# nonlinear

## Incrementally linear constitutive model. Nonlinear solution procedure

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Hello everyone,

My doubt is related with the obtenion of the true stress when using incrementally linear constitutive models (hypoelastic models). These models, alternatively to total stress strain models, related increment of strain and increment of stress. The predicted stress is obtained by adding to the previous stress the stress increment obtained by using the tangent matrix. By using total stress-strain models it is clear that the true stress is obtained by substituting the current strain into the constitutive equation. How do we do this for hypoelastic models?

I am getting displacement and force both zero. I am attaching .cae file please have a look where i am making mistakes.

https://www.dropbox.com/s/it3rkmfd31bk0k3/25mmMS.cae

https://www.dropbox.com/s/buz5ar62z6faf26/25mmMS.jnl

Thanks

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## Problems with numerical integration of discontinuous functions

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Hi everybody,

I am a very beginnerin doing research :-) and my topic is about "micro indentation analysis using continuum dislocation theory". I am applying high-order finite element method for this nonlinear problem.

My plan is first writing a subroutine for the element. However, when I intend to compute the internal force by using Gauss integration, I see a problem with the integrand function of some index of the internal force vector. This integrand is discontinuous function. It is therefore, I cannot get a good approximation with the standard Gauss integration.

## Problems with numerical integration of discontinuous functions

Hi everybody,

I am a beginner in doing research :-) and my topic is about "Micro Indentation Analysis using Continuum Dislocation Theory". I am applying high-order finite element method for this nonlinear problem.

My plan is first writing a subroutine for the element. However, when I intend to compute the internal force  by using Gauss Integration, I see a problem with the integrand function of some components of the internal force vector. This integrand is discontious function. It is therefore, I cannot get a good approximation with the standard Gauss integration.

## How to get inside the ABAQUS incremental/nonlinear static solver

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Hi guys,

I'm working on an ABAQUS extension/plug-in of a sort and I'd like to replicate results for a single 4-node plane stress element produced by the ABAQUS incremental/nonlinear static solver.

I assumed the relationship is:
t[K] {Δx} = t+Δt {P} - t{F}

## UEL ABAQUS Subroutine

Hi,

I'm stucking with my subroutine. May ask anybody to have a look the the file.

I run a simple model that and try to run it,but an error message was appeared as below;   ***ERROR: USER SUBROUTINE UEL MISSING

I don't know what is the problem. I did locate the input (.inp) and user (.f) in the same folder and run it (abaqus job=.... user= ...ff int )

Hope to get help from anybody...

Aida

## Post crack behaviour in ANSYS for concrete beam-column connection.

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Have a prob in Analysing  FEM discrete model of Beam column connection [both monolithic and precast] for crack behaviour indisplacement controlled cyclic loading program.

Tried with various values of closed and open crack and co-efficient.

applied -1 for crack and changed even the keypoint

in stiffness multiplier also 0.6 also set keypoint 7 to "1" instead of default value "0"

But even by all these the analysis runs only for 0.3mm of deflection..

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## Instabilities in Material Behaviors

The linked two of my studies can be used as references for Zhigang’s lecture on Instabilities.

## viscoelasticity

This blog focuses on viscoelasticity (http://en.wikipedia.org/wiki/Viscoelasticity)

## Energy conservation in nonlinear finite element explicit dynamics

I am writing to ask about the state of the art in finite element simulation using nonlinear elasticity and explicit dynamics.

Consider, for instance, a 3-d simulation of a hyperelastic beam that's fixed on one end, then  twisted about its long axis by 360 degrees and released. If we apply no friction or viscosity, the sum of kinetic plus potential energy should remain constant as the material springs back and oscillates.

Which FEM codes do the best at conserving KE+PE for a simulation of this type?  If you drop the time step, can you get energy conservation to many significant figures, as one can with, for instance, molecular dynamics simulation?

I'm curious because I've recently written my own 3-d nonlinear explicit dynamics code that provides very high precision energy conservation, and I'm wondering if it's any better or worse than the nonlinear explicit dynamics codes already available.