Transcript Impulse Loading With an Application in the Lower Leg using

Impulse Loading on the Lower Leg
using a Synthetic Bone
Marley Winfield
Department of Biochemical
Engineering and Medical
Biophysics
MBP 3302
Outline
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Introduction
Materials and
Procedure
Results and Discussion
Conclusion
Acknowledgments
References
Introduction
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Synthetic bones have recently become available as substitutes for
cadaveric specimens used in testing
Many advantages, including low variability as this makes them
more consistent, available, easy to work with, handle and store
Have been validated for quasi-static tests, but not fracture studies
http://www.sawbones.com/products/bio/composite.aspx
Background
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Upon axial loading of the lower leg during impact events,
fractures of the tibia can occur
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Life altering injuries can take place depending on the
magnitude of the axial loading
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Fracture analysis using synthetic bones to determine
injury limits is yet to be studied
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Appropriate injury limits for lower limbs can be found
using an apparatus designed to simulate these types of
events
Purpose
Carrying out a fracture analysis on synthetic
tibias, enables us to understand the impact
that can be applied to a lower limb before
fracture occurs.
These experimental results can be compared
with a fracture analysis of a cadaveric
specimen to validate whether or not synthetic
bones are suitable substitutes.
Materials and Procedure
Potting and Alignment of Bones
 Bones were potted in
PVC tubing
 Alignment of the anterior
of the tibia was done
using a laser
 PVC tubing was filled with
cement and spread
equally
 Important for all bones to
be aligned and potted the
same for consistency
Materials and Procedure
Strain Gaging
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Bone was cleaned using rubbing alcohol
Strain gage rosettes were placed along the tibia approximately 6
mm apart, 3 at the top and 1 at the bottom
Gages were fixated to the bone using glue and a catalyst
Important to make certain that the gages were completely secured
and would not come off during testing
Apparatus
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Can test Cadaveric and
synthetic lower leg specimens
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Velocity the specimen is struck
at can be varied, independent
of the force applied
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Specimen receives a controlled
impulse from a projectile using
pneumatics
Data Collection
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Bone was placed in the
chamber and hooked
up to operating system
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The projectile was
propelled causing
impact on the bone
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Projectile mass, 3.9kg,
and force of impulse at
16KHz
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Data was collected
using a data acquisition
system
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Custom-written
LabVIEW program
calculated the
momentum, energy,
acceleration, force of
impulse, exit velocity,
and strain
Data Collection
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High speed camera records the event
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Protocol to increase impact until failure occurred –
failure when broken into 2 or more pieces
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Impact varied by altering pressure, which correlates
to the energy, of the pneumatic device using an
electrically-controlled regulator
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5 sawbones were tested for comparison
Results and Discussion
Failure occurred at:
Average Exit Velocity = 5.5m/s
Energy = 60J
Fracture Limitations
Average Failure Force = 4609N
Standard Deviation = 505N
Fracture Force
6000
Force (N)
5000
Sawbone 1
4000
Sawbone 2
3000
Sawbone 3
2000
Sawbone 4
Sawbone 5
1000
0
Sawbone
Force and Energy
Average Force (N)
Average Force at each Energy
5000
4000
3000
2000
1000
0
20
40
Energy (J)
60
Principle Strain Along Bone
Peak Failure Strain at each Gage
0.012
0.01
Gage 1
Strain
0.008
Gage 2
0.006
Gage 3
0.004
Gage 4
0.002
0
Strain Gage
Strain
Strain at 20J
Strain
0.0014
0.0012
Sawbone 2
0.001
0.0008
0.0006
0.0004
Sawbone 3
Sawbone 4
Sawbone 5
0.0002
0
1
2
3
Strain Gage
4
Strain at 20J
0.014
0.012
Sawbone 2
Strain
0.01
0.008
0.006
0.004
Sawbone 3
Sawbone 4
Sawbone 5
0.002
0
1
2
Strain at 40J
3
4
Strain Gage
Sawbone 2
0.01
0.008
0.006
0.004
Sawbone 3
Sawbone 4
Sawbone 5
0.002
0
1
2
3
4
Strain at 60J
Strain Gage
0.014
0.012
Strain
Strain
0.014
0.012
Sawbone 2
0.01
0.008
0.006
0.004
Sawbone 3
Sawbone 4
Sawbone 5
0.002
0
1
2
3
Strain Gage
4
Conclusion
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Synthetic bones fractured at an energy of
60J
Fracture of synthetic bone occurred at an
average force of 4609N
Current injury limit of cadaveric lower leg is
5.4kN (Yoganandan)
Average exit velocity was 5.5m/s
At fracture the highest principle strain was at
point of impact
Conclusion
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Fracture analysis is significant when determining the
injury limits of a bone
Experimental results of cadaveric and synthetic
bones can be compared, allowing for appropriate
fracture limits to be determined
Knowledge of fracture limitations enables
manufacturers to improve designs, i.e. cars, to
reduce the possibility of injury
Understanding the properties of synthetic bones will
increase their use in testing and research
Acknowledgments
I would like to thank Dr. Cynthia Dunning, and Cheryl
Quenneville for their guidance and support with the six week
project to make it successful and enjoyable
References
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Cristofolini, L., Viceconti, M. (1999). Mechanical Validation of
whole bone composite tibia models. Journal of Biomechanics 33
(2000), 279-288.
Quenneville, C., Fraser, G., Dunning, C. (2008). Development of
an Apparatus to Produce Fractures From Short-Duration HighImpulse Loading With an Application in the Lower Leg. London,
Ontario: University of Western Ontario, Department of Mechanical
and Materials Engineering
Sawbones Worldwide: A Division of Pacific Research Laboratories,
Inc. (2009) Retrieved April 3, 2009, from
http://www.sawbones.com/
Vishay Micro-Measurements: Strain gages and Instruments
(2008).
Yoganandan, N. (1997). Axial Impact Biomechanics of the Human
Foot – Ankle Complex. Journal of Biomechanical Engineering Vol
119, 433-437