Flexural Strength of Oak Branches vs Aluminum and Carbon Fiber

Image: A sketch of a robotic arm built from a frame of interwoven oak branches

It's springtime and the frost of winter has yielded to the explosion of buds and blossoms across various species of plants and trees. Recently while cleaning, I came across an oak twig I had saved sometime last year, having whittled the bark off of it, the twig seems exceptionally strong. This left me thinking about the attributes of various materials, and wondering how something like oak compares to items such as aluminum or carbon fiber when it comes down to evaluating their strength vs their costs.

Relative Cost

Could variables such as availability, cost, and strength leave wood outperforming metal? The difficulty in answering this question is greatly increased by relative costs. For example, location often affects the price of materials - wood not native to an area costs more to ship it to that location. Likewise, scale plays a tremendous factor. It might be efficient for one person to harvest oak branches to build a structure, but less practical to do that at an industrial scale where farming methods and machinery become necessary.

In my case, I want to determine a rough cost evaluation that's just relative to me. I'm just getting twigs and branches from naturally planted trees using regular/sustainable trimming and pruning methods). Additionally, mining ore and refining it might require tools, energy, and materials not currently available to me (although I'm up for attempting this for a future blog post).

Flexural Strength

Given my lack of testing equipment, and materials, I've compiled the following table from a variety of sources. Not that many of these are approximations or can vary significantly depending on how the material is treated, tempered, etc. Additionally conditions such as temperature can impact the strength of materials and how/when they fail.

Table References:

1. https://www.atlasfibre.com/understanding-flexural-strength-guide-to-flexural-strength-in-materials/
2. https://www.ijert.org/research/processing-and-flexural-strength-of-carbon-fiber-and-glass-fiber-reinforced-epoxy-matrix-hybrid-composite-IJERTV3IS040781.pdf
3. https://www.smicomposites.com/carbon-fiber-cost-factors-that-influence-the-most/
4. https://alvibel.pl/en/what-determines-the-strength-weight-of-plywood/
5. https://workshopcompanion.com/know-how/design/nature-of-wood/wood-strength.html
6. https://blog.lostartpress.com/2021/03/21/buying-wood-by-the-pound/
7. https://pmc.ncbi.nlm.nih.gov/articles/PMC4233722/