McHenry Software, Inc.
Presented at the 2004 ATB Users' Conference
Injuries to the head are
responsible for 50,000 deaths and nearly one million hospitalizations per year
Parameter studies using mathematical modeling of motor vehicle occupants have been used to complement mechanical testing using anthropomorphic test dummies (ATD), animal, cadaver and live human test subjects. This has considerably advanced the understanding of head injury mechanisms.
One of the mathematical
models used to complement full scale mechanical testing is the Articulated
Total Body (ATB) model. The Articulated Total Body (ATB) Model is a
public domain computer program that is used to simulate the dynamic motion of
jointed systems of rigid bodies. The ATB includes the ability to calculate for
any given simulation the Head Severity Index (
This paper presents background on head injuries, head injury criterion and the use of the ATB in research and litigation to simulate occupant motions and calculate the head injury criterion.
The human head is a complex system. The human head consists of three components:
1. The bony skull
o Cranial and facial bones
2. The skin and other soft tissue covering the skull
o Which consists of layers known as the SCALP (Skin, Connective Tissue, Aponeurosis (Galea), Loose connective tissue and Periosteum)
3. The contents of the skull
o Most notably the brain, but also including the brain's protective membranes (meninges) and numerous blood vessels (see Figure 1).
Figure 1 The Scalp, Skull, Meninges and Brain (Figure 2.1 from Reference 3)
Injuries to the skin may be categorized as superficial or deep, and include contusion (bruise), laceration (cut), and abrasion (scrape). Injuries to the skull may break one or more of the bones of the skull in which case the skull is said to have been fractured (broken). Two aspects of a skull fracture are whether it is open or depressed.
Injuries to the brain and associated soft tissue are the result of either head impact or abrupt head movement (e.g., deceleration injury) or some combination of the two. Injuries may be due to the skull fracturing and being pushed inward (a depressed fracture), or from the brain impacting the interior of the skull, or from internal stressing of the brain (i.e., shear, tension and/or compression). The complexities of the head and brain system are reflected in the rather bewildering array of head injury consequences.
Three various methods are used to categorize brain injuries:
In injury producing events, there are generally 3 collisions which occur:
The human head is a complex system.
Attempting to categorize the possible injuries to the human head is a complex process. Brain injury assessment functions are based on the observed impact responses of cadavers, animals, volunteers, or accident victims. There are limitations of each of these sources of data.
A relationship between the acceleration level and impulse duration with respect to head injury was first presented by a series of six data points that indicated a decreasing tolerable level of acceleration as duration increased. The relationship became known as the Wayne State Tolerance Curve (WSTC), named for the affiliation of the researchers, and has become the foundation upon which most currently accepted indexes of head-injury tolerance are based. The original data only covered a time duration range of 1 to 6 milliseconds and only addressed the production of linear skull fractures in embalmed cadaver heads. The curve was later extended to durations above 6 msec with comparative animal and cadaver impact data and with human volunteer restraint system sled test data.
The WSTC has been criticized on various grounds since its inception: the limited number of data points, possible questionable instrumentation techniques, a lack of documentation regarding the scaling of animal data used in its extension to longer durations, and the uncertainty of definition of the acceleration levels.
From a biomechanical
standpoint the main criticism of the
The WSTC data was plotted by
log paper and an approx straight line function was developed for the weighted
impulse criterion that eventually became known as the Gadd Severity Index
(GSI). In ATB, the program calculates
the Head Severity Index (
In response to a study of the
analysis of the relationship between the Wayne State Tolerance Curve and the
Gadd Severity Index by Versace in 1971, a
new parameter, the Head Injury Criterion (
a is a resultant head acceleration
t2-t2 £36 ms
selected so as to maximize
Some questions which arise
with respect to
For example: for a 36 ms
Recent research by NHTSA
related to Improved Injury Criteria have included reviewing the existing
regulations which specify a
Figure 3 NHTSA FMVSS 208 revised Head Injury Criterion (
Another recent report included the proposal of a new head injury criterion entitled the Head Impact Power (HIP). The HIP was proposed to consider not only kinematics of the head (rigid body motion of the skull) but also the change of kinetic energy of the skull which might relate to the deformation of and injury to the non-rigid brain matter. The Head Impact Power (HIP) is based on the general rate of change of the translational and rotational kinetic energy. The HIP is an extension of previously suggested “Viscous Criterion” first proposed by Lau and Viano in 1986 , which states that a certain level or probability of injury will occur to a viscous organ if the product of its compression C and the rate of compression V exceeds some limiting value.
Categorizing the possible injuries to the human head is a complex process. There is currently not any consensus opinion on a standardized procedure or predictor.
For research purposes
mathematical models have been used to complement full-scale testing of
cadavers, animals, volunteers, and used in the development and refinement of
ATDs. The ATB has been used to complement full-scale
mechanical testing for over 30 years. When
used to interpolate and/or extrapolate full-scale testing, the ATB has been
demonstrated to provide a useful tool to assist in the understanding of
occupant responses in a variety of environments. In controlled laboratory
correlation experiments, wherein the detailed setup, starting conditions and
acceleration environment are know beforehand, sensitivity studies can be
performed on unknown or immeasurable variables to improve understanding and correlation.
The ATB includes the ability to calculate the HIS and
Every simulation model, particularly occupant simulation models like the ATB, is "an approximation of the physical system it represents and, of necessity, is based on simplifying assumptions concerning the various aspects of the nature and behavior of the real system. For this reason differences between predicted and observed responses of an actual system are to be expected, the disparities depending in part on the adequacy of the assumptions and approximations for the particular operating environment of the system".
Parametric studies of ATB for a limited number of model parameters have been performed in which some parameters were altered from their baseline values to investigate the effects on the occupant kinematics. They demonstrated the sensitivity of various responses of ATB to some parameters. Parameters investigated included: shoulder belt stiffness, lap belt stiffness, knee bolster stiffness, the guide loop location, the guide loop coefficient of friction. It should be noted that for an accident reconstruction, there are few if any known baseline values and therefore any conclusions or results may be subject to variations of 50% or greater (see Figure 4).
Recent studies comparing the
responses of the latest Rear Impact Dummy (BioRID I) with volunteer human
demonstrate improvements in correlation with human responses to that of the
Figure 4 Sample response Sensitivity of ATB to model parameters
When the ATB is used in accident reconstruction and/or applied to individual accidents, there are inherent limitations on the predictability and veracity of the results of ATB. The following lists some of limitations of the ATB for individual accident reconstruction,,
There is no
direct correlation of and/or values for
The human head is a complex system. Attempting to categorize the possible injuries to the human head is a complex process. The ATB has been used to complement full-scale mechanical testing for over 30 years. When used to interpolate and/or extrapolate full-scale testing, the ATB has been demonstrated to provide a useful tool to assist in the understanding of occupant responses in a variety of environments.
The ATB should be used in
forensics and accident reconstruction only as a tool to assist in understanding
gross occupant kinematics. Any results or conclusions drawn from an ATB
application related to
 Bandak, F. A., Eppinger, R. H. and Ommaya A. K.(eds.) (1996) Traumatic brain injury: Bioscience and Mechanics. Mary Ann Liebert Publishers.
 Cheng, Rizer, Obergefel, "Articulated Total Body Model Version V – User's Manual", Report AFRL-HE-TR-1998-0015, February 1998
 Portions from Pike, J. A., Automotive Safety:
Anatomy, Injury, Testing and Regulation,
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"Criteria for injury potential. Impact Acceleration Stress Symposium,
National Research Council publication no 977, National Academy of Sciences,
W.F., Mertz, H.J., Human Impact Reponse, Measurement and Simulation, Proceedings
of the Symposium on Human Impact Response, GM Laboratories,
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Stapp Car Crash Conference,
“State-of-the-Art Human Impact Tolerance,
 Eppinger, et al, "Development of Improved Injury Criteria for the Assessment of Advanced Automotive Restraint Systems – II", NHTSA, Nov 1999
 Eppinger, et. al, "Supplement: Development of Improved Injury Criteria for the Assessment of Advanced Automotive Restraint Systems – II", NHTSA, March 2000
Shewchenko, Welbourne "A Proposed New Biomechanical Head Injury Assessment
Function - The Maximum Power Index",
 Lau, I.V., and
 Yih-Charng Deng, "An Improved Belt Model in
 Linder, et al, Design and Validation of the Neck for a Rear Impact Dummy (BioRID I), Traffic Injury Prevention, 3:167-174,2002, Taylor and Francis
Derosia, et al "Rear Impact Responses of Different Sized Adult Hybrid
see: James, Nordhagen ,et al, "Limitations of ATB/
 Also see: McHenry, B "Occupant Kinematics in Forensics: Evaluating the Appropriateness and Applicability of an ATB Application", 2002 ATB Users' Group Conference