CONDITIONS FOR THERMAL CYCLE TESTING OF LONG-LIFE RADIATOR COATINGS.

AN ANODIC ALUMINUM OXIDE COATING HAS BEEN RECOMMENDED FOR THE SPACE STATION CREW SYSTEMS RADIATOR. CRACKING BY THERMAL FATIGUE IS ITS PROBABLE LONG-TERM FAILURE MECHANISM, BUT IT IS NOT CLEAR HOW TO PERFORM ACCELERATED THERMAL CYCLE TESTS TO GET A RELIABLE PREDICTION OF LIFETIME. WE PROPOSE TO MEASURE THE STRESS, AND TEMPERATURE DEPENDENCE OF STRESS OF ANODIC COATINGS. A THERMAL STRAIN PARAMETER IS DEFINED IN TERMS OF A TEMPERATURE OF ZERO STRESS, TO. COATINGS PREPARED TO HAVE AWIDE RANGE OF TO VALUES ARE EXPECTED TO ALSO HAVE A WIDE RANGE OF LIFETIMES. IN PHASE I THE EXTREME VALUES FOR TO WILL BE DETERMINED EXPERIMENTALLY, AS WELL AS TO VALUES FOR TWO PARTICULAR COATINGS FOR WHICH ACCELERATED THERMAL CYCLE TEST DATA ARE AVAILABLE. IF IT SEEMS FEASIBLE TO USE THE TO CRITERION AS A GUIDE IN PREPARING CYCLE TEST SPECIMENS, THIS WILL BE DONE IN PHASE II. THE CYCLE TEST DATA CAN THEN BE EXTRAPOLATED TO PREDICT LIFETIMEOF OPERATIONAL COATINGS FOR KNOWN TO. IN PHASE II SOME PARTICULAR QUESTIONS REGARDING STABILITY OF THESE COATINGS IN ZERO HUMIDITY SPACE ENVIRONMENT, AND THE POSSIBILITY OF PREPARING COATINGS WITH A STRUCTURE THAT IMPROVES FRACTURE TOUGHNESS, WILL BE EXAMINED.