There are three nonlinear sources in structural mechanics simulation: material nonlinearity, boundary nonlinearity, geometric nonlinearity. The same ABAQUS analysis also contains these three nonlinearities. In ABAQUS software, nonlinear simulation is the most common, because all physical structures are non-linear, and linear analysis is only a convenient approximation, in a certain range , The design can generally achieve the required accuracy, but for many of the actual structure of the simulation can not meet the requirements, for example, forging, stamping and other processing simulation analysis is the case.

Geometric nonlinearity

Geometric non-linearity occurs at the magnitude of the displacement that affects the structure of the response. Generally caused by the following three situations: large deflection or large rotation; sudden flip; initial stress or load rigidity.

In the ABAQUS analysis, the definition of geometric nonlinear problem is relatively simple, only in the * STEP option to join NLGEOM parameters can be removed and PERTURBATION parameters. You can also add INC parameters to specify the maximum number of incremental steps allowed in the analysis.

And in the CAE definition is also very simple, only need to define STEP, the NLGEOM parameter can be set to ON.

2 material nonlinearity

 Many metals exhibit near-linear elastic properties at small strains. At this point the elastic modulus of the material is constant, and in the case of high stress or strain, the metal begins to exhibit non-linear properties, which we call plasticity.

In ABAQUS it is necessary to define plasticity with true stress and true strain. ABAQUS Enter these values in the input file that you want. However, most experimental data are often given by nominal stress and nominal strain. The formula should then use the formula to convert the plastic material's data from nominal stress / strain to true stress / strain.

3 boundary nonlinearity

If the boundary conditions change with the analysis process, the boundary nonlinear problem arises. For example, the two parts of the bolted connection will come into contact with the applied bolt preload, that is, the boundary nonlinearity. The contact is actually a series of special discontinuous constraints. When tightening the bolts, the surface of the two parts is separated by a gap of zero and the application of the contact constraint is applied. When the contact condition is "open" to "closed", the contact pressure is severe Change, make contact simulation very difficult.

The first step is to define the surface with the * SURFACE DEFINI TION option, then use the * SURFACE INTERACTION option to define the interaction between surfaces, and then use the * CONTACT PAIR option to define the surface that you may be exposed to. Correct.

yes both the values are Peak values. 

To be sure, I had run simulations without sample and NLgeom OFF where I find the results somewhat coherent. 

I do know that NLgeom is used to trace the non-lienar effects i.e. if the stress levels are in linear domin, we see no non-linear effects. 

Firstly I had defined it using Stress-Strain data from Uniaxial test and evaluated it. For the following simulations, I defined it using Ogden Parameters (N=1)

There are three nonlinear sources in structural mechanics simulation: material nonlinearity, boundary nonlinearity, geometric nonlinearity. The same ABAQUS analysis also contains these three nonlinearities. In ABAQUS software, nonlinear simulation is the most common, because all physical structures are non-linear, and linear analysis is only a convenient approximation, in a certain range , The design can generally achieve the required accuracy, but for many of the actual structure of the simulation can not meet the requirements, for example, forging, stamping and other processing simulation analysis is the case.

Geometric nonlinearity

Geometric non-linearity occurs at the magnitude of the displacement that affects the structure of the response. Generally caused by the following three situations: large deflection or large rotation; sudden flip; initial stress or load rigidity.

In the ABAQUS analysis, the definition of geometric nonlinear problem is relatively simple, only in the * STEP option to join NLGEOM parameters can be removed and PERTURBATION parameters. You can also add INC parameters to specify the maximum number of incremental steps allowed in the analysis.

And in the CAE definition is also very simple, only need to define STEP, the NLGEOM parameter can be set to ON.

2 material nonlinearity

 Many metals exhibit near-linear elastic properties at small strains. At this point the elastic modulus of the material is constant, and in the case of high stress or strain, the metal begins to exhibit non-linear properties, which we call plasticity.

In ABAQUS it is necessary to define plasticity with true stress and true strain. ABAQUS Enter these values in the input file that you want. However, most experimental data are often given by nominal stress and nominal strain. The formula should then use the formula to convert the plastic material's data from nominal stress / strain to true stress / strain.

3 boundary nonlinearity

If the boundary conditions change with the analysis process, the boundary nonlinear problem arises. For example, the two parts of the bolted connection will come into contact with the applied bolt preload, that is, the boundary nonlinearity. The contact is actually a series of special discontinuous constraints. When tightening the bolts, the surface of the two parts is separated by a gap of zero and the application of the contact constraint is applied. When the contact condition is "open" to "closed", the contact pressure is severe Change, make contact simulation very difficult.

The first step is to define the surface with the * SURFACE DEFINI TION option, then use the * SURFACE INTERACTION option to define the interaction between surfaces, and then use the * CONTACT PAIR option to define the surface that you may be exposed to. Correct.