The purpose of this research is to develop a constitutive equation for collagen fibers, and to compare the results of a number of basic tests with the mathematical model. The collagen was obtained in a pure form by the extraction of fiber bundles from the tails of mature rats, and the specimens were immersed during testing in a constant temperature saline bath. Three types of basic tests were conducted on the fiber bundles. The first test series were relaxation tests at various levels of strain. A second series of loading and unloading cycles were performed at different strain rates. A third series of tests were conducted for a sinusoidal strain of various amplitudes and frequencies.

A "quasi-linear" viscoelasticity law has been developed based on a suggestion presented by Y. C. Fung. From the results of the relaxation tests the material constants in this equation were determined and the.constitutive equation was then used to predict the results of constant strain rate tests, hysteresis loops, and sinusoidal tests.