RESEARCH ON NONDESTRUCTIVE MEASUREMENT OF FATIGUE DAMAGE

本课题的目的是建立一种无损测量和评估疲劳损伤的方法，以防止各种工程结构的疲劳失效。疲劳损伤过程可分为三个阶段，一是疲劳损伤积累阶段，微观组织发生变化，但不形成裂纹；二是裂纹萌生和小裂纹扩展阶段；三是宏观裂纹扩展阶段，可以用断裂力学方法来解释。摘要本课题提出了两种新型无损检测核压力容器钢、镍基超合金和烧结低合金钢损伤累积和裂纹萌生扩展的方法。第一种是感应电流聚焦电位降技术（以下简称icfpd），第二种是电化学方法。ICFPD已成功地应用于疲劳损伤过程的监测，可以检测到疲劳引起的微结构变化导致磁导率降低，从而导致测量电位的降低，从而导致损伤累积。裂纹萌生后，根据裂纹引起的电流路径的增加来测量潜在的增加。这种测量电位的变化可以用一个简单的模型来解释，即材料的磁导率下降和裂纹引起的电流路径增加。二是利用电化学方法对疲劳损伤累积进行检测。位错密度的增加和由此形成的位错细胞结构可引起损伤积累。这种方法是基于检测这些可能的电化学或化学活性位点通过适当的电解质和极化程序。对于压力容器钢，最佳电解液为钼酸钠溶液；对于铬镍铁合金718，最佳电解液为hcl、h2so4、cuso4和水的混合物。这些结果可为核电厂、化工厂和航空航天工程部件的疲劳损伤无损评估提供一种潜在的方法。少

THE OBJECTIVE OF THIS PROJECT IS TO ESTABLISH A NONDESTRUCTIVE MEASUREMENT AND EVALUATION OF FATIGUE DAMAGE TO PREVENT FATIGUE FAILURES IN VARIOUS ENGINEERING STRUCTURES.FATIGUE DAMAGE PROCESSES CAN BE CATEGORIZED INTO THREE,ONE IS FATIGUE DAMAGE ACCUMULATION STAGE WHERE MICROSTRUCTURAL CHANGES WILL TAKE PROCESS WITHOUT ANY CRACK FORMATION,SECOND CRACK INITIATION AND SMALL CRACK GROWTH STAGE AND THIRD MACROSCOPIC CRACK GROWTH STAGE WHICH CAN BE INTERPRETED BY FRACTURE MECHANICS APPROACH.IN THIS PROJECTS,TWO NOVEL NONDESTRUCTIVE TECHNIQUES ARE PROPOSED FOR DETECTION OF DAMAGE ACCUMULATION AND CRACK INITIATION AND PROPAGATION ON NUCLEAR PRESSURE VESSEL STEELS,Ni-BASE SUPPER ALLOY AND SINTERED LOW ALLOY STEELS.FIRST PROPOSAL IS INDUCED CURRENT FOCUSING POTENTIAL DROP TECHNIQUE (HERE AFTER DENOTED AS ICFPD) AND SECOND IS ELECTROCHEMICAL METHOD.ICFPD HAS BEEN SUCCESSFULLY APPLIED FOR MONITORING OF FATIGUE DAMAGE PROCESSES AND CAN DETECT DAMAGE ACCUMULATION AS A DECREASE OF MEASURED POTENTIA … More L DUE TO REDUCTION OF MAGNETIC PERMEABILITY CORRESPONDING TO MICROSTRUCTURAL CHANGES BY FATIGUE.AFTER CRACK INITIATION,MEASURE POTENTIAL INCREASES AS EXPECTED FROM AN INCREASE IN CURRENT PATH DUE TO CRACKS.THIS KIND OF VARIATION OF MEASURED POTENTIAL CAN BE INTERPRETED BY A SIMPLE MODEL OF A COMBINATION OF DECREASE IN MAGNETIC PERMEABILITY OF MATERIALS AND INCREASE IN CURRENT PATH CAUSED BY CRACKS.SECOND ONE IS BY ELECTROCHEMICAL METHOD FOR A DETECTION OF FATIGUE DAMAGE ACCUMULATION.DAMAGE ACCUMULATION CAN BE CAUSED BY INCREASE IN DISLOCATION DENSITY AND RESULTANT FORMATION OF DISLOCATION CELL STRUCTURES.THIS METHOD IS BASED ON DETECTION OF THESE POSSIBLE ELECTROCHEMICALLY OR CHEMICALLY ACTIVE SITES BY A PROPER ELECTROLYTE AND POLARIZATION PROCEDURES.THE BEST ELECTROLYTES ARE SODIUM MOLYBDATE SOLUTION FOR PRESSURE VESSEL STEELS AND MIXTURE OF HCL,H2SO4, CUSO4 AND WATER FOR INCONEL 718, RESPECTIVELY.THESE RESULTS CAN PROVIDES A POTENTIAL PROCEDURE FOR NONDESTRUCTIVE EVALUATION OF FATIGUE DAMAGE IN THOSE OPERATING PLANTS SUCH AS NUCLEAR POWER PLANTS,CHEMICAL PLANTS AND AEROSPACE ENGINEERING COMPONENTS. Less