estress=matmtx*estrain; % compute stresses
for i=1:3
strain(intp,i)=estrain(i); % store for each element
stress(intp,i)=estress(i); % store for each element
end
location=[ielp,intx,inty] % print location for stress
stress(intp,:) % print stress values
end
end % end of integration loop
end
%---------------------------------------------------------------