Abstract：Metal structures are widely used in modern industrial fields and various composite defects are probably produced during its manufacture and service. For example, both the surface and bottom of structures emerge defects, which seriously affect the mechanical properties and service life of metal structures. Facing such complex conditions, a single nondestructive testing (NDT) method usually cannot meet all needs. However, two or more targeted NDT methods have the problems of low efficiency and high cost. To solve this problem, a novel electromagnetic-acoustic integrated testing method (PECT-EMAT) is developed, and the detection capability of witch is evaluated according to the theory of probability of detection (POD) in this study. Firstly, the simulation method and experimental system of PECT-EMAT are developed for the aluminum alloy specimen with both surface cracks and bottom thinning defects, respectively, the signal separation method based on spectrum analysis theory is studied. Then, the POD model based on statistics is established and the signal database of composite defects is built. Lastly, the signal database is analyzed statistically and the POD of the composite defects detection is analyzed according to the established POD model to determine the minimum detectable size of the PECT-EMAT hybrid testing method. The results of research shows that: (1) For the composite defects with both surface cracks and bottom thinning defects of metal structures, the proposed PECT-EMAT hybrid testing method can detect the composite defects effectively by signal separation. (2) The PECT signals and EMAT signals separated from the original detection signals have obvious signal characteristics for surface cracks and bottom thinning defects, respectively. Moreover, The signal features database of composite defects can been established through above association relationship. (3) Through POD analysis, it finds that the minimum detectable length of the surface crack is 2.72mm and 2.12mm for simulation and experiment, respectively. Similarly, the minimum detectable length of the bottom thinning defect is 4.13mm and 1.92mm, respectively. Through the verification of the detection ability, this paper provides theoretical basis for the popularization and application of the proposed PECT-EMAT hybrid testing method. More importantly, it affords one type of reliable technical means for the complex defects detection for practical engineering structures.
2025, Vol. 46 
