Research on Interaction of Multiple Cracks and Nondestructive Evaluation by Means of Electromagnetic Techniques

1.提出了一种利用直流电势降技术对二维多裂纹进行简化无损评估的方法。介绍了一种用来表示裂纹间相互作用的项来计算势降的新方法。分析可以在短时间内在个人计算机上完成。提出了一种简化的多裂纹无损评估方法，该方法利用含多个裂纹的分区的直流电势降技术。在简化裂纹相互作用分析的基础上，计算了一个子区域内裂纹的势降分布。提出了一种利用直流电势降技术对三维多裂纹进行简化无损评估的方法。利用描述裂纹间相互作用的项，并考虑侧壁的影响，来表示势降。提出了一种通过测量材料中直流电流在空气中产生的磁场来简化多裂纹无损检测的方法。用表示这些裂纹之间相互作用的项来表示三维多表面裂纹引起的磁通密度的变化。以三维辐射多裂纹为例，研究了多个微小缺陷的形成，即金属线中空洞的形成。结果表明，用来预测空穴形成的原子通量散度是决定空穴形成的主要参数。利用该参数，利用电阻测量方法对金属线中空洞的形成进行了无损评价。最后，在第四届远东无损检测会议上，该研究项目的技术总结作为一篇特邀论文《电磁技术的多裂纹无损检测》发表。

1. A method was proposed for simplified nondestructive evaluation of two-dimensional multiple cracks by means of the d.c.potential drop technique. A new methodology was introduced to calculate the potential drop by using terms representing the interaction between cracks. The analysis was able to be done with personal computer in a short time.2. A method was proposed for simplified nondestructive evaluation of multiple cracks by means of the d.c.potential drop technique for a subregion containing some cracks. The distribution of the potential drop for cracks in a subregion was calculated based on simplified analysis of crack interactions.3. A method was proposed for simplified nondestructive evaluation of three-dimensional multiple cracks by means of the d.c.potential drop technique. The potential drop was expressed by utilizing terms representing the interaction between cracks and considering the effect of the side walls.4. A method was proposed for simplified nondestructive evaluation of multiple cracks by means of measurement of magnetic field produced in the air by d.c.current flow in a material. The change in magnetic flux density due to three-dimensional multiple surface cracks was expressed by using terms representing the interaction between these cracks.5. As an example of three-dimensional radiated multiple cracks, formation of multiple minute defects, i.e., void formation in metal line was investigated. It was found that the atomic flux divergence formulated to predict void formation was the parameter dominating the void formation. By utilizing the parameter, nondestructive evaluation of void formation in metal line by means of electrical resistance measurement was enabled.Finally, it is noted that the summary of the techniques developed in this research program has been presented as an invited paper "NDE of Multiple Cracks by Electromagnetic Techniques" at the 4th Far East Conference on NDT.