Project Grant 2152369

MULTIMODAL AND MULTISCALE-DRIVEN QUANTIFICATION OF MICROMECHANICAL METRICS FOR LOCATION-SPECIFIC FATIGUE MICROCRACKING -NONTECHNICAL SUMMARY THIS AWARD SUPPORTS RESEARCH AND EDUCATION ACTIVITIES AIMED AT IDENTIFYING AND QUANTIFYING THE MECHANISTIC DRIVERS FOR FATIGUE DAMAGE IN METALLIC MATERIALS. FATIGUE IS A PHYSICAL PROCESS THAT IS ASSOCIATED WITH THE FAILURE OF CRYSTALLINE MATERIALS UNDER CONTINUOUS AND REPEATED APPLICATION OF LOADS. THE KNOWLEDGE OF FATIGUE IS OF IMMENSE VALUE IN PREVENTING THE FAILURE OF METALLIC STRUCTURAL COMPONENTS IN MACHINERY, EQUIPMENT AND STRUCTURES. THE ACCURATE PREDICTION OF FATIGUE LIFE REQUIRES THE NEED TO KNOW THE GOVERNING MECHANISTIC DRIVERS FOR CRACK INITIATION AT THE MICROSCALE (THE SCALE AT WHICH CRACKS INITIATE). HOWEVER, SINCE THE MICROSTRUCTURE IN THE VICINITY OF THE CRACK INITIATION SITES IN METALLIC MATERIALS EVOLVES CONTINUOUSLY WITH LOADING, THE IDENTIFICATION OF THESE MECHANISTIC DRIVERS IS A CHALLENGING TASK. IN THIS PROJECT, THE PI WILL ADDRESS THIS CHALLENGE WITH AN INTEGRATED COMPUTATIONAL AND EXPERIMENTAL APPROACH THAT WILL PROVIDE A DEEPER UNDERSTANDING OF THE FACTORS INFLUENCING FATIGUE CRACK INITIATION. THE PRIMARY FOCUS OF THE PROJECT WILL BE ON PURE METALS WITH VERY LARGE GRAINS SUCH AS NICKEL. INSIGHTS AND TOOLS OBTAINED FROM THE RESEARCH WILL IMPROVE THE ACCURACY OF FATIGUE LIFE PREDICTIONS FOR A VARIETY OF LARGE-GRAINED METALLIC STRUCTURAL COMPONENTS AND THIN FILM DEVICES THAT UNDERGO CYCLIC STRESSES. ADDITIONALLY, THE PROJECT WILL SUPPORT THE EDUCATION AND TRAINING OF A DIVERSE FUTURE WORKFORCE IN DATA-INTENSIVE MATERIALS RESEARCH. TO INSPIRE MIDDLE AND HIGH SCHOOL STUDENTS TO PURSUE MATERIALS SCIENCE AND ENGINEERING DEGREES, THE PI WILL DEVELOP BRIEF, AGE-APPROPRIATE LECTURES THAT EXPLAIN HOW STUDENTS? BASIC CLASSROOM LEARNING RELATES TO THE ACTUAL TOOLS AND MODELS THAT PROFESSIONAL ENGINEERS USE AND GIVE THE STUDENTS THE CHANCE TO PERFORM VERY BASIC SIMULATIONS USING THE TOOLS. TECHNICAL SUMMARY THIS AWARD SUPPORTS RESEARCH AND EDUCATION ACTIVITIES TO IDENTIFY AND QUANTIFY THE MICROMECHANICAL DRIVING FORCE METRICS FOR FATIGUE CRACK NUCLEATION IN COARSE-GRAINED FACE CENTERED CUBIC MATERIALS WITH A HIGH STACKING FAULT ENERGY. UNDERSTANDING FATIGUE DAMAGE IN CRYSTALLINE MATERIALS IS CHALLENGING BECAUSE THE MICROSTRUCTURAL FEATURES SUCH AS PERSISTENT SLIP BANDS AND THEIR INTERACTIONS, IN THE VICINITY OF THE CRACK INITIATION SITES EVOLVE CONTINUOUSLY WITH CYCLIC LOADING. THE CONTINUOUS EVOLUTION OF THE MICROSTRUCTURE GENERATES COMPLEX MICROMECHANICAL FIELDS AND INTERACTIONS WHICH MAKES IT DIFFICULT TO PINPOINT THE GOVERNING MECHANISTIC DRIVERS FOR CRACK INITIATION. SPECIFIC GOALS OF THIS WORK INCLUDE: (1) IDENTIFY HOW STRAIN LOCALIZATION AFFECTS THE SURFACE DEFORMATION DURING CYCLIC LOADING; (2) ESTABLISH A UNIFYING UNDERSTANDING OF MECHANISTIC DRIVERS FOR SUBSURFACE DEFORMATION; (3) INVESTIGATE THE MICROSTRUCTURAL AND MICROMECHANICAL RATIONALE FOR STRAIN LOCALIZATION AS A PRECURSOR TO CRACK INITIATION AND, (4) IDENTIFY THE INFLUENCE OF HIGH STRAIN GRADIENTS ON MICROCRACKING AT PERSISTENT SLIP BAND-MATRIX INTERFACES. THIS WILL BE ACHIEVED THROUGH AN INTEGRATED COMPUTATIONAL AND EXPERIMENTAL APPROACH. INSIGHTS AND TOOLS OBTAINED FROM THE RESEARCH WILL IMPROVE THE ACCURACY OF FATIGUE LIFE PREDICTIONS FOR A VARIETY OF LARGE-GRAINED METALLIC STRUCTURAL COMPONENTS AND THIN FILM DEVICES THAT UNDERGO CYCLIC STRESSES. ADDITIONALLY, THE PROJECT WILL SUPPORT THE EDUCATION AND TRAINING OF A DIVERSE FUTURE WORKFORCE IN DATA-INTENSIVE MATERIALS RESEARCH. TO INSPIRE MIDDLE AND HIGH SCHOOL STUDENTS TO PURSUE MATERIALS SCIENCE AND ENGINEERING DEGREES, THE PI WILL DEVELOP BRIEF, AGE-APPROPRIATE LECTURES THAT EXPLAIN HOW STUDENTS? BASIC CLASSROOM LEARNING RELATES TO THE ACTUAL TOOLS AND MODELS THAT PROFESSIONAL ENGINEERS USE AND GIVE THE STUDENTS THE CHANCE TO PERFORM VERY BASIC SIMULATIONS USING THE TOOLS. THIS AWARD REFLECTS NSF'S STATUTORY MISSION AND HAS BEEN DEEMED WORTHY OF SUPPORT THROUGH EVALUATION USING THE FOUNDATION'S INTELLECTUAL MERIT AND BROADER IMPACTS REVIEW CRITERIA.