
Why Things Fail: From Tires to Helicopter Blades (2012) - entangld
http://www.wired.com/2012/10/ff-why-products-fail/all/
======
krschultz
People often complain that there is no "science" behind writing software, so
therefore it is not an engineering discipline. Articles like this one do a
good job showing that the other disciplines aren't nearly as cut and dry as
software engineers often think.

Mechanical and civil engineers can lean on equations to make sure that the
part will handle expected loads - but that is just step 1 of many. It's
effectively the equivalent of "will it compile". After that step are many open
questions around maintainability, reliability, costs, etc that have even more
unknowns than the average software project. Engineering is an art based in
science, no matter what the discipline.

~~~
nether
And then once you "compile" the drawing into a manufactured part, each output
is unique since we can't yet assemble them by placing atoms. And you have to
test a slew of them to make sure the variation in structural properties is
acceptable. The manufacturing isn't 100% automated for many complex parts, so
occasionally a machinist forgets to bevel a hole edge. Inspection dept somehow
missed this (they pull 1 of 5 parts from the line and take key measurements)
and so it showed up in testing as a drastically reduced part life. And you
spent two weeks setting up and running a fatigue test on a part that was
improperly made, which now must be repeated (true story).

~~~
pixl97
Just wondering, would computer vision inspection systems fit in to the work
flow listed above?

I had a friend that worked for an electronics test equipment manufacture, some
of the systems they had were pretty awesome. If a component were off center by
something like 1/1000 of a meter the visual inspection system would flag a
board for review. The sped that it could find defects was amazing. No human
could hope to keep up, so every part on the line could be inspected.

~~~
krschultz
That is definitely in use on many assembly lines in the world today. I saw a
camera system that was used to ensure that diabetic needles had the proper cut
on the end. It processed thousands of needles an hour.

However, there is always the question of ROI for these types of systems. For
many consumer goods it's usually cheaper to just replace broken items than to
QA everything to that extent. Thats not allowable on medical devices,
airplanes, cars, etc.

------
chiph
_Eventually she found more than 20 accidents, which killed nearly 30 people,
all involving Ford Explorers riding on Firestone tires._

Only, as it turns out, it wasn't just Ford Explorers. GM vehicles on the same
tires also had tread separations. Explorers running on Goodyear tires didn't
have the problem.

For a good account of what went on inside Ford during the Wilderness AT
crisis, read Jason Vines' _What did Jesus drive?_

[http://www.amazon.com/gp/product/B00OQOWBCG](http://www.amazon.com/gp/product/B00OQOWBCG)

------
WalterBright
During WW2, aircraft engine manufacturers would have a row of engines on test
stands running at full power continuously until they broke. Then the engineers
would examine the part that broke, and redesign it. Then continue the test.

This resulted in vastly improved engine reliability.

~~~
lutorm
There are other interesting studies from WW2. "The Waddington Effect"
describes the fact that the less maintenance was done on the airplanes, the
less they broke: [http://blog.aopa.org/opinionleaders/2014/01/14/the-
waddingto...](http://blog.aopa.org/opinionleaders/2014/01/14/the-waddington-
effect/)

Also, the analysis of failure modes in
[http://www.sportaviationonline.org/sportaviation/201001#pg94](http://www.sportaviationonline.org/sportaviation/201001#pg94)
is interesting. It turns out that most things do _not_ work behave like the
"If you chart failures over time, you will almost always see some form of
bell-shaped curve" alluded to in the article. In particular, a discouragingly
large fraction fail shortly after being put into service.

~~~
pluma
First I thought the Waddington Effect would just be the usual inverse
causality (broken planes require more maintenance, ergo planes receiving more
maintenance are more likely to turn out to be the ones that break a lot).
Turns out it's something different entirely. Interesting read.

------
throwaway90446
Maybe I have a lack of imagination, but what on earth could possibly be the
failure modes of floor tile?

~~~
lmkg
Cracking would be considered a failure. You can still step on it, but it looks
bad, so you don't want that to happen. This can happen from prolonged stress,
sudden impact, or expansion/contraction from thermal cycling. The surface
becoming slippery or uneven due to wear, resulting in a tripping hazard.
Discoloration. Flaking/crumbling. Debris becoming embedded. Chemical reaction
with air, spilled liquids, or cleaning substances resulting in toxic fumes.

~~~
pluma
Keep in mind that cracked or loose tiles can be damaging to more than just
cosmetics. If the surface is damaged, there is a higher risk of injuries
(cuts, tripping, etc). If it's come loose entirely or in part you could slip
on it, and so on.

The problem with ground coverings is that you generally expect it to be
reliable and consistent if it looks like it should be. A single loose, chipped
or cracked tile might be worse than an entire floor of them.

------
nl
Note that modern racing bicycles are actually generally over engineered. The
UCI established a 6.8 kg weight limit in 1999 and haven't updated it since,
despite dramatic advances in carbon fibre engineering.

These days many bikes carry ballast to bring them up to the limit.

~~~
jdietrich
Carrying ballast is generally a PR move used to sell superlight bicycles to
amateurs. What has happened more generally is that the minimum weight has led
to innovation, as reducing the importance of weight brings a lot of other
factors into consideration.

The most significant change has been the shift towards aerodynamics. Component
shapes have been optimised in ways that are far from ideal structurally, but
provide considerable aerodynamic benefit.

A Cervelo S5 frame (optimised for aero) is 300g heavier than an R5 frame
(optimised for weight). A set of 60mm-deep wheel rims might add 400g over a
30mm-deep pair, but pay for itself in drag reduction.

Weight reduction is still significant, but not purely for its own sake -
saving weight allows you to 'spend' it on aero improvements. Notably, most
time trial bikes are still well over the UCI minimum weight, because drag
reduction is much more valuable than weight savings on relatively flat TT
stages.

~~~
nl
_Carrying ballast is generally a PR move used to sell superlight bicycles to
amateurs._

This isn't true. Bikes like OGE's Scott Addict or (last year's) Garmin-Sharp's
R5/RCA are frequently ballasted. There'a video of Simon Gerran's Addict
somewhere showing the ballast under the bottom bracket.

In the 2013 Female Giro Fabiana Luperini was disqualified after she finished
4th on a stage after her bike was found to be under-weight[1]

I agree with the rest of your comments to some extent. The weight limit has
been great for other innovations, especially the use of power meters which
would have never happened if it weren't for the weight limit.

But now-days but it's pretty easy to build an aero-framed bike under the
weight limit, even for something like the S5 (which is hardly the lightest
aero frame around). There's a guy who got under 6kg (12.96lbs = 5.87kg),
admittedly using some fairly exotic parts[2]

[1] [http://www.podiumcafe.com/2013/7/5/4496564/abbott-again-
and-...](http://www.podiumcafe.com/2013/7/5/4496564/abbott-again-and-polemica-
giro-rosa-stage-6)

[2]
[http://weightweenies.starbike.com/forum/viewtopic.php?f=10&t...](http://weightweenies.starbike.com/forum/viewtopic.php?f=10&t=102298)

------
beefman
This article basically tells us to follow these two links

[http://en.wikipedia.org/wiki/Weibull_distribution](http://en.wikipedia.org/wiki/Weibull_distribution)

[http://www.vextec.com](http://www.vextec.com)

------
exratione
Reliability theory can be a very useful way to look at many of these things.

[https://en.wikipedia.org/wiki/Reliability_theory](https://en.wikipedia.org/wiki/Reliability_theory)

------
Kiro
I'm afraid of flying and one reason is that I can't get out of my head that
things break and that there are so many things that can break in an airplane.
Please tell me I'm wrong.

~~~
hga
The things that really count break very infrequently or at all (e.g. the wings
are not going to fall off); in that respect I'm only worried about engine
failure at takeoff, and modern turbine engines are very reliable. I'm a lot
more worried about pilot error.

If you drive in the US, and you're careful about it, the risks are probably
around the same magnitude (in raw risks for all drivers and passengers,
especially when done by distance, commercial flight is very much safer).

