Fatigue is a progressive failure due to the localized and cumulative damage that occurs when material is subjected to cyclic loading. This is vitally important, since a man lifting a 70-pound box actually exerts a normal compressive load of over 500 pounds on one of his vertebrae-just imagine the loads of Olympic weightlifters.Īn important area of engineering research is designing materials that are fatigue resistant. Compared to reinforced concrete, bone is more flexible and has more strength to resist crushing compressive loads. A microscopic view shows that individual apatite crystals are bound to the collagen fibers and linked as a continuous mesh-but at full size the structure appears solid. Apatite is a medium-hard mineral with properties similar to marble and is found widely distributed in rocks. The bone's equivalent of the cement/aggregate part of concrete is composed of apatite. Collagen fibers are linked so strongly that their resistance to being pulled apart in tension is actually greater than the resistance present in an equal amount of steel rebar. In order to work, this particular amino acid would need to be designated for every third position in each strand-which is exactly what is specified in the DNA code. The reinforcing 'rods' in bone are made from minute strands of collagen fibers, 360 of which could be put end-to-end in the width of a human hair.Įach fiber is composed of three substrands wound in rope-like fashion around each other so tightly that along the area of contact only the smallest amino acid would fit in the space between the strands. Bone is constructed much like reinforced concrete, in which a cage of steel reinforcing bars ('rebar') is embedded. In fact, studying bone construction and function provides a mini-course illustrating important engineering principles.Ī quality product begins with materials that have superior engineering properties.

The bones in the human body capitalized on this design feature long before farmers and architects did. This resourceful design allows for a very strong structure with a maximum of interior space available for other purposes.

Internal floors and walls, if any, function in a structural way to stiffen the building. A key design feature shared by many 100-year-old barns and some modern skyscrapers is that the external shell carries the building's load with a minimal use of internal columns for support.

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