MICROFRACTURING-BASED CONTINUUM DAMAGE MODELS FOR HYDROCODE APPLICATIONS

THE MATERIAL MODELS PRESENTLY USED IN HYDROCODES, ESPECIALLY THOSE DESCRIBING FAILURE AND FRACTURE, ARE ARGUABLY THE WEAKEST LINK AND THE LEAST DEVELOPED PART OF THOSE CODES; YET THEY ARE ESSENTIAL IN STUDIES WHERE THE FINAL RESULTING STATE OF AN IMPACT EVENT IS THE PRIMARY FOCUS OF THE CALCULATION. PARTICULARLY FOR BRITTLE MATERIALS, SUCH AS CERAMICS, THE EXISTING TOOLS SORELY NEED TO INCLUDE CONCEPTS OF FRACTURE MECHANICS THAT INCORPORATE MODELS OF CRACK AND FLAW DISTRIBUTIONS, THE GROWTH OF THOSE CRACKS AS A TIME-DEPENDENT PHENOMENON, AND THE ULTIMATE JOINING OR COALESCENCE OF THOSE CRACKS LEADING TO ULTIMATE FRACTURE. IN ADDITION, THE DEVELOPMENT OF DAMAGE MODELS HAS BEEN IMPEDED BY THE SPARSITY OF DATA THAT CLEARLY DEMONSTRATES HOW THE MICROSTRUCTURAL PROCESSES INTERACT TO YIELD THE APPARENT BULK BEHAVIOR OF THE MATERIAL UNDER IMPACT LOADING. THE OBJECTIVES OF THE PROPOSED EFFORT WILL BE TO DEVELOP A CONTINUUM DAMAGE MODEL BASED ON CONCEPTS OF MICROFRACTURE MECHANICS AND TO INCORPORATE AND TEST THE MODEL IN THE WELL-KNOWN CTH HYDROCODE; AND TO DEMONSTRATE THAT DIRECT MICROMECHANICAL FINITE ELEMENT ANALYSIS, SIMULATING THE DETAILED INTERACTION ON THE MICROSCOPIC LEVEL, IS A USEFUL TOOL TO GUIDE THE DEVELOPMENT OF THE CONTINUUM DAMAGE MODEL WHERE DIRECT OBSERVATIONS ARE NOT POSSIBLE. THE PROPOSED APPROACH WILL IMPROVE THE ABILITY OF HYDROCODES TO PREDICT THE OUTCOME OF HIGH-VELOCITY IMPACTS INVOLVING BRITTLE, MULTIPHASE MATERIALS SUCH AS CERAMICS. IN ADDITION, THE DIRECT NUMERICAL MICROMECHANICAL SIMULATIONS WILL PROVIDE AN IMPORTANT TOOL TO EVALUATE RATIONALLY AND QUANTITATIVELY NEW DAMAGE MODEL CONCEPTS AS THEY EVOLVE. THE MODELS DEVELOPED UNDER THIS EFFORT COULD POTENTIALLY BE APPLIED IN COMMERCIAL FINITE ELEMENT CODES FOR THE RELIABILITY ANALYSIS OF COMPOSITES. THE DIRECT NUMERICAL MICROMECHANICAL ANALYSIS COULD BE AN IMPORTANT TOOL FOR UNDERSTANDING THE BASIC MECHANISMS OF FRACTURE TOUGHENING.