# plot strain ellipse and principal stress axes using eigenvalues and eigevectors.

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Hello,

I am trying to plot strain ellipses and principle stress axes (longest and shortest axes of the ellipse) on a grid (x_new,y_new) according to followig instructions. I would be really greatful if someone could help me complete this code.

Thank you.

x = -333.6:5:831.4; %(1x234)

y = 0:5:500; %(1x101)

[xx, yy] = meshgrid(x, y);

dx = 5;

dy = 5;

u = flow values of each grid node in x direction.

v = flow values of each grid node in y direction.

%% Plot Principle axes

pick the 4, center most u and v values. Using this 4 grid nodes u and v values we can compute ux, uy, vx, and vy values for the center point.

then using computed ux,uy, vx, vy values, ( e.g. ux=(u1+u2/dx) )

strain_tensor = [ux uy; vx vy];

[V,D]=eig(strain_tensor);

Now I want to use this eigenvalues and eigenvectors to plot strain ellipeses at the center of each four grid nodes along with quiver arrows inside the ellipses.

##### 2 Comments

Matt J
on 8 Dec 2023

### Answers (1)

Matt J
on 8 Dec 2023

a=10; %long axis

b=3; %short axis

theta=30; %rotation angle

p=rotate( scale(nsidedpoly(1000),[a,b]) ,theta);

plot(p)

##### 4 Comments

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