What are the best practices for NDT of surface and internal defects in metal-matrix composites?

1 NDT Methods for MMCs

The most common NDT methods for MMCs are ultrasonic testing (UT), eddy current testing (ECT), radiographic testing (RT), and acoustic emission testing (AET). Each method has its own advantages and limitations, depending on the type, size, and location of the defect, as well as the geometry, composition, and thickness of the MMC. For example, UT is effective for detecting internal defects in thick and homogeneous MMCs, but it may not be sensitive to surface defects or thin and heterogeneous MMCs. ECT is suitable for detecting surface defects and conductivity changes in MMCs, but it may not penetrate deep into the material. RT can reveal internal defects in thin and low-density MMCs, but it may not be able to distinguish between different types of defects or materials. AET can monitor the initiation and propagation of defects in MMCs under load, but it may not be able to locate or quantify the defects.

2 Specimen Preparation for NDT

The specimen preparation for NDT of MMCs is crucial to ensure the accuracy and repeatability of the measurements. The specimen should be representative of the actual MMC component in terms of shape, size, orientation, and surface finish. The specimen should also be free of any external contamination, such as dust, grease, or paint, that may interfere with the NDT signals. The specimen should be properly aligned and secured in the NDT equipment, avoiding any gaps, misalignments, or stresses that may affect the results. The specimen should also be calibrated and verified using reference standards or known defects, to ensure the validity and comparability of the data.

3 Result Interpretation for NDT

The result interpretation for NDT of MMCs requires a thorough understanding of the principles and parameters of the chosen method, as well as the characteristics and behavior of the MMC. The result interpretation should consider the type, size, shape, orientation, and location of the defect, as well as the influence of the matrix, the reinforcement, and the interface on the NDT signals. The result interpretation should also account for the possible sources of error, noise, or ambiguity in the data, such as reflections, scattering, attenuation, interference, or artifacts. The result interpretation should be consistent and objective, based on established criteria and standards, and supported by adequate documentation and records.

4 Reliability Validation for NDT

The reliability validation for NDT of MMCs is essential to ensure the confidence and quality of the NDT results. The reliability validation should involve the evaluation of the accuracy, precision, sensitivity, repeatability, and reproducibility of the NDT method, as well as the verification of the defect detection, characterization, and sizing capabilities. The reliability validation should also include the assessment of the human factors, such as the qualification, training, and experience of the NDT personnel, as well as the communication, feedback, and reporting of the NDT findings. The reliability validation should be based on statistical methods, performance indicators, and quality control procedures, and should be periodically reviewed and updated.