John O Toole

Project Title: Source Location of Cracks in Bone using Acoustic Emission

Name: John O Toole

Supervisor: Dr. John Hession

Abstract:

The ability to predict the location of an imminent bone fracture is useful in the prevention of fractures and in the ongoing research of the cracking process in bone. Acoustic emission (AE) has been used by researchers to study the fracture process in bone. Before a fracture takes place micro cracks occur at the site of the impending fracture.  These micro cracks produce AE waves which can be detected with special AE instrumentation. Work carried out by previous researchers has found a relationship between the quantity of detected AE activity and the stage in the fracture process a bone sample is at.  Knowing the location of this AE activity can be used to predict where a bone will fracture.  This research set out to determine if micro cracks can be accurately located in bone using acoustic emission and if so can their detection and location be used to predict where and when a bone will fracture.

To date AE source location has been attempted on small rectangular samples (60x20x5.5mm) which have been machined from bovine femurs.  Source location algorithms have been developed to locate where the AE waves produced by micro cracks originated from.  These micro cracks have been induced in the bone samples by applying a load in a three point bend test. Then the resulting AE data has been used to predict where the bone will fracture before it actually shows visible signs of failing. The results to date demonstrate that AE source location to a good accuracy is achievable and that it does indicate the site of impending fracture.

The next stage is the source location of micro cracks in whole bone. This is currently being undertaken. Bovine femurs will be subjected to a mechanical load to induce micro cracking and eventually fracture.  AE source location algorithms will be employed to locate these micro cracks as they occur.  The location of these micro cracks will be used to specify where the bone will fracture.

The AE source location system will be designed to work in real time so that as a load is being applied to a bone the system will indicate where the bone sample will fracture. The source location algorithms will now have to be adapted to work with whole bone which is considerably more complex in terms of geometry and composition, than the previously used rectangular samples. 

The AE system was custom designed and built by John O’Toole and will now be upgraded to handle whole bone AE source location.  The source location algorithms were developed by John O’Toole with invaluable help from Dr Leo Creedon (Dr. Creedon Research).  John O’Toole and Leo Creedon will adapt them to deal with whole bone.

 Conference Contribution:

Conference Attended Date Contribution Title of Contribution
BINI Limerick 2009  31 January 2009 1)Published Abstract2)Oral presentation Source Localization of cracks and the propagation of cracks in bone using Acoustic Emission