Fatigue resistance of wood...

[Tommy D]

I have always found this test on fatigue resistance fascinating ... and although most of this information relates to boat building ... I couldn’t help but think that it’s pretty applicable to a bow too!



If anyone wants more info it’s all here  https://www.westsystem.com/wp-content/uploads/GougeonBook-061205-1.pdf in appendix C ... plus a lot of interesting stuff on epoxy resins.

[DC]

So after 10 million arrows you should check for set? Keep us posted
Interesting

[willie]

thanks for the link

I was searching for this exact info recently

[mmattockx]

So after 10 million arrows you should check for set? Keep us posted
Interesting

I too look forward to hearing about the 10 million cycle inspection. Since that is tensile stress I would expect the back to blow up when the endurance limit is reached, so heads up for that. Safety glasses may be in order...


Mark

[PatM]

I'm going to write a  warning for the great grandchildren to not string up and shoot " ol' suredeath"

[Jim Davis]

I remember reading in some text book decades ago that for engineering purposes, wood is consider to have no fatigue limit to cycles short of its elastic limit.

And since wood is at least 3 times stronger in tension, it will fail first in compression--assuming growth rings are not cut.

[bownarra]

I wonder when all the glass and carbon bows are gonna start blowing up.....

[Yooper Bowyer]

I think set is when the elastic limit is exceeded, because there is no deformation in the material before the limit is reached. Chrysals and fractures are actual failure.

[Tuomo]

Please, read the original document:

"All the curves illustrated in Figure
C-1 begin at a maximum level, with 100% corresponding
to the one-time load-to-failure capability of each
material. The curves represent the combined results of
many individual samples, each tested at a different peak
stress. As the peak stress is decreased, the number of
cycles required to produce failure is increased. Each
individual peak stress and failure point is then plotted
to form a fatigue curve. The goal of fatigue testing is to
find the level of peak stress where a material can
withstand a given cyclic loading for a very long or
indefinite period, without undergoing further degradation."

So, for example "Laminated wood": If the maximum tensile stress is about 90 % of the maximum tensile stress laminated wood can withstand, it will fail after about 1000 cycles. And, if carbon fiber composite (sorry...) is stressed at maximum 60 % of maximum tensile stress, it will survive infinite cycles. And so on.

[Eric Garza]

I wonder how much the wood's curve varies from one type of wood to another. According to the graphic the wood used to create that curve was laminated douglas fir. I wonder what osage or yew's curve would look like, or any more typical bow wood, laminated or otherwise.