Elastic Plastic Analysis

[john84]

I am working on elastic plastic analysis of a composite material unit cell and would like to obtain a stress strain curve. I have defined true stress strain curve for matrix when defining the plastic properties. I am applying a pressure loading. How do I obtain a stress strain curve of the composite material?

1. From the field output do I have to get the reaction forces divided by the area on which pressure load acts?

2. The strain would be displacement divided by the original length and then do I have to use the combine (x,y) function?

Is this the procedure or do I have to use something else.

Thanks in advance.

 

[ESPcomposites]

I would think you could just apply the max load, it would have a value of 1.0 in the nonlinear run. All the steps below that would be scalable. Then just collect the deflection (and convert) or strain at each step.

Alternatively, you would apply a displacement instead of a pressure, which might give you better control of the behavior.

Is there any practical use to this exercise or this is just for research or academic purpose?

Brian

http://www.espcomposites.com

 

[Odforu]

Thanks Brian for your comments. This is just for research/academic purpose. If I apply displacement then the procedure for obtaining the stress strain curve of 3D composite would be still the same (Stress = reaction force/area)(strain = displacement/original length) or do I use something else??

 

[ESPcomposites]

I think so. Any effect due to Poisson's ratio, etc. would be addressed by those terms.

I would suggest you start with an isotropic material and prove that your method yields the correct result. There can be subtle, but important, differences depending on the boundary conditions. Provided the isotropic solution is appropriate, you could then use the same procedure for the composite material.

Brian

http://www.espcomposites.com

 

[john84]

Brian,

I also would like to clarify a stupid question, since I have two materials to form a composite, do I have to insert the plasticity data of the fibers (Since fibers are brittle and their stress strain curve would be a straight line, mostly brittle materials are defined by their ultimate tensile values). If yes how do I do that since in abaqus while defining plasticity true values of yield stress and plastic strain are required? (Brittle materials like fibers do not have a yield point)?

Thanks in advance.

 

[ESPcomposites]

For this problem, the fiber should be brittle, making it a moot point.

*Side note (does not affect your problem): Though people often call general composites brittle, they are not. In other words, using the peak stress concentration for failure analysis is not always correct. Just want to mention that because there is a lot of misinformation in that regard.

Brian

http://www.espcomposites.com

 

[john84]

Brian,

Thanks for your valuable comments, you referred to applying max load, how do I scale the max load,is it that the load at yield point from the true stress strain curve of the matrix material is the max load, or its the UTS? Coz while performing a nonlinear analysis yield stress and plastic strain data are included. I also have fibers with matrix, so I was just wondering how do I proceed?Right now I am just applying the load corresponding to the yield( yield stress and plastic strain data) of matrix. Correct me if I am wrong anywhere.

Thanks in advance.