Really nice to see you do a backed bow, always love seeing your projects. I would HIGHLY advise AGAINST using Kevlar for a bow backing though, Kevlar is very strong and resistant to breaking when stressed, but only for a couple times like in a bullet-proof vest, it was never designed to be REPEATEDLY bend/stressed. Pretty much the only ones who use it for archery gear are the Japanese, they use it on some strings for yumi, and depending on the draw weight of the bow they usually break after 300-1000 shots. The Japanese use it because they want their string to fail after a couple hundred shots (supposed to be healthy for the yumi). Kevlar will break suddenly and without warning. Used as a bow backing it might hold up longer, but you should expect the kevlar backing on that bow to fail after 500-2000 shots or so. Fibreglass or carbon fibre is MUCH BETTER for a bow backing, it is much better suited for the repeated bending stresses on a bow.
The numbers:kevlar has a tensile strength of ca 3000-3500 MPa, glasfibers between 3000-4500 based on subtype. So can be pretty similar.
Please buy a chrono, I will contribute, really curious, how kevlar holds up in your bows. Pretty much an advanced bowmaker by now π, impressive precision.
Glasfibers, carbonfibers, kevlar give longlasting waste at the end of their lifetime. I search for materials that can deteriorate at the end of life time but perform also well. I thought about using diatomes (natural silicium sand) with epoxy for the compression side and see how that performs. For the tension side, ancestors used sinew, I wonder if hair can substitute (a.e horse hair). I guess performance with organic materials will be lower as with modern materials, but may be not much.
Nice job. I'm working on an adjustable riser that i can vary the angle of the limbs and the distance between them. To find the optimal angle and weight for my bows