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Over in Programmers chat we were discussing whether a gold skeleton would be feasible. That got me thinking:

If I were to build a Terminator (T-800) using pure gold as the endoskeleton, would the skeleton be able to support the weight of the terminator? If so, what type of force would cause it to deform under stress? Would it be able to handle normal human tasks such as running, walking, or jumping? What about the superhuman feats of strength the terminator performs in the movies?

For the sake of this calculation, assume a T-800 weighs an extra 30% more than a human its size. Based on what Google says Arnold's size is and a rounding slightly, that assumption is 2m tall and 150kg.

The question Stacking gold Bars indicates that gold has quite a bit of strength given its reputation as a soft metal. However, that question talks about the compressive strength: also, I am not an engineer and unable to calculate the types of stresses a skeleton would undergo and whether those would be greater than the tensile strength of gold.

Finally, assume the same or similar motors and supports: there is very little information out there, but clearly this machine is capable of supporting great loads compared to humans, throwing grown men across rooms like dolls, etc. Only the skeleton is gold: motors, electronics, etc. could remain as other metals (steel, titanium, copper).

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  • $\begingroup$ Should I assume average human size bone dimensions (Ref: robmech.co.za/proceed/…) ? $\endgroup$
    – Mark
    Commented Jul 9, 2015 at 21:58
  • $\begingroup$ Fun question -- interesting to analyze the various stresses that a mechanism like the T-800 would experience -- but still: why gold? There is no universe following our physics in which that element exists in significant quantities relative to other metals that are even denser than gold but stronger in every measure except malleability. I.e., gold is relatively weak in all performance per mass measures. It's most interesting due to its rarity and its malleability. $\endgroup$
    – feetwet
    Commented Jul 9, 2015 at 23:21
  • $\begingroup$ I am with @feetwet on this. Why gold? $\endgroup$
    – Algo
    Commented Jul 9, 2015 at 23:52
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    $\begingroup$ Read through the chat log (I'm surprised the room isn't called compiling. Glad we stayed away from drawing board.) It started with a spam email selling "Tibia gold." $\endgroup$
    – Mark
    Commented Jul 10, 2015 at 0:02
  • $\begingroup$ What @Mark said, plus gold is an interesting metal. It is an excellent conductor of electricity, very shiny (even my scuffed wedding ring), malleable, soft, yet if I threw a gold brick at someone's head it would really hurt. That is the crux of the question: gold is a metallic substance known to be more dense yet more soft than other metals, but is still a lot harder than the organic matter from which humans are made. Clearly a steel robot works, we have those (visit a car factory). Clearly a mercury robot would not work (it would be a puddle). Gold is like... Goldilocks? Just right. $\endgroup$
    – user608
    Commented Jul 10, 2015 at 1:01

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The following table gives some of the material properties of four metals: gold, aluminium, titanium and iron. 

Metal    Tensile      Shear    Bulk    Young's Brinell   Density
         Strength     Modulus  Modulus Modulus Hardness
           MPa         GPa      GPa     GPa      GPa      g/cm^3
Gold       120          27      180      79    188-216    19.300
Aluminium  125-300      26       76      70    160-550     2.700
Titanium   210          44      110     116    716-2770    4.506
Iron       150-430      82      170     211    200-1180    7.874

From the table, gold has tensile and shear strengths similar to that of aluminium but its bulk density is more than double that of aluminium and slightly stronger than that of iron.

The Young's modulus for gold is similar to that of aluminium, so both metals have similar level of stiffness and from the Brinell hardness numbers gold is a soft metal.

An endoskeleton made of gold could support itself but having shear and tensile properties similar to aluminium it would not be able to withstand large external forces that would try to destroy it.

The other issue with using gold as the main metal for the endoskeleton is moving the endoskeleton and other body parts would require a lot of energy and strong motors due to its weight as gold is more than twice as dense as iron.

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  • $\begingroup$ Bigger motors mean more to carry and bigger dynamic loads on the skeleton. So while possible it would be a really bad tradeoff... unless your smugling gold? $\endgroup$
    – joojaa
    Commented Jul 10, 2015 at 13:19
  • $\begingroup$ This would be an even better answer if you could factor the density into the shear and tensile properties. For example, the "residual tensile strength" would be nothing like aluminum. I.e., a key part of the OP could be phrased as, "How strong is a skeleton made of pure gold relative to one made of structural metals/alloys?" And the key point to quantify is that the density of gold "uses up" so much of whatever strength it has that its structural strength is abysmal. $\endgroup$
    – feetwet
    Commented Jul 10, 2015 at 16:41

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