Rentala Vamsi Krishna, Mylavarapu Phani, Gautam Jai Prakash
School of Engineering Sciences and Technology, University of Hyderabad, Hyderabad 500046, India.
Defence Metallurgical Research Laboratory, Kanchanbagh, Hyderabad 500058, India.
Ultrasonics. 2018 Jul;87:59-70. doi: 10.1016/j.ultras.2018.02.012. Epub 2018 Feb 13.
In order to successfully implement Damage Tolerance (DT) methodology for aero-engines, Non-Destructive Testing (NDT) techniques are vital for assessing the remaining life of the component. Probability of Detection (POD), a standard measure of NDT reliability, is usually estimated as per MIL-HDBK-1823A standard. Estimation of POD of any NDT technique can be obtained by both experimental and model assisted methods. POD depends on many factors such as material, geometry, defect characteristics, inspection technique, etc. These requirements put enormous limitations on generating experimental POD curves and hence, Model Assisted Probability of Detection (MAPOD) curves are currently in vogue. In this study, MAPOD approaches were demonstrated by addressing various issues related to selection of crack sizes distribution, challenges involved in censoring and regression, estimation of distribution parameters, etc. Ultrasonic testing on volumetric defects has been identified as a platform to discuss the challenges involved. A COMSOL Multiphysics based FEM numerical model developed to simulate ultrasonic response from a Ti-6Al-4V cylindrical block has been validated experimentally. Further, the individual ultrasonic response from various Flat Bottom Hole (FBH) defects following lognormal distribution has been generated using the numerical model. a (detecting a flaw with 90% probability and 95% confidence) value obtained from POD curve showed that the POD value increased with an increase in decision threshold.
为了成功地将损伤容限（DT）方法应用于航空发动机，无损检测（NDT）技术对于评估部件的剩余寿命至关重要。检测概率（POD）是无损检测可靠性的一项标准指标，通常按照MIL-HDBK-1823A标准进行估算。任何无损检测技术的POD估算都可以通过实验方法和模型辅助方法获得。POD取决于许多因素，如材料、几何形状、缺陷特征、检测技术等。这些要求给生成实验POD曲线带来了极大限制，因此，模型辅助检测概率（MAPOD）曲线目前很流行。在本研究中，通过解决与裂纹尺寸分布选择、删失和回归中涉及的挑战、分布参数估计等相关的各种问题，展示了MAPOD方法。已确定对体积缺陷进行超声检测作为讨论其中涉及挑战的一个平台。已通过实验验证了一个基于COMSOL Multiphysics开发的有限元数值模型，该模型用于模拟Ti-6Al-4V圆柱块体的超声响应。此外，使用该数值模型生成了遵循对数正态分布的各种平底孔（FBH）缺陷的个体超声响应。从POD曲线获得的a（以90%概率和95%置信度检测到缺陷）值表明，POD值随着决策阈值的增加而增大。
