Materials

Bone-inspired struts could increase materials' fatigue life

Bone-inspired struts could inc...
A piece of 3D-printed bone-like material (gray) is subjected to cyclic load testing
A piece of 3D-printed bone-like material (gray) is subjected to cyclic load testing
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A piece of 3D-printed bone-like material (gray) is subjected to cyclic load testing
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A piece of 3D-printed bone-like material (gray) is subjected to cyclic load testing

Thanks to a new understanding of how bones maintain their strength, we may someday see bone-inspired materials used in the production of longer-lasting products such as aircraft wings. The findings could also lead to better treatments for conditions like osteoporosis.

A bone's lattice-like internal structure typically consists of a network of vertical plate-like struts, along with thinner horizontal rod-like struts that run between them. When a bone receives a single heavy load all at once, it is largely the density of the vertical struts that determines whether or not it will break. Previously, it had been thought that the horizontal struts had little effect on bone strength.

Utilizing computer models, however, researchers from Cornell, Purdue and Case Western Reserve universities recently determined that the higher the density of horizontal struts, the greater the number of smaller load cycles a bone could endure over time before breaking – this is known as its long-term fatigue life.

"If you think about how many cycles of low-magnitude load something can take, these little sideways twiggy struts are what really matter," says the lead scientist, Cornell's Prof. Christopher J. Hernandez. "When people age, they lose these horizontal struts first, increasing the likelihood that the bone will break from multiple cyclic loads."

In order to put the computer model data to a physical test, the researchers 3D-printed multiple samples of a bone-inspired urethane polymer material, then subjected them to repeated load cycles. It was found that by increasing the thickness of the horizontal struts, the material's fatigue life could be increased by up to 100 times.

It is now hoped that the team's findings could inspire manmade materials that are better able to withstand multiple loads over their operational lives. Hernandez points to aerospace materials as a prime example, as he states that "an airplane wing gets loaded thousands of times during every flight."

The research – which is described in a paper that was recently published in the journal Proceedings of the National Academy of Sciences – may additionally help guide the development of treatments for degenerative bone disorders.

Source: Cornell University

2 comments
Bob Stuart
Does the "density of the vertical struts" refer to the specific gravity of the material, or the frequency of struts of uniform size? Are thicker struts never used, with their reduced need for bracing to stay in column?
Douglas Rogers
Regular composites that have 70% reinforcement already outlast all fatigue tests. Some have been under test for 30 years.