Head Kinematics in Mini-Sled Tests of Foam Padding: Relevance of Linear Responses From Free Motion Headform (FMH) Testing to Head Angular Responses

[+] Author and Article Information
J. Ivarsson

UVa Center for Applied Biomechanics, 1011 Linden Avenue, Charlottesville, VA 22902

D. C. Viano

Crash Safety Division, Department of Machine and Vehicle Systems, Chalmers University of Technology, SE-412 96 Göteborg, SwedenGeneral Motors Research and Development Center, Warren, MI 48090-9055Saab Automobile AB, SE-461 80 Trollhättan, Sweden

P. Lövsund

Crash Safety Division, Department of Machine and Vehicle Systems, Chalmers University of Technology, SE-412 96 Göteborg, Sweden

Y. Parnaik

Bioengineering Center, Wayne State University, Detroit, MI 48202

J Biomech Eng 125(4), 523-532 (Aug 01, 2003) (10 pages) doi:10.1115/1.1590360 History: Received February 12, 2002; Revised April 01, 2003; Online August 01, 2003
Copyright © 2003 by ASME
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Dynamic stress-strain characteristics for seven of the nine foam types used in the mini-sled tests
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(a) The mini-sled in its starting position with the pneumatically controlled accelerating piston contacting a bracket at the rear of the sled. Note the support bar preventing the dummy head from moving rearwards during sled acceleration, which here has been put into supporting position. The support bar rotates downward during sled transit and is not a factor in the subsequent head impact. (b) The mini-sled in a position just prior to the dummy head contacts the foam. A layer of tape to reduce the friction between the head and foam during impact covers the face and forehead. A sample of EPS is mounted on the aluminum plate. Below the foam sample is a piece of honeycomb to decelerate the sled. Note that the support bar for the head is in its nonsupporting position.
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Midsagittal plane positioning of accelerometers inside the dummy head. The biaxial array accelerometers denoted CG-x and CG-z were also used to measure linear x and z acceleration at the head CG. The coordinate system, which is attached to the head CG, follows the Hybrid III sign convention, i.e., the x axis coincides with the posteroanterior direction (anterior direction positive) and the z axis coincides with the superoinferior direction (inferior direction positive).
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Illustration of head kinematics during the first 35 ms following initial head-foam contact at t=0. The frames are taken from the video sequence of test 49, a 7.03 m/s impact into FPU of 64.0 kg/m3.
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Responses as measured in the test shown in Fig. 4. (a) x,z, and resultant linear acceleration at the head CG and sled deceleration. (b) Sagittal plane angular acceleration as calculated from the in-line system and biaxial array, neck force Fx acting on the head in the x direction and neck moment My acting on the head about an axis parallel to the y axis through the head CG. The noise in the acceleration time history from the in-line system occurring between t=22 ms and t=26.5 ms is due to the support rod hitting the back cap of the dummy head, thus causing a slight ringing in the in-line accelerometers. (c) Sagittal plane angular velocity calculated by integration of the acceleration time histories shown in (b).
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Peak values of angular acceleration and change in angular velocity as functions of peak values of resultant linear acceleration and HIC36 as measured in all the mini-sled tests.
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HIC36 as a function of peak resultant linear acceleration for the low-, intermediate-, and high-speed tests. Nonlinear regression functions, in which HIC36 was a function of peak resultant linear acceleration raised to the power of 5/2, have been fitted to the results from the low- (r=0.981), intermediate- (r=0.949), and high-speed (r=0.694) tests. The use of linear regression would have resulted in slightly lower correlation for the low- (r=0.970) and intermediate-speed (r=0.944) tests and slightly higher correlation for the high-speed tests (r=0.720).
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Head-foam contact force in the direction of sled motion (as recorded by the load cells backing up the inclined aluminum plate) and linear x acceleration of the dummy head (as recorded by the CG-x accelerometer in the biaxial array) for two high-speed tests in which the foam did not bottom out (test 59, a 9.87 m/s impact into EPP of 48.0 kg/m3) and bottomed out (test 54, a 9.69 m/s impact into EPP of 20.8 kg/m3).
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Peak responses in the high-speed tests in which the foam samples did not bottom out (solid circles) and bottomed out (open circles). (a) Peak angular acceleration as a function of peak resultant linear acceleration. (b) Peak angular acceleration as a function of HIC36. (c) Peak resultant linear acceleration as a function of HIC36.




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