Research Papers

Hyperbolic Source Location of Crack Related Acoustic Emission in Bone

[+] Author and Article Information
John O'Toole

e-mail: otoole.pjohn@gmail.com

Leo Creedon

e-mail: creedon.leo@itsligo.ie

John Hession

e-mail: hession.john@itsligo.ie

Gordon Muir

e-mail: muir.gordon@itsligo.ie
School of Engineering,
Institute of Technology,
Sligo, Ireland

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received April 25, 2012; final manuscript received October 21, 2012; accepted manuscript posted November 28, 2012; published online December 27, 2012. Assoc. Editor: Richard Neptune.

J Biomech Eng 135(1), 011006 (Dec 27, 2012) (9 pages) Paper No: BIO-12-1158; doi: 10.1115/1.4023091 History: Received April 25, 2012; Revised October 21, 2012; Accepted November 28, 2012

Little work has been done on the localization of microcracks in bone using acoustic emission. Microcrack localization is useful to study the fracture process in bone and to prevent fractures in patients. Locating microcracks that occur before fracture allows one to predict where fracture will occur if continued stress is applied to the bone. Two source location algorithms were developed to locate microcracks on rectangular bovine bone samples. The first algorithm uses a constant velocity approach which has some difficulty dealing with the anisotropic nature of bone. However, the second algorithm uses an iterative technique to estimate the correct velocity for the acoustic emission source location being located. In tests with simulated microcracks, the constant velocity algorithm achieves a median error of 1.78 mm (IQR 1.51 mm) and the variable velocity algorithm improves this to a median error of 0.70 mm (IQR 0.79 mm). An experiment in which the bone samples were loaded in a three point bend test until they fractured showed a good correlation between the computed location of detected microcracks and where the final fracture occurred. Microcracks can be located on bovine bone samples using acoustic emission with good accuracy and precision.

Copyright © 2013 by ASME
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Fig. 1

(a) The TDOA between two sensors describe a hyperbola on which the AE source must lie. (b) The addition of a third sensor allows a second hyperbola to be drawn. The AE source is at the point of intersection of the two hyperbolas. (c) Show how the hyperbolic source location setup is implemented on a bone sample with the addition of a fourth sensor.

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Fig. 2

Experiment 1 setup: a pencil lead break is used to create AE sources at any desired location on the bovine bone sample

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Fig. 3

Bovine bone sample loaded in three point bend testing to induce microcracks and ultimately cause fracture

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Fig. 4

(a) Longitudinal AE velocity quartile analysis, after the outliers have been removed. (b) Transverse AE velocity quartile analysis, after the outliers have been removed.

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Fig. 5

Error analysis for three sensor constant velocity location showing the quartiles

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Fig. 6

The error analysis for four sensor constant velocity location showing the quartiles

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Fig. 7

The error analysis of four sensor variable velocity location showing the quartiles

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Fig. 8

Locating microcracks on bone samples in three point bend tests using acoustic emission. The AE locations are the computed location of individual microcracks and the fracture lines are where the sample fractured by the end of the test.

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Fig. 9

The AE hits detected and located for sample 1 during the three point bend test. The plot shows that not alone are AE hits detected before the sample fractures but that some are also located, predicting the fracture location.




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