Theme: Material – Decay

Cars start decaying the moment they are built. Some manage to accumulate character while most don’t. What do you do?

Rust.
Rust.

One response is obsessive polishing and maintenance. The other is stoic acceptance. For many the response is to oscillate in between the two, starting with careful stewardship of the new possession. Why do people fight physics? And why is it that cars don’t last longer?

More rust.
More rust.

Every material has an inherent problem. That problem is that the material inevitably has a disadvantage. Compounding that is that entropy only increases though it locally can be reversed (while still increasing it in aggregate). So, engineers can only ever balance compromises when selecting materials. All of them will one day rust, break or dissolve or flow away.

The unfortunate thing with the failures of certain cars is that you don’t tend to see the trade-off. So, this small meditation on the characteristic ways vehicles decay is almost necessarily unbalanced. Who knows what useful feature of the 1993 Mondeo balances the propensity of its side-glass rubbers to curl where the meet at the B-pillar?  Maybe the paint was a fraction thicker or the interior lamp just a shade more illuminating. The Volvo 240 tended to rust around the vent at the base of the rear-window. What advantage came of the fact Volvo never invested in a way to stop that?

In the last twenty years Alfa Romeo badges became more prone to flaking. Did someone invest the money saved in enamel in a better ink for the interior graphics? Renaults, as I like to say, have a strangely uniform failure rate so that everything seems to go wrong at once. And clearly no particular aspect of Renaults can make up for this fact. With a few exceptions, Renaults are uniformly mediocre cars but are demonstrable proof that good materials analysis can result in very carefully planned obsolescence.

Knocks and weathering
Knocks and weathering

The single heaviest material in a car is steel. The biggest advantage it has is that it’s cheap and plentiful. It isn’t actually the best material for the job but on balance it’s better than all the others. It’s main competitor is aluminium which is also lighter, plentiful but not nearly as cheap. It scores over steel in that it’s lighter but apart from that it comes with a host of disadvantages. People are aware it doesn’t rust which is what steel is known for. Thus, 120 years into the Car Epoch, we find most of a car’s body is still steel, prone as it is to oxidization. Steel versus aluminium characterises the general point about trade-offs and also about decay.

Around about now all the Mk1 Audi A8s are getting into the start of their second decade on the road. Famously made of aluminium, the Audi A8 weighed 200 kg less than an S-class of the same time. That figure is to be taken with a pinch of salt as the W-140 was enormous and the Audi less so. Key among the potential problems is that aluminium fatigues faster than steel as it’s more brittle. So, while the A8 is not visibly rusting, small cracks are propagating somewhere in its structure and we’ll be finding out where they are in due course.

UV damage
UV damage

As I mentioned elsewhere, plastic is taking up a larger proportion of non-load-bearing parts of cars but still hasn’t displaced glass except on a few racing cars. That’s because glass is harder. How does it decay? It tends to become crystalline when exposed to ionizing radiation which is why you should never park near plutonium or uranium. Glass flows slowly too. It doesn’t rust and can withstand extreme temperatures as well. Alas, it’s even more brittle than steel which is one reason we don’t have Lalique cars.

So back to plastic. It’s quite stable (perhaps too stable) but doesn’t like sunlight which breaks down the long-chain molecules that account for its flexibility. That explains the lightening of unpainted plastic parts on car exteriors. For many, the Opel Corsa B is synonymous with faded wheel arch trim and so too is the Ford Ka Mk1 which borrowed the theme and moved it on. Still, the parts don’t fail as such, they just look a bit grim. Another type of plastic, vinyl, we have discussed here but it’s worth recapping that in return for adding questionable style and reducing the need for paint, the vinyl roof served as a rust-trap and cracked with age.

Yet more rust
Yet more rust

It all wears out. Tyres harden, copper cables oxidises and crack, small connectors gradually dissolve in the hot, acidic, wet, dry, cold hell of the engine bay. Stress – I haven’t really dealt with this but from a stress-hinge on a cheap Mitsubishi to the flexure that causes cars (especially Renaults) to become loose and rattly – stress is everywhere acting on a car. So, even a car driven on dry, dust free roads of some motoring utopia would still begin to fall apart.

Flaking enamel
Flaking enamel

The decay of the materials of which the car is made is emblematic of the decay we are all subject to which is why I tend to view the fight against decay as a sublimated wish to deny mortality. The wish to buy a brand new car is another sublimation of this wish as well as the simple expression of the need to have a reliable, nice-looking vehicle. Interestingly, the more durable a car gets the less like an ordinary car it becomes. Grumman made a long-life vehicle for the US Post Office and it is incredibly durable but it also looks like it a train carriage; the Rolls-Royce Silver Shadow seems to go on indefinitely but cost five times the annual wage to buy and is so fabulously heavy it consumes petrol twice as fast as its typical contemporaries.

That said, both Volvo and Saab found methods to manufacture relatively affordable cars from quite normal materials: the 240 and 900 are virtually eternal cars, possibly more durable than the Silver Shadow and as durable as the W-123 Mercedes. That old car again – it too resisted rust and could enduring million-mile service. All three of our entropy resistant cars come from around the same time and it makes you think.

What if the secret of the everlasting car has been found and but for some minor revisions could still be made to work? It seems the trade-off for a durable car is in weight, adding a few percent extra seems to result in a profound lengthening of the service life. It also results in a trade-off you can feel, a lumbering quality that lends the cars a driving character nobody seems to like too much. Evidently, humans are not as rational as we would like since the wish for handling advantages is that we have chosen to have cars with a shorter lifespan.

Author: richard herriott

I like anchovies. I dislike post-war town planning.

10 thoughts on “Theme: Material – Decay”

  1. Good Lord, this famed brittleness of Al you mention is of dire consequence. We must recall all the world’s cars bar a few of Mercedes’ newer diesels, and replace well over 5 billion Al pistons. At once! They’re not up to the job!

    I’d be quite surprised to find A8 structures which have cracks in them. The science of fatigue came into its own with Al-structured aircraft. We all remember the Comet where square apertures caused stress concentrations that led to fatigue. Conversely in the early 1970s many DC-3s were still happily buzzing around and there was no obvious design error cropping up time and again. And they’re still lumbering about today, even though spare parts have run out and dead planes are raided for bits of old luggage racks.

    The theory gradually developed that cyclic alternating deflections in Al below a certain stress level would not cause any fatigue problems because the DC-3 was massively overdesigned and safe. Later, it has been decided that there is no fatigue limit, but connections to causes of failure at low stress levels are not well-understood, 20 quadrillion cycles later. Nevertheless, Al airframes are stable enough that predicted life is quite well established or the jet commercial aircraft market would never have existed. Maximum use is made of the material’s properties. Differences between various alloys have to be taken into account as well. Regular ally will deflect about 3 times more than steel before it yields, so to me is more ductile, not brittle – but then you have alloys and etrusions to complicate matters.

    A car is a far chunkier design than a plane, designed to be stiff while a plane bends all over the place on purpose. Stonking great lumps of structural ally in a car aren’t going to crack unless some idiot designed a poor mount somewhere that doesn’t transfer load properly. All Ford F150 pickup trucks (highest selling vehicle in US and Canada at 700,000 per year) are Al except for the ladder chassis – I don’t suppose Ford expects them to rip, tear or fatigue apart! So why would an A8?

    Also, my cast alloy lower suspension arms on me Subie show no signs of conking out, nor have I ever heard of Corvette or NSX Al suspensions keeling over in ultimate distress. Rattly old Land Rovers with Al panels and bends with radii more severe than anticipated in the text books live on for yonks before stress cracks appear, because they’re relatively thick for the load. Perhaps every recent Range Rover or big Jag also be expected to crack as well, because they’re Al as well and must be viewed with grave suspicion?

    Just sayin’. I see far fewer problems with Al than you do. BMW welded Al front structures to steel cabins during the mid ’00s. GM and Ford have come up with great pad designs to separate Al from steel to prevent galvanic corrosion. My 9 year old Al hood (bonnet) on the Subie – I just checked in a panic. Phew! No cracks there either. 🙂

    1. It’s only a matter of time, Bill. One by one those Audi A8s will crumble.

      I’ll look into the matter.

      Seriously, that’s a strong and thorough response which indicates I may have waved my hand a bit too much on Al versus steel.

      Aren’t piston rods subject to compression and tension more than flexure? Bodies are subect to flexure and to compensate for Al’s egg-shell fragility they need to use thicker blanks, which slightly cancels the advantage. My Audi A8 versus Buick Park Avenue comparison indicated a less impressive difference than the Al boosters would lead one to expect.

      More research!

      Thanks for reading the article though – it has been a bit of a sleeper so far so the attention is welcome.

  2. Loved this article, in fact reread it twice! Durability is probably my greatest automotive obsession. I love the idea of vehicles that outlive their owner. Always have.
    So I’ve had many a Toyota, Volvo and Benz.
    Currently I’m driving a “lumbering” 1994 Isuzu Trooper with the 5-speed. It is such a quality vehicle. Underrated.

    1. Hi LW:
      A warm welcome to DTW. I am glad you liked the article. Who is doing durability best these days, would you say?
      It’s very hard to tell from the way cars are now assembled. In the 80s you could see the difference. Now cars look quite fragile, all surface and little depth.

  3. I’m a USA resident, and I feel that the most durable vehicles offered today in my own country are the ubiquitous full-size pickup trucks offered by General Motors. Body-on-frame construction seems to be our forte, our front-wheel drive cars have always been crap with some exceptions.
    Durability is such a mixed bag.
    I agree on the “brittle” construction but the mechanicals are so great now! My dream car would be that one that Mercedes-Benz built a few years back, the 1980’s 190 with the modern turbo-diesel drivetrain. The performance and mileage were amazing!

    1. The trucks are tough but lumbering, perhaps. They suit US road conditions though.
      What about a 300D sedan? The 190E is a horrible car in many ways. A 240 Volvo surpasses it in most respects.

  4. So much depends on the owner. I think that durable cars tend to draw abusive owners so don’t get to live as long as they could. The 300D being a good example. It’s getting very hard to find a nice one.
    Wasn’t it David E. Davis who said that American cars are designed to be”abuser-friendly” ?

    1. Hmmm. That’s not a point to dismiss or accept in one go. The Saab 900s, Volvo 240s and W-123s have hung around in numbers out of proportion to their sales. Certain cars attracted taxi companies that killed them off: diesel Fords and Peugeots plus bog-standard family cars that are tough but have nine years of heavy use and one final, careless owner.
      Trucks, which you mention, must get wiped out by small businesspeople and utilities.

  5. 45 year old pickup trucks are not uncommon where I live (Pacific Northwest) in fact, in a rust free zone like this many cars have proven to be usable for decades. I definitely think rust or the lack thereof is a major factor.

    1. Those old trucks are mostly mechanical: really simple hardware and little by way of soft trim and probably no electronics. They’ll run as long as rust is kept in check. From around 1995 more electronics and soft trim come with the body and I think bode ill for longevity. I contend 2000 was the sweet spot for a balance of reliability and durability.

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