A PHENOMENOLOGICAL MODEL TO DESCRIBE THE NONLINEAR VISCOELASTIC BEHAVIOR OF BROILER GASTROCNEMIUS TENDON

The viscoelastic stress (sigma)-strain (epsilon) relationship of broil er gastrocnemius tendon can be described by the phenomenological model sigma = E epsilon + C epsilon(1+P) + L(partial derivative epsilon par tial derivative t)(K) epsilon d. Model parameters E, C and p describe the elastic behavior while parameters L, K, and d describe viscous beh avior The model is developed specifically for the initial nonlinear re gion of the loading curve the accepted region of normal tendon perform ance. Changes in the linear and nonlinear elastic parameters E and C h ave the potential to relate to changes in the crimp and structure of c ollagen fibers. However the effects due to C may be more predominant s ince this parameter reflects the nonlinear behavior of the toe region. Viscous effects tend to be nonlinear at low strain rates and to incre ase in linearity as strain rate increases. Also, viscous effects are d ependent on both strain rate and applied strain. During normal physiol ogical function, tendons are loaded at high strain rates but these rat es are difficult to mimic in in vitro testing. This model could be use d to predict the function of tendon at these high strain rates and cou ld help identify undesirable loading conditions.