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.

Investigators have been studying the mechanical phenomena associated with impact to the head for many years. Several theories on the behavior of the brain during head impact have come from these studies but there has been a notable lack of information on the bulk mechanical properties of the brain which are necessary for the evaluation of these theories. This paper represents an initial attempt at providing such information. The dynamic complex shear modulus of in vitro samples of human brain have been measured. Specimens from eight brains have been subjected to a sinusoidal shear stress input under resonant conditions in an electro-mechanical test device. Tests were conducted to determine the effects of time after death, refrigeration of material and shear strain dependence. A device to measure the dynamic properties of brain in vivo is described and preliminary data on in vivo tests on Rhesus monkeys is presented. The results of the dynamic shear-testing on in vitro human brain indicate that the storage modulus G' lies between 6-l 1 X 103 dyn/cm2, the loss modulus G" lies between 3.5-6.0 x LO3 dyn/cm2 and the loss tangent tan 6 is in the range 0.40-0.55.

Samples of descending mid-thoracic aortas were obtained from human autopsies and experiments were performed to determine the effect of strain rate and direction of loading on the failure properties of the tissue in uniaxial tension. The tests were performed at quasi-static strain rates in the range 0.01 s-1-0.07 s-1 and dynamic tests in the range 80 s-1-100 s-1. Ultimate stress and extension ratio values have been calculated for specimens tested in the longitudinal and transverse directions of the aorta.

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Descending mid-thoracic aortas were obtained from 16 autopsies and biaxial inflation tests performed on the tissue at dynamic (approximately 20 s-1) and quasi-static (approximately 0.01 s-1) strain rates. A bubble inflation technique was developed for this purpose. Extension histories of the specimens were recorded photographically and values of ultimate stresses and extension ratios in biaxial stretch have been calculated. Under conditions of uniform biaxial stretch the tissue consistently failed in a direction perpendicular to the long axis of the aorta and pressure values at failure were greater by a factor of two in the dynamic tests than those in the quasi-static tests.