Do Airplanes Dream of Bionic Parts?

One of the best ways to innovate is by combining two different technologies. I am going to show you an example. This ultra-lightweight metallic part is the result of the combination of two state of the art technologies: additive manufacturing and topology optimization.

A350 XWB Bracket (© Airbus S.A.S 2014)

Topology optimization is a type of structural optimization which was discovered studying bones. Our bones are very lightweight because they have suffered an optimization through millions of years of evolution. On the one hand, holes have grown in low stressed areas. On the other hand, highly stressed areas have been reinforced. That is why our bones are lightweight and strong at the same time. There is bone only where it is needed. This has been studied and topology optimization software has been created. Now we can do the same as nature does in millions of years just in a couple of minutes. The result is a bionic design that is not only very lightweight but also very strong.

Topology optimization leads to designs that tend to be very complex and difficult to manufacture by conventional methods. Here is where additive manufacturing - also known as 3D printing - comes into play. Additive manufacturing is a technology that creates parts layer by layer. That means that almost any geometry can be manufactured by this method. In addition, there is practically no material waste and no tooling is required. However, it has to be said that surface roughness can be high, which reduces fatigue strength. And due to the manufacturing process, strength in the z-axis (perpendicular to the layers) will be lower than strength in the x- and y-axis (parallel to the layers). Therefore, it has to be taken into account that strength will be lower than expected.

In my opinion, the combination of these two great technologies has a lot of potential. It not only allows for weight reduction on aircraft and other vehicles, but also reduces material use, which can be very expensive for certain materials such as titanium. What do you think?

 

Safety First: How to calculate the Factor of Safety

In Mechanical Design there is a very important concept that allows engineers to design safe components. It literally saves your life every time you take a flight, cross a bridge or climb a mountain.

Beto is relaxed because he knows that his climbing equipment is safe

It's known as the Factor of Safety and it's defined as follows:

where:

• FS: Factor of Safety
• Strength: Mechanical Strength of the component (in stress units)
• Stress_max: Maximum stress allowed in the component

The objective of this formula is to find Stress_max. This is the stress that shouldn't be surpassed in your design.

In order to find Stress_max you need to know the other two variables:

• FS
• Strength 

You can use the following table to get them:

Factor of Safety: Table

Once you have calculated the Factor of Safety (FS) and you have the value of the Strength, you will get Stress_max using the formula. Now you have the value of stress that sets a limit for your design.

In conclusion, the Factor of Safety is a very important concept in Mechanical Engineering because it allows engineers to design safe products. It can also help you make efficient designs by avoiding a Factor of Safety larger than necessary.

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3D Printing Saves the Life of a Young Child

This component is 3D printed and it's made of a biopolymer:

It was developed by 2 professors from the University of Michigan.

Watch this amazing video in order to see how it saved the life of a young child:

3D Printing Makes You Fly Cheaper

General Electric is very interested in reducing weight in aircrafts, so they published a challenge in GrabCAD.com. The challenge consisted on reducing the weight of this component:

Image taken from www.grabcad.com

 

This component is a jet engine bracket. It's made of titanium (Ti-6Al-4V) and the new design will be manufactured using a 3D printer. Yes, you read it right! 3D printing nowadays is capable of printing metals.

The winner of the challenge will be rewarded $8,000.

The bracket will have to withstand the following loading cases:

Image taken from www.grabcad.com

The bracket is fixed with 4 bolts (interfaces 2 to 5) and the loads are applied by means of a pin (interface 1).

 

In my opinion, the best way to solve this problem is by doing a topology optimization. Why? Because a topology optimization will give you the lightest component that can withstand those loading cases.

I downloaded the bracket to be optimized and did a Finite Element Analysis. I wanted to know the stress level of the component before any weight reduction was carried out.

The maximum von Mises stress (of all loading cases) was around 530 MPa and was located at the pin hole. Considering a yield strength of 900 MPa for this titanium alloy and a Factor of Safety of 1.5, a maximum von Mises stress of 600 MPa shouldn't be surpassed. That means that there was still some room for material removal.

I used OptiStruct to perform the topology optimization. I took into account the 4 loading cases.

The objective of the optimization was to maximize the stiffness of the bracket and as constraint I chose a volume reduction of 60 %. The result was:

I exported the result to a CAD program and made the final design of the optimized bracket:

STL file imported to CAD

Final Design in CAD

After a Finite Element Analysis of the new bracket (for all the loading cases) I obtained a maximum von Mises stress of 585 MPa, which is under the limit of 600 MPa. The maximum was also located at the pin hole.

The results are AMAZING:

• 60 % weight reduction (from 2 kg to 800 g)
• Only 10 % increase in maximum von Mises stress (from 530 to 585 MPa). Stress under 600 MPa and therefore Factor of Safety over 1.5

In conclusion, topology optimization is a very powerful tool, which combined with 3D printing can lead to super-lightweight and super-strong components like the bracket of the challenge.

Lighter planes need less fuel. And fuel is very expensive. So this technology could really make your flight tickets cheaper! And you will fly as safe as always!

Furthermore, the benefits of producing less CO₂ and pollutants will benefit the whole planet!

So, will I win the challenge?

NOTE

You can see the whole GE Challenge here:

http://grabcad.com/challenges/ge-jet-engine-bracket-challenge

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The Secret to Design Super-Lightweight Components

In mathematics, an optimization problem consists on minimizing or maximizing a function taking into account some constraints.

I want to show you an example of how to apply mathematics in order to solve a problem in the real life: the design of super-lightweight components. That's possible by means of a topology optimization.

In a topology optimization, the function to be maximized is the stiffness of a component. The constraint to be satisfied is a limit on the mass.

Therefore, the result of the optimization is a component that not only is lighter but also is the stiffest possible for its weight.

That's the secret to design super-lightweight components. And they will be very strong!

Let me show you a practical example.

The first thing to do in a topology optimization is to determine the space to be optimized. That's called the design space.

Then, it's necessary to mesh the component and apply the boundary conditions (loads and constraints).

During the optimization process, it's decided which elements are really working and which are being a little bit lazy. The working elements are kept, while the lazy ones are removed. That's the way to keep the really important elements. That's Intelligent Use of Material!

Result of the topology optimization

In this case, the optimization has been carried out with a weight reduction of 70%.

Final Design

As you can see in the Finite Element Analysis of the optimized design, low-stressed areas (dark blue) are minimal, which means good use of material. This is the objective of a topology optimization, to use material only where it is necessary. There are no lazy elements. And there are no excessive working ones.

If you would like to learn more about topology optimization or want to find out how you can do it too, I invite you to visit my website:

www.topologyoptimizationforyou.jimdo.com 

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Learning From Trees - How to Reduce Notch Stresses

Bionics is the science that applies systems and methods found in nature to engineering and technology.

Trees, for example, can show us how to design optimized mechanical components by reducing notch stresses. Let's take a look at the base of a tree:

As you can see, the shape of the base is not a quarter-circle. It can be approximated using the Method of Tensile Triangles, developed by Claus Mattheck and his co-workers from Karlsruhe Institute of Technology in Germany.

The procedure to draw the tensile triangles is quite simple. The first triangle starts at the bottom with a 45º angle. This creates a new notch on top of the triangle, which can be bridged symmetrically with a second triangle. This second triangle has to start from the middle of the hypotenuse of the first triangle. The third triangle is drawn in the same way. Three tensile triangles are usually enough. The corners have to be rounded, except the lower one.

As you can see in the picture below, the method is quite accurate:

This is a biological solution to the serious problem of reduction of notch stresses. However, engineers still utilize quarter-circle transitions in order to do the same.

Quarter-circle transition

In the following pictures we can see the two options. On the left, the engineering solution: the quarter-circle transition. On the right, nature's solution: tensile triangles. Which one is the best?

Using the Finite Element Method to calculate the stresses, we can figure it out.

The quarter-circle transition shows red spots, which indicate high stressed areas. On the contrary, the transition using tensile triangles is less stressed (maximum von Mises stresses are about 20% lower than using quarter-circles).

This means that by imitating the optimized shape from the base of trees we could reduce 20% the maximum stresses in a notch, making our mechanical components not only stronger but also more durable.

We still have a lot to learn from nature!

So please treat it with care!

 

Lightweight Design of a World Champion

You can see here the rear Bell Crank of a Formula SAE car. It's made of aluminium (7075-T6) and the design is topology optimized. It weights only 45 g.

Topology Optimization allows the designer to create superlightweight components that are also very strong.

The component is part of the Suspension System of the racecar F0711-7 made by the team Rennteam Uni Stuttgart:

This masterpiece of hi-tech engineering was made by 40 students of the University of Stuttgart in 2012. The car won 3 international competitions, reaching 1st place on the World Ranking.

Suspension uprights, brake pedal, differential carriers... many components of the car were topology optimized, making each of them as light and strong as possible. The result: 180 kg.

Topology Optimization is a very useful tool that allows engineers to create superlightweight designs - like this car. I'm sure you are going to hear a lot more about this cutting edge technology in the future!

- Dad, why do they put holes right there?

- Because they want to make the structure lighter and spare some material.

Dad was right. But he didn't have a clue what his son was about to discover some years later.

His son graduated as a Mechanical Engineer and became a specialist in Structural Optimization. He was able to create superlightweight designs. And they were strong. Very strong...

He started his own company - Aligerator - and began doing things like this:

Costumer: Can you improve this design for us?
Aligerator: What do you really want? A cool design? Or something light and strong?
Costumer: Both.
Aligerator: OK. Let's see what we can do.

The problem was the following: We want to find the lightest component that can withstand 5000 N. The component is made of steel (S235) and the maximum dimensions are shown here:

If you ask an experienced Mechanical Engineer, he would say: Make some holes!

However, in Aligerator we don't believe in experience. We always want to find the best solution. So what we did is a Topology Optimization!

Taking into account the solution of the Topology Optimization, we designed a new component:

Which design is better: the design with holes, or the optimized one?

Let's compare both. Let's do a Finite Element Analysis and decide which one is better. In the following pictures you can see the stress values (von Mises) of both designs:

Both options are within safe values of stress. The design with holes is 20% lighter than the original. Not bad. However, the design made by Aligerator is 40% lighter. AMAZING!

NOTE FOR ENGINEERS

Steel S235 has a yield strenght of 235 MPa (for 5 mm thickness). Using a Factor of Safety of 1.5, maximum von Mises stress should be below 155 MPa. Both cases are below that level (with holes: 110 MPa, optimized: 130 MPa). Maximum displacements are around 0.4 mm in both cases.

A Topology Optimization maximizes the stiffness of a component applying a volume constraint (for example, you can maximize the stiffness of the component reducing 40% in volume). Translation: you get a very lightweight solution which is also very strong.

You can also see that the stress distribution in the model optimized is much better than in the model with holes. Why? Because most of the component is under stress, leaving no area unstressed. This means material being used only where it's going to be necessary (under stress). Intelligent use of material!

Welcome to Aligerator!

Aligerator

We are going to change the world.

Let´s go lightweight!