MICROMECHANICAL MODEL FOR STRUCTURAL RESPONSE AND FAILURE OF RAPIDLY HEATED CARBON-PHENOLIC LAMINATES

A MICROMECHANICAL MODEL IS PROPOSED TO ENABLE IMPROVED PREDICTIONS OF THE STRESS-STRAIN RESPONSES AND FRACTURE OF CARBON/PHENOLIC LAMINATES UNDER RAPID HEATING CONDITIONS. IN CONTRAST TO CURRENT TREATMENTS, WHICH MODEL STRUCTURAL BEHAVIOR OF ABLATIVES USING COMPOSITE-MATERIAL (MACRO) DATA AS INPUT, THE NEW MODEL WOULD PREDICT COMPOSITE BEHAVIOR FROM CONSTITUENT-MATERIAL (MICRO) DATA. ADVANTAGES WOULD INCLUDE A REDUCED NEED FOR FULL TESTING OF EACH NEW COMPOSITE MADE WITH THE SAME FIBER AND MATRIX; AND IMPROVED UNDERSTANDING OF THE PHYSICAL PHENOMENA UNDERLYING COMPOSITEBEHAVIOR IN RAPID-HEATING ENVIRONMENTS. THIS MODEL WOULD DIFFER FROM CONVENTIONAL MICROMECHANICAL REPRESENTATIONS OF LAMINATES BY INCORPORATING THE DEVELOPMENT OF POROSITY AND PORE-GAS PRESSURE DURING HEATING, BY TREATING MATRIX STRAIN CAPABILITIES IN EXCESS OF15%, AND BY INCLUDING PREDICTION OF GAS PERMEABILITIES. THE PHASE I EFFORT IS AIMED AT ESTABLISHING FEASIBILITY OF ACOMPUTER IMPLEMENTATION OF SUCH A MODEL IN A FORM SUITABLE FOR USE WITH (OR WITHIN) FINITE-ELEMENT STRUCTURAL ANALYSIS CODES. ISSUES TO BE ADDRESSED INCLUDE THE MATHEMATICAL FORMULATION AND THE TYPES OF EXPERIMENTATION NEEDED TO DEFINE CONSTITUENT INPUT DATA. IF FEASIBILITY SEEMS ASSURED, A PHASE II EFFORT WOULD BE PLANNED.