Gérard Maurice

Investigation of 3-D mechanical properties of blood vessels using a new in vitro tests system: results on sheep common carotid arteries

In order to investigate the three-dimensional (3-D) mechanical properties of blood vessels, a new experimental device is described allowing in vitro static and dynamic measurements on segments of arteries with high technical performances. Static tests are applied to sheep common carotid arteries. Considering a thick-walled cylindrical model of orthotropic material under large deformations, a classical 3-D approach based on strain energy density is used to calculate the resulting mechanical behavior law in radial and circumferencial directions and stresses distribution throughout the wall thickness. Results are presented with reference to unloaded and zero-stress initial state thanks to simple measurements of inner and outer circumferences. A particular ratio relating the two main stresses (circumferential and longitudinal) is calculated that put into the forth the progressive modifications in the direction of the predominant stress in the wall and the specific radial location where these changes occur. The authors observe that this point location is a function of the test conditions of the specimen, i.e., stretching length and level of pressure.

An experimental and theoretical approach of elasticity and viscoelasticity of compact and spongy bone with periodic homogenization.

An experimental study on samples from a fresh human femur highlighted the viscoelastic behaviour of bone. The memory aspect of the behaviour is weak compared to the elastic aspect. A theoretical and numerical approach based on the finite element method illustrates the existing bond between the structure and the micro behaviour on the one hand, and the macro behaviour on the other. The orthotropic elastic behaviour observed by various authors is shown numerically. The memory functions of compact and spongy bone are given. The numerical results illustrate the behaviour observed in the experiments.

Heat equation in a perforated composite plate: influence of a coating

Abstract This paper deals with the homogenization of the heat equation in a periodically perforated composite plate. After giving a dimension analysis of the original mathematical model, we are led to an anisotropic singular perturbation boundary-value problem which involves non-standard boundary conditions. There are several dimensionless physical variables like the Biot numbers B p (p=−,+,c − and c + ) , the period e of the distribution of the holes, the respective relative thickness e, δ of the plate and the coating, and ratio λ of the heat conductivities. We only study situations in which the parameters B−, B+ and e are of the order of unity and e≺≺1,δ≺≺1,λ≺≺1.

Analysis of Elliptical Cracks in Static and in Fatigue by Hybridization of Green's Functions

A hybrid weight function technique is presented. It consists of dividing an elliptical crack into two zones, then using the appropriate weight function in the area where it is more efficient. The proportion between zones is determined by optimizing two crack parameters (axis ratio and curvature radius). Stress intensity factors are hence computed by a self developed computer code. Static and fatigue loadings are considered. The results found by the present approach are in good correlation with the analytical and experimental solutions (when available) as well as with those obtained numerically by other researchers.

Coupling of the Deformation of a Model Endothelial Cell and a Steady Laminar Flow

Abstract Mechanical forces influence endothelial cells (EC) morphology and functions. In this work it was proposed a numerical analysis of steady laminar flows near a modelled monolayer of elastic ECs in order to determine the local distributions of mechanical forces on the surface and inside the cell. Numerical results showed that the flow induced non uniform mechanical stresses on cell surface and led to a cell deformation. These numerical results were compared with experimental measurements of the deformation of cultured human aortic endothelial cells under flow. It will be interesting to study eventual correlations between the distributions of biological receptors (cytoskeleton, adhesion molecules, etc.) and that of the non-uniform mechanical forces.