Tag Archives: Engineering

Is the Maximum Strain Theory a non-interactive failure criterion?

Failure criteria for composite materials are usually classified in two categories: non-interactive and interactive theories. In literature, you can find that the main non-interactive failure criteria are the Maximum Stress Theory and the Maximum Strain Theory. However, one question arises: is the second one a non-interactive theory in reality? Let’s figure it out.

To begin with, a non-interactive failure criterion is that one which only takes into account the effect of one stress or strain component for each failure condition. In other words, it does not consider any interaction between the different components. For example, the Maximum Stress Theory considers that the material fails when one of the stress components reaches a maximum value. Hence, considering a sample loaded in tension:


Where subindex 1 refers to the fibre direction and 2 corresponds to the transverse direction. When the stress reaches the limit value (measured experimentally under uniaxial stress conditions), the material fails. It is clear how in that failure criterion only one stress component is considered for each condition.

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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?

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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

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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.

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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.

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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.

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Science in the NFL

As the 50th edition of the Super Bowl is coming up next weekend, I think it is a good time to share this interesting video about how engineering can help a professional American football team to win championships.

Next Sunday Carolina Panthers and Denver Broncos will fight for becoming the champions of the NFL at the Levi’s Stadium, Santa Clara. In order to get to the Super Bowl, any team has to get a huge amount of first downs during the season and to achieve that goal there are two factors which can play a decisive role: penalties and opponent’s concentration during the game. In those terms, the fans can have a big influence on those two factors. How? Let’s find out.

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