Fea software non linear

Rigid body rotations in particular invalidate the linear stiffness matrix and require it to be updated as it rotates. When multiple bodies come into contact, or if a body contacts itself, then there is an abrupt change in behavior, hence the contact nonlinearity. The friction between the two would be an additional nonlinearity. Frictional effects are path dependent, another characteristic of nonlinear behavior. Your browser does not support the video tag. Sign Up for our Blog.

We promise that we won't SPAM you. The nonlinear is very important term in FEA. Most of engineer gets stuck in this topics as it is not simple as linear simulations.

Most of FEA related issues you will find while simulating nonlinear simulation such as solution is not converging, solution taking too much time, contact abrupt changes, displacement converging but moments does not or wise versa. Just changing linear to nonlinear zone is not enough, you will need to decide the load step increments, solver setting, and various contact setting.

In this blog we will discuss the types of nonlinear analysis, types of non-linearity and nonlinear FEA issues. As name suggest, nonlinear means the force versus displacement plot is not as straight line. The stiffness of the structure is no longer constant but varies with respect to loading. Majority classes of structures does not have linear relationship between force and displacement.

A structure is said to be nonlinear, if the loading causes the significant changes in the stiffness. Typical reasons for stiffness changes are:. Figure 1 shows the types of non linearity. The changing geometric configuration due to large deformation of the structure cause nonlinear behavior. The geometric nonlinearity causes to change in geometry cross section due to large deformation.

Geometry buckling is also cause of geometric non linearity, in case of buckling huge compressive load causes the structural member to buckle resulting higher displacement.

FEA models come in all shapes and sizes. This post is aimed at providing a summary of how linear and nonlinear geometry works within FEA, and then some examples and recommendations regarding when you might need to use these settings in your own simulations.

Well in a typical linear FEA model, this stiffness matrix, K , is defined at the beginning and it is assumed not to change throughout the entire analysis. While that is true, in most engineering problems, deformations are so small that the deviation from the initial geometry is essentially imperceptible. The potential errors that are associated with the small-strain assumptions are not significant enough to warrant any extra effort to eradicate.

But how about occasions where we cannot make small-strain assumptions? What do we need to do during our analysis to ensure that we capture the effects of shape change on stiffness? Well, it might seem like a somewhat brute force approach, but what we must do is redefine the stiffness matrix after each increment of the analysis.

That way the subsequent increment is beginning its calculations with respect to the updated stiffness matrix, rather than the one that was defined at the start of the analysis. As you can imagine, that can become quite computationally expensive, but it is absolutely necessary for a whole myriad of different simulations. You also need to understand what you wish to do, and how to set the solver, so it can increment the loads you applied in a way that allows for the solution to converge!

I think, that the big part of being successful in nonlinear FEA is understanding what can be nonlinear in your task and if it will play a role! I decided to do it in a bit more robust way. Since this is not a book, I get to hyperlink stuff! This will come in handy now! The idea is simple — I make a small introduction to all of the nonlinear things that can be nonlinear in your model. In fact such a strategy is a loosing one… since you will never know everything, so you will never start!

Then do the step! When you will do it, you will have the mental energy to learn a bit more, and do a second step. This way you can learn much quicker, and remain motivated to do so! This post contains all you need tu understand at the begining. Play with this first, and when you will feel you have a handle on things, read more, and play more with nonlinearities! Unless of course, you are on some useless 5h meeting, or during your commute!

It is a useful thing to know for sure! After that, you will learn how the load incrementation works , so you can launch your first nonlinear analysis. And finally, I will show you a simple problem you can try to solve , to start with your nonlinear adventure! I admit that I usually start with nonlinear geometry because this is how I got into this. There are a lot of different nonlinear material models.

You can easily be an expert in a specific niche of FEA, and this is so cool! Each material has a stress-strain curve, usually obtained from tensile tests in labs. Just remember not to base your actual design on data that you guessed! But the above problem is also, why I like steel so much. This makes it a perfect material to start with. Often time, you will be interested in what is the actual value of stress, as you will need it for design.

Firstly, your material deforms, which causes strain. High strain means there were heavy deformations in the region. Based on the strain, you can judge how much stress your material is in. While in linear FEA you simply assume that there is a linear relationship between stress and strain, nonlinear FEA allows for more!

Take a look at the chart above… only the beginning is actually linear, but ignoring the rest may not be the best approach! I hope that now you know, why you need a stress-strain curve for your material. To put this bluntly, FEA will calculate the deformation of your model, then it will calculate strains from those deformations. Of course, the simplest approach is to use a linear relationship between stress and strain.

Linear FEA analysis does that for you, but I think we are beyond this point now. It works very well for mild steels:. Many codes i. Most likely your FEA package will ask you about the hardening slope usually denoted as H. In such a case it is 0 zero. Assuming the above model you are on the safe side unless you are designing joints for plastic redistribution of load… but in such cases, you should know what you are doing anyway! Difference between linear and nonlinear FEA.

I explain there, how nonlinearity works, and why with the linear material model you may get stresses a lot higher than the yield stress. Useful stuff if you are beginning with nonlinear FEA for sure! In In this article, you can read about the most common material models at least in my opinion. There is even a geek version for NX Nastran users with the keywords and all the jazz! Difference between linear and nonlinear elastic materials.

Usually, engineers associate material nonlinearity with yielding. But this is not always the case. Elastic materials that do not yield at all! You can learn a lot about that in this post! How does nonlinear material work? Here, you can learn how does yielding works. No worries there is no complex math there. Just 3 guys carrying a heavy rock, and few simple drawings. I think you may like it! Do I need a nonlinear material Flowchart. I figured that this may be a useful thing.

It guides you from the beginning to a clear decision on whether you need nonlinear material in your model or not. Isotropic and Kinematic Hardening. While this is a rather advanced topic, it fits here nicely. If those things interest you, you can learn more about how materials react to loading past yield in tension and then compression or the other way around. Useful stuff if you try to calculate low-cycle fatigue for instance!

Somewhere in your analysis setup, you can pick whether you want to have nonlinear geometry or not. There are no models, nothing to choose, no specific parameters you need to set. Actually far from it! Nonlinear geometry does not hand out warnings like that. The difficulty of most nonlinear geometric problems comes with load incrementation.