I will be writing articles about the different aspects of Bladesmithing and Bow making:  This is the first article:

This article will be about how wood bows work. When a wooden bow is bent as it is being drawn back toward full draw, the fibers in the wood are being both stretched and compressed. The fibers on the back of the bow, the part facing away from the archer, are being pulled apart and the fibers on the belly of the bow, the part facing the archer, are being compressed together. For this reason most wooden bows that break do so because either the fibers on the back pull apart entirely or the fibers on the belly compressed to the point of collapsing. The bowyers job is to understand the capabilities and limitations of the individual wood that he is using when making a bow. He must shape and design the bow to withstand the amount of force that is placed on the fibers in tension and compression.

All woods are either stronger or weaker in tension or compression. Woods that are strong in tension can withstand more stretch on the back than weaker tension woods. Woods that are strong in compression can withstand more pressure on the belly as the bow is being bent then weaker compression woods. Weak woods need to have more wood fibers, or surface area, to withstand the same amount of stress as strong woods. Weak wood bows need to be either taller or wider or both. Strong wood bows can be narrower or shorter in design.

The other aspects that affects woods ability to withstand the stresses of tension and compression would be the bows profile or the limb cross-section. A bow with a rounded back or belly is under more strain because the tension and compression forces are concentrated at the top of arc of the curve on the back or belly. This means that there is less wood fiber available to withstand the stress. A bow with a flat back or belly has more surface area so there is more fibers to withstand the stress of being bent.

This is why not all bow designs work with all types of woods and the reason wood bows need to be designed for the poundage at the individual archers draw length. An example would be when a bow is made for a 26" draw and if it were to be pulled back past that length, the bow would either break or over-compress the fibers on the belly and over-stretch the fibers on the back to a higher poundage than the bow was designed for. This would cause the bow to never shoot the same at 26" again.

I hope this helps in understanding how wooden bows work and one of the things that make them unique.