A FINITE-ELEMENT BASED METHOD TO DETERMINE THE PROPERTIES OF PLANAR SOFT-TISSUE

A finite element based method to determine the incremental elastic mat erial properties of planar membranes was developed and evaluated. The method is applicable to tissues that exhibit inhomogeneity, geometric and material nonlinearity, and anisotropy. Markers are placed on the t issue to form a four-node quadrilateral element. The specimen is loade d to an initial reference state, then three incremental loading sets a re applied and the nodal displacements recorded. One of these loadings must include shear. These data are used to solve an over-determined s ystem of equations for the tangent stiffness matrix. The method was fi rst verified using analytical data. Next, data obtained from a latex r ubber sheet were used to evaluate experimental procedures. Finally, ex periments conducted on preconditioned rat skin revealed nonlinear orth otropic behavior. The vector norm comparing the applied and calculated nodal force vectors was used to evaluate the accuracy of the solution s.