DEVELOPMENT OF A MICROCIRCUIT GRID TECHNIQUE FOR AUTOMATED CRACK LENGTH MEASUREMENT FOR FATIGUE TESTING AT ELEVATED TEMPERATURES

DEVELOPMENT AND APPLICATION OF A MICROCIRCUIT GRID TECHNIQUE FOR MEASURING CRACK LENGTHS IN FATIGUE CRACK GROWTH TEST SPECIMENS IS DESCRIBED. CRACK LENGTH IS DETERMINED FROM STEPWISE CHANGES IN THE VOLTAGE OUTPUT OF THE GRID CIRCUIT CAUSED BY THE SEQUENTIAL RUPTURE OF THE MICROSTRIPS BY THE ADVANCING CRACK TIP. THE ADVANTAGES OF THE GRID TECHNIQUE AS COMPARED TO OTHER TECHNIQUES FOR MONITORING CRACK LENGTHS INCLUDE: HIGH CRACK LENGTH RESOLUTION ( M) MADE POSSIBLE BY TODAY'S ADVANCED MICROCIRCUIT TECHNOLOGY, APPLICABILITY AT ELEVATED TEMPERATURES (1200 C) BY AN APPROPRIATED SELECTION OF THE CONDUCTING METAL STRIPS, LACK OF A NEED FOR QUANTITATIVE CALIBRATION OF THE VOLTAGE OUTPUT, AND THE COMPATIBILITY TO AUTOMATE THE DATA ACQUISITION AND ANALYSIS. DIRECT COMPARISON OF FATIGUE CRACK GROWTH RATES IN METALLIC SPECIMENS MEASURED BY THE GRID TECHNIQUE AND OTHER TECHNIQUES AND THE DEVELOPMENT OF A MULTIPLE GRID TECHNIQUE ARE THE OBJECTIVES OF THE PHASE I EFFORT.