Experimental and Numerical dynamic characterization of a human tibia

Many studies form the early 70s have determined the possibility, through the use of vibrations, to analyze the response of a human tibia in order to study its dynamic behavior under different excitation conditions and for different purposes. Comparative studies between contact and non-contact techniques have been carried out over the years, but in the case of non-uniform structures in form and materials, such as a human tibia, there is a lack of information. The aim of this paper is to dynamically characterize a human tibia replica,with the same mechanical and morphological proprieties, with and without an external fixation system highlighting limits and advantages of contact and non-contact approaches. This work proposes a comparison, in terms of FRFs and modal parameters, between the tibia alone and in the presence of an external fixation system, moreover the experimental data are compared also with a numerical model of such structures. Tests have been carried out using a mono-axial accelerometer for the contact measurement approaches and a laser Doppler vibrometer (632nm wavelength) for the non-contact one. The tibia has been placed on a foam support in order to simulate free-free conditions. The input was supplied both by a shaker and by a micro-hammer, keeping the same excitation direction. Results show that shaker-based excitation and micro-hammer excitation method can cause issues on the response measured with lasers. Modal analysis results tend to smooth these issues, even though laser-based data tend to senses a vertical in-plane in correspondence of the third horizontal mode because multiple components are sensed simultaneously during the scan.