A Continuum Mechanical Model of the Lung
Abstract
A continuum model for lung parenchyma is constructed. The model describes the thermomechanical response over a range of loading rates from static to dynamic to shock waves and a range of stress states, including isotropic expansion, triaxial extension, simple shear, and plane wave compression. Nonlinear elasticity, viscoelasticity, and damage are included. A free energy function is designed for loading at low to moderate rates and tensile pressures, whereby the tissue response, with surface tension, is preeminent. An internal energy function is designed for wave propagation analysis, including shock waves, where by compressibility of the air inside the alveoli is addressed via a composite stiffness based on a closed-cell assumption. The model accurately represents the response with relatively few measurable parameters, most with an obvious physical interpretation. Longitudinal wave speeds are reasonable for ranges of internal airway pressure and transpulmonary pressure. Airway pressure is shown to strongly affect the response to plane wave compression. Criteria for local injury and damage progression depend on a normalized energy density and its gradient, where the latter is paramount for impact problems involving fast pressure rises.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 2019
- Accession Number
- AD1086066
Entities
People
- Alan D. Freed
- John D. Clayton
Organizations
- United States Army Research Laboratory