Hardness is a characteristic of a solid material expressing its resistance to permanent deformation. The Rockwell or Vickers hardness scales are most commonly used in the industrial blade industry.
Toughness on the other hand is the maximum amount of energy a material can absorb before fracturing, which is different than the amount of force that can be applied. Toughness tends to be small for brittle materials, because it is elastic and plastic deformations that allow materials to absorb large amounts of energy.
There are several material property terms that get mixed around when converting to layman's. Toughness and hardness are two of them. Another set is Plasticity and Elasticity which measure tension properties.
Elasticity is how much you can deform (stretch) an object, before the deformation is no longer reversible. Think of a rubber band, you can stretch it a little, and it returns to its original shape. Stretch it a lot, and it breaks down and does not return to its original shape.
Plasticity is how much you can deform an object before it breaks. This is the snapping point in the rubber band, where it completely breaks.
These two properties are different, and have to do with how the material is deforming on an atomic level. During elastic deformation, the individual bonds stretch. During plastic deformation, regions, layers, or fibers of the material slip. The relationship is best described by the stress-strain curve [1]. This plots deformation versus the pressure required.
Hardness and Toughness are the compression version of Elasticity and Plasticity.
These properties are often found experimentally, because they are a summation of many different atomic level interactions. Infact most materials are anisotropic, meaning if I measured the toughness of a material along two axises, I would get two different values.
> Elasticity is how much you can deform (stretch) an object, before the deformation is no longer reversible. Think of a rubber band, you can stretch it a little, and it returns to its original shape. Stretch it a lot, and it breaks down and does not return to its original shape.
> Plasticity is how much you can deform an object before it breaks. This is the snapping point in the rubber band, where it completely breaks.
These both are completely false.
Elasticity is the idealistic property of a solid material to get back to it's original shape after a deformation force is retracted. (property of most solid metals where stress is much below the yield point)
Plasticity is the idealistic property of a solid material to stay in the deformed shape after a deformation force is retracted. (Plasticine)
You are correct, but the statement you're quoting can be easily corrected: replace "elasticity" with "The elastic limit of a material". The elastic limit is also conventionally called the "yield strength".
"Plastic limit" is not a real term, but if it were, it might be a synonym for "ultimate tensile strength". There's also compressive strength and shear strength.
A relevant test for toughness is called the Charpy impact test. It uses a fixed size piece of material and a fixed weight pendulum to snap the material. The amount of force needed to snap the material becomes a score for toughness.
According to the ASM manual in front of me, toughness is the ability of metal to absorb energy and deform plastic ally before fracturing. The Charpy test is a test of absorbed energy, not force.
I misspoke earlier when I said force. I was inadvertently sloppy in my writing.
Usually anyway. IIRC, Acrylic is a plastic that shatters instead of deforming. But most plastics (ABS (aka Legos), polypropylene (PP, #5 Plastic), Pete (most bottles), HDPE (aka cutting boards)) all are "plastic", as in having high plasticity.
IIRC, metals are actually more "plastic" (deform more before breaking) than erm... plastics. See iPhone aluminum bending issue for details.
I recall that "plastic" was so named because of the material's formability. Thermoplastics soften or liquefy when heated, becoming malleable and can be molded or extruded, retaining shape when cooled. Thermosetting types are products that are cured by heat, UV or chemical reaction, having high plasticity before curing but irreversible rigidity after.
"Plastics" are mostly petrochemical derived organic polymers. Properties of some, like acrylic glazing are relatively hard and brittle, others quite elastic and soft, e.g., foam rubber. Obviously modern life is utterly dependent on these materials which are employed in virtually everything we use from food to space probes.
There are good reasons to believe that production of "plastics" is among the highest and best use of petroleum resources, it's a shame we continue burning it up at a prodigious rate. Trends to find alternative energy sources would have benefit in this respect too.
The history of plastics discovery is pretty interesting too.
The first were based on coal tar, starting around 1870-1880 IIRC. Then came bakelite, still used in cookware handles -- it has exceptionally good thermal resistance properties.
Discovery accelerated through the 1900s, 1910s, and 1920s, and exploded in the 1930s, with the number of materials about doubling IIRC.
Names started changing too -- from chemical (polypropelene, polyester, polystyrene) to brand (nylon, teflon, orlon).
I've also noted that with both coal and oil, there seems to have been an adoption and technological development cycle in which the first use was to burn the materials, and only later, by some decades, did the chemistry develop for materials based on the substrates. There's probably a lesson here.
Since the elastic modulus (slope/derivative of deformation vs stress graph) the energy absorbed is not necessarily very high even though you can get high deformations (multiple 100%, compared to 30% or so for soft steels).
"Conventional knee and hip implants have to be replaced after about 10 years due to wear and tear."
this is really amazing to me! you put metallic, designed-to-last object inside an organic blend of tissue and bone and human activity and in 10 years its worn out. So much opportunity in the area!
Along the same lines, interesting how delicate our bodies are in the short term but rather durable in the long term.
Your own body basically goes through a skeleton every 7 years, although it's a gradual procedure of course. Your bones are constantly being eaten away, and replaced as part of their maintenance. It's truly amazing, but the secret is definitely, "We can rebuild it" not "Unbreakable".
We should adjust our justice systems to this cycle. You can sit in jail for max 7years. After that you are considered a different person. The justice apparatus needs to use that 7 years to form this new person in a way that it can behave according to the outside system.
I thought that's why coral was used for bone implants it's first shaped like the part needed then once implanted your own bone cells gradually take over.
Maybe it was just a trial I saw to see if it worked or maybe it can only be used for small patches not entire sections of bone like a femur or hip joint.
I imagine any inorganic implamt is going to degrade, and have proprietery patents included. Your last question reminded me of the Jarvik Heart, in particular. Interesting read on evolution of the permanent to impermanent artificial heart:
It really only avoids being an issue now because of the nature of surgery, the longevity of typical patients vs. implants, and so on. Hopefully, eventually, both of those factors will change and the law is going to be shown to be woefully behind.
Regenerative medicine is the goal, and hopefully the future, but it's not easy to get right without accidentally setting off cancers or immune responses you didn't expect or want.
The bone is a living organ coating it with stuff can kill it.
I think there was a darpa paper about surrounding bones with carbon nano tube meshes that would renforce them, prevent or reduce shattering and could be used as an internal cast with minimal fixture but I hope we never get to that point.
I think that the defining characteristic for Wolverine is the regeneration rate, not the metallic skeleton (which has as a prerequisite the regeneration rate).
Don't give up so easily. According to Marvel[1], Wolverine is only 5'3, but Hugh Jackman played him at 6'2. For me, the most surprising stat from that page is that he weighs 195 lbs without the metal skeleton, and 300lbs with. He must be insanely stocky for that height.
While lots of hip and knee prosthetics last longer than 10 years, too many don't. The implants use synthetic materials to replace both sides of the joint, so there isn't for example, a metal femoral ball running against the patient's original hip socket in a hip prosthetic. It's metal/metal or metal/plastic.
I've done a little work in prosthetic materials. It's amazingly complicated. There are metals, plastics, and ceramics as basic options. There is every combination of one of those running against the other in hip implants. There's at least a half-dozen variants within each of the three materials classes. Typical materials are CoCr (metal), Al2O3 or ZrO2 (ceramics) and radiation cross-linked ultra high molecular weight polyethylene (UHMWPE plastic).
Prosthetic lifetime gets more and more important as the population of recipients gets younger. They're more athletic, put more load on their implants and they're going to use them longer than the earlier, older recipient population.
Yes, serious opportunity here. I hope implants are a once in a lifetime procedure if I ever need them.
Since it's 58% gold by weight, just the raw materials cost is going to be high. I expect for most applications it will be used as a thin coating over titanium or some other material. I wonder if it's a good choice for jewelry. Phase diagram: http://www.himikatus.ru/art/phase-diagr1/Au-Ti.gif
> Titanium is one of the few metals that human bone is able to grow around firmly, allowing it to be used widely in medicine and dentistry.
How good are we at concentration gradients in alloys? For a replacement joint, say, could the part that the bone bonds to be mostly titanium, and then the bearing portion be this new alloy?
Although I've only spent a few weeks in an ortho rotation in med school, I think pretty good. Many implants are coated with silver to help prevent infections. I've never heard of such silver layers ever "peeling off" or somesuch, so it seems the silver/titanium mix is effective.
It's been quite a long time since I studied this, but the primary problem with materials in implants is the quality of being bioinert. Many titanium alloys are not bioinert. Any combination would have to be tested separately.
This. Anytime you have metal in the body, you want to make sure it's not going to leach into the bloodstream and cause heavy metal toxicity, like mercury or amalgam fillings do.
Not only leach. Even titanium alloys used in implants have narrow specifications. For example, the Ti6Al4V that is used in implants differs from the used in airplanes by the amount of Iron on it. From 0.05% to 0.5% makes your body react to it and reject the implant.
Mercury/amalgram fillings isn't the best example, but biocompatibility is still the primary constraint.
Mayo clinic has a good overview and timeline regarding the discovery process for cobalt-chromium, which was previously thought to be a good all-around implant material:
Thinking about this perhaps the Titanium gold would be a surface layer or coating over Titanium.
No doubt there would be metallurgical issues with this.
Funnily I had a pre-student job in a coatings company using detonation guns to fire tungsten carbide into metals in order to make them tougher. Could a similar treatment be used for Titanium hip replacements?
I would disagree with the 'almost uniformly' but I understand your point. I would tend to exempt arstechnica for example.
I feel like most of the issue comes when journalists comment or repurpose journal articles. What seems to get dropped is the background, the context, and the limitations that are often expressed in a nuanced language. In the end, as a scientist, I blame scientists...you created the knowledge, try and take some ownership of it (having been in the situation myself).
Well, titanium has a a lot of strength relative to its weight, but I think you might need some kind of tungsten alloy for your budding weapon X program :-)
I have no idea how toxic tungsten is, buy hey, it's Wolverine, right?
Other mixes of Au/Ti have been made and used. There is plenty of prior research which the paper also cites.
The phase diagram posted in another comment shows that the region in which this particular phase exist is fairly small. Additionally the paper mentions that they had to add a few trace alloying components to stabilize it in that phase. I.e. it takes some effort to get to the point.
And even if you can spot a trend by lining up properties of various alloys on the right diagram, investigating that trend may be out of scope for the research you're currently doing.
And corrosion-resistant contacts of all kinds, and soft and biocompatible and corrosion-resistant tooth fillings, and low-resistance conductors (e.g. for bond wires), and coating glass to get ultra-low-loss mirrors well into the infrared, and measuring electrical charge in electroscopes, and coloring glass deep red, and conductive sheets so thin they are transparent, and in anti-inflammatories for arthritis, and in immunogold labeling, and in making random things conductive and emit lots of secondary electrons so you can easily look at them in an electron microscope...
This is why you're being downvoted. Check Wikipedia before commenting next time.
It was meant to be tongue-in-cheek. Gold has some nice useful properties, but it seems the properties that have mattered most to people throughout the millenia are 1) it has a pleasing color, and 2) it's hard to come by.
Probably more important, it's chemically inert (so it doesn't rust away to nothing) and it's easy to assay, at least once you can make aqua regia, an ability which was mastered by the 13th century CE, and possibly by the 14th century BCE. Harappan touchstones have been recovered, and although cupellation can't separate gold from silver, it can certainly separate it from iron, lead, tin, and copper, and we've found cupels with litharge deposits from the 4th millennium BCE.
Cupellation plus touchstones are adequate both to refine electrum and to destructively measure the quantity of gold in the electrum. By Roman times, we were smelting electrum with salt to separate out the gold by chloriding the silver, and the Lydians may have been doing that already by the fifth century BCE, when they started debasing their electrum coins with extra silver.
This sounds kind of stupid, since at this point we're used to being able to purify and quantify all kinds of materials, but in fact these attributes made gold and silver unique among rare elements for centuries.
That's cool! I don't know much about chemistry or metallurgy. I can see a connection from making gold for real to alchemy to chemistry. So perhaps gold is partially responsible for creating science? If for no other reason than its a really good motivator.
He was probably expecting an article about Dragonforce ("the hardest metal known to man"). Super-hard metal sounds like it would be an interesting genre, if slightly cheesy.
Even worse, using real metallurgy words, titanium is really strong per volume and doesn't care about high heat and is practically corrosion proof and a couple other weird properties... ironically what its NOT known for is its rather pedestrian hardness and toughness specs. There's a lot of reasons to talk up titanium and they carefully sidestepped around each of them LOL in favor of talking up two things titanium is fairly worthless at (at least worthless at per dollar or whatever).
If you want something tough that can absorb surprising amounts of energy without breaking there are exotic nickel steels that require exotic heat treatment, or maybe some of the military armor plates from the old days (before HEAT rounds forced other criteria as a figure of merit). Maybe a chunk of battleship armor plate or maybe the crankshaft from an old diesel ship engine.
If you want something hard there are some oxidized titanium coatings that are somewhat hard and industrially useful but nothing unusual or worth writing home about. Besides that's cheating because its a titanium containing compound, kinda like saying coal cures scurvy because vit C is merely a peculiar arrangement of carbon atoms much like coal. Industrial diamonds are not going to be replaced by titanium rod anytime soon...
It sort of plays to a very simplified layman's understanding of structural metals as following some sort of uni-dimensional good/better/best scale with titanium being on the best end of the spectrum. (And, hence, "titanium" being used in all sorts of product names, such as clothing, which have absolutely to do with metal except insofar as the production equipment has metal parts--though probably not many titanium ones.)
The actual paper (http://advances.sciencemag.org/content/2/7/e1600319.full) is much better and is free.