INTRODUCTION METHODOLOGY RESULTS

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application of FEA will allow the detection system to be tested and developed much more rapidly. METHODOLOGY. Sheep tibiae are obtained from an abattoir ...
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VIBRATION ANALYSIS OF BONE FRACTURE USING FINITE ELEMENT ANALYSIS AND EXPERIMENTAL MODAL ANALYSIS 1

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Varley, P. , Hession, J. , Muir, G Department of Mechanical and Electronic Engineering, Institute of Technology Sligo email: [email protected]

INTRODUCTION A review of census records reveals the percentage of over 65’s in Ireland has increased from 4.5% to 11% of the total population in the last century [1]. This can be linked to the enhancement of medical treatments in recent years. The occurrence of fracture related diseases in this age group is high and thus the assessment of bone fracture risk is an important area in modern clinical medicine. A system is proposed to predict fracture, thus improving quality of life by intervening before total fracture occurs. Vibration analysis has been used to assess the mechanical properties of bone [2].Experimental Modal Analysis (EMA) is a form of vibration analysis used to measure frequency characteristics of a structure. EMA measures resonance, a property associated with structural stiffness and mass. As fracture occurs in bone the stiffness and mass properties are modified and the resulting resonance is altered. Therefore EMA is a viable method of fracture prediction and its suitability for identifying fracture in bone will be investigated. Finite Element Analysis (FEA) has been used to numerically calculate bone vibrations [3]. It is used here to calculate resonant frequencies of bone and offers the advantage of simulating many scenarios before a physical measurement is carried out. The application of FEA will allow the detection system to be tested and developed much more rapidly.

a free-free condition to determine modal characteristics. The bone will be loaded incrementally until total failure and EMA repeated at each increment. Results from EMA will be compared to FEA and the FEA model will be adjusted accordingly to match experimental results.

RESULTS Preliminary EMA has been carried out on mild steel beams to determine the relationship between resonant frequency and mass. A resonant frequency shift of 30Hz was observed for a change in mass of 9 grams.

Figure 1 Resonant frequency response of mild steel beams to EMA testing.

METHODOLOGY Sheep tibiae are obtained from an abattoir and all soft tissue is removed. Tibiae undergo Computed Tomography (CT) scans to identify their geometric and density properties. This information is then used to build a Finite Element (FE) model in Abaqus software. Abaqus will be used to determine resonant frequencies by finding eigensolutions of the bone model in a free-free boundary condition. Material properties of the bone are adjusted incrementally to represent changing fracture levels while simultaneously finding an eigensolution at each increment. This provides a numerical relationship between fracture and resonance. The same sheep tibiae are then subjected to mechanical loading which induces fracture and Experimental Modal Analysis (EMA) is carried out in

DISCUSSION Initial testing on mild steel beams reveals a definite shift in resonant frequency as the mass is modified. The results provide confidence that the measurement setup is functioning correctly and can be used to detect fracture in bone.

REFERENCES [1] Central Statistics Office records, Census 1901, Census 2006. [2] Bediz (et al), Clinical Biomechanics, Volume 25, Pages 365-371, 2010. [3] Couteau (et al), Journal of Biomechanics, Volume 31, Pages 383-386, 1998.

Bioengineering In Ireland17, January 28–29, 2011, Galway