EFFECT OF COATINGS AND PROCESSING ON FAILURE MECHANISMS OF POLYCARBONATE MATERIALS

MATERIAL REQUIREMENTS FOR TRANSPARENT ARMOR INCLUDE OPTICAL CLARITY OVER A RANGE OF WAVELENGTHS, IMPACT RESISTANCE, AND MANIFESTATION OF DUCTILE FAILURE WHEN THE COMPONENT IS SUBJECT TO IMPACT. THIS LAST REQUIREMENT INCLUDES RESISTANCE TO CRACK PROPAGATION AND SPALLATION AND THE PREDOMINANCE OF LOCAL YIELDING ABOUT THE CONTACT AREA RESULTING IN A WELL DEFINED HOLE AS OPPOSED TO RADIAL OR CONCOIDAL FRACTURES. THIS DUCTILE FAILURE MODE RESULTS IN OPTICAL COMPONENTS RETAINING CLARITY OVER MOST OF THE OPTICAL SURFACE EXCEPT IN AREAS LOCAL TO THE CONTACT REGION. CONSISTENT WITH THE ABOVE, ORGANIC PLASTICS HAVE DISTINCT ADVANTAGES OVER INORGANIC GLASSES FOR BALLISTIC PROTECTION. THE MAIN DISADVANTAGE OF PLASTIC HOWEVER IS ITS SUSCEPTIBILITY TO SCRATCHING AND DEGRADATION DUE TO EXPLOSURE OF ULTRAVIOLET RADIATION WHICH PROMOTES DEGRADATION OF OPTICAL AND MECHANICAL PROPERTIES. THESE DISADVANTAGES HOWEVER CAN BE MITIGATED BY INCLUSION OF SURFACE COATINGS. UNDER CERTAIN CONDITIONS HOWEVER PLASTICS BEHAVE IN A BRITTLE FASHION AND CRACKS AND SPALLS UNDER BALLISTIC IMPACT. THIS BEHAVIOR IS OFTEN ASSOCIATED WITH THE PRESENCE OF PROTECTIVE COATINGS ON THE PLASTIC. THE CURRENT EFFORT INVESTIGATES THE STRESS WAVE RESPONSE OF THE COATING AND PLASTIC ASSEMBLY RESULTING FROM BALLISTIC IMPACT AND INTERACTION OF REFLECTED WAVES WITH SURFACE FLAWS AS A MEANS OF EXPLAINING THE MECHANISMS UNDERLYING THIS BRITTLE BEHAVIOR LEADING TO METHODOLOGIES FOR PREVENTION.