Hello I have a homework question about lamina failure My lam

Hello, I have a homework question about lamina failure. My lamina is subjected to global strains at angle 45 and Im supposed to look for global strains failure according to the max stress failure theory.

I tried the following :

1-Find local strains from global strains

2-Find local stress from local strains

3-From the sign stress has, I choose between the tensile and compressive strength for my lamina.

4-The new local stress is basically the three values of the strengths.

5-I look for the local strains with those new local stresses.

6-I loove for the global strains from the local strains.

Basically, I end up with value for shear strain whereas I started with just x-strain and y-strain.

I also don\'t understand the logic behind going through the global strains during the first part. Why can\'t I just compute my global strains at failure from local stresses when THOSE equal to the strength values?

Thanks

Solution

Grobal strains are measured by device called strain gauges , after getting this experimental values at definate angles we can easily calculate force and related parameters like stress and and displacements by formula .

step 1 . find local strain from global strain .

step 2 . find normal stress from normal strain.

step 3 . find shear stress and stress at any angles .

lamina under pure shear condition . it can be equal to strength values