Richard M. Morgan

Dynamic Axial Tolerance of the Human Foot-Ankle Complex

Dynamic axial impact tests to isolated lower legs were conducted at the Medical College of Wisconsin laboratory in the USA. The aim is to develop a more definitive and quantitative relationship between biomechanical parameters such as specimen age, axial force, and injury. Twenty-six intact adult lower legs excised from unembalmed human cadavers were tested under dynamic loading using a mini-sled pendulum device. Results from these tests were combined with the data from the studies by Wayne State University and Calspan Corporation, both in the USA. The total sample size available was 52. Statistical analysis of these data was performed using Weibull techniques. Age and dynamic axial force were the most significant discriminant variables that defined the injury risk function. Consequently, the probability of foot-ankle injury was described in terms of specimen age and force. The findings are a first step towards the quantification of the dynamic tolerance of the human foot-ankle complex under the axial impact modality.For the covering abstract of the conference see IRRD 891635.

Field Investigation of Child Restraints in Side Impact Crashes

Objective. Various test procedures have been suggested for assessing the protection afforded by child restraints (CRS) in lateral collisions. Analyses of real world crashes can be used to identify relevant characteristics of the child, restraint, collision, and injury mechanisms that should be incorporated into the design of the test procedures as well as in the design of related ATDs and injury metrics. The objective of this work is to use in-depth crash investigations of children restrained in CRS in side impacts to elucidate specific sources and mechanisms of injuries and explore the role of crash severity variables such as magnitude and location of intrusion and specific impact angle. Methods. Real world crashes involving children restrained in forward facing CRS in side impacts were analyzed from Partners for Child Passenger Safety, an on-going child specific crash surveillance system in which insurance claims are used to identify cases. In-depth crash investigations using standardized protocols were used to calculate the crash severity and determine the mechanisms and sources of the injuries sustained. Results. Cases of 32 children restrained in CRS in 30 side impact crashes were examined. Twenty-five percent sustained AIS 2+ injuries. The most common injuries sustained by children restrained in CRS in side impact crashes were to the face, head, and lower extremity. Characteristics of the crashes that appeared related to injury were intrusion that entered the childs occupant space or caused an interior part of the vehicle to enter the childs occupant space, forward component of the crash, and the rotation of the CRS, restrained by a seat belt, towards the side of the impact. Conclusions. The ability to assess the injury potential in a laboratory setting for the body regions of common injury, the head, face, and lower extremity, must be explored. Characteristics of a regulatory-based test procedure to assess injury risk should include a frontal component to the crash and intrusion into the occupants seating position. Design enhancements of the CRS should address rotation during lateral impacts. These results provide guidance to current efforts to design and regulate these restraints for the safety of child passengers in side impacts.

Thoracic trauma assessment formulations for restrained drivers in simulated frontal impacts

Using cadaveric specimens, sixty-three simulated frontal impacts were performed to examine and quantify the performance of various contemporary automotive restraint systems. To characterize the mechanical responses during the impact, test-specimens were instrumented with accelerometers and chest bands. The resulting thoracic injury severity was determined using detailed autopsy and was classified using the Abbreviated Injury Scale.

Human Response to and Injury from Lateral Impact

Lateral impacts have been shown to produce a large portion of both serious and fatal injuries within the total automotive crash problem. These injuries are produced as a result of the rapid changes in velocity that an automobile occupants body experiences during a crash. In an effort to understand the mechanisms of these injuries, an experimental program using human surrogates (cadavers) was initiated. Initial impact velocity and compliance of the lateral impacting surface were the primary test features that were controlled, while age of the test specimen was varied to assess its influence on the injury outcome. Instrumentation consisted of 24 accelerometer channels on the subjects along with contact forces measured on the wall both at the thoracic and pelvic level. The individual responses and resulting injuries sustained by 11 new subjects tested at the University of Heidelberg are presented in detail. An examination of the relationship between forces applied and responses observed in the thorax is discussed. The average injuries for different sled test conditions are presented based on a total of 42 cadaver tests (11 of which are the ones discussed above). The comparison of rigid wall and padded wall sled tests is made based on these average injuries. For the covering abstract of the conference see HS-036 716. (Author/TRRL)

RAID - AN INVESTIGATIVE TOOL TO STUDY AIR BAG/UPPER EXTREMITY INTERACTIONS

A study of frontal collisions using the NASS data base showed that there were four times as many arm injuries to belt restrained drivers who had an air bag deploy than for the drivers who were simply belted. By far, the distal forearm/hand was the most commonly injured region. Hard copy review identified two modes of arm injury related to the deploying air bag: (1) The arm is directly contacted by the air bag module and/or flap cover, and (2) The arm is flung away and contacts an interior car surface. Based on the field studies, a mechanical device called the Research Arm Injury Device (RAID) was fabricated to assess the aggressivity of air bags from different manufacturers. Results from static air bag deployment tests with the RAID suggested that the RAID was able to clearly distinguish between the aggressive and non-aggressive air bags. Two factors were identified as critical to the test setup. The first was the orientation of the arm with respect to the air bag module. The second was the distance of the arm from the plane of the air bag module face. The maximum moment and fling velocity increased when the initial distance between the RAID and the air bag module was reduced. (A) For the covering abstract see IRRD 893297.

Thoracic Deformation and Velocity Analysis in Frontal Impact

The objective of the present study was to measure dynamic chest deformations and compute chest velocity and viscous criterion during real world frontal impacts conducted on a horizontal sled. Four unembalmed human cadavers were restrained using a three-point belt restraint in the driver seat of a sled buck. Two chest bands (each with a 24 gauge capability) were placed on the thorax to record the temporal deformation patterns during impact. All tests were conducted at a velocity of approximately 50 kph. Biomechanical data were gathered digitally at a sampling rate of 12,500 Hz. Multiple rib fractures were identified in all specimens at autopsy. Analysis of approximately 800 temporal deformation contours of the thorax demonstrated regional differences. The overall mean maximum normalized chest deflections, maximum chest compression velocities, and peak viscous response variables ranged from 0.15 to 0.51, 1.79 to 4.87 m/s, and 0.15 to 1.95 m/s, respectively. These findings clearly illustrate the potential use of the chest band output to correlate injury with biomechanical variables and establish thoracic impact tolerance.

Correlation of side impact dummy/cadaver tests

This paper is part of a four year study to systematically define side impact injury in terms of the kinetic response of a suitable anthropomorphic dummy. Last year a paper was presented at the Experimental Safety Vehicle Conference in Germany which analyzed side impact dummy response and injury prediction based on cadaver data generated by the Highway Safety Research Institute. These subjects were generally older than those discussed in the current paper. This paper includes data from a number of University of Heidelberg cadaver sled tests-- including padding tests which we recently found to be (1) critical for a definitive analysis and (2) previously not available. Two advanced dummies, whose design specifications are based upon biomechanical data, are currently being evaluated by the biomechanical community. The two dummies are (1) a Side Impact Dummy (SID) designed by the Highway Safety Research Institute (HSRI) and (2) the Association Peugeot-Renault (APR) dummy from France. The performance of these two candidate dummy designs is compared by a variety of techniques in seven identical tests using cadavers. These tests are chosen for use in evaluating biofidelity, repeatability, and dummy/ padding interaction. Among these techniques is a cumulative variance analysis--similar to a root-mean-square analysis-- of the acceleration signal for the seven unique sled/pendulum tests where acceleration response data exists for APR dummy, SID, and cadavers. This cumulative variance approach allows an objective comparison of the response of each dummy design with respect to the cadaver data.

On the synergism of the driver air bag and the 3-point belt in frontal collisions

Forty-eight kph frontal collisions were performed using human cadavers. The results show, that by using a combined standard 3-point belt (6% and 16% elongation)/driver air bag, the thoracic injury pattern remained located under the shoulder belt. Chest contours derived from the chest bands showed high local compression and deformation of the chest along the shoulder belt path. In tests where the air bag was the only available torso restraint, forces were distributed uniformly over the front of the chest. This study investigates if it is possible to obtain both the thoracic injury mitigating benefits of an air bag only restraint and the all-impact-direction benefits of the belt from a combination restraint system by adding a force limiter to the shoulder belt. For this reason, tests with force limiters were performed. Initially, the investigation was carried out with Hybrid III dummies using two different levels of force limiters: 4 kN and 5 kN.By using the same restraint combination and force limiter, comparable vertebral accelerations and chest compressions were measured in cadaver testing. Analytical simulations were also conducted using different size occupants in both the baseline and the optimized belt/air bag restraint and in other crash conditions. For the covering abstract of the conference see IRRD 882980.

THE NEW CAR ASSESSMENT PROGRAM: HAS IT LED TO STIFFER LIGHT TRUCKS AND VANS OVER THE YEARS?

In the New Car Assessment Program (NCAP) frontal crash tests, vehicles are crashed at 35 mph such that the entire front impacts against a rigid, fixed barrier. Instrumented anthropometric dummies are placed in the driver and right front passenger seats. Accelerometers are placed on the vehicle to record the response of the structure during the crash. In this paper, the acceleration data from accelerometers in the occupant compartment and from the dummies are analyzed to determine: (1) the trend of total stiffness or aggressivity characteristics of light trucks and vans (LTVs) since model year 1983; (2) the trend of the approximate linear stiffness of LTVs during the first 200 mm of crush since model year 1983; and (3) the effect of these structural characteristics on the NCAP safety ratings.

Injury Risk Investigation of the Small, Rear-seat Occupant in Side Impact

For children seated next to the struck side, real-world crash outcome was determined for the rear-seat of passenger vehicles over the entire range of side impact crash severities. The method was first to calculate the actual risk for an occupant based on field data. The data sources were non-rollover, tow-away crashes from the 1997 - 2009 National Automotive Sampling System. By limiting the struck passenger vehicle to model year 1985 or newer, field data were identified for a total of 588 children. In all crashes, the child was seated in the rear-seat area on the struck side of the passenger vehicle. A matrix of MADYMO model simulations calculated the response of child dummies over the entire range of the field data. Age dependent, moderate to serious (AIS ≥ 2) injury risk curves were derived and evaluated for children in side impact. Risks to the children were calculated by combining the derived child risk curves with the MADYMO model simulations. The evaluations were conducted from the point of view of an aggregate approximation of AIS ≥ 2 injury rates across the crash severity range for the entire child group of all ages. The results were that the simulations and biomechanical injury risks reasonably matched the actual NASS-CDS-based trauma risks. For all children, the accumulated injury risk approximation was 10.66% and the field-based approximation was 10.73%. This field-based methodology focuses occupant safety design toward a more far-reaching system approach where the entire range of side-impact crash severities and occupant variability are considered. Language: en