The Rationale:
I was recently told by a LT that a set of Wyvernbone platemail is heavier than standard steel, yet provides the exact same protection. I have found this illogical and underwhelming, so I have gone on to calculate exactly how effective a set of bone armor, compressed to the point of being 1.25 times heavier than steel, would be. I wasn’t completely sure where to put this, so I’ve placed it in the story feedback section due to it being feedback to material lore.
This investigation is operating under the following assumptions:
1.Cortical bone is 4.27 times lighter than steel, thus wyvernbone must be compressed to achieve a weight that is heavier than steel.
2. Wyvernbone has the same weight/hardness/tensile strength ratios as human cortical bone, and if uncompressed to a weight of 1.85g per cm3 they would have the same properties. Thus the ratios of human cortical bone are the standard ratios.
Key Terms:
Mohs= a 1-10 scale used when determining the hardness of a solid substance named after F Mohs, a German mineralogist.
Mpa= Megapascal, used to denote the tensile strength of an object.
First, let's consider the properties of each material
Bone
For the sake of consistency human cortical bone will be considered. Cortical bone makes up the majority (80% in humans) of skeletal mass in animals, and excludes bone marrow.
Weight: 1.85g per cm3
(Source: https://www.aqua-calc.com/calculate/weight-to-volume)
Hardness: 5 Mohs
(Available from a Google search)
Tensile Strength: 130Mpa
(Source: https://www.montefiore.ulg.ac.be/systems/GBIO/gbio001/chap_2.3.pdf)
Steel
For sake of consistency in the medieval time period, untempered mild steel will be considered. Mild steel is created with a lower carbon content than contemporary steel, thus it possesses a lower tensile strength than today's steel yet nearly-equivalent hardness (.5 Mohs scale difference).
Weight:7.9g per cm3 (Source:https://www.aqua-calc.com/calculate/weight-to-volume)
Hardness: 4 Mohs
(Available from a Google search)
Tensile Strength: 402.45Mpa (Source: https://www.omicsonline.org/open-access/analysis-of-mechanical-behavior-and-microstructural-characteristics-change-of-astm-a36-steel-applying-various-heat-treatment-2169-0022-1000227.php?aid=67903)
Why Tensile Strength is Important in Using Bone Armor
Judging from the above data, one can see that bone is both 4.27 (7.9/1.85) times lighter and 1 Mohs harder than mild steel. That begs the question: Why didn't we have knights-in-shining-bonemail in the medieval era? That boils down to bone's lower tensile strength. Tensile strength is the resistance of a material against shattering under tension, and can be increased by increasing the density of the material in the case of porous natural materials such as wood and bone.
(Source:https://www.quora.com/If-the-density-of-a-material-increases-does-the-tensile-strength-increase-as-well)
Wvyernbone’s Tensile Strength
Now we have to consider that, in equal masses, wyvern bone is reported to be heavier than steel. That means that it must be denser/more compressed than normal bone. For sake of argument, let's assume that Wyvernbone is 1.25x heavier than steel of the same mass. This means that 1 cm3 of wyvernbone weighs 9.875g (7.9x1.25) per cm3, and thus is 5.34 (9.875/1.85) times denser than normal bone. Raising the density of a material increases its hardness on the Mohs scale, as well as often increasing its tensile strength. In the case of porous natural materials such as bone, increasing the density of the material increases its tensile strength at about a 1:1 rate. This would give Wyvernbone a tensile strength of 694.2Mpa (130x5.34), on-par with high-quality modern steel which would have been impossible to produce through the medieval period. (Source:https://www.quora.com/If-the-density-of-a-material-increases-does-the-tensile-strength-increase-as-well)
What does this mean?
Unlike the brittle uncompressed bone, Wyvernbone would be far more resilient when taking hits. Due to its tensile strength of 694.2Mpa, it would be impossible to fragment a plate of armor made from Wyvernbone without a godlike show of blunt force. Additionally, its Mohs hardness would increase from bone's 5 (already harder than steel) to an even higher number due to its density. This would make the plates of armor more difficult to slash or stab through than plates of the best modern steels which only rank 4.5 on the Mohs scale.
Conclusion:
Wyvernbone armor needs to be buffed. Either reduce the weight to match steel pound-for-pound (thereby reducing the density by .25, making the tensile strength 520.65Mpa) while having it as effective as bluesteel, or keep the weight at 125% that of steel and increase its effectiveness to above that of bluesteel.