GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Skip to content. Permalink Dismiss Join GitHub today GitHub is home to over 40 million developers working together to host and review code, manage projects, and build software together. Sign up. Branch: master. Find file Copy path.

Cannot retrieve contributors at this time. Raw Blame History. INC '! This means that, by default, any variables with! The rest are integers. Note that this also means that if you type a variable! Jacobian matrix of the constitutive model. Unless you invoke the unsymmetric equation solution capability! The symmetric part of the matrix! This array is passed in as the stress tensor at the beginning!

If you specified! In finite-strain problems the stress tensor! An array containing the solution-dependent state variables. These are passed in as the values at the beginning of the! In all cases! The size of the array is defined as described in!The stress-strain behaviour of viscous soils is rate-dependent. Specifically, Two important engineering parameters, i.

**Abaqus Utility: Modeling Elastic Plastic material Behavior**

This report first reviews the theoretical background the EVP constitutive model. The next section introduces the numerical solution algorithm adopted in the subroutine. The following section illustrates how to determine the input parameters according the given viscous soil.

Finally, the appendix of this report provides a series of verification numerical tests in a format of ABAQUS Benchmark problem and evaluates the obtained numerical results in reference to the corresponding theoretical solution. Benchmark problem 4 â€” CID Drained compression tests at various strain rates.

This user-defined subroutine is now free to download for research purposes. E-mail: guangfengqu hotmail. The links you provided in this post do not work, could you please fix this?

Thank you so much. The detailed flow chart was recorded in the note. Main program: a Plastic potential dilation based on M,i. Main Pragram: Rewrite codes to call this Sub. Correct the part obtaining Overstress. Add a check when the mean stress became negative in the main program.

Swith to address the geostatic step problem. TIME 2. Debug by Qu Nov. GO TO ! The sqrt 2J2 on the M-line corresponding to mean stress. When Stress on or very close to the M line. The stress is not on M-line. IF SR2J2. The stress lies Below the Critical State Line!!!

## UMAT for rigid-plastic model?

Not use so far. C C HN I IF PC. QU Nov. R2J2SY: 2J2 of the static yield surface top.Specify elastic material properties. This option is used to define linear elastic moduli. Type Model data. Level Model. The use of a factor that is different from 1. Set this parameter equal to the number of field variable dependencies included in the definition of the moduli.

If this parameter is omitted, it is assumed that the moduli are constant or depend only on temperature. See Material data definition for more information.

See Distribution definition. Any data lines given will be ignored. See Translating Moldflow data to Abaqus input files for more information. When using a distribution to define elastic moduli, the TYPE parameter must be used to indicate the level of anisotropy in the elastic behavior. The level of anisotropy must be consistent with that defined in the distribution.

D Repeat this set of data lines as often as necessary to define the elastic behavior as a function of temperature and other predefined field variables. This shear modulus is needed to define transverse shear behavior in shells. Shear modulus, G. Repeat this set of data lines as often as necessary to define the elastic shear modulus as a function of temperature and other predefined field variables. Distribution name.

The data defined in the distribution must be in units that are consistent with the prescribed TYPE.

### Automatic Generation of User Material Subroutines for Biomechanical Growth Analysis

Second line D Third line D First field variable. Second field variable. Second line G Related Topics. Linear elastic behavior.Specify a metal plasticity model. This option is used to specify the plastic part of the material model for elastic-plastic materials that use the Mises or Hill yield surface. Type Model data. Level Model. Set this parameter equal to the factor by which you want the yield stress to be scaled.

Set this parameter equal to the number of field variable dependencies included in the definition of hardening behavior, in addition to temperature and possibly strain range. If this parameter is omitted, the hardening behavior does not depend on field variables. See Material data definition for more information. Set this parameter equal to the number of backstresses.

The default number of backstresses is 1, and the maximum allowed is Repeat this set of data lines as often as necessary to define the dependence of yield stress on plastic strain and, if needed, on temperature and other predefined field variables. Repeat this set of data lines as often as necessary to define the dependence of yield stress on plastic strain and, if needed, on strain range, temperature, and other predefined field variables.

### General Questions Hypoplastic Umat on Abaqus

Kinematic hardening parameter, C 1. Repeat this data line a maximum of two times to define linear kinematic hardening independent of temperature. Repeat this set of data lines as often as necessary to define a variation of the linear kinematic hardening modulus with respect to temperature. Plastic strain. First field variable. Second field variable. Strain range. Subsequent lines only needed if the number of entries is greater than eight Etc.

Temperature, if temperature dependent. Repeat this data line as often as necessary to define all hardening properties. Related Topics. Classical metal plasticity. Models for metals subjected to cyclic loading. Johnson-Cook plasticity. Permanent set in rubberlike materials.Abaqus Users.

Search everywhere only in this topic. Advanced Search. Classic List Threaded. How to define Elasto-Plastic material property Hi; I am facing a little difficulty in defining the elasto-plastic material property in abaqus. The model is bilinear kinematic hardening model, in which i need to define the yield stress and tangent modulus slope of the plastic region. I dont have the value of plastic strain. My other qs is how to define the elastic-perfectly plastic material property in abaqus.

Thanks in advance Regards Jawad Qarni. Alankar Alankar. Re: How to define Elasto-Plastic material property UMAT is a high end subroutine and is not straight forward to implement. UHARD is a simple subroutine and can be used to implement simple models like power law hardening. RE: How to define Elasto-Plastic material property Do make sure that you cover the entire plastic strain range expected.

Otherwise abaqus would assume perfect-plasticity beyond the last point. Dave Lindeman. Dear Mr. Lindeman Many thanx for the elastic-perfectly plastic model. Sir can u plz be a little more specific about the bilinear kinematic hardening.

For example here are some of the date values i have Once again thanx Re: Re: How to define Elasto-Plastic material property Dear Sir; Thanks a lot for the technical support I have been able to successfully implement this technique and also generated the graph for verification which seems to be ok.

Sir can u plz. Ibekwe Achinike.After successfully testing a linear elastic Umat on Abaqus, I am now trying to test the Hypoplastic model Umat. I intend to carry out a drained triaxial single element tests and reproduce the results from Dr. Masin PhD [ table 4. Are there other simple test results for me to back analyse to check whether I am using the UMAT correctly? Is parameter 18 responsible for whether a 2D or 3D analysis is being perfomed? Dear Hashmi, â€” To check, you can run equivalent tests in soilmodels.

The same model is used in 2D and 3D, nothing special is specified. Regards David. Thank you for these information. Can you please also advise on the following: 1.

Thank you for confirming that nothing has to be input in the Hypoplastic Clay UMAT for it to be compatible with a specific type of analysis 2D or 3D, stress or strain controlled or type of elements.

In the guide that I have, it mentioned to set parameter 18 to 2 in PLaxis 2D and thus I wrongly inferred that it relates to whether the analysis is 2D or 3D.

As you said, it is only indicating where vertical is in the model. No, you can select Ciup undrained or Cid drained 2. I wanted to try to compare the prediction q vs ea and ev vs ea of a drained single element test using the MCC model and basic hypoplasticity. Are there empirical equations that link lamda to lamda-star and the same for kappa? As there is this ambiguity, transformations are not provided in the software, you need to work it out yourself in a spreadhseet. Thank you for the advices.

I understand, it wants initial void ratio as parameter. Hi Hasmi â€” inic. For a particular model, run any input file with this model and you can read required order of state variables on the screen. You must be logged in to post a comment. Email address:.

Toggle navigation. General Questions Hypoplastic Umat on Abaqus. Hashmi Sohawon Hi all, After successfully testing a linear elastic Umat on Abaqus, I am now trying to test the Hypoplastic model Umat. Thank you and looking forward to hear useful responses. Share this. Related Articles. Hello all, i have another question regarding the calibration process. Why do the initial void ratios differ between the input file and the output from excalibre? What is done during [â€¦].Louis, MOTel:Fax: The analysis of the biomechanics of growth and remodeling in soft tissues requires the formulation of specialized pseudoelastic constitutive relations.

The nonlinear finite element analysis FEA package Abaqus allows the user to implement such specialized material responses through the coding of a user material subroutine called UMAT. However, hand coding UMAT subroutines is a challenge even for simple pseudoelastic materials and requires substantial time to debug and test the code. To resolve this issue, we develop an automatic UMAT code generation procedure for pseudoelastic materials using the symbolic mathematics package Mathematicaand extend the UMAT generator to include continuum growth.

The performance of the automatically coded UMAT is tested by simulating the stressâ€”stretch response of a material defined by a Fung-Orthotropic strain energy function, subject to uniaxial stretching, equibiaxial stretching, and simple shear in Abaqus.

In turn, the UMAT accurately simulates the pseudoelastic response. In order to test the growth UMAT we simulate the growth-based bending of a bilayered bar with differing fiber directions in a non-growing passive layer.

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The anisotropic passive layer, being topologically tied to the growing isotropic layer, causes the bending bar to twist laterally. The results of simulations demonstrate the validity of the automatically coded UMAT, used in both standardized tests of hyperelastic materials and for biomechanical growth analysis.

Finite element analysis FEA is essential for modeling advanced problems in finite strain growth and remodeling of soft tissues [ 1 â€” 5 ]. Adapting a material description that provides good agreement with experimental results, the elastic response of the structures in these models is assumed to be both incompressible and hyperelastic, and therefore the constitutive relation is defined in terms of a pseudoelastic strain energy density SED function W. Additionally, many soft tissues have an underlying network of anisotropic fibers, the effect of which must be included in the SED.

The components of these arrays can be challenging to derive and code, especially for anisotropic materials. Thus, once a UMAT subroutine has been coded, it must be extensively debugged and tested before it can be used reliably.

The reader is referred to Ateshian and Costa [ 7 ] and Lubarda and Hoger [ 8 ] who carefully derived the spatial tensor of elasticity for varying levels of anisotropy of materials defined by pseudoelastic strain energy functions, and Sun and Sacks [ 9 ] who implemented such a material for use in FEA. The reader will quickly recognize the great care involved in deriving such terms by hand, not to mention the tedium in coding such arrays.

Our objective is to automate UMAT coding for soft tissues by writing a universal Mathematica Wolfram notebook, which automatically derives the required UMAT subroutine variables and outputs a ready-to-use UMAT code for materials defined by a stable pseudoelastic strain energy function.

Additionally, continuum growth will be implemented through the framework of Rodriguez et al. Using this framework allows the subdomains of growing structures to change volume and shape without causing elastic straining.

The elastic strains then act to connect discontinuously growing, topologically connected subdomains of the structure, as well as contain the response of external loads. However, UHYPER cannot be used to model growth because the total deformation gradient is not available within the subroutine.

Therefore, in the interest of generality, our focus is only on the terms needed for coding UMAT, although a similar approach may be taken in automatically coding the variables required in these alternative user material subroutines. The relationship of indices for reducing the order of symmetric tensors using the UMAT convention.

The Jaumann rate is a corotational rate, where the material coordinates rotate with deformation [ 14 ]. Linking the components of the spatial tensor of elasticity to the components of the corotational tensor of elasticity is accomplished by using Equation Since the term U J represents the isovolumetric constraint it does not contribute to strain energy and is not included in SSE. The strain energy density function is given by Equation A1 in Appendix A. A cubic specimen of Fung-Orthotropic material was subjected to uniaxial stretching, equibiaxial stretching, and simple shearing tests as presented by Ogden [ 17 ] and shown in Figure 1.

The analytical stress-stretch responses were derived using Equation 2 and are presented for each test case in Appendix A. The analytical stresses were compared to Abaqus predicted results, where the material was defined by the automatically generated UMAT.

In the FEA models, the stress results were reported at the centroid of a single linear hybrid hexahedral element. Analytical and numerical results of the hyperelasticity tests, where both the reference dashed and deformed solid configurations are presented. The stress results are reported at the centroid of the element. An additional subroutine was added to the UMAT generating Mathematica notebook to include the effect of material growth before the Cauchy stresses and tensor of elasticity were calculated, as presented by Ramasubramanian and Taber [ 18 ].

The hyperelastic response of the material was governed by a modified Fung-Anisotropic material see Equation B1 in Appendix B and both the decomposition subroutine and the hyperelastic response were automatically output directly from Mathematica into a single growth-based UMAT subroutine.

Note that previously, the components of the growth tensor G were rotated to the local coordinate systems attached to the integration points of the FE model [ 18 ].

In our work, no local coordinate systems were attached and therefore, the components of the growth tensor were not rotated.

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