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 correlations 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 observed variation.

Small tension and compression specimens were made from beef femurs and alternate specimens were embalmed. The stress-strain diagrams were then obtained using automatic recording equipment. From this diagram the modulus of elasticity, ultimate strength, and maximum strain to failure were determined. The hardness of all specimens was measured. A statistical evaluation of the data indicated that embalming causes a significant reduction (12%) in the ultimate compressive strength of beef bone, but only very slight reductions in ultimate tensile strength, maximum strain, and modulus of elasticity. The change in hardness was found to be insignificant. ultimate strength of beef bone; modulus of elasticity of beef bone; hardness of beef bone; tensile testing of beef bone; compressive testing of beef bone Submitted on October 1, 1963

The mechanical impedance of the human and monkeytMoc~crc.o ~nulurtu I head u a\ determined over the frequency range 30-1X)00 Hz Miniature accelerometers and pressure transducers were placed in the brain to measure its response to vibration at constant g-levels and variable frequency. The maximum acceleration studied was 20 g's, /rl rirro experiments on a fresh human cadaver and irk uico and it? ci?ro experiment> on monkeys were performed. The effect of varying blood pressure was investigated as well as the contribution to the mechanical impedance of the scalp. skull and brain. A linear two-degree-of-freedom model that summarizes the result, with acceptable accuracy is presented. Certain non-linear responses were observed for various input accelerations. No significant effect on impedance due to time after death was found for times up to five hours. The implantable accelerometer and pressure transducer experiments indicated that the brain is very nearly critically damped. Raising the blood pressure was shown to stiffen the hram. causing the resonance frequency of the head to increase. DRIVING POINT IMPEDANCE CHARACTERISTICS OF THE HEAD

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