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Why aluminum isn't the cause of the bending reports - Interesting read

K

kalebnate

macrumors 6502
Original poster
Sep 11, 2014
341
1
On a reply to the bending video posted on reddit : (click for source)

This isn't right. iPhone's bending problem has nothing to do with aluminum. It has everything to do with geometry.

((Edit: Material choice matters, always. But material has to work together with the geometry it's been shaped into. The choice of aluminum here isn't the limiting factor. The geometric design of the aluminum chassis is.))

Nobody uses pure aluminum for general purpose manufacturing. They use aluminum alloys instead. And the alloys themselves are incredibly diverse.

You can get extremely rigid alloys that will be incredibly difficult to bend even in thin structures prone to bending (such as 7075), but the disadvantage of that is difficulty of machining (and often welding too). This type is dominantly used in transportation industry (automotive, marine, aircraft, etc). Manufacturers take the additional manufacturing costs in order to reap the great strength-to-density ratio.
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This counters the idea of people discussing here and around different forums that aluminum usage in the iPhone was a bad choice. Someone actually replied here and told me it was a bad decision from their part that they chose aluminum, hopefully this explains that they use alloys to strengthen the material, they're not using aluminum foil.

Apple uses anodized 6003 series aluminum, which is similar to 6061 in properties). This is a good compromise between the extremes, and is the most ubiquitous aluminum alloy out there. It's got good mechanical properties, easy to machine, easy to weld. Their choice of material was correct in this case.
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Further explanation to the type of alloy Apple chose in their design.

The problem with the iPhone 6 chassis comes from something we call "stress concentration" in engineering and this phenomenon is related to the geometry of an object. More specifically, it has to do with the cross section profile that is being bent.

If you watch the bending test video, you'll notice that iPhone 6 bent exactly at the root of the volume buttons. And if you look even more closely, you'll notice that the bending is actually on just one side -- the side of the volume buttons. The opposite side is actually mostly unscathed.

This is because the cross section area of the bending profile decreases dramatically right at that point. They have cut out a hole to accommodate the volume buttons, and when under loading, the internal stresses of the structure are being concentrated at the base of this cutout. So when the structure fails, it fails at that point. The lower cross section area decreases the resistance to bending, and makes it possible to bend the chassis at a lower applied force than what it would take otherwise, had the volume buttons not been there (but of course they have to be there).
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Many people, including me, were wondering why does it always bend near the volume buttons, indicating a possible structural weakness there. This sheds some light on the issue and explains why.

The result here wouldn't have changed if Apple had used plastic in place of aluminum. In fact, it probably would have been worse. Typically phone manufacturers use brittle plastic in their devices (ductile plastic is the kind that feels really cheap and terrible), so the chassis would have broken entirely at the same point. They could have avoided the issue, maybe, if they opted for steel or a tougher aluminum alloy but then you run into other problems and have to retool essentially your entire product line.
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Further explanation to design choice and avoiding plastic. Apple wanted to keep the premium feel and did not want to incorporate other materials because that might delay production and release dates, something no one is fond of.

The reason why Galaxy Note 3 passes the bending test doesn't have anything to do with the material it's made out of. It has everything to do with the internal geometry of the chassis. The internal magnesium alloy chassis (which isn't any better than aluminum as a material) has an I-beam cross section that is great against bending, and it's further sandwiched between two shells, which are in this case plastic. It's reinforced very thoroughly, to the point where human-applied forces cannot bend the device beyond its "elastic range" (this is the deformation range within which the device can recover to its original state when loads are removed).

Apple could have designed the aluminum chassis in a way that would accomplish the exact same thing, and if they had, people wouldn't be mistakenly criticizing the aluminum here. They would just be talking about how nice the material feels to the touch (because it does, and yes, it is "premium" much more so than plastic). Unfortunately, they ****ed it up. Again, it's all in the geometry.

Edit: Some more detail because people are pointing out the magnesium alloy internal chassis in Note 3, even though the material is not what makes the difference.
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The final argument. This has been aggressively discussed on all networks regarding how the galaxy note does not bend because it is plastic, and is therefore more superior to the iPhone's design. However, they do mention that this whole bending issue could have been avoided by a redesign to the phone's structure.


I advise you continue reading at the source's link as it is an interesting one, and can aid in understanding what was going on based on the commenter's thoughts (they sound like they know what they're talking about). You can also follow up with the hundred replies to that post with opinions from all sides.

I hope you find this thread useful, what's your thoughts ? Agree or disagree with what they say ?
 
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Makes me wonder if there is some type of skeleton or webbing inside. Unfortunately doing so would add thickness which is probably where engineering lost out to the marketing.

When people around me said "Guess you have to get a case for it then", I said how can a plastic case offer more protection then aluminum?!?!? Unless you're talking a monster case.
 
westrock2000 said:
When people around me said "Guess you have to get a case for it then", I said how can a plastic case offer more protection then aluminum?!?!? Unless you're talking a monster case.
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Because some people think the phone is made out of aluminum foil. This is why I felt that more people need to read this guy's thoughts on the issue, they're using strengthened alloys (obviously), but some people can't seem to understand that (as one person replied here a few days back telling me it's their fault for using a weak material).
 
Why aluminum isn't the cause of the bending reports - Interesting read

kalebnate said:
Is that everything you deduced from the whole post ? :\
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For some of us, the post was not new.
It was restating the obvious, even if the media monkeys aren't clued in.
1. The large flat area on rear of iphone vs 2. The arched style on the rear of m8.
And
The compromise to the iphone's tub shape at the vol buttons.

None of this is new to some, nor surprising. Nor shocking.

That guy was just pointing out that its physics + geometry. Geometry doesn't deal in forces.
 
Cash4Jesus said:
It's not geometry; that's math. This is physics which is the application of math.
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This fundamental engineering formula sums it up nicely

Stress = load / area
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As the cross sectional area decreases (from drilling holes) the stress goes up.

I noticed in the ifixit teardown what look like metal "bridging" pieces attached to the frame behind the buttons. I'm thinking these are the reinforcing elements Apple referred to yesterday.
 
Menel said:
None of this is new to some, nor surprising. Nor shocking.

That guy was just pointing out that its physics + geometry. Geometry doesn't deal in forces.
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Good for you. Hopefully others can benifit from this.

Also, please avoid discussing geometry and physics noting that they're not connected. Anyone with an engineering background will know that they're heavily intertwined.
 
kalebnate said:
Good for you. Hopefully others can benifit from this.

Also, please avoid discussing geometry and physics noting that they're not connected. Anyone with an engineering background will know that they're heavily intertwined.
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Did you even read what you quoted? Where did I say not connected?
You even directly quote me as stating 'geometry + physics'?

Also... *benefit
 
why are we still talking about this? didnt apple release a statement that the bending is rare...only 9 people contacted apple
 
I've been getting it in the neck from anyone and everyone about the bending plus, I've been saying it must be the users fault.. I can see my plus starting to bend today, and I have been carrying it around like an egg, taking it out of my pocket every time I sit, never putting any force on it at all, really devastated to see the thing starting to curve
 
arliu said:
why are we still talking about this? didnt apple release a statement that the bending is rare...only 9 people contacted apple
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Agree this is extremely rare and overblown, but it is silly to trust a corporation like Apple with that statement.
 
christyd20 said:
I've been getting it in the neck from anyone and everyone about the bending plus, I've been saying it must be the users fault.. I can see my plus starting to bend today, and I have been carrying it around like an egg, taking it out of my pocket every time I sit, never putting any force on it at all, really devastated to see the thing starting to curve
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So it's starting to bend like a noodle just by itself? Either you are seeing things, or maybe it was bent to begin with. How can it bend with "never putting any force on it at all" ? I have one, been in my pocket every day since last Friday. Flat as a pancake. I would take it to apple and have them look at it.
 
Could there be more contradictions in this?

This isn't right. iPhone's bending problem has nothing to do with aluminum.

You can get extremely rigid alloys that will be incredibly difficult to bend even in thin structures prone to bending (such as 7075)



The reason the phone bends easily and retains it's bend is the thin 6061 non-tempered aluminum and the small material cross section at the button locations. Period.
 
lke said:
Use liquidmetal.com and the problem will end.
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You want them to build a phone out of a website?

Seriously though, there will always be problems. Nothing is perfect. Or are you saying that liquid metal IS perfect? I beg to differ. Re: Terminator.
 
rantor49 said:
So it's starting to bend like a noodle just by itself? Either you are seeing things, or maybe it was bent to begin with. How can it bend with "never putting any force on it at all" ? I have one, been in my pocket every day since last Friday. Flat as a pancake. I would take it to apple and have them look at it.
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It's been put under normal stress, in my front jeans pocket, I don't sit on it in my back pocket, I don't have it in my pocket for hours on end, I haven't put excessive force on it.. I'll post some pics shortly
 
christyd20 said:
It's been put under normal stress, in my front jeans pocket, I don't sit on it in my back pocket, I don't have it in my pocket for hours on end, I haven't put excessive force on it.. I'll post some pics shortly
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If it's bendimg, then by definition you HAVE put excessive force on it. Otherwise it would go back to flat. You've exceeded the limits. It can't bend on its own.
 
This isn't new information.....

I'm sure this all came up when there was bend-gate for the 5, when pictures were published of the stress point being below the bottom volume down button.
 
As I said, I haven't put excessive force... I love the plus, have no reason to try and bash it! I love apple so not trying to bash them, if you don't accept what I'm saying, then I don't give two ****s, trying to tell people who are clearly interested in this issue about my experience today, if nobody cares, then I'll not bother
 
christyd20 said:
As I said, I haven't put excessive force... I love the plus, have no reason to try and bash it! I love apple so not trying to bash them, if you don't accept what I'm saying, then I don't give two ****s, trying to tell people who are clearly interested in this issue about my experience today, if nobody cares, then I'll not bother
Click to expand...

This is why I believe new cases of the bent gate will pop up everyday...prime example ....
 
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