Finite element simulation of viscoelastic biomaterial behavior during drying
Abstract
The purpose of this study was to simulate and analyze the thermo-hydro viscoelastic stresses developed in single grain kernels during drying using the finite element method. The grain kernels considered were soybean, barley and corn. A computer graphics program was developed to display the finite element solutions (temperature, moisture and stress components) and to identify the potential failure zones, when drying-induced stresses exceed the failure strength of the material. The temperature and moisture distributions in grain kernels during drying were described by a set of coupled heat and mass transfer equations. Two different heat and mass transfer models were considered. The finite element program developed (GRAINFEM), with its graphical interface, allows parametric studies using different drying conditions. The thermo-viscoelastic boundary value problem of Christensen (1971) was extended to a thermo-hydro-viscoelastic boundary value problem, to predict the stresses due to temperature and moisture gradients. Constitutive equations for a thermo-hydro viscoelastic boundary value problem were derived for non-uniform temperature and moisture states. An incremental finite element formulation for stress predictions was developed using the principle of virtual work. Stresses were simulated for drying temperatures of 35$\sp\circ C$ for soybean and 75$\sp\circ C$ for barley. The inner layers of the axisymmetric soybean and barley kernels were in compression while the outer regions were in tension. The change of the normal stress components reveals that the outer layers were shrinking faster than the interior. Tangential stress was observed to be the maximum in the spherical models for soybean and barley. For the prolate spheroidal model of the barley kernel the maximum tensile stress (tangential) was observed at the outermost layer. Failure in soybean cotyledon was observed at 75$\sp\circ C$ because at that temperature the maximum von Mises stress in the outermost layer of the soybean cotyledon exceeded the tensile failure strength. All the stress components were maximum at the surface of the corn kernel, at locations where the boundary of the kernel is irregular. Failure in the corn kernel was predicted (using von Mises criteria) for a drying temperature of 85$\sp\circ C$ where, the compressive failure strength was exceeded in the hard endosperm, germ and soft endosperm. (Abstract shortened by UMI.)
Degree
Ph.D.
Advisors
Haghighi, Purdue University.
Subject Area
Agricultural engineering
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