Evaluation of destructive processes in FRC composites using time-frequency analysis of AE signals

Modern fiber-cement boards currently used in construction are made of natural raw materials such as cement, cellulose fibers and of polyvinyl alcohol (PVA) and water. They replaced the eternitic plates, which were harmful to health, originated by Ludwig Hatschek. Materials made of fiber-cement are used in construction industry as a building and finishing material for facades, internal walls and roofs. Therefore, they are exposed to environmental conditions including rainfall and temperature changes, and in particular to frequent temperature transition through 0°C in a 24-hour cycle (cyclic freezing-thawing). In addition, fibrous cement materials, primarily used as cladding elements, are exposed to exceptional conditions, which include the high temperature caused by fire. The article presents the results of experimental tests of flexural strength of cement fiber boards subjected to exceptional conditions, to which the operation of fire belongs. The paper also presents a proposal to use a non-destructive method of acoustic emission based on time-frequency analysis for testing fiber-cement boards. Interesting research results were obtained that allowed to trace the differences in the mechanisms of material destruction under the influence of the changing time of external factors

The Use of the Acoustic Emission Method to Identify Crack Growth in 40CrMo Steel

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

Localization and identification of gas infrastructure defects by acoustic emission

Durability, reliability and usability are three foundations of reliable construction, crucial in economic and social context. Because localization and monitor of potential defect and assessment of its impact on condition of the construction are part of the durability assessment, we should develop appropriate methods, which would detect the beginning of technical condition process getting worse and could allow monitoring its progress during exploitation of the construction, not only at areas chosen subjectively or based on unverifiable computer models. One of this NDT methods complied with user expectations is acoustic emission method based on analysis of active destruction processes. The article presents results of AE applications to locate, monitor and identify destruction processes caused by exploitation burdens made to assessment the technical condition of gas infrastructure made from cast iron, steel and plastic

Acoustic emission for diagnosing cable way steel support towers

The paper reports results of the study on the possibility of using the acoustic emission method in diagnosing fatigue and corrosion damage in steel elements of the cable way support towers. The assessment of the sensitivity of the structure to the recorded destructive processes is based on the structural damage classification method using the patterns created as a result of statistical and mathematical processing of acoustic emission signals through image analysis and grouping methods

Wpływ warunków eksploatacyjnych na wytrzymałość i częstotliwości niszczenia kompozytów cementowo-włóknistych

The paper examines the impact of possible operational factors on strength and frequency parameters generated by bending of fibre-cement panels. The tests were performed on elements cut out of a standard commercially available panel. The samples were exposed to factors described as environmental (soaking in water, bath-drying cycles, freeze-thawing cycles) and unique (flame ignition and high temperature exposure) and then subjected to three-point bending tests. Acoustic emission (AE) signals were acquired during the external load application. After the measurements were completed, the strength of individual elements was determined and the frequencies generated during bending were calculated. The obtained results were analysed statistically. Comparing the results obtained for a group of samples subjected to environmental and unique factors, significant differences between them were noted. It was noted that the decrease in the strength of the samples is related to the emission of lower frequency sounds. It was found that the application of the presented methodology allows to determine the condition of the fibre-cement boards in use.W artykule przedstawiono wyniki testów trzypunktowego zginania dla elementów włóknisto-cementowych poddanych działaniu czynników środowiskowych i wyjątkowych z jednoczesną akwizycją sygnałów AE. Analizie poddano wartości wytrzymałości na zginanie oraz częstotliwości generowanych przed momentem zniszczenia. Na podstawie otrzymanych wyników wyciągnięto następujące wnioski: Obniżenie wytrzymałości elementów włóknisto-cementowych wiąże się z generowaniem niższych częstotliwości przy zginaniu w odniesieniu do próbek o niezmienionych parametrach mechanicznych. Zastosowanie metody emisji akustycznej umożliwia śledzenie częstotliwości powiązanych z powstawaniem różnego rodzaju zmian w strukturze materiału. Przebieg procesu niszczenia struktury płyty cementowo-włóknistej jest mechanizmem złożonym i powiązanym w sposób ścisły z obecnością włókien zbrojących oraz stopniem wiązania pomiędzy zbrojeniem a matrycą. Częstotliwości generowane przez zmiany zachodzące w strukturze włókno-cementu są ściśle powiązane z obecnością zbrojenia w postaci włókien oraz stopniem wiązania między zbrojeniem a matrycą. Zastosowanie techniki emisji akustycznej umożliwia skuteczne wykrywanie i monitorowanie inicjacji zmian w strukturze wpływających na obniżenie parametrów mechanicznych płyt. Otrzymane rezultaty dają możliwość zastosowania metody AE do oceny stanu pełnowymiarowych elementach cementowo-włóknistych

Evaluation of destructive processes in FRC composites using time-frequency analysis of AE signals

Modern fiber-cement boards currently used in construction are made of natural raw materials such as cement, cellulose fibers and of polyvinyl alcohol (PVA) and water. They replaced the eternitic plates, which were harmful to health, originated by Ludwig Hatschek. Materials made of fiber-cement are used in construction industry as a building and finishing material for facades, internal walls and roofs. Therefore, they are exposed to environmental conditions including rainfall and temperature changes, and in particular to frequent temperature transition through 0°C in a 24-hour cycle (cyclic freezing-thawing). In addition, fibrous cement materials, primarily used as cladding elements, are exposed to exceptional conditions, which include the high temperature caused by fire. The article presents the results of experimental tests of flexural strength of cement fiber boards subjected to exceptional conditions, to which the operation of fire belongs. The paper also presents a proposal to use a non-destructive method of acoustic emission based on time-frequency analysis for testing fiber-cement boards. Interesting research results were obtained that allowed to trace the differences in the mechanisms of material destruction under the influence of the changing time of external factors

The Acoustic Emission Method Implementation Proposition to Confirm the Presence and Assessment of Reinforcement Quality and Strength of Fiber–Cement Composites

This article proposes to use the acoustic emission (AE) method to evaluate the degree of change in the mechanical parameters of fiber–cement boards. The research was undertaken after a literature review, due to the lack of a methodology that would allow nondestructive assessment of the strength of cement–fiber elements. The tests covered the components cut out from a popular type of board available on the construction market. The samples were subjected to environmental (soaking in water, cyclic freezing–thawing) and exceptional (burning with fire and exposure to high temperature) factors, and then to three-point bending strength tests. The adopted conditions correspond to the actual working environment of the boards. When applying the external load, AE signals were generated, which were then grouped into classes, and initially assigned to specific processes occurring in the material. The frequencies occurring over time for the tested samples were also analysed, and microscopic observations were made to confirm the suppositions based on the first part of the tests. Comparing the results obtained from a group of samples subjected to environmental and exceptional actions, significant differences were noted between them, which included the types of recorded signal class, the frequency of events, and the construction of the microstructure. The degradation of the structure, associated with damage to the fibers or their complete destruction, results in the generation under load of AE signals that indicate the uncontrolled development of scratches, and a decrease in the frequency of these events. According to the authors, the methodology used allows the control of cement–fiber boards in use. The registration and analysis of active processes under the effect of payloads makes it possible to distinguish mechanisms occurring inside the structure of the elements, and to formulate a quick response to the situation when the signals indicate a decrease in the strength of the boards

Non-Destructive Testing Methods for In Situ Crack Measurements and Morphology Analysis with a Focus on a Novel Approach to the Use of the Acoustic Emission Method

This article presents a concise review of modern non-destructive testing (NDT) methods that allow the detection, tracking, and measurement of cracks in reinforced concrete structures. Over the past decades, the range of solutions available on the market has increased. This provides excellent opportunities when choosing and designing systems for diagnosing and continuously monitoring structures. Cracking affects the mechanical properties, durability, and serviceability of a structure or its elements. Therefore, there is a need to develop methods that would allow the determination of the moment of a destructive process’s formation, i.e., a crack’s appearance. At the same time, it is crucial to be able to track the development of cracks for the entire structure, not just selected locations. This work also presents the concept of combining selected NDT methods and creating a system for the continuous monitoring of structural integrity and predicting changes in the durability of existing and future buildings

Time-frequency analysis of acoustic emission signals generated by cement-fiber boards during bending test

Fiber-cement building materials have been used in civil engineering for over one hundred years. Contemporary fiber-cement boards are made of natural raw materials such as cement, cellulose fibers, PVA and water. Materials made of fiber-cement are used in construction as a building and finishing material for elevations, internal walls and roofs, hence are exposed to environmental conditions such as rainfall and temperature changes, in particular, frequent temperature transition through 0°C in a 24 hour cycle (cyclic freezing-thawing). In addition, fibrous cement materials, primarily used as cladding elements, are exposed to exceptional conditions, which include the high temperature caused by fire. The article presents the results of experimental tests of bending strength of cement-fiber boards subjected to environmental factors and exceptional factors. The paper also presents a proposal to use a nondestructive method of acoustic emission (AE) based on time-frequency analysis for testing fiber-cement boards. Interesting research results were obtained, which allowed to trace the differences in the mechanisms of material destruction under the influence of various factors

Scanning electron microscopy in the tests of fibre-cement boards

The subject of this article is research on fiber-cement boards, which are currently used in civil engineering as cladding for ventilated facades, but also as internal claddings. When these boards are used on elevations, they are exposed to changing weather conditions, and therefore they are given the appropriate requirements for strength, mass moisture, absorbability and, above all, durability in accordance with the relevant regulations. The paper presents a proposal for using a nondestructive microscopic method for testing fiber-cement boards using a scanning electron microscope (SEM) with an EDS analyzer. Fibercement boards subjected to various environmental factors (moisturizing, freezing-thawing) and exceptional factors (burning at 230°C and setting on fire for 5 and 10 minutes) were tested. Interesting research results were obtained, which allowed to observe changes occurring in the microstructure of the tested boards under the influence of various factors