How composite stress in OptiStruct compute? What is the equation behind it?

Paphatsorn
Paphatsorn Altair Community Member
edited March 2022 in Community Q&A

I am working on free-size optimization in OptiStruct with composite material. And I use composite stress as one of my responses and I have to constraint it to have a safety factor more than 1.5. So, I would like to know how OptiStruct compute the composite stress to find the allowable composite stress that I allow it to occur with my model and will set this value as a upper bound of my constraint.

Is it calculate from longitudinal tensile strength, longitudinal compressive strength, transverse tensile strength and transverse compressive strength?

 

image

Thank you in advance.

I tried to find the equation in Help, but it did not work out. 

Tagged:

Answers

  • Adriano_Koga
    Adriano_Koga
    Altair Employee
    edited March 2022

    You need to define that from the list.

    Once you select the composite property, it will show you the options.

    Ply stresses are computed using regular Classic Lamination Theory.

    image

  • Paphatsorn
    Paphatsorn Altair Community Member
    edited March 2022

    Hello,sir. Thank you so much for your kindly help. But I still do not know how to deal with it. Could you please specify the equation that I can compute the composite strength in Major principal. I've find some information about the CLT but i still confuse how can I calculate the composite stress (Composite strength) 

    nwp.engr.udel.edu/ccm/CDS/index.html?ThinPlateClassicalLaminateModel This is the website that I read.

    (If you deal with isotropic material such as Steel, we can compute the allowable stress that can occur with our work using its yield strength and then divided by the value of Safety factor, then we will get the value of allowable stress that can occur.

    But when it change to composite material, how can I find the value of composite strength.) **In case that you are not clearly understand my point. 

     

  • Adriano_Koga
    Adriano_Koga
    Altair Employee
    edited March 2022
    Paphatsorn said:

    Hello,sir. Thank you so much for your kindly help. But I still do not know how to deal with it. Could you please specify the equation that I can compute the composite strength in Major principal. I've find some information about the CLT but i still confuse how can I calculate the composite stress (Composite strength) 

    nwp.engr.udel.edu/ccm/CDS/index.html?ThinPlateClassicalLaminateModel This is the website that I read.

    (If you deal with isotropic material such as Steel, we can compute the allowable stress that can occur with our work using its yield strength and then divided by the value of Safety factor, then we will get the value of allowable stress that can occur.

    But when it change to composite material, how can I find the value of composite strength.) **In case that you are not clearly understand my point. 

     

    Please, take a look at this ebook:

    Hopefully it will get more clear to you.

    https://community.altair.com/community?id=kb_article&sys_id=aaf078c11bd478d0c4dfdbd9dc4bcb03

     

    Composites have different failure prediction model when it comes to the laminate itself.

    But essentially you will have a maximum stress/strain for the composite too, and it depends on your material (matrix and fiber).

    just an example here:

    http://www.performance-composites.com/carbonfibre/mechanicalproperties_2.asp

     

    this is an input data, coming from your material supplier, or test, as any other material used in FEA.

    Have in mind that composites have different strength according to the fiber orientation, so you need to take special care with this, as well.

Categories