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A test program has been conducted to determine the fracture behavior of the human frontal bone against two different rigid cylindrical surfaces; one surface was of 1 in. radius and one was of 5/16 in. radius; both were 6½ in. long. The purpose of this research program was to provide human tolerance data which would: 1. Assist in the design of structures likely to be impacted by the human head. 2. Extend the calibration range of frangible headforms. Twelve cadavers were tested in this program; seven against the 1 in. radius cylinder and five against the 5/16 in. radius cylinder. The test arrangement employed a guided drop of the test surface against a stationary head which was free to rebound. Drop heights were increased progressively until borderline fractures were obtained. The large radius shape consistently yielded linear fractures indicating that it is effectively a blunt surface. Fracture loads ranged 950-1650 lb.

A human head model has been developed primarily for use in evaluation of impact attenuation properties of football helmets, but is also applicable in automobile impact safety tests. Using firm silicon rubber molds made from impressions of cadaver bones, a skull and mandible were each cast in one piece using a self-skinning urethane foam that hardens into cross section geometry similar to the human bone. A rubber gel material is used to simulate the brain. The skull and attached mandible are overlayed with repairable silicon rubber skin having puncture and sliding-over-bone characteristics similar to human skin. At present, the model has a rudimentary solid silicon rubber neck, through the center of which runs a flexible steel cable attached at the foramen magnum. The cable is used to attach the head to a carriage or anthropometric dummy and can be adjusted in tension to give various degrees of flexibility.

Skull fracture was produced in forty cadavers which were dropped with their heads striking rigid, flat, hemispherical, and cylindrically shaped surfaces on the front, side, and rear. The heads were instrumented with biaxial accelerometers and force of impact was measured. Severity Index and Effective Displacement Index are compared at fracture level for all frontal impacts and the frontal flat plate results are compared to the Wayne State Cerebral Concussion Tolerance Curve. Indices calculated for Alderson 50th percentile dummy frontal head impacts onto a rigid flat plate are found to be higher than those for cadaver skull fracture impacts in the same drop height range.

Certain physical characteristics such as apparent mass and stiffness influence the dynamic response of the head and thereby the degree of trauma suffered from impact with another body. These characteristics are a function of frequency and can be determined by mechanical impedance measurement techniques. A force generator was attached directly to the skull and the force input and resulting motion at the point of attachment were measured respectively by a force and acceleration transducer. The magnitude as well as phase angle between these two vectors were measured over the frequency range from 5 to 5,000 Hz. A plot of the ratio of force and acceleration vs. frequency and phase angle vs. frequency on a nomograph reveal that both the apparent mass and stiffness of the head vary markedly from static values, and with location.

Experiments have revealed that the brain of the experimental animal behaves elastically in response to dynamic forces in situ. The response of the skull of the human cadaver has been investigated by means of static load-deflection tests and impact and mechanical impedance tests. This information has been used to construct a two-dimensional head model consisting of a polyester resin shell reinforced with fiberglas with plexiglass sides; a clear silicone gel brain; and spinal cord simulated by a plexiglass tube containing silicone gel supported by a piston-spring assembly. Several frames taken from motion pictures recorded at 7,000 frames/sec. show how pressure gradients in the model are displayed by observing the growth and location of bubbles during impact.

The head acceleration pulses obtained from monkey concussion, cadaver skull fracture (t = 0.002 sec), and football helmet experiments (0.006< t< 0.011 sec) have been subjected to injury hazard assessment by the Severity Index method. Although not directly applicable, the method correlates well with degree of monkey concussion. The range of Severity Indices for acceleration pulses obtained during impact to nine cadavers, all of which produced a linear fracture, was 540-1760 (1000 is danger to life) with a median value of 910. The helmet experiments showed good correlation between the Severity Index and the Wayne State University tolerance curve. These helmet tests also showed that a kinematics chart with curves of velocity change, stopping distance, average head acceleration, and time, with a superimposed Wayne State tolerance curve, can be useful in injury assessment.

Three human male cadaver heads were statically loaded along anteroposterior, posterioanterior, side to side, and vertex to base lines of action, while simultaneously measuring skull deflections at four or five locations and intracranial volume changes. Volume changes due to loading along the long (A-P) axis were small and either increased or decreased, while loads transverse to the A-P axis decreased the volume. Transverse loads produced volume changes on the order of 10 times larger than those due to A-P forces. Two skulls loaded to fracture in the A-P direction, failed at 1150 and 2200 lb, respectively, into the right orbit. These magnitudes and linear fracture direction correspond to four fractures produced by impact to the frontal bone of intact cadavers in previous work.

The purpose of this study was to increase our understanding of the head impact level that will produce concussion in humans. The technique employed was that of accident restaging. The investigation reported here was composed of three parts: 1. The Cornell accident records were reexamined to establish the frequency of brain concussion as a function of windshield damage. 2. Tests were conducted with instrumented cadavers to determine the head accelerations achieved when the appropriate windshield damage levels were obtained. 3. Head injury indexes were calculated from the measured accelerations, and their predictions were compared to the Cornell field data. The present reexamination of the Cornell accident data found that the percentage of victims who received a concussion involving known unconsciousness reduces to, at most, 11% for the case of radial crack with bulge. The percentage obtained for radial crack-no bulge was, at most, 2.8%.

A freshly dead Stumptail (Macaca speciosa) monkey brain hemisection model has been subjected to translation, pure rotation and a combination motion. Linear and angular head accelerations were measured as well as brain displacement relative to the skull and shear strain at several locations. Much higher than previously predicted shear strain was measured at acceleration levels which have been recorded during impacts which produced concussion in live monkeys. Pure rotation produced the highest, most diffuse and long lasting shear strain and brain displacement, while translation produced very low shear strain. Highest shear strain during rotation was recorded in the brainstem rather than on the periphery as many have predicted. Results suggest that the mechanism of brainstem injury, regardless of head motion, is due to shear caused by stretching of the cervical cord.