Nonlinear Viscoelasticity and Damage of Soft Tissue: Experimental and Constitutive Study of Ligament

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The research is primarily directed toward study of nonlinearly viscoelatic behavior of soft connective tissues, particularly the constitutive behavior. Because of their simplicity, ligaments are chosen as an experimental model. The research is organized as follow (i) an experimental study will be performed that defines viscoelastic behavior throughout the range of reversible ligament deformations. This study will use creep and relaxation plus recovery protocols to allow discrimination among various nonlinearities. (ii) a robust viscoelastic constitutive model will be developed from experimental data. This model will appropriately account for nonlinearities and interrelate creep and relaxation. (iii) The reversible deformation limits for levels of applied stress and strain (as a function of load-time) will be experimentally identified from the data in (I), thus defining the onset of sub-failure tissue damage for a single overload. A sub-failure criterion for the onset of damage will be formulated. (iv) Creep and relaxation testing will be performed on additional specimens to quantify the compromise in mechanical behavior after higher loading and deformations produce greater levels of tissue damage (from a single overload). (v) The microtrauma and damage associated with irreversible deformations will be morphologically characterized using scanning electron microscopy.