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Fiber Stresses in Bows
Part 5 of 5

The first answer is: Perhaps we should. Another answer is that the back of a yew bow is usually made of sap wood which may have a lower modulus of elasticity, so that the neutral plane is moved toward the belly side a sufficient amount to more than compensate for the shift due to the shape of the belly. Still another answer is that the elastic limit is not a definite value but depends upon the shape of the specimen. It has been shown by the Forests Products Laboratory that the elastic limit in compression is increased considerably by the presence of other less stressed fibers. The elastic limit in bending is much greater than for compression parallel to the grain, where the entire specimen is subjected to the same stress. This is probably due to the fact that in bending, only the surface layer of the compression side is subjected to the maximum stress. The adjacent layers of less stressed fibers help to support those receiving the highest stress. This raises the limit to which the specimen may be stressed before failure is reached.

There is a strong probability however, that for homogeneous woods, such as osage and lemonwood, that a better cast may be secured by reversing the traditional construction of a bow, by making the belly side the back. In such a bow, however, greater precautions must be taken against slight imperfections on the back surface. A trapezoidal shape with the narrow side for the back, well protected with a thin layer of some good backing material, would probably be the most practical shape.

At the present time we do not have enough data on the tensile strength of woods to reach any definite conclusion as to the best cross-section for a bow.

Past experience has shown that in many arts, the adoption of a specific design was accompanied with a very good reason and science has only been able to make slight improvements. The construction of a bow is an art which has been developed as most arts, by the method of trial and error. It may be found that this method has developed the best bow that can be made. However there is the possibility that this method has not developed the best type of construction and that science may point the way to a considerable improvement. In fact there are already indications that those of us who can not pull a 50 to 60 pound bow, may be able to have our point of aim on the gold at 100 yards with a bow weighing less than 40 pounds.

During the period that Dr. Hickman was writing these articles for Ye Sylvan Archer he included a few which gave the results of experimental investigations. A brief summary of the experimental investigations will now be given.