A Multi-Level Hierarchical Finite Element Model for Capillary Failure in Soft Tissue

• Main Author: Huang, Lu
• Format: Others
• Published: ScholarWorks@UMass Amherst 2012
• Subjects: Capillary; Bruising; Human upper arm; Sub-modeling; failure stress; Finite element model; Biomechanical Engineering
• Online Access: https://scholarworks.umass.edu/theses/909; https://scholarworks.umass.edu/cgi/viewcontent.cgi?article=2050&context=theses

Developing a more scientific way to determine the load threshold for capillary wall failure would be a big step forward in characterizing whether bruising is result from an abuse or an accident. In this thesis, the upper portion of the human arm was modeled and analyzed under dynamic loading conditions. Since the diameter of the arm is much larger than that of the capillary, a four-level hierarchical sub-modeling method was used to mathematically link the transient response of the global arm model to the response of a small volume in the muscle tissue containing one capillary. Soft tissue in the arm was modeled in two distinct ways. In one method each component of soft tissue was modeled used isotropic linear elastic properties to find the loading threshold that produces a hoop stress in the capillary wall equal to the capillary failure stress. In the other approach, nonlinear, hyper-elastic properties for skin, adipose, muscle tissue and capillary wall were employed to make the tissue behavior more realistic to that of a human arm. Material-appropriate constitutive functions were chosen for each layer. A mathematical technique implement in MATLAB was used to estimate and subtract rigid body motion from the total displacement to avoid excessive displacements of sub-models and focus more on the deformation-only displacement. It was found that modeling the skin, adipose, muscle and capillary as hyper-elastic resulted in significantly smaller deformations but larger loads that resulted in capillary failure.