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Result of FEA does not change, on changing the Material properties with same load

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Rajbir Singh
Rajbir Singh on 16 Jul 2019
Commented: infinity on 17 Jul 2019
I have written a code for structural analysis of block with a hole at centre as shown below. The problem arises when i change the material properties (Young's Modulus, Density, Poison Ratio) while keeping the force same, result does not chnge.
STL file has been attached with this question.
clear all;
model = createpde('structural','static-solid');
importGeometry(model,'block1.stl');
figure
pdegplot(model,'FaceLabels','on')
rotate3d on
force = 200;
YM = 2e11;
PR = 0.3;
Mass_Density = 7850;
Mesh_Size = 0.8;
structuralProperties(model,'YoungsModulus',YM,'PoissonsRatio',PR,'MassDensity',Mass_Density);
structuralBC(model,'Face',11,'Constraint','Fixed');
structuralBoundaryLoad(model,'face',9,'SurfaceTraction',[0,force,0]);
generateMesh(model,'Hmax',Mesh_Size,'Hmin',Mesh_Size,'GeometricOrder','Quadratic');
figure
pdeplot3D(model)
rotate3d on
result = solve(model);
figure
pdeplot3D(model,'ColorMapData',result.VonMisesStress)
title('Von Mises stress: Static Analysis')
rotate3d on
maxx = max(result.VonMisesStress);
minn = min(result.VonMisesStress);

  2 Comments

KSSV
KSSV on 16 Jul 2019
May be you need to have a look on the boundary conditions.....are you sure the boundary conditions applied are correct?

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Accepted Answer

infinity
infinity on 16 Jul 2019
Edited: infinity on 16 Jul 2019
Hello,
I have run your code, results were not constants when parameters had changed.
For example, if you set "PR" (poisson ratio) to be 0.4, the results of von misses stress are different in comparision with PR = 0.3.
Max and min of von misses stress do not change in case of variety of young modulus. But, the displacement is changed.
If you extract the maximum of displacement, you could see this.
max(result.Displacement.uz)
It is seen that the displacment (at least in z direction) depend linearly on young modulus. For example,
for YM = 2e5, max(result.Displacement.uz) = 4.7362e-03
for YM = 2e9, max(result.Displacement.uz) = 4.7362e-07
for YM = 2e11, max(result.Displacement.uz) = 4.7362e-09
Maybe the von misses stress is normalized, so that we could not see the change of von misses stress when YM changes.

  2 Comments

Rajbir Singh
Rajbir Singh on 16 Jul 2019
Thank you Mr. Trung, it helped me.
I have one more question that what is the unit of mesh size that we use to generate mesh ? Or is depends upon the STL file units that we import ?
infinity
infinity on 17 Jul 2019
Hello,
You are wellcome.
I have checked the difference between various mesh size. It shown that when the mesh size changes, number of elements and nodes also varies. For example,
for Mesh_Size = 0.8;
size(model.Mesh.Elements)
size(model.Mesh.Node
is biger than for Mesh_Size = 0.9;
Therefore, the answer is yes.

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