bending/shift of neutral axis/nonlinear simulation
bending/shift of neutral axis/nonlinear simulation
(OP)
Hello,
I am trying to simulate bending of a composite.
My compression strengths and tension strengths are different in all directions.
My question is: when I start applying the displacement (or load) during experiment, the contact point is under compression and at this point, my material behaves differently compared to tension region (down side of the composite) due to different stress-strain behavior under tension and compression.
As a result, I assume that my neutral axis is displaced. I am wondering what is the best way to simulate this? What should I take care of?
I would really appreciate any help.
I am trying to simulate bending of a composite.
My compression strengths and tension strengths are different in all directions.
My question is: when I start applying the displacement (or load) during experiment, the contact point is under compression and at this point, my material behaves differently compared to tension region (down side of the composite) due to different stress-strain behavior under tension and compression.
As a result, I assume that my neutral axis is displaced. I am wondering what is the best way to simulate this? What should I take care of?
I would really appreciate any help.
Best Regards,
Sartor





RE: bending/shift of neutral axis/nonlinear simulation
You mentioned different "strengths" in tension and compression and also different "stress-strain behavior", which means different stiffness. The strength in many applications is modeled using a material failure condition. Having different stiffness in tension and compression is easy for 1D elements, harder but doable in 2D and 3D.
Nagi Elabbasi
Veryst Engineering
RE: bending/shift of neutral axis/nonlinear simulation
maybe you mean that fty and fcy are different ?
RE: bending/shift of neutral axis/nonlinear simulation
rb1957, I have defined a stress strain curve (NA).
Best Regards,
Sartor
RE: bending/shift of neutral axis/nonlinear simulation
RE: bending/shift of neutral axis/nonlinear simulation
When I simulate bending on an element(different geometry than a normal bending coupon), I have maximum principal at bottom (due to tension) and minimum principal at top (due to compression), which is also the case for normal bending coupon.
However, I have different values for Max (60 MPa) and Min (-100MPa) principal. I am trying to understand why it is like this.
At first, I thought that this might be due to the displacement of neutral axis. I have different tension and compression behavior but I do not have any input for my compression!
When I simulate bending with a bending bending coupon, as elabasi suggested, fe-code is capable of arranging it, and simulation results are the same as my experiments.
Do you have any idea why min. principal is higher than max. principal?
Best Regards,
Sartor
RE: bending/shift of neutral axis/nonlinear simulation
a sketch would help.
is there any axial load, in the FEA or in the real world ??
RE: bending/shift of neutral axis/nonlinear simulation
Imagine a normal bending case, bottom surface is under tension, and top surface (where I apply the dsplacement)is under compression.
Normal X is almost same as Max Principal.
I am just applying a displacement!
I attached an excel graph, here you can see for the distance 0, i have almost two times higher minimum principal stress than maximum principal.
I am trying to understand why that is like this.
again: Max principal is located at the bottom
Min principla is located at the top (where displacement is introduced during the test)
Best Regards,
Sartor
RE: bending/shift of neutral axis/nonlinear simulation
in a rectangular beam in pure bending the upper and lower fibers have the same magnitude stress 'cause the areas they act on are the same.
if your beam has a tapering x-section (like a trapezoid) then the NA will be lower on the section (closer to the fat end) and the stresses on the fat end will be lower than on the narrow end (bigger area, lower stress = the same load as smaller area, bigger stress, therefore only a couple is produced by the internal stresses).
RE: bending/shift of neutral axis/nonlinear simulation
Thank you very much for your patience rb1957.
Best Regards,
Sartor