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Fortisan for Backing Bows

The last article which Dr. Hickman has written appeared in the March 1946 issues of The American Bowman Review and Archery. Since the article shows curves comparing Silk, Nylon and Fortisan the contents are given in this book.

During the war Dr. Hickman was connected with research on rockets and established a ballistic laboratory for testing them at Cumberland, Md. It was there that he learned that the Celanese Corporation had developed a new fiber which was two to three times as strong as silk. While the product was of a confidential nature and was being used for making shrouds for parachutes, he obtained samples of the material and tested it in many ways. The graph shows the results of laboratory tests in comparison with silk and Nylon. The steep curve indicates that the modulus is higher. The breaking strength is higher than Nylon and over twice as high as silk. The elongation of the fibers is plotted as a function of the load in grams per denier. A denier is a fiber that is 10,000 meters long and which weighs 1 gram. Silk fibers weigh about two to three grams per 10,000 meters of length, i.e. have a size of about 2 to 3 denier. The Fortisan fibers weigh less than one gram per 10,000 meters of length, i.e. have a size of less than one denier.

Samples of Fortisan backing were made and sent to old customers of silk backing. The Fortisan is made into sheets about 11 ½ inches wide and 72 inches long. It is made in thicknessess of 0.025 and 0.037 inches.

Due to the extra strength of the Fortisan, it is not necessary to prestretch the strips as much as silk. He recommends a stretch of less than 1½ percent. It will be noted that the elongation may be carried to over twice as high a value as silk.