ACOUSTIC EMISSION AND ELECTROMAGNETIC MONITORING OF THIN TRC SANDWICH COMPOSITES IN BENDING

Textile Reinforced Cementitious (TRC) sandwich composites are innovative materials that combine the loadbearing capacity of TRC facings, with a lightweight core. However, these materials may fail under early interlaminar debonding, substantially reducing the load-bearing capacity of the composite. For this reason, thin TRC sandwich composites are subjected to three-point bending test, and monitored with Acoustic Emission (AE), and millimeter wave (MMW) spectrometry.
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APPLICATION OF ACOUSTIC EMISSION TESTING IN ORDER TO UNDERSTAND MODE I FRACTURE PROCESS IN STEEL FIBRE REINFORCED CONCRETE

This article presents characteristics of acoustic emissions (AE) generated during the mode I fracture process in steel fibre reinforced concrete (SFRC). Three-point bend SFRC specimens were tested in the laboratory by following EN-14651-2005 guidelines. A 2D planar location was adopted to mount the four 57 kHz resonant-type AE sensors on the test specimen to record the generated AE. The number of AE events reduced with the increase in the steel fiber content under the same experimental conditions. The fracture process zone (FPZ) was divided into major damage zone comprised of AE events with (i) high peak amplitude, (ii) low information entropy (iii) longer AE waveform duration. The major damage zone was located ahead of the notch tip very closely. AE testing is a useful testing method to study the fracture process in SFRC.
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INVESTIGATION OF THE MECHANICAL PERFORMANCE OF THE UNSATURATED POLYESTER/CENOSPHERE SYNTACTIC FOAMS USING ACOUSTIC EMISSION TECHNIQUE

Cenospheres are special class of filler materials, commonly used in preparing lightweight structural
composites. They are hollow and thin-walled microspheres which entraps inert gas inside them. Composite
materials filled with thin-walled microspheres are known for their energy absorption properties and
improved mechanical performances. Such class of materials are known as syntactic foams. In this study,
unsaturated polyester composites are prepared by adding different compositions of cenospheres as fillers.
The influence of cenospheres on the mechanical performance of unsaturated polyester syntactic foams are
investigated. The acoustic emissions due to the failure of the syntactic foams under mechanical loading are
studied. Acoustic emission signals are recorded using a piezoelectric transducer and are analysed in their
time domain, frequency domain, and time-frequency domain. Different acoustic emission features of the
recorded signals are compared with the mechanical test results. The fracture behaviour of the syntactic
foams is, thus, investigated using the acquired acoustic emission signals.
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RECENT ADVANCES IN ULTRASOUND MONITORING OF CRACKING AND SELF-HEALING OF CONCRETE [Keynote]

Elastic waves have been long used for structural integrity evaluation of concrete materials and structures. Ultrasonic parameters are well related to crack density, deterioration of the elastic modulus, even empirical characterization of the strength. Recently, several ultrasonic studies have emerged also in the field of repair monitoring. Manual repair actions or self-healing strongly contribute to the sealing of the crack, and the regain of the mechanical properties. However, the restoration cannot be evaluated in a non-destructive manner, especially in-situ. Ultrasonic parameters exhibit strong sensitivity to the degree of filling of a single crack or of a distributed system of cracks, while they also have the capacity to monitor the self-healing process, due to the increase of elastic modulus of the healing compounds in the crack volume. The present abstract intends to give an overview of the recent developments in the field of ultrasound as a means of fracture and repair characterization. Through-the-thickness wave transmission, ultrasonic mapping, surface waves as well as air-coupled applications are reviewed as standalone methods or in conjunction with simulations in the framework of an optimal material assessment after fracture and consequent repair.
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EXPERIMENTAL ANALYSIS BY ACOUSTIC EMISSION ON FULL-SCALE PC DECK BEAMS AFTER 50 YEARS OF SERVICE [Keynote]

The AE technique is highly adopted for the structural integrity assessment of materials as well as large-sized structures (buildings, bridges, etc.) due to its ability to offer information on their stability conditions. This paper presents a loading test on a prestressed concrete (PC) full-scale beam. It was taken from a bridge built in Turin (Italy) in 1970 and dismantled in 2018 for urban redevelopment works. The efficacy of the AE technique for determining the progression of damage is confirmed by the observed relations between the measured strain and the recorded AE activity.
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GYPSUM AND QUARTZ SPECIMENS IN COMPRESSION FAILURE: FRACTO-EMISSIONS AND RELATED STOICHIOMETRIC BALANCES [Keynote]

Extensive experimental investigations were conducted on Gypsum and Quartz compression specimens of different sizes. They were brought to complete failure, showing two different failure modalities: (1) Very brittle loading drop for micro-crystalline Gypsum and Quartz; (2) Strain-softening behaviour for macro-crystalline Gypsum. All the tested specimens emitted acoustic and electromagnetic waves and the single events cumulated up to the peak load (Figs.1,2). On the other hand, neutron emissions were evident only for the largest specimens, which are more brittle than the smaller ones [1-4]. The significant chemical composition changes occurred on the fracture surfaces are consistently explainable by the assumption of Low-energy Nuclear Reactions (LENR), both fusion and fission reactions [5-7]. It is the first time that fusion reactions emerge, whereas fission reactions have already explained the results related to other materials like the iron-rich natural rocks [5]. Let us observe that, in the case of macro-crystalline Gypsum, an original correlation seems to appear between mechanical behaviour (strain-softening) and LENR modalities (multi-body fusion reactions).
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INTEGRATION OF ELASTIC WAVE VELOCITY INTO BIM OF DAM FACILITY [Keynote]

As for building information modeling (BIM), digital twin of point-clouds of spillway of a rock fill dam is demonstrated. Reproduction of existing structures with point-clouds from still or movie images are shown. Necessary information in addition to the point-clouds such as surface and internal condition of the structure are depicted. Information such as surface deterioration condition as well as internal condition composed of elastic wave velocities, which will be crucially important to realize life-cycle-oriented design, construction, and maintenance, is incorporated into the digital twin. Through the suggested model, overall damage of the spillway is discussed in combination with the pin-point excavations for verification. Through the life cycle of the civil engineering structures roles of elastic wave approaches will be suggestively indicated.
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STRUCTURAL HEALTH MONITORING OF FATIGUE BEHAVIOR FOR TI ALLOYS BY DATA ASSIMILATION OF AE

The main purpose of this research is to develop a structural health monitoring method for fatigue behavior of Ti alloys. Experiments were conducted on the effect of microstructure on fatigue behavior at room temperature. Analysis of fracture and deformation behavior using finite element method simulation was also performed. Resutls of AE measurements during fatigue crack initiation and propagation was used to assimilate the mechanical informations using data science methods. For example, a method to directly predict the crack growth rate with variance from the AE measurement results was developed.
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