arXiv subjects

P. Chabrand

Publications and source records attributed to P. Chabrand.

3 recordsLinked to original sources

arXiv2005

An alternative ultrasonic method for measuring the elastic properties of cortical bone

We studied the elastic properties of bone to analyze its mechanical behavior. The basic principles of ultrasonic methods are now well established for varying isotropic media, particularly in the field of biomedical engineering. However, little progress has been made in its application to anisotropic materials. This is largely due to the complex nature of wave propagation in these media. In the present study, the theory of elastic waves is essential because it relates the elastic moduli of a material to the velocity of propagation of these waves along arbitrary directions in a solid. Transducers are generally placed in contact with the samples which are often cubes with parallel faces that are difficult to prepare. The ultrasonic method used here is original, a rough preparation of the bone is sufficient and the sample is in rotation. Moreover, to analyze heterogeneity of the structure we measure velocities in different points on the sample. The aim of the present study was to determine in vitro the anisotropic elastic properties of cortical bones. For this purpose, our method allowed measuring longitudinal and transversal velocities (CL and CT) in longitudinal (fiber direction) and radial directions (orthogonal to the fiber direction) of compact bones. Young's modulus E and Poisson's ratio , were then deduced from the velocities measured considering the compact bone as transversely isotropic or orthotropic. The results are in line with those of other methods.

physics.class-ph↗

arXiv2005

Comparison of compact bone failure under two different loadings rates: experimental and modelling approaches

Understanding the mechanical behaviour of bones up to failure is necesary for diagnosis and prevention of accident and trauma. As far as we know, no authors have yet studied the tensile behaviour of compact bone including failure under dynamic loadings (1m/s). The originality of this study comes from not only the analysis of compact bone failure under dynamic loadings, the results of which are compared to those obtained under quasi static loadings but also the development of a statistical model. We developed a protocol using three different devices. Firstly, an X-ray scanner to analyse bone density, secondly, a common tensile device to perform quasi static experiments and thirdly, a special device based upon a hydraulic cylinder to perform dynamic tests. For all the tests, we used the same sample shape which took into account the brittleness of the compact bone. We first performed relaxation and hysteresis tests followed by tensile tests up to failure. Viscous and plastic effects were not relevant to the compact bone behaviour so its behaviour was considered elastic and brittle. The bovine compact bone was three to four times more brittle under a dynamic load than under a quasi static one. Numerically, a statistical model, based upon the Weibull theory is used to predict the failure stress in compact bone.

physics.class-ph↗

arXiv2005

Constitutive Laws and Failure Models for Compact Bones Subjected to Dynamic Loading

Many biological tissues, such as bones and ligaments, are fibrous. The geometrical structure of these tissues shows that they exhibit a similar hierarchy in their ultra-structure and macro-structure. The aim of this work is to develop a model to study the failure of fibrous structures subjected to dynamic loading. The important feature of this model is that it describes failure in terms of the loss of cohesion between fibres. We have developed a model based on the lamellar structure of compact bone with fibres oriented at 0 degrees, 45 degrees and 90 degrees to the longitudinal axis of the bone, and have studied the influence of the model parameters on the failure process. Bone porosity and joint stress force at failure were found to be the most significant parameters. Using least square resolution, we deduced a phenomenological model of the lamellar structure. Finally, experimental results were found to be comparable with our numerical model.

physics.class-ph↗