very quick question for the engineering types – role of thickness in bow limbs
hey guys, im a bit puzzled right now. i am reading jürgen junkmanns freshly released book (some may remember the detailed measurement tables he once posted for the holmegaard and mollegabet bows –...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
Not an engineer, but I've always heard 8x. That is, just under 8x increase in stiffness by increasing thickness as opposed to increasing same amount of width. Sounds like a great book! Ken
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
thats what i read, too, ken. also, beam theory seems to say (to my uneducated eyes) that the correlation of force applied to a beam and its deflection is the product of the materials elastic modulus...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
soo, i went to the library and found the articles. junkmanns mainly seems to draw on an article where beckhoff mathematically analyzes a bronze age bow artifact found at vrees. i did not understand...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
100 cm X 1cm X 1cm unknown really stretchy wood that is for these purposes not compressible. Lets say it stores exactly 100 J of energy when bent into half a circle. Double the thickness and the back...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
gekitsu-mathematical engineering formulas used for calculations with beams are useful only so far as the material obeys Hooks Law (stress and strain are proportional when the materiel is perfectly...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
bluestone: yes, im just as unsure about what im thinking now. i read junkmanns talking about a double thick bow drawing 4× as much and jim hamm saying it draws 8× as much. i can see where both come...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
Raphael- without the complete formulas to look at, it is hard to suppose if one is right, or one is wrong. Perhaps one of the the formulas in question already has some sort of "factor" incorporated...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
bob, junkmanns doesnt go into anything concerning arrow choice, just draw weight at a draw length suggested by the bows length and layout. of course, interpreting artifacts that way is bound to lead...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
Raphael- Thanks for sharing some more about junkmanns latest work. I know that many would like to be able to see his research and illustrations in english. Of course, one must make reasonable...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
Raphael, It sounds like a great book, with a lot of real data on ancient bows. What language is it in? The bending stiffness in a bow is proportional to the thickness cubed (T^3), and that is what is...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
bob: after checking for holmegaard and mollegabet, i immediately checked for hjarno – sadly, it seems to be a tad too recent. if it is indeed his dissertation (or at the very least, based on his...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
Now that I have had a few hours to think about it, perhaps a bit or re-arrangement of the formulas will make clear the difference between calculating bend and surface strain and stress. For bend the...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
ah, so stress is the purely geometric fact how a certain shape results in how much elongation and compression at any given point? and strain is the relation of a shape's stress at a certain...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
I think stress and strain are difficult to keep straight even in english. Strain has to do with the percent elongation (or compression), and is what tells one the amount of bend. Stress has to do with...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
dave, 55 euro for a book you dont even get all it contains out of is steep, indeed. let me know when i can help with providing stuff from it, like measurements of certain artifacts, or bows from a...
View ArticleRe: very quick question for the engineering types – role of thickness in bow...
A limb 2X as thick has these properties: - It will be 8X stiffer (goes as cube of thickness) - It will withstand 4X the force before breaking (goes as square of thickness) - It can only bend 1/2 as...
View Article
