On‐line ultrasonic monitoring of injection molding of a simple polymer box is studied using pulse‐echo techniques. The flow front of molten polymers inside the mold has been probed by a multiple‐channel probing system with a time resolution of 2 ms. This information can be used to control the plunger movements. The gap development, because of the shrinkage of the part in the mold, is also monitored. This information, which is important for the understanding of the part's cooling process, has been found to be superior than that measured by a conventional pressure probe. The relation between the gap formation time and the packing pressure has been investigated at various part locations characterized by different thicknesses. The velocity and the amplitude variations of ultrasonic waves, in a reflection as well as in a transmission configuration, have also been measured in the part's material during its solidification. The behavior of these ultrasonic parameters contributes to the interpretation of the solidification process.

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Ultrasonic guided waves are particularly interesting for SHM applications because they have the ability to propagate long distances with minimal attenuation. Using the baseline subtraction approach, the signal from a defect free structure is subtracted from the actual monitoring signal to detect and characterize defects. Low frequency guided wave SHM and the interaction of the fundamental guided wave modes with various types of defect are well documented in the literature. There are, however, only a very limited number of studies on high order modes. High frequency guided waves may enable the detection of smaller cracks relative to conventional low frequency guided wave SHM. The main difficulty at high frequency is the existence of several modes with different velocities. This study investigates the scattering of high frequency Lamb waves around a through-thickness hole with a view to developing a highly sensitive SHM system for safety-critical components. A 3D finite element model of a 305 × 305 × 1.6 mm aluminum plate was used to determine the scattered field generated by cracks on the circumference of a through-thickness hole in the middle of the plate. Crack properties such as orientation, length and depth were studied. A subset of the finite element simulations were validated against experimental results. The experimental setup comprised a classic contact piezoelectric transducer bonded on the side of the plate and a laser interferometer detector.

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. Design of an advanced automatic inspection system for aircraft parts based on luorescent penetrant inspection analysisNon-destructive testing (NDT) of aircraft parts has become increasingly important in improving the safety and reliability of the aerospace industry, especially in the testing of high-temperature and high-pressure turbine engine parts. Among the various types of NDT methods available, luorescent penetrant inspection (FPI) is comparably more cost-eicient and is widely used in NDT on aircraft parts. However, current FPI still requires considerable labour forces in its processing, inspection and analysis procedures. In this paper, we have developed an advanced automatic inspection system (AAIS) that uses image processing and pattern recognition techniques to aid human inspectors. The system can automatically detect, measure and classify discontinuities from the FPI images of aircraft parts. Tests have been performed on the sample images provided by our industrial partners to evaluate our developed AAIS. The test results demonstrate that the developed system has signiicantly improved the eiciency of FPI with satisfactory accuracy.

Applying life estimation approaches to determine in-service life of structures and plan the inspection schedules accordingly are becoming acceptable safety design procedures in aerospace. However, these design systems shall be fed with reliable parameters related to material properties, loading conditions and defect characteristics. In this context, the role of nondestructive (NDT) testing reliability is of high importance in detecting and sizing defects. Eddy current test (ECT) is an electromagnetic NDT method frequently used to inspect tiny surface fatigue cracks in sensitive industries. Owing to the new advances in robotic technologies, there is a trend to integrate the ECT into automated systems to perform NDT inspections more efficiently. In fact, ECT can be effectively automated as to increase the coverage, repeatability and scanning speed. The reliability of ECT scanning, however, should be thoroughly investigated and compared to conventional modes of applications to obtain a better understanding of the advantages and shortcomings related to this technique. In this contribution, a series of manual and automated ECT tests are carried out on a set of samples using a split-D reflection differential surface probe. The study investigates the level of noise recorded in each technique and discuss its dependency on different parameters, such as surface roughness and frequency. Afterwards, a description of the effect of crack orientation on ECT signal amplitude is provided through experimental tests and finite element simulations. Finally, the reliability of each ECT technique is investigated by means of probability of detection (POD) curves. POD parameters are then extracted and compared to examine the effect of scanning index, frequency and automation on detection reliability.

Structural health monitoring is a prominent alternative to the scheduled maintenance of safety-critical components. The nondispersive nature as well as the through-thickness mode shape of the fundamental shear horizontal guided wave mode (SH0) make it a particularly attractive candidate for ultrasonic guided wave structural health monitoring. However, plane wave excitation of SH0 at a high level of purity remains challenging because of the existence of the fundamental Lamb modes (A0 and S0) below the cutoff frequency thickness product of high-order modes. This paper presents a piezoelectric transducer concept optimized for plane SH0 wave transduction based on the transducer geometry. The transducer parameter exploration was initially performed using a simple analytical model. A 3D multiphysics finite element model was then used to refine the transducer design. Finally, an experimental validation was conducted with a 3D laser Doppler vibrometer system. The analytical model, the finite element model, and the experimental measurement showed excellent agreement. The modal selectivity of SH0 within a 20∘ beam opening angle at the design frequency of 425 kHz in a 1.59 mm aluminum plate was 23 dB, and the angle of the 6 dB wavefront was 86∘.

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