Softening Behavior in Drucker Prager Concrete Model

Hi,

I am trying to model "push" of a layered masonry wall. After meddling with SOLID65 for a long time, I moved to SOLID185. With DP Concrete model, I have gained results that match closely with the experimental results (I am satisfied!). I have been trying to get displacement vs. Base Shear during the push, and have succeeded in doing so. I believe that DP Concrete does a good job on that regard.

However, I now want to incorporate softening behavior into the model (I am trying to use linear HSD model: HSD6). The base shear should go down after about 75 mm. However, after using the softening parameters, the solution doesn't go beyond the linear limit. Here's what I got:

I will be happy to get just the cutoff point (the ultimate displacement). Maybe, someone can point on what I am doing wrong, and point me in the right direction. As always, your help is highly appreciated.

Thanks in advance.

P.S: I have attached the input file for Mechanical APDL.

 

 

Comments

  • MirghaniMirghani Posts: 27Member
    edited February 2019

     

    Hi Sujitbhandrai,

    If you are using SOLID185 with DP concrete model, then you are using what's called a Micro-plane model.

    There are 2 ways of inputting the micro-plain model, as the Release Notes explain for the Version 19:

    "The micro-plane material model is now available in two forms: an elastic micro-plane model with damage, and a new coupled damage-plasticity micro-plane model."

    I think you need to go for the 2nd option (coupled damage-plasticity micro-plane model with CPT215)

    •  A) The Elastic Micro-plane model with damage is supported by the element Solid185. A snippet example

    ET,MATID,185                      ! Define elements as SOLID185

    MP,EX,MATID,29100           ! Define Elasticity Modulus

    MP,NUXY,MATID,0.2           ! Define Poisson's ratio     

    TB,MPLANE,MATID,,6         ! Define the microplane model parameters

    tbdata,1,0.75,0.75,0.208,6.109e-05,0.512,98    !k0,k1,k2,α_mic, β_mic, beta_mic

     

    • B) The Coupled Damage-plasticity Micro-plane model is supported by the element CPT215. This model was presented on the paper by Zreid and Kaliske (2014, 2016, 2018)

    (Link to the 2018 paper: https://dl.acm.org/citation.cfm?id=3296167)

     

    A snippet example

     

    ! Material Properties

    ET,1,215         ! Define elements as CPT215 (Coupled damage plasticity) (Change Number 1 with Matid (material ID) if using workbench)

    KEYO,1,18,2  ! Activate extra degrees of freedom

     

    ! Parameter values

    E = 40300

    nu = 0.2

    dens = 2.4e-09

    fuc = 36.5 

    fbc = 41.975

    fut = 2.56

    Rt = 1    

    D = 4e4

    sigVc = -40  

    R = 2   

    c = 1500    

    m = 2.5  

    gamt0 = 0 

    gamc0 = 2e-6 

    betat = .4e4

    betac = .25e4

     

    ! Define elastic properties of material

    MP,EX,1,E                 ! Define Elasticity Modulus (enter a value for E)- (Change Number 1 with Matid (material ID) if using workbench)

    MP,NUXY,1,nu           ! Define Poisson's ratio     

    MP,DENS,1,dens       ! Define material Density     

     

    ! Define microplane model properties

    TB,MPLA,1,,,DPC                                 ! Define Drunker-Prager

    TBDATA,1,fuc,fbc,fut,Rt,D,sigVc

    TBDATA,7,R,gamt0,gamc0,betat,betac

     

    TB,MPLA,1,,,NLOCAL

    TBDATA,1,c,m

     

  • sujitbhandarisujitbhandari Posts: 26Member
    edited February 2019

    Hi Mirghani,

    Thanks for your response. Your suggestions are highly appreciated.

    However, I am under the impression that Drucker-Prager Concrete and Microplane models are different models. DP Concrete falls under Geomechanics (microscopic behavior, while MP model uses the Drucker-Prager Cap model that is similar, but not identical to the macroscopic Extended Drucker-Prager Cap model.

    The results that I have got from DP Concrete model are quite good compared to the experimental results. Microplane model has too many parameters, which are hard to obtain for masonry which I am modeling. And, I haven't used that model. So, I am a bit skeptical about using that model. However, as I am familiar with the DP model, and the parameters for DP Concrete are easily obtainable, I want to stick to that model. I just want to introduce Hardening, Softening, and Dilatation(HSD) behavior to the model, but unfortunately, am unable to do so.

    So, I am in need of help from someone who might have used the model in the past. Your suggestions are really appreciated.

    Once again, thanks Mirghani for your response. Cheers!

    -Sujit

  • sujitbhandarisujitbhandari Posts: 26Member
    edited February 2019

    Hi,

    Just another question: If I want the material to sustain damage (have no or very less force taking capability) after reaching a certain strain value. I haven't modeled that before. May someone guide in that regard?

  • sujitbhandarisujitbhandari Posts: 26Member
    edited February 2019

    Hi there,

    I don't just know what did I do wrong in defining the softening parameters for material to use with Drucker-Prager Concrete model. Please, suggest me on this regard. The solution doesn't converge after invoking HSD parameters.

    kcm_out = 0.075 !Plastic Strain at uniaxial compressive strength

    kcr_out = kcm_out*2 !Ultimate Effective plastic strain in compression

    om_ci_out = 0 !Relative stress at onset of nonlinear hardening

    om_cr_out = 0.2 !Residual compressive relative stress

    ktr_out = kcm_out*fct_out/fck_out !Plastic Strain limit in tension

    om_tr_out = 0.2 !Residual tensile relative stress

     

    TB,CONCR,1,,,HSD6

    TBDATA,1,kcm_out,kcr_out,om_ci_out,om_cr_out,ktr_out,om_tr_out

     

    Your help is really appreciated. Thanks in advance.

  • antonyonyantonyony Posts: 4Member
    edited October 2019

    Sujit,

    Have you been able to find a solution to your problem?

    When I invoke the HSD parameters it keeps going down with the same error:

    The material solution failed for element X with material 2 (that is the number I use for concrete). 

    Thank you in advance. 

  • RubisRubis Posts: 2Member
    edited December 2019

    Hi everyone,

    I'm facing the same problem trying to implement the DP concrete model with HSD behaviour.

    The solution doesn´t converge when reaches the softening part of the yield function (due to the transition to a negative slope).

    Any hints already to try to solve this problem?

  • vaibhavtaranekarvaibhavtaranekar Posts: 66Member
    edited December 2019

    Hi everyone,

    I'm facing the same problem trying to implement the DP concrete model with HSD behaviour.

    The solution doesn´t converge when reaches the softening part of the yield function (due to the transition to a negative slope).

    Any hints already to try to solve this problem?

    Hi, can you provide me commands for DP concrete? I need them for my cyclic behaviour tests.

    thanks!

  • RubisRubis Posts: 2Member
    edited December 2019
    An example from Ansys Help:

    /prep7
    ! ELASTIC CONSTANTS
    MP,EX,1,20.0E9
    MP,NUXY,1,0.2

    ! Base Drucker-Prager concrete
    Rc=30.0E6 ! uniaxial compressive strength
    Rt=3.0E6 ! uniaxial tensile strength
    Rb=36.0E6 ! biaxial compressive strength

    delta_t=0.25 ! dilatancy factor tension
    delta_c=1.0 ! dilatancy factor compression

    ! Linear hardening/softening
    kappa_cm=0.0025-Rc/20.0E9
    kappa_cr=0.0025
    omega_ci=0.33
    omega_cr=0.1

    kappa_tr=0.0005
    omega_tr=0.2

    TB,CONCR,1,,,DP
    TBDATA,1,Rc,Rt,Rb

    TB,CONCR,1,,,DILA
    TBDATA,1,delta_t,delta_c

    TB,CONCR,1,,,HSD6
    TBDATA,1,kappa_cm,kappa_cr,omega_ci,omega_cr,kappa_tr,omega_tr
  • vaibhavtaranekarvaibhavtaranekar Posts: 66Member
    edited December 2019

    Thank you for your reponse. Have you tried the coupled plasticity damage model yet? i am having trouble using it.

  • Diegoandree1311Diegoandree1311 Posts: 15Member
    edited January 2020

    hello and greetings to all, I have a question, when I define the Micro plane commands, in that command is the fault criterion already entered? or it is something that I must introduce, because in the literature of that command, they only introduce what Mr. Mirghani,

    for example, for my slab model I entered the command:

     

    ! Data Element Type

    ET, 1, SOLID185

     

     

    ! Data Material Properties

    MP, EX, 1,13500

    MP, NUXY, 1, 0.2

     

     

    ! Data Input Non Metal Plasticity-Concrete

    TB, MPLAN, 1,1,6

    TBDATA, 1,0,784,0,784.0.123.5.33e-5,0.7,30

     

    ! Data Input Stress-Strain Non Linear - Multilinier Kinematic Hardening (Model Kent-Park Unconfined)

    TB, KINH, 1,1,5

    TBPT, DEFI, 0.0001.1.35

    TBPT, DEFI, 0.0005.6.04

    TBPT, DEFI, 0.001.10.35

    TBPT, DEFI, 0.0015.12.94

    TBPT, DEFI, 0.002.13.8

     

     

     

    As you can see, I feel that things are missing, such as stress and compression limits, I also don't know if it is necessary to enter the stress versus strain data.

    These are questions that I ask myself because, for example, I used the solid65 with the CONCR model before and there if the effort limits were annexed, while in the microplane no ... thank you very much in advance.

  • b0274b0274 Posts: 7Member
    edited February 2020

    sujitbhandari

    Hi!

    Did you solve your problem?

    I´m modeling masonry walls with Solid65 with Drucker-Prager Concrete Model and maybe we can help each other.

    Do you think that Solid185 is better than Solid65?

    I´m combining DP with WW model.

     

  • shw419shw419 Posts: 7Member
    edited June 2020

    Hi, all. 

    I am trying to study plastic model for reinforced concrete under thermal effect and I am trying Solid 65 as well. 

    Does anyone know how I can define different stress-strain relationship at different temperature?

Sign In or Register to comment.