Development of Ultrasonic Angle Beam Technique of Quantitative Nondestructive Evaluation of Small Closed Cracks

The main results obtained are as follows 1. Clarification of mechanism to enhance The sensitivityultrasonic inspection of closed cracks using the ultrasonic angle beam techniqueA new evaluationapproach, namely the optimum incidence method, has been developed，which the way to deal with sensitivity to the smaller cracks，specially the closely ones. It has been verified experimentally by using both fully open and tightlyclosed 2-D cracks the evaluation sensitivity can be enhanced significantly when the beam isdirected with a small angle of incidence, θ D2i - D2【similar or equal】2deg .，the response of which is characterized by the nearly antisymmetric variation in amplitude of theback-wall echo signal around the position of the crack.2. Establishment of theoretical modeling ofultrasonic angle beam response for the evaluation of small closed cracksFor 2-D fatigue crackshaving depth of 0.5 - 5.0 mm，我们已开发的方法为sizing their depths together with the information of crack closure，by solving an inverse problem ona个人计算机. The evaluation method has been extended forplates having different thickness and also for different materials，where it has been found that the evaluation sensitivity is enhanced significantly for the情况3. Extension of the evaluation method to small 3-D closed cracksThe evaluation methoddeveloped above been extended to small 3-D closed cracks.4. Verification of the method byusing small closed 3-D surface cracksWe已证实该方法可以成功应用for the evaluation of depths of small 3-D closed cracks together with the information of their crackclosure。

The main results obtained are as follows :1. Clarification of mechanism to enhance the sensitivity of ultrasonic inspection of closed cracks using the ultrasonic angle beam techniqueA new evaluation approach, namely the optimum incidence method, has been developed, which provides the way to deal with sensitivity to the smaller cracks, specially the closely ones. It has been verified experimentally by using both fully open and tightly closed 2-D cracks that the evaluation sensitivity can be enhanced significantly when the beam is directed with a small angle of incidence, θィイD2iィエD2 【similar or equal】 2 deg., the response of which is characterized by the nearly antisymmetric variation in amplitude of the back-wall echo signal around the position of the crack.2. Establishment of theoretical modeling of ultrasonic angle beam response for the evaluation of small closed cracksFor 2-D fatigue cracks having depth of 0.5〜5.0 mm, we have developed method for sizing their depths together with the information of crack closure, by solving an inverse problem on a personal computer. The evaluation method has been extended for plates having different thickness and also for different materials, where it has been found that the evaluation sensitivity is enhanced significantly for the case of thinner plates.3. Extension of the evaluation method to small 3-D closed cracksThe evaluation method developed above has well been extended to small 3-D closed cracks.4. Verification of the method by using small closed 3-D surface cracksWe have verified that the method can be successfully applied for the evaluation of depths of small 3-D closed cracks together with the information of their crack closure.