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Thread: New 2018 Defender to share D5's Aluminium monocoque body.

  1. #31
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    Quote Originally Posted by JDNSW View Post
    Properly designed, an aluminium structure can be just as strong as a steel structure.

    The critical property in any practical structure such as a car body is Young's Modulus (for practical materials). This is the factor that is relevant in Euler buckling, which is the failure mode of relatively long narrow structures in compression, such as the top of a chassis rail where the load is between front and rear wheels. Interestingly, for all practical materials (except some exotic ones- e.g carbon fibre), this property is proportional to the specific gravity of the material. This means that everything else being equal, steel and aluminium structures would be the same weight.

    But everything else is not equal - a lot of the bits of the body have a minimum thickness requirement to cope with minor damage and corrosion - for the same strength, aluminium is about three times as thick, so a lot of it can be made the thickness needed for strength rather than this minimum thickness. And it is still likely to be stiffer than the steel part, simply because it is still perhaps twice as thick - and the dimensions come into the formula as well.

    Consider, for example, the chassis of a Series Landrover. Except for a few reinforcing spots, it is all made of the same thickness metal, this being the minimum feasible thickness to sustain minor damage and corrosion - if it were made of aluminium, it would not have to be three times as thick - probably the top and bottom of the rails maybe twice as thick, sides the same thickness (an engineering calculation to decide), and a lot lighter - but significantly more expensive.

    John
    That's a good point, but my understanding of why steel has always been used for chassis is that it has a fatigue limit. I understand that Land Rover would've done their homework on this and designed for acceptable cycle life, but unlike steel there will be a cycle life. I'd like to believe the aluminium chassis is a step made purely in the belief that the vehicle will be better for having it, but I can't shake the feeling it is to get low emissions/fuel consumption/0-100km/h times and to hell with longevity.

    Will an aluminium chassis bent if you hit it, or will it gouge - causing stress concentration points and dramatically reducing the cycle life? Can an aluminium chassis be repaired?

  2. #32
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    Quote Originally Posted by Dervish View Post
    That's a good point, but my understanding of why steel has always been used for chassis is that it has a fatigue limit. I understand that Land Rover would've done their homework on this and designed for acceptable cycle life, but unlike steel there will be a cycle life. I'd like to believe the aluminium chassis is a step made purely in the belief that the vehicle will be better for having it, but I can't shake the feeling it is to get low emissions/fuel consumption/0-100km/h times and to hell with longevity.

    Will an aluminium chassis bent if you hit it, or will it gouge - causing stress concentration points and dramatically reducing the cycle life? Can an aluminium chassis be repaired?
    Steel has always been used for chassis because it is the most cost effective. Actually, steel has not always been the material of choice - in the early days of motoring, wood was a common chassis material, and in a few instances continued possibly as late as the 1970s - for example in some model Morgan sports cars.

    Aluminium does not necessarily have a fatigue life (e.g. the alloy used on the DC-3), and steel does not necessarily not have one. It all depends on the alloy used and the structural design.

    An aluminium chassis will bend if you hit it hard enough, same as a steel one - and will undoubtedly crack like the steel 130 ones do if overloaded with a poorly engineered tray. There is nothing to suggest that an aluminium chassis would be harder to repair than steel, except for slightly greater demands on welding equipment and skill. And the corrosion problem should be markedly less, meaning fewer repairs are required. It will gouge to a greater extent than does steel, but the effects of this can be neutralised by proper design.

    John
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  3. #33
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    Good point John. Fatigue-wise, the DC-3 was practically indestructible!

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    Just a quick thought, i think it was JLR's former owner or maybe toymota who had a "flashy" alloy suspension system on an overseas model that was adapted locally using steel to a previous model.
    Lets say JLR do the same with the defender(i mean production is rumored for Uzbekistan isn't it? ), certain large bits like body are still aluminium, but some of the chassis or suspension is made from steel where its cheaper, kind of like ford did with the latest F1-350 series which have aluminium bodies!
    Have a look at Section 3: 2017 Ford F-150 Full-Size Pickup Truck | Built Ford Tough | Ford.com
    They state 78% of the chassis is steel with a aluminium body. Hmmm, Whats the other 22% ???

  5. #35
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  6. #36
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    Quote Originally Posted by cripesamighty View Post
    Good point John. Fatigue-wise, the DC-3 was practically indestructible!
    Purely by accident - they knew little about metal fatigue in 1936 (or 1934 if it is the same alloy as the DC-2, which it probably is).

    And, if my memory serves correctly, metal fatigue of steel structural members was behind an Australian Stinson? it had been converted from three to two airliner losing a wing in about 1940 (it had been converted from three to two more powerful engines because of wartime parts shortages).

    John
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    If they do an good quality auto and put in cruise with 4 wheel discs and coils I might be able to drag myself out of the Amarok, back to LR. In fact, probably not even then considering my lease is up mid-17 I'll probably just replace the Rok with another and watch to see what happens with the new Defender, maybe get the SII in 2020...

  8. #38
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    I just had a look over the new G-wagen commercial fitted up as a light unit for fire fighting..very impressive bit of kit, I personally think that with the roll out of the government units, it will be only a matter of time before they are available to the public.. Landrover will need to hit the commercial market hard with a brilliant vehicle if in fact they are doing a cab chassis option. The only thing that should be carried over to the new defenders is it's off road load carrying capacity.

  9. #39
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    Perhaps worth mentioning that aluminium chassis are not new. Designs by Gregoire using these were in production as early as 1938 (Hotchkiss) and post war by Panhard and abortively by Hartnett in Australia. (Panhard nearly went broke building in Aluminium and changed to mostly steel in the fifties!)

    So alloy chassis are not really new.

    John
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  10. #40
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    Here's the new Merc dual cab designed to take on the amarok and top line Japanese utes( all Thai built) due in showrooms about 6-12 months before defender.
    https://pickup.mercedes-benz.com/con...ighlights.html

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