Does the 'unibody' design of the MB/MBP actually help increase the strength of the MBP/MB?

Solution 1:

There are some basic approaches to making a laptop as strong as it needs to be. One is the internal chassis, IBM Thinkpads (pre-Lenovo) were famous for having a cast magnesium chassis along with a metal skin - they defined "business class" and were much imitated. Another is the Toughbook approach. Another is unibody. If size and weight did not matter we'd probably all carry Toughbook-style machines because they're, ah, tough. Big rubber bumpers everywhere are pretty good protection, but unibody is the nicest compromise between toughness and size/weight. You get more toughness for a given size and weight by combining the skin with the chassis.

Before its introduction in laptops the idea of a monocoque design was well known in aircraft, automobiles, even armoured vehicles and rockets. Ignoring the structural strength of the skin material and relying on the strength of an internal chassis wastes weight. By using the skin for structure as well, there is no wasted space or weight. By making the skin a single rigid piece, structural integrity (not to mention appearance) is not harmed by joins or fasteners. By machining out what is unnecessary only, the case can be left stronger (thicker) where it matters, at the stress points. Cheaper laptops of a few years ago would flex and creak if not picked up with two hands, just the weight of the parts inside would cause the skin to deform. I can't flex my MBP 15" at all, not even if I grab the sides and try to twist.

All materials being equal this design is responsible for the strength of the machine. As a material, aluminium (you may know it as aluminum) is desirable because:

• it is easy to source and relatively cheap
• it is easy to treat for surface toughness (anodizing)
• it is relatively light and strong
• it is easy to machine
• what is machined away is easy to recycle simply by sweeping the floor and re-casting

Additionally, unibody design can actually reduce cost by reducing the amount of parts in the laptop, by reducing the number of assembly steps and opportunities for failure during and after the manufacturing process.

The video here, at Apple's MacBook Pro page is the usual stuff with a lot of sexy shots of perfectly arranged MacBook Pros, you've seen it before. But the segments with huge billets of aluminium being extruded and then machined into unibody components are just incredible so watch it all!

"In many ways I think it's more beautiful internally than externally" - Sir Jony Ive.

(How do you know the Dell is even stronger? Destructive test results with photos, please :-)

Solution 2:

Yes - unibody design offers more strength at the same weight.

The idea of unibody design is not very new and not limited to manufacturing processes of the modern industry.

E.g. you can find unibody-like designs in furniture quite often. An example is crafting a chair out of once piece of wood - or at least the same tree. This has several advantages:

• all parts of the cover have the same thermal coefficient of expansion
• all parts of the cover have the same heat conducting coefficient

Those two points especially matter in the design of the portable Macs. They 'suffer' from extreme variations in temperatures which stresses the material. Unibody design causes the whole cover to expand at the same rate and thus avoids unpleasant side effects:

• Just little divergences can cause a bottom piece to not exactly fit a connected side piece. This creates tensions to the construction's edges and may result in unpleasant squeaking noises when you touch the device as attacking forces does not get distributed evenly over the whole construction.

In the unibody design, pieces are connected at the lowest level possible, making them...

• torsion-resistant
• stiff
• more stable at the same weight than a modular design for the body frame
• higher customizable design (no limitations for connecting elements)

Solution 3:

Look at nature. A lobster has an exoskeletal structure (shell is both skin and structure) while a mouse has an internal structure, where the skin has little structural value.

The lobster will not survive a long fall onto a hard surface without cracking its skin, but the mouse might survive from that same distance.

The mouse will not survive a certain steady weight placed on top of it, but the lobster might.

Each structure has its own benefits, and you can't strictly say that one is stronger than another.

If your environment involves a lot of falls and dropping, it's possible for one style of laptop architecture to survive better than another. If it involves being placed in a bookbag with 40 pounds of books on top, it might survive better with one architecture than another.

Neither base structure is better, stronger, or worse in every environment. The designers can, of course, take a little from both (and other) structure basics, and attempt to find a moderate solution that provides enough strength for all scenarios they believe their products will be subject to, but they all involve tradeoffs.

The unibody design is the strength of the macbook line. Being machined from a solid billet of aluminum means you get better flexibility than cast aluminum (ie, less brittle), and the fact that the skin is thicker than the skin on most laptops lends additional strength.

However, Apple does this primarily for looks, and they have made many tradeoffs to increase the laptop's appeal. For instance, the screen has very little protection, and the aluminum flexes enough that the screen may break under the wrong impact. Laptops with a different structure can protect the screen better. Not because the unibody design is inherently weaker, but the way Apple implemented that design to increase appeal at the cost of robustness means that Apple's overall design is weaker for that particular use case or environment.