Verne L. Roberts

Mechanical properties of cranial bone

Samples of human and Macaca mularta cranial bone have been tested quasistatically in tension, compression, simple shear, and torsion. The results of these experiments have been analyzed, taking into account observed anisotrophies and varying structures. Statistical correla- tions of properties have been made with density and a model proposed that summarizes these results. The cranial bones appear to be transversely isotropic and they are generally much stronger and stiffer in the transverse or tangent to the skull direction in comparison to the radial direction. The structure of the dip& region was found to be highly variable and this strongly influenced many of the mechanical responses. The model, however. explains much of the ob- served variation.

Impact Injury Mechanisms in Abdominal Organs

Blunt abdominal trauma is a major cause of death in the United States. However, little experimental work has been done to clarify the mechanism of blunt abdominal injury and to quantify tolerance parameters for the abdominal organs. This paper describes a joint study by the Highway Safety Research Institute and the Section of General Surgery of The University of Michigan in which direct impacts were applied to livers and kidneys. The tests were performed in a high-speed testing machine at a controlled ram velocity and stroke limit. The organ was surgically mobilized in anesthesized Rhesus monkeys and then placed on a load cell while still being perfused in the living animal. Tests were performed at ram speeds of 120, 6000, and 12000 in/min (5, 250, and 500 cm/s). The resulting load-deflection data were normalized and average stress-strain curves plotted for each test. In addition, the resulting injury severity was estimated immediately after impact using an injury scale of 1 to 5. A discussion of the injury mechanisms observed in the tests is given, and correlation between injury severity and the mechanical parameters of stress, strain, and strain energy produced in the tissue of the organ is presented.

Dynamic Characteristics of the Tissues of the Head

The mechanical causes of head injury have been the subject of much research and controversy. While there is a large amount of literature concerning the overall physiological and pathological effects of head injury, there is considerably less information available on the mechanical characteristics of the tissues of the head. Yet it is these characteristics that determine the mechanism and extent of injury resulting from a blow to the head. As so well put by Ommaya (1968), ‘an understanding of the effects of trauma and the development of an exact, rational prophylaxis and therapy for head injury cannot be satisfactorily achieved without a quantitative description of the mechanical properties of the tissues involved’.

Biomechanical Aspects of Head Injury

With the advent of high speed air and land transportation, engineers have become increasingly aware of the mechanical frangibility of the human body. Thus, we have seen the evolution of various isolating and load distributing devices ranging from seat belts and padded sun visors, to ejection seats, crash helmets, and acceleration couches. While there is a large amount of information available regarding the response of inanimate systems to vibration and impact, there is a comparable dearth of knowledge pertaining to the mechanical responses of biological systems. Therefore, the design of much supporting and protective equipment is often based on intuition because of the lack of information available about the mechanical behavior of the human body. In addition, such knowledge would be helpful in the treatment of injury by serving to identify the mechanism of trauma. Thus, both a rational design procedure for impact protection and a rational therapy for treatment of trauma cannot be developed until a quantitive description of the mechanical responses of the human body is obtained.

Human Torso Response to Blunt Trauma

The most frequent causes of blunt abdominal injury are the steering wheel and the lap belt. The organs most often injured are the liver, pancreas, spleen and intestines. Based on this information, a series of animal abdominal impacts were designed to study the relationship between shape and type of impactor, velocity and direction of impact, body region impacted and injury level. The results of this study are given in the form of an experimental scaling factor which relates the sensitivity to impacts of the various body regions. This scaling factor was found to be dependent of body weight, making it applicable for evaluating human tolerances to abdominal impacts.

Side impact tolerance to blunt trauma

The object of this research program has been to extend the scope of earlier work to include long-duration head impacts and to develop new scaling relationships to allow extrapolation of impact data from infrahuman primates to living humans. A series of living primate side impacts to the head and torso was conducted in parallel with a series of impacts to human cadavers. Dimensional analysis techniques were employed to estimate in vivo human tolerance to side injury. The threshold of closed brain injury to humans was found to be 76 g for a pulse duration of 20 ms and an impact velocity of 43 ft/s (13.2 m/s). The maximum tolerable penetration to the chest was found to be 2.65 in (6.72 cm) for both the left and right sides. Scaling of abdominal injuries to humans was accomplished by employing a factor that relates impact contact area, animal mass, impact force, and pulse duration to injury severity. The maximum tolerable contact pressure to the upper abdomen of a human was found to be 32 lbf/inu2 (220 kPa).

DOOR CRASHWORTHINESS CRITERIA

The object of the program was to make long duration head impacts and to develop scaling relationships to allow extrapolation of impact data for infra-human primates to living humans. A series of primate side impacts, to the head and body was conducted in parallel with a series of impacts to human cadavers. Dimensional analysis techniques were employed to estimate in vivo human tolerance to side impacts. The threshold of closed brain injury to humans was found to be 76Gs for a pulse duration of 20 msec and an impact velocity of 29.5 mph. The maximum tolerable penetration to the chest was found to be 2.65 inches for both the left and right sides. Scaling of abdominal injuries to humans was accomplished by employing a factor which relates impact contact area, animal mass, impact force, and pulse duration, to injury severity. The maximum tolerable contact pressure to the upper abdomen of a human was found to be 32 psi.

Evaluation of Dummy Neck Performance

As the structural link between the head and chest, the neck plays a vital role in determining the dynamics of the head during indirect impact. This paper discusses the factors involved in specifying and quantifying the dynamic performance of dummy neck simulations.

A viscoelastic model of the human spine subjected to +gz accelerations

IhTRODUCTION THE NEED for an accurate mathematical model of the spine subjected to +gz accelerations IS apparent from areview of the problems involved in the seat ejection of pilots from aircraft (Levy, 1964). The prediction of spinal failure due to acceleration can be accomplished either experimentally through a statisticahy representative series of destructive volunteer tests, or mathematically by using subtolerance level testing of volunteers or cadavers to provide a model for mathematical extrapolation. The mathematical model is more feasible and should be developed on the assumption that it would act similarly to the spine in all responses, e.g. accelerations and stresses. The model should be constructed so as to correlate with experimental subtolerance response and then used to obtain accurate predictions of the response up to the MAN

Improved Neck Simulation for Anthropometric Dummies

This paper describes the development of an improved neck simulation that can be adapted to current anthropometric dummies. The primary goal of the neck design is to provide a reasonable simulation of human motion during impact while maintaining a simple, rugged structure. A synthesis of the current literature on cervical spine mechanics was incorporated with the results of x-ray studies of cervical spine mobility in human volunteers and with the analysis of head-neck motions in human volunteer sled tests to provide a background for the design and evaluation of neck models. Development tests on neck simulations were carried out using a small impact sled. Tests on the final prototype simulation were also performed with a dummy on a large impact sled. Both accelerometers and high-speed movies were used for performance evaluation. A mathematical model of the cervical spine was developed for the purpose of comparing the neck simulation responses to the results obtained from the human volunteer sled tests. The features of the final prototype neck simulation are discussed and comparisons are made with current dummy neck performance.