# About Hashin´s failure criteria in FEA

When using Finite Element Analysis (FEA) for studying composite materials, one of the most used failure criterion is the one which was proposed by Hashin in 1980. This theory is included in all the main FEA packages and, probably, you are more than familiar with this particular model. However, what you might not know is that the failure criteria that you are defining is not exactly the Hashin’s one. If you want to know why, this is your place.

Since the available failure criteria at that point presented some inconsistencies, in 1980 Hashin developed a new criteria which differentiated between failure modes. His theory considered four different ways in which the material could fail:

# FEA for beginners (Part IV): Material models

Every time you use Finite Element Analysis you need to assign a material model to all the components. Since there are plenty of them, one question arises: which one should you use for your particular case?

To begin with, there might be more than one material model which can provide an accurate solution to your problem. However, it is likely that one of them will present some advantages when compared to the others, such as computational time or the number of parameters which have to be defined. When you have spent time working with a certain kind of material (e.g. metals) you will have gained some experience that will help you choosing between different options whenever you face a similar Finite Element model. But, what happens when you are new and you don’t know where to start?

# FEA for beginners (Part III)

One of the dangers of FEA is that it provides results, even if they are wrong. Hence it is the engineer’s responsibility to critically analyse and validate them. In these terms, one of the most common rookie mistakes is “hourglass”. If you want to learn what it is and how to correct it, this is your place.

To begin with, let me introduce two different concepts: underintegrated elements and fully integrated ones. Underintegrated elements are only evaluated at one single integration point, whereas fully integrated ones have more than one. In order to illustrate this idea, Figure 1 is introduced.

Figure 1 (a) Underintegrated element; (b) Fully integrated element

# FEA for beginners (Part II)

Some of you may have found some difficulties when trying to create a structured mesh for circular/spherical parts. For that reason, this week I’m going to write about a simple procedure that you can follow in order to solve this problem: the “Butterfly Method”.

For achieving more accurate results, it is always recommended to use quad-structured meshes. Most of the FE packages include options for meshing parts in an automatic way, where you only have to define the number (or size) of elements and the type (i.e. quad, tri or even a combination of quad+tri elements). However, when geometries include circular parts or when you are creating an sphere or a cylinder, the automatic option for creating a structured mesh is not available any more. How can we solve that? Let’s find out.

# FEA for beginners (Part I)

The main idea of this post is to provide an overview of the outline of a Finite Element Analysis for people who are not familiar with this engineering tool.

The starting point for every Finite Element Analysis is a real problem which has to be solved. For that purpose we have to create an idealised structure and, from that idealisation, we should be able to design a discrete model. Hence, using the Finite Element Method, a discrete solutions can be obtained for that model.

# A brief introduction to Finite Element Analysis

Have you ever come across the term “FEA” or “FEM” when talking about structural analysis? If you have and you still don’t understand  what it means and how it works, this post is for you. Don’t be afraid, no scary equations are presented here!

Finite Element Analysis (FEA), or Finite Element Method (FEM), can be defined as a methodology for solving field problems using numerical approaches. This kind of problem needs the determination of a spatial distribution and this can be seen, for instance, as the distribution of temperature in the piston of an engine. From a mathematical point of view, a numerical solution of a field problem is defined by differential equations or by integral expressions.