Why 3D-printing is not the answer to the world’s housing problem.

3D printing is a really cool technology. Unfortunately it is also an over-hyped technology. In future I may consider this from a more general point of view, but in this post I want to focus on one example of the hype: how 3D-printing is going to solve the world’s housing problem.

“About 1.6 billion people live in substandard housing and 100 million are homeless. We can solve this problem using 3D Print technology.”

Thus begins the Kickstarter page of 3D Print Homes International. Their proposed solution? Build 3D printers capable of building an entire home within a day and ship them off to developing countries. Sounds good right? So why is it not actually a solution? To answer that, let’s think for a moment about what makes up the cost of a house.

3D Print Homes house printer concept Image credit: 3D Print Homes International, via: https://www.kickstarter.com/projects/894655292/3d-printed-homes-house-building-using-a-3d-printer
3D Print Homes house printer concept
Image credit: 3D Print Homes International, via: https://www.kickstarter.com/projects/894655292/3d-printed-homes-house-building-using-a-3d-printer

The cost of a house can be broken up into 3 components: land, labour, and material. If you want to build a house, first of all you need to pay for the land it will be built on. Then you need to pay the people who will build it. Finally you have to buy the stuff that the house will be built out of. It’s plain to see that a 3D printer will only tackle one of these costs. Automating construction by using a 3D printer will significantly reduce the cost of labour, but it won’t do much for the cost of materials, and it certainly won’t bring down the cost of land. Of course labour is the one thing that is in cheap supply in developing nations, so is that really the best place to save money? Replacing labour by capital-intensive automation is something we typically see happening in highly developed economies, not developing ones. Furthermore, wouldn’t it be better for the local economy to hire local workers (who will then spend that money at local stores) rather than just parachuting in a robot to build free houses?

A project that goes further towards cutting cost is the Wasp (Word’s Advanced Saving Project) 3D printer, which can build houses out of locally available material , specifically, mud; albeit at the cost of now taking weeks to print a house.

WASP printer prototype in action. Image credit: WASP press release http://www.wasproject.it/w/en/2014/10/wasp-press-release-rome-maker-faire/
WASP printer prototype in action. Image credit: WASP press release http://www.wasproject.it/w/en/2014/10/wasp-press-release-rome-maker-faire/

Assuming for the sake of argument that suitable material can indeed always be sourced on site for free, that just leaves the cost of land. Many of the areas with the worst housing conditions are the shanty towns that spring up around cities that are rapidly expanding. However, not only is this expansion attracting many people to the city, it is also driving up real estate prices. For example in Mumbai, land prices in some areas have reached nearly $875 per square meter. Meanwhile half of India’s workers earn less than $2 / day. No matter how inexpensive to operate your house-building robot is, if you have to work more than a year (including weekends and holidays) to be able to afford a plot of land you can just lie down in, it’s not going to help much.

It’s not just the price of land that the issue either. Let’s go back to the statement by 3D Print Homes. They identified the issue as not just people not having homes, but as having a substandard ones. What makes a home substandard? Well the quality of the material making up the walls and roofs is of course part of it, but more important is connection to infrastructure like electricity, running water, and sewerage. While the printing robots can print walls and ceilings, adding in all the required cabling and piping will have to be done separately (i.e. by hand), increasing costs again. That’s assuming there’s a power grid and water mains for those cables and pipes to be attached to in the first place of course. In most shanty towns this is not the case, an issue which a house-printing robot does nothing to solve.

While the idea behind developing 3D printers to solve the world´s housing problem is admirable, the problems are far more complex than just needing to be able to build houses more quickly and with fewer people. 3D printing is a cool technology, with a lot of potential, but it does no one any favours to pretend that the world´s housing shortage can be solved by just pressing print.

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What I do and why you should care

A brief introduction of my work might go something like this: I am a PhD student at the faculty of Aerospace Engineering at Delft University of Technology where I am studying the damage tolerance of adhesive bonds and composite materials. That might sound impressive, but what does it actually mean? Let’s break it down into chunks: PhD student, adhesive bonds and composites, and damage tolerance.

Being a PhD student means that you study a certain topic for four years (in the Dutch system) and at the end write a book summarising your contributions to science on that topic. If the book is deemed good enough by a committee of experts in that field you are awarded the academic degree of ‘doctor of philosophy’ (abbreviated to PhD, because Latin).

Adhesive bonds is a fancy way of saying ‘things that have been glued together’. Composite materials are technically any material composed of two or more distinct components, but in the context of aerospace by composites we usually mean fibre reinforced plastics (FRPs). FRPs are composed of laminated layers of carbon or glass fibres embedded in a resin. Apart from aircraft structures you might have encountered FRPs in sailing boats or high-end sporting gear such as tennis rackets or hockey sticks (both of the field and ice variety).

Now for the final piece of the puzzle: damage tolerance. When we build a structure and use it out in the world it is often subjected to repeating loads. For example in an aircraft every flight the fuselage is pressurised so that you can keep breathing normally when at cruise altitude. You might also have noticed how the wings flex up and down during flight, especially if you encounter turbulence (yes, they’re supposed to do that, there’s no need for worry). These repeated loads are called fatigue cycles, and they can cause small cracks to appear and grow in the structure. You have probably heard about ‘metal fatigue’, but this is something that can happen in nearly all materials (so we just call it ‘fatigue’). What we mean by damage tolerance is how and when these cracks appear, how fast they grow, and how big they can get before posing a threat to the integrity of the structure.

In my research I’m looking specifically at cracks between the different layers of an adhesive bond (so growing in the adhesive that is between the two things that are stuck together) or between the layers of a composite laminate. The ultimate goal is to take the properties of a fatigue cycle (e.g. the maximum and minimum force or deflection) and from that be able to predict how much further the crack will grow during that cycle.

So why should you care about this research? Well, as you might know an aircraft is built up of different parts. Tens or hundreds of thousands of parts in fact, and these need to be joined together somehow. The most common way of doing this currently is by using rivets. You can see a nice example of this in the picture.

IMG_4336
Rivets holding together the structure of a C130 Hercules transport plane.

The problem with using rivets is that in order to install them you have to drill holes in your structure. This introduces stress concentrations, which are areas where the forces in your structure are greatly intensified. To compensate for this we have to add reinforcing materials to riveted joints, which makes them a lot heavier. In contrast, if we join parts using adhesive bonding the stress concentrations that we introduce are much smaller, so we can get away with using less reinforcement, resulting in a lighter structure.

The amount of fuel a plane uses is directly related to how heavy it is. By using adhesive bonds we can build lighter planes, which therefore use less fuel. As a result the environmental impact of those planes is lower and it’s cheaper to fly on them. So not only can adhesive bonds reduce the price of your holiday or business trip, they can reduce the ecological footprint you’ll be leaving too, which sounds like a win-win to me (unless you’ve invested heavily in oil companies). Before we can use adhesive bonds effectively and safely however, we need to understand and be able to predict their crack growth behaviour, which is what I’m working on.

To sum all that up into a tl;dr version: I’m trying to understand the growth of cracks due to fatigue loads in adhesive bonds, well enough that we can predict how fast it will be. This will allow us to safely and efficiently use adhesive bonding to join aircraft parts together, resulting in planes that use less fuel.

If there’s anything in there that is unclear, let me know in the comments and I’ll do my best to explain it.

The Great Myth of Science

As human beings we make sense of the world around us by telling each other stories. Who told the first story is unknown; but that we’ve been doing it for millennia is certain. Over time some of these stories were so powerful that entire religions sprung up around them. Today we usually call those stories myths. Fanciful tales that are obviously not true. Imaginative explanations from a time when science was not there to give us the True answers.

Yet for all that we believe ourselves to be living in more rational times, we still have plenty of myths of our own, even if we don’t use them as inspiration for ritual sacrifice. One prevalent myth is the myth of how scientific advancement comes to be. It usually goes something like this:

Once upon a time scientists in -field of science- were just bumbling along, not really making any kind of progress. Then along came a young man who was a Genius. During a sudden flash of inspiration he suddenly understood the Truth of how the world worked. Only the Genius could have understood this, because he was so much smarter than normal people. When he told the other scientists about this Truth they first laughed at the Genius, but later they understood that the Genius had actually been right all along. Eventually everyone was Enlightened by the Truth, and lived happily ever after. The End

This myth is rather pervasive in western culture, showing up not only in science lessons, but also in movies, and media coverage of science topics. If you’re watching a Hollywood movie and a brilliant young scientist has an idea that all the older scientists laugh at, you can be 100% certain that the young guy is actually right. Even the people with the most nonsensical of scientific hypotheses can demand to be taken seriously in the media, because after all people laughed at Einstein too didn’t they?

So apart from the casual sexism ignoring all the women who have contributed to science, what is wrong with this myth? Well it simply is not true. While we usually ascribe scientific ideas to certain people, that doesn’t mean that no one else would have been smart enough to come up with them. Newton and Leibnitz both invented calculus independently (and had a huge fight over who was first). Darwin only published his theory of evolution after being contacted by Alfred Russel Wallace, who had independently come up with some very similar ideas.

Apart from that, the revolutionary ideas that completely shake up a field are the exception. In general science is slowly advanced, paper-by-paper, experiment-by-experiment, observation-by-observation, by the collected effort of the hundreds or thousands of people working in a certain field. Science advances by collaboration, not the sudden inspiration of exceptional people. Newton (hardly the most modest man) himself ascribed his ideas to ‘standing on the shoulders of giants.’ Darwin discussed his ideas with others for many years, shaping them into the form he finally published. In the case of Einstein, the wikipedia page on the history of special relativity gives a good overview of all the prior work by other researchers that went into it: .

In this blog I hope to give a clearer picture of how science actually works (warts and all) by using my own work as an example. As I’m an aerospace engineer by training I’ll also be writing about aerospace topics in general, and my field (materials science, i.e. the science of the stuff that stuff is made of) in particular. I hope you enjoy reading. Please feel free to leave any feedback in the comments.
John-Alan Pascoe