Modeling of blade cutting of viscoelastic biomaterials

Abstract

The work in this thesis focuses on the modeling of blade cutting of viscoelastic materials. The blade cutting procedure is modeled in two stages. The first stage is the contact of the blade with the cutting material and the second stage is the fracture during continuous cutting. The modeling of the first stage is used to predict the initiation of the cutting fracture and the modeling of the second stage is use to characterize the cutting force during continuous fracture. Experiments that are used to determine the material parameters for the simulations and calculations of the cutting process are also carried out.The first stage is modeled as the area contact between the edge of the blade and cutting materials. It is modeled by applying the elastic-viscoelastic correspondence principle to the solutions for point load and then by performing a numerical integration scheme to extend the solutions to distributed pressure cases. The stress tensor was analytically obtained at any given point inside the viscoelastic material. The effect of slicing angles on the stress distribution is then evaluated. Using the principal stresses, the location of damage is predicted using Tresca's failure criterion. In the continuous damage stage, FEM simulation using ABAQUS is used as the modeling method. A bi-layered structure is applied to represent the tissue-bone structure which could be widely seen in a deboning process. In the simulation, the cutting force is monitored during the blade cuts through the interface. The dynamic change of the force pattern when the blade approaches the interface is analyzed in order to propose a control algorithm that prevents the blade cutting into bones. In order to provide realistic data for the simulation, several relaxation tests are designed to obtain the tensile relaxation modulus for biomaterials. Ligaments obtained from chicken wings and legs are used as specimens. The experimental data was theoretically fitted into a Burgers Model for the simulation and calculation. The model developed in this research can serve as a guideline for many applications such as the design of a surgical simulator to facilitate the training of new doctors and the intelligent control of a robot for deboning process to improve cutting yield and meat harvesting quality.