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The principal objective of this study was to evaluate the potential of real-time radiography as a diagnostic tool for measuring propellant crack propagation speed. The scope addressed either a non-propagating or a propagating axial bore crack in a 6-in.-diam solid-propellant motor. Simulations of X-ray emissions from a low-energy source, a model of propellant burn recession, and analysis of the simulated images provided the basis of the results. The complete simulation was performed on an IBM RISC-based workstation and the resulting images were evaluated using an image processor. The results show that the transmitted X-ray intensity profiles can be analyzed to determine the velocity of the crack tip during motor operation. A crack that was modeled to propagate at 5.0 in./sec was “measured” to within ± 1.0 in./sec using the simulated data. The simulation included the effects of finite pixel resolution and finite (8-bit) intensity digitization.

Cushioning and load distribution performance of plastic foams was investigated, using a human faceform as the loading object. A technique for measuring contact surface between faceform and plastic foam was developed. Transferrable paint applied to the foam facilitated determination of average stress over its surface, which in turn was employed to evaluate load distribution properties of the foam. Impact and static testing results on several plastic foams were analyzed. It was found that a good cushioning material characterized by low peak deceleration might show high average stress, thus making it an inefficient load distributor. The faceform used in the study incorporates the effect of face geometry during loading and thus provides a realistic simulation. Variation of material response with loading geometry and possible correlation between load distributing properties and rigidity of the foam are also discussed.