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Technical Briefs

Development of an Apparatus to Produce Fractures From Short-Duration High-Impulse Loading With an Application in the Lower Leg

[+] Author and Article Information
Cheryl E. Quenneville

Jack McBain Biomechanical Testing Laboratory, Thompson Engineering Building, The University of Western Ontario, London, ON, N6A 5B9, Canada; Department of Mechanical and Materials Engineering, The University of Western Ontario, London, ON, N6A 5B9, Canada

Gillian S. Fraser

Biomedical Engineering Graduate Program, The University of Western Ontario, London, ON, N6A 5B9, Canada; General Dynamics Land Systems Canada, Engineering Design and Development, London, ON, N5V 2Z7, Canada

Cynthia E. Dunning

Jack McBain Biomechanical Testing Laboratory, Thompson Engineering Building, The University of Western Ontario, London, ON, N6A 5B9, Canada; Biomedical Engineering Graduate Program, The University of Western Ontario, London, ON, N6A 5B9, Canada; Department of Mechanical and Materials Engineering, and Department of Surgery, The University of Western Ontario, London, ON, N6A 5B9, Canadacdunning@uwo.ca

J Biomech Eng 132(1), 014502 (Dec 08, 2009) (4 pages) doi:10.1115/1.4000084 History: Received December 19, 2008; Revised May 25, 2009; Posted September 01, 2009; Published December 08, 2009; Online December 08, 2009

Axial loading of the lower leg during impact events can cause significant fractures of the tibia. The magnitude of lower leg axial loading that occurs during short-duration high-impulse events, such as antivehicular landmine blasts, can lead to life-altering injuries. These events achieve higher forces over shorter durations than car crashes, the current standard used for protective measures. In order to determine appropriate injury limits for the lower limb, a testing apparatus has been designed that can simulate these types of events for testing of anthropomorphic test device (ATD) lower legs as well as cadaveric specimens. Moreover, the design allows for the velocity at which the specimen is struck to be varied independently of the force applied, thus allowing independent investigation into the effect of momentum or energy on fracture strength. Test specimens are supported on a low-friction bearing system, and receive the controlled impulse from a projectile of variable mass that is accelerated using pneumatics. The apparatus includes velocity sensors, a six-degree-of-freedom load cell, and an accelerometer to completely quantify the loading event. The apparatus’ performance was validated against an ATD lower leg. It was able to create impulse events with forces from 0.5 kN to 17.0 kN, and projectile speeds of 2.3–13.9 m/s. Various momenta could be achieved at a constant force level by varying the mass of the projectile, with a maximum difference of 65%, whereas kinetic energy was inherently linked to the impact force. This apparatus will be useful in future studies for determining the appropriateness of currently used injury limits for the lower limb to high-impulse events, as well as for quantifying the relationship between cadaveric fracture response and ATD measurements. This device can also be readily applied to other bones of the body, to create realistic fracture patterns for known injury mechanisms.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

Testing chamber. A projectile (inset) passes through the acceleration tube and strikes the distal bracket, which is instrumented with a load cell. Both the distal and proximal brackets travel on bearings, and support a lower limb specimen. The flange ring restricts the projectile from fully exiting the tube, and is instrumented with optical sensors to detect the velocity of the projectile immediately prior to impact.

Grahic Jump Location
Figure 2

Projectile velocity versus pressure for each mass (m1=1.0 kg, m2=1.7 kg, and m3=3.9 kg) over the four travel distances (d1=8 cm, d2=24 cm, d3=40 cm, and d4=56 cm). Velocity increased with projectile mass and travel distance. R2>0.99 for all mass-distance combinations.

Grahic Jump Location
Figure 3

Axial force versus projectile velocity for each mass (m1=1.0 kg, m2=1.7 kg, and m3=3.9 kg) over the four travel distances. Impact force increased for a given exit velocity with increasing projectile mass, but was unaffected by travel distance. R2>0.96 for all masses.

Grahic Jump Location
Figure 4

Impact momentum versus force for each mass (m1=1.0 kg, m2=1.7 kg, and m3=3.9 kg) over the four travel distances. The highest momentum for a given force was achieved using the heaviest projectile mass. R2>0.97 for all masses.

Grahic Jump Location
Figure 5

Impact force versus kinetic energy for each mass (m1=1.0 kg, m2=1.7 kg, and m3=3.9 kg) over the four travel distances (d1=8 cm, d2=24 cm, d3=40 cm, and d4=56 cm). The relationship was not dependent on projectile mass or travel distance. R2=0.98 for all tests.

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