Case Studies in Nondestructive Testing and Evaluation最新文献

Digging is necessary to detect plant roots under the water bottom. However, such detection is affected by the transparency of water and the working skills of divers, usually requires considerable time for high-resolution sampling, and always damages the survey site. We developed a new automatic non-destructive acoustic measurement system that visualizes the space under the water bottom, and tested the system in the in situ detection of natural plant roots. The system mainly comprises a two-dimensional waterproof stage controlling unit and acoustic measurement unit. The stage unit was electrically controlled through a notebook personal computer, and the space under the water bottom was scanned in a two-dimensional plane with the stage unit moving in steps of 0.01 m (±0.0001 m). We confirmed a natural plant root with diameter of 0.025–0.030 m in the reconstructed three-dimensional acoustic image. The plant root was at a depth of about 0.54 m and the propagation speed of the wave between the bottom surface and plant root was estimated to be 1574 m/s. This measurement system for plant root detection will be useful for the non-destructive assessment of the status of the space under the water bottom.

Resistance spot welding is widely used in the fabrication of vehicle bodies and parts of their equipment. The article presents the methodology and the results of non-destructive ultrasonic testing of resistance spot welded joints of thin steel sheet with closed profile. Non-destructive test results were verified on the basis of welded joint area after destructive testing. The obtained results were used to develop an assessment technique for spot welded joints of closed profile with steel sheet, which could be used in factories employing such joints. In addition, the article makes comparison between the costs of the developed assessment technique and currently used destructive method.

In this paper, ferromagnetic impurities in paramagnetic aeroengine turbine disks are investigated. Because such inclusions represent a significant threat in aviation, a detailed analysis is required for impured turbine disks. For this purpose, sensitive fluxgate magnetometers are used. After a premagnetisation, this sensor is able to detect small ferromagnetic particles by recording the variation of the magnetic flux density while the disk rotates below the sensor head. This trajectory creates a unique signature. However, the measured signatures are often distorted. A main reason for these distortions is that the particles are not oriented in axial direction (in the direction of the disks axis). Up to now, it was not possible to interpret the measured signatures. Thus, a simulation tool has been developed that provides a catalogue of different magnetic flux density distributions of typical orientations, positions and various distances to the fluxgate magnetometer position. For these simulations, the particles are assumed to be dipoles. As part of impurities are not caused by concentrated particles but by elongated ones, so-called or dipole lines, the model has been expanded for these cases by using numerical integration techniques. Measurements verify the assumption to approximate impurities by dipoles.

In this paper the application of X-ray microCT to the non-destructive testing of an additive manufactured titanium alloy component of complex geometry is demonstrated. Additive manufacturing of metal components is fast growing and shows great promise, yet these parts may contain defects which affect mechanical properties of the components. In this work a layered form of defect is found by microCT, which would have been very difficult or impossible to detect by other non-destructive testing methods due to the object complexity, defect size and shape and because the pores are entirely contained inside the object and not connected to the surface. Additionally, this test part was subjected to hot isostatic pressing (HIPPING) and subsequently scanned. Comparing before and after scans by alignment of the volumes allows visualization and quantification of the pore size changes. The application of X-ray microCT to additive manufacturing is thus demonstrated in this example to be an ideal combination, especially for process improvements and for high value components.

Air void content is one of the most important characteristics of in-place asphalt concrete, substantially affecting early deterioration and long term performance. Destructive measures at limited locations, such as coring, are typically conducted as part of the air-void content evaluation after the pavement has been fully constructed. In this paper, use of an air coupled step-frequency array system for nondestructive assessment of air-void variability is explored. The dielectric properties of the asphalt were determined from the asphalt surface reflection amplitude of all 21 adjacent transmitting and receiving pairs of the array and related to air void content through plotting of dielectric changes with core measured air void content. This approach is an extension of the procedure developed for a single bistatic antenna pair determining properties within top millimeters of the asphalt surface. While cores provide information concerning bulk properties across the depth, the proposed method with an array system provides an opportunity for increased lateral coverage. The case study demonstrated good repeatability and correspondence with core measured air void content. The array-based method improves the coverage and productivity of the measurements, making it an attractive alternative to current state-of-the-practice procedures.

Characterization of planar flaws by non-destructive evaluation is crucial from the point of view of structural integrity assessment. An approach involving SAFT processing of B-scan image collected by electronic scanning using linear array has been used for detection and characterization of planar flaws. The study was carried out on stainless steel plate with slots inclined at various orientations and carbon steel plates having implanted weld planar flaws. The results of these investigations are presented in this paper.

This case study demonstrates the type of non-destructive analysis possible using X-ray micro computed tomography (microCT) for a titanium aerospace investment casting of 225 mm in its longest axis. The advantages of the method are highlighted while the limitations are also discussed. Recently the method has become more accessible and affordable due to multi-user service facilities and the analysis has become simpler due to software and hardware improvements. This case study demonstrates a typical analysis including defect detection, wall thickness and part to CAD comparison, which can be done in less than 4 h, while simpler results are possible in under 1 h. This will be particularly useful for industries requiring quick but detailed non-destructive analysis.

X-ray scatter dark field imaging (SDFI) tomography was used to investigate the glass fibre orientation of short fibre-reinforced polymers (SFRPs). The fibre orientation of fibre-reinforced polymers is decisive for the mechanical strength of injection-moulded parts. For this paper four different positions, with volumes along the melt flow and with weld lines, of an injection-moulded part were investigated with SDFI computed tomography with a voxel size of (43 μm)³ and absorption-based high resolution X-ray computed tomography (XCT) with a voxel size of (6.5 μm)³. The results of the SDFI computed tomography are compared with the fibre orientation to investigate the dependence of the SDFI signal on fibre orientation. The exact fibre orientation was determined by evaluation of the high resolution absorption XCT data. In particular, it is shown that the weld line and areas with different fibre orientations can be characterised by SDFI even at a voxel size of (43 μm)³ and that fibre orientation properties can be detected.

This paper presents a case study of guided waves in a steel plate with one side immersed in water. A hybrid sensing system that uses PZT as the guided wave actuator and a scanning laser vibrometer as the guided wave receiver is employed to acquire the time–space wavefield data. By using the two dimensional Fourier transform, the time–space wavefield is transformed into the frequency–wavenumber domain where the wave modes and the guided wave dispersion can be determined. The study confirms the existence of quasi-Scholte wave in the one-sidedly water-immersed plate in addition to fundamental guided waves. The results also show the quasi-Scholte wave can be directly generated and measured in the immersed plate at low frequencies using the present sensing system. Through pitch–catch sensing tests, the influence of water on guided wave propagation in the one-side water-immersed plate is investigated. It is seen that the water level affects the wave propagation time linearly and can be potentially used for estimation of water level in a container.

Joule heating losses in the working coil of up to 50% make thermal loads a crucial influencing factor on the coil lifetime in electromagnetic forming processes. Thus, especially in case of discharge sequences with short cycle times knowledge about the temperature distribution is essential to avoid thermal overstressing. This paper presents an approach for temperature measurement inside the working coil during the electromagnetic forming process. Based on fiber-based optical frequency domain reflectometry (OFDR), the spatio-temporal temperature distribution inside the coil is determined. Temperature profiles for long-term discharge sequences are provided. The results prove the qualification of this measurement technique for electromagnetic forming processes. Due to the comparatively high acquisition rate the temperature increase and drop between two discharges can be analyzed in detail. This renders new possibilities for process analysis and monitoring. Especially the effectiveness of approaches aiming at a decrease of thermal loading can be rated easily using the presented measurement technique.