ramdas chennamsetti's blog

Hi all!!!

General theories of failure of laminated composites are Tsai-Hu, Tsai-Hill, Maximum stress and maximum strain. These thoeries do not specify which component (fiber or matrix) of lamina fails.

Sigma_zz, sigma_xz and sigma_yz are out of plane stresses which cause delamination failure of laminated composite structures.

I am looking for exclusive theories of failure which govern delamination failure in laminated composites. I request those who work in this area to help.

Thanx in advance,

Regards,

- Ramdas

Hi all,

I have a fundamental question on Tensors. The length of a vector (firts order tensor) is independent of the reference co-ordinate system. In case of second order tensor (stress/strain), the invariants (I1, I2, I3) are independent of the co-ordinate system.

If I consider 4th order tensor (of course 3rd order also), say Cijkl, what parameters are constant? (Like length in vector and invariants in second order tensors).

Thanks in advance,

- Ramdas

Hi all!!!

I have a very basic question in Fracture Mechanics. The question is as following.

"Stree Intensity Factor (SIF) is more in plane stress problems (plasic zone size is big) than in plane strain problems (plasic zone size is small). How do we explain this, without refering or invoking energy conecpt?"

I request to give some thoughtful explanation.

With regards,

- Ramdas

Hi all!

In theories of failure (e.g von-Mises, Tresca, Max. principal stress etc), yield funcion,          f(sigma ij, Y) = 0 is plotted in principal stress space (sigma 1, sigma2 and sigma 3). Why shouldn't we express the same yield function, f(epsilon ij, epsilon Y) = 0 and plot in principal strain space?

Y = Yiled stress, sigma ij = stress ij, epsilon ij = strain ij. and espsilon Y = Yield strain = Y/E,   E = Young's modulus

Any thoughtful comments???

With regards,

- Ramdas

Hi all!

I read that the "cmplementary starin energy of a structure is not equal to sum of the complementary strain energies of it's components, if there is non-linearity like geometric"

That means for e.g. if I consider a truss stucture subjected to loading so that it undergoes geometric non-linearity, then the sum of the complementary strain energies from members is not equal to complementary strain energy of the structure.

 I request somebody to explain why is it so??

 Thanks and regards,

- Ramdas

Hi all!

I have a very fundamental question as follwing.

In Nonlinear FE formulations, we use rate equations (virtual work), but, in linear FE we don't use rate equations. Why???

Is it because Nonlinear solution is iterative solution (time may be virtual time).

I request those who have an idea to give some explanations.

Thanks in advance,

Regards,

- Ramdas