### Tech Briefs

User-Coded Material Models in ADINA

One of the important goals in the development of ADINA is to provide an open and flexible environment for users to implement their own routines to meet their individual and industry-specific needs. In the ADINA News of Nov. 15, 2005, we provided a brief overview of the user programmable capabilities in ADINA Structures, ADINA Thermal and ADINA CFD.

Now we focus more on the user-coded material models in ADINA Structures. Here is a list of some of the user-coded material models provided as examples with the ADINA installation CD to help users implement their own models:

- Viscoplasticity
- von Mises plasticity with isotropic hardening
- Viscoelasticity and creep (for rubber, concrete,…)
- Ramberg-Osgood with mixed hardening
- Piezoelectricity (for piezoelectric actuators, sensors,…)
- Poroelasticity (for soil consolidation, biological tissues,…)
- Ogden (for rubber-like materials)
- Mooney-Rivlin (for rubber-like materials)

Of course, some of the models are also in the standard ADINA material library.

As an example of another user-coded material model, we present below an application of a nonlinear isotropic elastic material model that can be particularly useful when experimental uniaxial stress-strain data is available. In the material model, loading and unloading follow the same curve so no permanent inelastic strain is present, but different stress-strain behaviors in tension and compression are included. Also, tension or compression cut-off can be modeled.

We use the model with the uniaxial stress-strain data for concrete, see Figure 1. The model captures some basic features of the nonlinear behavior of concrete but does not include the permanent loss of stiffness due to cracking or crushing. Rebars can be included as usual in the analysis.

Figure 1 shows a simply supported beam with a box cross-section, loaded with a linearly varying lateral pressure. Only half of the beam is modeled with appropriate symmetry boundary conditions. The concrete beam is reinforced with pre-tensioned rebars, and as a result, the cross section of the beam is initially under compression.

The above movie shows the variation of the 'effective stress' in elements 1 and 2 (see Figure 1)
as the external load changes. The effective stress is defined as usual, see Ref., but
the sign is determined by the mean stress. In both elements the stress is initially
compressive, due to pre-tension in the rebars, but as the load increases, the stress
in element 1 remains compressive while the stress in element 2 becomes tensile.

Fig. 1. Schematic of the model geometry, boundary conditions, loading

and uniaxial stress-strain curve used

This is a simple example of the material models that users can implement in ADINA through the user-coded material model option, but it illustrates how ADINA can be used flexibly in many applications.

*Keywords:*

Nonlinear elastic material model, user-coded material, concrete,
rebar, ADINA, nonlinear finite elements

**Reference**