Equivalent Material Properties Research Articles

Viscoelastic Approach to Rutting in Flexible Pavements

Permanent deformation (rutting) in bituminous pavements is treated as a linear viscoelastic flow phenomenon and is calculated using the linear elastic layered pavement model VESYS, reported by Kenis in 1978, supplied with equivalent viscous material properties. After an initial compaction period, the model predicts that the permanent deformation per wheel pass is proportional to the static axle load and inversely proportional to the vehicle speed. The predicted permanent deformation field is realistic and independent of the material elasticity. To determine the viscosity of asphalt mixtures operating under a wide range of environmental conditions, a simple new theoretical method is introduced which is based on routine test data and requires only one parameter to be fitted to experimental data. Published wheel-tracking tests were used to determine this parameter. Rut depth predictions are compared with experimental data from a recent full-scale test in France. Agreement is generally good, indicating the applicability of this linear rutting model.

Fundamental solutions of biot's equations of dynamic poroelasticity

Fundamental solutions pertaining to Biot's equation of three-dimensional dynamic poroelasticity are derived in the Laplace transform domain. These solutions define the displacement field in fluid-saturated media due to point forces in the solid and fluid phases. In addition, for the two extreme cases of a medium with low and high permeabilities, time domain approximations of the fundamental solutions are derived by inverting Laplace transform expressions. Finally, numerical results are presented to highlight the salient features of the problem as well as investigate the accuracy of the time domain solutions. These analytical expressions are also used to define the equivalent one-phase material properties for the more usual undrained dynamic analyses.

Material properties of living soft tissue composites.

Collagen sponges seeded with fibroblasts have been used as a soft tissue substitute in wound healing applications. This biomaterial is a good in vitro analog of a connective tissue. Therefore, analysis of the properties of this material may be useful for theoretically modeling soft tissues. Stress-strain curves for such cell-seeded collagen sponges were measured to determine composite stiffness and ultimate tensile strength. Theoretical modeling was done by defining a particle-reinforced matrix using the composite sphere model. A system of uniaxially oriented fibers was then introduced to this equivalent homogeneous media and material properties were determined using the composite cylinder model. Geometric averaging was performed to yield the stiffness and Poissons' ratio for a composite with randomly oriented fibers. Inputs to the model were constituent material properties, cell volume fraction, and fiber volume fraction. From theoretical results, material properties of soft tissues and their substitutes depend on fiber mechanical properties and volume fraction and not cellular mechanical properties and volume fraction. Therefore, the increase in experimentally observed composite stiffness with increased cell number was due to deposition of newly synthesized stiffer collagen fibers, and not due to the physical presence of cells themselves.