The Dynamic Compression and Release of Mechanical Mixtures in the Presence of a Phase Change.
AIR FORCE MATERIALS LAB WRIGHT-PATTERSON AFB OHIO
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An experimental investigation of the shock compression and release be-havior of simple homogeneous mechanical mixtures of selected solids was conducted to provide a basis for modeling the dynamic behavior of continuous filament reinforced and plate laminate composites at stress levels where hydrostatic behavior is approximated. The binary mixtures investigated all consisted of a polyethylene matrix with the rigid com- ponent chosen from the following 40 wo, and 90 wo copper 94.5 wo tantalum and 70 wo alumina. A 20 mm smooth bore powder gun was used to launch either copper o-tantalum flat-face projectiles against the theoretically dense mixtures the hydrostatic pressure ranging from 25 kilobars to 270 kilobars. The rule of mixtures described the shock loading and release up to the stress required for shock melting the polyethylene streak photographs and flash x-radiographic techniques gave identical measurements of the free surface velocity. Beyond the shock melting pressures for polyethylene, the free surface velocity measurements by the two techniques were not in agreement. A model was developed which assumed the two constituents of the mixture decoupled and physically separated upon release from states above this shock melting pressure. The free surface velocity of the decoupled polyethylene as measured by the streak camera agrees with the prediction of the decoupling model when the assumption is made that the shock compression is accomplished with no heat transferring between constitutents. A similar analysis assuming perfect heat transfer between constitutents did not agree with the observations, as expected. Author-PL
- Laminates and Composite Materials