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The article presents the application of the acoustic emission (AE) technique for detecting crack initiation and examining the crack growth process in steel used in engineering structures. The tests were carried out on 40CrMo steel specimens with a single edge notch in bending (SENB). In the tests crack opening displacement, force parameter, and potential drop signal were measured. The fracture mechanism under loading was classified as brittle. Accurate AE investigations of the cracking process and SEM observations of the fracture surfaces helped to determine that the cracking process is a more complex phenomenon than the commonly understood brittle fracture. The AE signals showed that the frequency range in the initial stage of crack development and in the further crack growth stages vary. Based on the analysis of parameters and frequencies of AE signals, it was found that the process of apparently brittle fracture begins and ends according to the mechanisms characteristic of ductile crack growth. The work focuses on the comparison of selected parameters of AE signals recorded in the pre-initiation phase and during the growth of brittle fracture cracking.

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This paper outlines a design for a fibre-cement panel ventilated façade smart control system based on the acoustic emission method. The paper also provides methodology and test results, as well as statistical analysis of the three-point bending results with AE signal acquisition as a basis for the development of the system in question. The test items were samples cut from a full-size fibre-cement panel for interior and exterior use, according to the standard guidelines. The recorded acoustic emission signals were classified statistically into four classes, which were assigned to the processes occurring in the material structure as a result of the applied load. The system development was based on the differences between the characteristics of the individual signal classes and their number for each test case, as well as on the different distribution of successive classes over time. Given the results of the tests and the resulting conclusions indicating the applicability of the acoustic emission method (based on signal classification using the k-means algorithm for the assessment of variations in the mechanical parameters of cement-fibre composites), a methodology for such assessment was therefore developed. The approach proposed is a reasonable method for assessing the variation in mechanical parameters of fibre-cement panels on the basis of the parameters determined by the non-destructive method indicated.