THE PRIMARY OUTCOME OF THIS PROJECT WILL BE A STATE-OF-THE-ART MODELING TOOL TO QUANTITATIVELY PREDICT THE PYROLYSIS AND ABLATION OF PHENOLIC IMPREGNATED CARBON ABLATOR (PICA) MATERIALS FOR THERMAL PROTECTION SYSTEMS (TPS) AT THE MESOSCALE IN 2D AND 3D. IT WILL ALSO PREDICT THE EVOLUTION OF THE MECHANICAL AND THERMAL PROPERTIES OF THE PICA TPS DURING OPERATION. THIS TOOL WILL BE USED TO INVESTIGATE THE IMPACT OF PICA MICROSTRUCTURE ON TPS PERFORMANCE PROVIDING RESULTS THAT CAN BE USED TO INFORM THE DEVELOPMENT OF MORE MECHANISTIC MATERIALS MODELS FOR MACROSCALE TPS CODES. ABLATIVE TPS PLAY A CRITICAL ROLE IN THE PROTECTION OF VEHICLES AND PROBES DURING FLIGHT THROUGH A PLANETARY ATMOSPHERE. THUS IT IS ESSENTIAL THAT THE PERFORMANCE OF TPS MATERIALS IS WELL UNDERSTOOD TO ENSURE ADEQUATE SAFETY MARGINS. THE DEVELOPMENT AND TESTING OF TPS MATERIALS CAN BE TIME CONSUMING AND EXPENSIVE AND CURRENT TESTING CAPABILITIES ARE INSUFFICIENT FOR TESTING TPS MATERIALS FOR MARS AND FAR SOLAR SYSTEM ENTRIES AND RETURNS. MODELING AND SIMULATION ARE ESSENTIAL FOR DECREASING DEVELOPMENT COSTS AND FACILITATING THE INVESTIGATION OF MATERIAL PERFORMANCE IN CONDITIONS FOR WHICH TESTING FACILITIES DO NOT CURRENTLY EXIST. MACROSCALE TOOLS FOR MODELING THE BEHAVIOR OF TPS MATERIALS HAVE BEEN UNDER DEVELOPMENT FOR MANY YEARS; HOWEVER THEY EMPLOY SIMPLIFYING ASSUMPTIONS AND SIMPLIFIED CONSTITUTIVE MODELS THAT CAN DECREASE THEIR ACCURACY. IN THIS PROJECT WE WILL DEVELOP A MESOSCALE MULTIPHYSICS MODELING TOOL THAT WILL QUANTITATIVELY PREDICT THE PYROLYSIS AND ABLATION OF PICA TPS. PICA IS COMPOSED OF A PHENOLIC RESIN AND CARBON FIBERS THAT ABLATE DURING REENTRY. THE PYROLYSIS OF THE RESIN TO FORM A CHAR LAYER AND THE ABLATION THROUGH OXIDATION OF THE CHAR AND FIBERS WILL BE MODELED USING THE PHASE FIELD METHOD AND WILL BE COUPLED TO MECHANICS AND HEAT CONDUCTION TO INCLUDE THE THERMOMECHANICAL BEHAVIOR OF THE MATERIAL. THE EVOLUTION OF THE THERMOMECHANICAL PROPERTIES DURING PYROLYSIS AND ABLATION WILL ALSO BE PREDICTED. THE TOOL WILL BE IMPLEMENTED USING THE FINITE ELEMENT METHOD IN THE OPEN SOURCE MULTIPHYSICS OBJECT ORIENTED SIMULATION ENVIRONMENT (MOOSE) FRAMEWORK. IT WILL BE DEVELOPED USING ROBUST QUALITY ASSURANCE PRACTICES INCLUDING DETAILED VERIFICATION AND THE USE OF REGRESSION TESTS. THIS MESOSCALE TOOL WILL REQUIRE VARIOUS MATERIAL PROPERTIES AND PARAMETERS MANY OF WHICH ARE NOT CURRENTLY AVAILABLE ESPECIALLY FOR THE CHAR. THEREFORE ATOMIC-RESOLUTION SIMULATIONS WILL BE EMPLOYED TO DETERMINE THESE NECESSARY PARAMETERS. THIS USE OF LOWER-LENGTH SCALE SIMULATION METHODS WILL BOTH ACCELERATE THE DEVELOPMENT OF HIGH-FIDELITY MODELS OF ABLATIVE SYSTEMS OF CURRENT INTEREST AND WILL ALSO ENABLE NEW CANDIDATE MATERIALS TO BE EXPLORED AND EVALUATED IN AN EFFICIENT AND COST-EFFECTIVE MANNER. ONCE COMPLETE THE MESOSCALE TOOL WILL BE VALIDATED AGAINST PICA ABLATION DATA. THE UNCERTAINTY OF THE MODEL PREDICTIONS WILL BE QUANTIFIED USING THE DAKOTA TOOL TO PROVIDE STATISTICAL DISTRIBUTIONS OF A PREDICTED QUANTITY GIVING A CONFIDENCE LEVEL ON THE VALIDATION. WE WILL USE THE VALIDATED MESOSCALE TOOL TO INVESTIGATE THE IMPACT OF VARIATIONS IN THE PICA MICROSTRUCTURE ON ITS PERFORMANCE. WE WILL ALSO INVESTIGATE THE IMPACT OF DAMAGED MATERIAL ON THE PERFORMANCE AND THE MATERIAL BEHAVIOR AT INTERFACES BETWEEN PICA TILES. THESE RESULTS WILL PROVIDE A POWERFUL MEANS OF IMPROVING MATERIALS MODELS USED IN CURRENT TPS MACROSCALE CODES.