MODEL FOR THE CREEP-BEHAVIOR OF TENDON

A theoretical model is proposed to explain the viscoelastic behaviour of tendon. The model is based on the hypothesis that the mechanism of tendon deformation is one of shear of the mucopolysaccharide gel between the collagen ribbons in the 'toe' region1 of the stress strain curve followed by fibrillar extension in the 'linear' region2.3. Conventional linear viscoelastic parameters of the constituents of the tendon were used to describe the behaviour of the composite. Certain structural constants of the tendon and an appropriate form for the retardation spectrum of the composite also appear in the model. It was found that the following parameters play an important part in the viscoelastic deformation process; the mean value of the crimp angle of the strained fibres, 0O; the broadness of the distribution of crimp angles α; the magnitude of the compliance difference for the gel, ΔJG and for the fibres, ΔDF. Excellent agreement between experiment and theory has been observed for a variety of experimental circumstances. Values of 0O, α ΔJG and ΔDF were determined for a number of specimens by fitting the model equations to the experimental data. The theory illustrates the expected influence on the viscoelastic properties of tendon which would result from changes in these parameters, which may arise from disease or ageing, for instance. The model also provides a challenge for future experimental work in that an independent determination of the parameters, 0O, α ΔJG and ΔDF would confirm or refute the quantitative predictions of the theory presented here. © 1979.