bone is so much weaker than diamond (on my understanding) … Bone cleaves along the weaker fault line, not at its strongest point.
While it is true that the ultimate strength of diamond is much higher than bone, this is relevant primarily for its ability to resist continuously applied pressure (as is its hardness enabling cutting). The point about fault lines seems more relevant for toughness, another material property that describes how much energy can be absorbed without breaking, and there bone beats diamond easily—diamond is brittle.
There are materials that have both high strength and toughness, e.g. nacre and some metallic glass, both of which are composites.
What does this operationalize as? Presumably not that if we load a bone and a diamond rod under equal pressures, the diamond rod breaks first? Is it more about if we drop sudden sharp weights onto a bone rod and a diamond rod, the diamond rod breaks first? I admit I hadn’t expected that, despite a general notion that diamond is crystal and crystals are unexpectedly fragile against particular kinds of hits, and if so that modifies my sense of what’s a valid metaphor to use.
As an physicist who is also an (unpublished) SF author, if I was trying to describe an ultimate nanoengineered physically strong material, it would be a carbon-carbon composite, using a combination of interlocking structures made out of diamond, maybe with some fluorine passivization, separated by graphene-sheet bilayers, building a complex crack-diffusing structure to achieve toughness in ways comparable to the structures of jade, nacre, or bone. It would be not quite as strong or hard as pure diamond, but a lot tougher. And in a claw-vs-armor fight, yeah, it beats anything biology can do with bone, tooth, or spider silk. But it beats it by less than an order of magnitude, far less that the strength ratio between a covalant bond to a van der Vaals bond (or even somewhat less than to a hydrogen bond). Spider silk actually gets pretty impressively close to the limit of what can be done with C-N covariant bonds, it’s a very fancy piece of evolved nanotech, with a different set of anti-crack tricks. Now, flesh, that’s pretty soft, but it’s primarily evolved for metabolic effectiveness, flexibility, and ease of growth rather than being difficult to bite through: gristle, hide, chitin, or bone spicules get used when that’s important.
But yes, if I was giving a lecture to non-technical folks where “diamond is stronger than flesh-and-bone” was a quick illustrative point rather then the subject of the lecture, I might not bother to mention that, unless someone asked “doesn’t diamond shatter easily?”, to which the short answer is “crystaline diamond yes, but nanotech can and will build carbon-carbon composites out of diamond that don’t”.
I see the appeal of using “static cling” as a metaphor to non-technical folks, but it is something of an exaggeration for hydrogen bonds—that’s significantly weaker van der Vaals bonds. “Glue” might be a fairer analogy than “static cling”. The non-protein-chain bonds in biology that are the weak links that tend to fail when flesh tears are mostly hydrogen bonds, and the quickest way to explain that to someone non-technical would be “the same sort of bonds that hold ice together”. So the proportionate analogy is probably “diamond is a lot harder than ice, and the way the human body is built, outside of a few of the strongest bits like bones, teeth and sinews, is basically held together mostly by the same sort of weakish bonds that hold ice together”.
I checked this, and this post is correct. At least, when you’re talking about bones and common, natural diamonds, which are monocrystalline.
The toughness of bone is about 2-4MPa√m(depending on the exact form of toughness) and can increase to 3-20MPa√m locally as when bones crack, microfractures can deflect the crack from growing along the directions of maximum tensile stress.
As compared to common natural forms of diamond, which only have a toughness of 2MPa√m. Which is mediocre compared to other engineering materials. However! Other naturally occuring forms of diamond, such as Carbando, are much tougher and just as hard. Carbando’s strength comes from the random orientation of microdiamonds i.e. it is not mono-crystaline. There’s little numerical data in the literature on this, but it is predicted that its toughness will exceed 10-20MPa√m (paywalled article with a confusing preview). Some evidence for their toughness comes from industrial usage for thing like deep-drilling bits, unlike regular diamond. Moreover, designed dimaonds have achieved Pareto improvements in toughness and hardness compared to common natural diamonds (reaching upto 26.6MPa√mfor nanotwinned diamond).
So diamonds can be clearly superior to bone. And yeah, these things probably aren’t bound together on a large scale by van der waals forces (I haven’t looked into that aspect for unusual diamonds like Carbando, not an expert, just took a couple solid state physics courses in uni). But. Carbando seems to gain its strength from irregularities. Sometimes irregularities make materials much stronger, sometimes much weaker. Sometimes “fault lines” can be beneficial, because they allow the material to be ductile, which you want. Like the ductility of steel, IIRC, comes from irregularities in the lattice structure which are moved around as the material deforms.
Sometimes irregularities make materials much stronger, sometimes much weaker. Sometimes “fault lines” can be benificial, because they allow the material to be ductile, which you want. Like the ductility of steel, IIRC, comes from irregularities in the lattice structure which are moved around as the material deforms.
And in that deformation (of a metal or other crystal), you both create the discontinuities (esp. dislocations) that increase strength while also introducing brittleness (work hardening). But the highest strength you can get with this kind of process is still not as high as you’d get from a defect free crystal, such as a monocrystalline whisker.
Minor point about the strength of diamond:
While it is true that the ultimate strength of diamond is much higher than bone, this is relevant primarily for its ability to resist continuously applied pressure (as is its hardness enabling cutting). The point about fault lines seems more relevant for toughness, another material property that describes how much energy can be absorbed without breaking, and there bone beats diamond easily—diamond is brittle.
There are materials that have both high strength and toughness, e.g. nacre and some metallic glass, both of which are composites.
What does this operationalize as? Presumably not that if we load a bone and a diamond rod under equal pressures, the diamond rod breaks first? Is it more about if we drop sudden sharp weights onto a bone rod and a diamond rod, the diamond rod breaks first? I admit I hadn’t expected that, despite a general notion that diamond is crystal and crystals are unexpectedly fragile against particular kinds of hits, and if so that modifies my sense of what’s a valid metaphor to use.
As an physicist who is also an (unpublished) SF author, if I was trying to describe an ultimate nanoengineered physically strong material, it would be a carbon-carbon composite, using a combination of interlocking structures made out of diamond, maybe with some fluorine passivization, separated by graphene-sheet bilayers, building a complex crack-diffusing structure to achieve toughness in ways comparable to the structures of jade, nacre, or bone. It would be not quite as strong or hard as pure diamond, but a lot tougher. And in a claw-vs-armor fight, yeah, it beats anything biology can do with bone, tooth, or spider silk. But it beats it by less than an order of magnitude, far less that the strength ratio between a covalant bond to a van der Vaals bond (or even somewhat less than to a hydrogen bond). Spider silk actually gets pretty impressively close to the limit of what can be done with C-N covariant bonds, it’s a very fancy piece of evolved nanotech, with a different set of anti-crack tricks. Now, flesh, that’s pretty soft, but it’s primarily evolved for metabolic effectiveness, flexibility, and ease of growth rather than being difficult to bite through: gristle, hide, chitin, or bone spicules get used when that’s important.
But yes, if I was giving a lecture to non-technical folks where “diamond is stronger than flesh-and-bone” was a quick illustrative point rather then the subject of the lecture, I might not bother to mention that, unless someone asked “doesn’t diamond shatter easily?”, to which the short answer is “crystaline diamond yes, but nanotech can and will build carbon-carbon composites out of diamond that don’t”.
I see the appeal of using “static cling” as a metaphor to non-technical folks, but it is something of an exaggeration for hydrogen bonds—that’s significantly weaker van der Vaals bonds. “Glue” might be a fairer analogy than “static cling”. The non-protein-chain bonds in biology that are the weak links that tend to fail when flesh tears are mostly hydrogen bonds, and the quickest way to explain that to someone non-technical would be “the same sort of bonds that hold ice together”. So the proportionate analogy is probably “diamond is a lot harder than ice, and the way the human body is built, outside of a few of the strongest bits like bones, teeth and sinews, is basically held together mostly by the same sort of weakish bonds that hold ice together”.
I checked this, and this post is correct. At least, when you’re talking about bones and common, natural diamonds, which are monocrystalline.
The toughness of bone is about 2-4 MPa√m(depending on the exact form of toughness) and can increase to 3-20 MPa√m locally as when bones crack, microfractures can deflect the crack from growing along the directions of maximum tensile stress.
As compared to common natural forms of diamond, which only have a toughness of 2 MPa√m. Which is mediocre compared to other engineering materials. However! Other naturally occuring forms of diamond, such as Carbando, are much tougher and just as hard. Carbando’s strength comes from the random orientation of microdiamonds i.e. it is not mono-crystaline. There’s little numerical data in the literature on this, but it is predicted that its toughness will exceed 10-20 MPa√m (paywalled article with a confusing preview). Some evidence for their toughness comes from industrial usage for thing like deep-drilling bits, unlike regular diamond. Moreover, designed dimaonds have achieved Pareto improvements in toughness and hardness compared to common natural diamonds (reaching upto 26.6MPa√mfor nanotwinned diamond).
So diamonds can be clearly superior to bone. And yeah, these things probably aren’t bound together on a large scale by van der waals forces (I haven’t looked into that aspect for unusual diamonds like Carbando, not an expert, just took a couple solid state physics courses in uni). But. Carbando seems to gain its strength from irregularities. Sometimes irregularities make materials much stronger, sometimes much weaker. Sometimes “fault lines” can be beneficial, because they allow the material to be ductile, which you want. Like the ductility of steel, IIRC, comes from irregularities in the lattice structure which are moved around as the material deforms.
And in that deformation (of a metal or other crystal), you both create the discontinuities (esp. dislocations) that increase strength while also introducing brittleness (work hardening). But the highest strength you can get with this kind of process is still not as high as you’d get from a defect free crystal, such as a monocrystalline whisker.