Papers by Keyword: Acoustic Emission

Abstract: Laser Shock Peening (LSP) is increasingly employed across various industrial sectors, particularly in safety-critical applications where extending structural integrity and lifespan is paramount. This work investigates the influence of varying laser energies and confinement layers on the LSP process. Understanding these parameter variations is crucial for precise process control. To gain deeper insights into the process dynamics from an in-situ, non-destructive testing (NDT) perspective, acoustic bursts will be considered and measured. Acoustic Emission (AE) is a method that uses piezo-electric material to determine the level of emitted elastic waves from the source where transients in the form of displacement within piezo-electric crystalline structure (either in a tensile or compressive manner) provide a quantitative voltage for decerning different measurements. Most current testing methods use destructive tests with coupon parts; this process however directly measures the material state in question and is non-destructive in nature. Post-LSP, additional NDT techniques are utilised to characterise material modifications in terms of residual stress and hardness. This research aims to enhance material understanding, complemented by destructive testing for residual stress and microstructure analysis, and to lay the foundation for advanced algorithms and digital modelling for robust real-time, quality control in LSP.

Abstract: This paper presents the relationship between crack width and acoustic emission (AE) energy in reinforced concrete (RC) beams subjected to cyclic loading. Two types of RC beams were tested, each reinforced with different tensile bar diameters: 12 mm (Y12) and 16 mm (Y16). The average ultimate loads (P_ult) for beams with Y12 and Y16 were 31 kN and 51 kN respectively. Beams tested under cyclic loading using Y12 and Y16 were labelled FT12 and FT16. Cyclic loading was applied at 80% of the P_ult and tests were continued until failure. A three-point bending test was performed under a sinusoidal load frequency of 1 Hz. AE monitoring was performed with six sensors installed at selected locations on the beams. The results showed that the crack width increased with the number of cycles, with correlation coefficients (R²) of 0.95 for FT12 and 0.93 for FT16, indicating a stronger linear relationship for both beams. Based on the trends in AE energy and crack width, three crack propagation stages were identified, with high AE energy found in both the initial microcrack formation and the final unstable failure stage. The results confirm that AE is an effective tool for early damage detection and fatigue monitoring in RC structures.

Abstract: During the last years, some concerns have arisen in relation to the outcome of mechanisms of failure in composite materials according to its mechanical behavior. Such interest resulted in the development of new complex structures in order to enhance its mechanical resistance and the controlling of damage processes. Nevertheless, it is imperative to understand the degree of mechanical performance that these materials can achieve when under external stresses. In this regard, applying Acoustic Emission (AE) technique is widely known as a very effective technology for identifying and monitoring damage progression on different kind of materials and structures providing valuable information. AE is a non-destructive technique (NDT) capable of detecting micro damage initiation and propagation along several types of failure modes such as reinforcement/matrix interfacial debonding, matrix cracking, delamination, fracture, etc. This paper examines applications of AE regarding to composite materials where fracture processes are generally more complex and data interpretation is correspondingly more difficult. Finally, in order to continuously improve the reliability of this technique, several researches have advanced its trustworthiness through innovations in AE technology. Some perspectives are discussed.

Abstract: This work presents results of a study of the influence assessment based on the recorded acoustic emission (AE) parameters of thermo-oxidative aging conditions on the destruction process of a polymer composite material (PCM). The objects of the study were specimens cut from a fiberglass reinforced plastic (FGRP) plate. The plate was made by vacuum infusion technique using Derakane 411-350 resin and 9 layers of St-62004 glass fabric. Specimens aging were done by holding in a muffle furnace for 96 hours at temperatures of 60, 100, 120, and 200 ° C. Mechanical test was the three-point static bending method. For the AE recording was used a hardware-software complex developed at KnASU. The AE signal Fourier spectra were two-stage clustered with the self-organizing Kohonen map according to the technique previously developed and tested by the authors. The types of the PCM structure damage were characterized by the obtained clusters centroids. The fracture process kinetics is described depending on the conditions of thermo-oxidative aging and based on the accumulation of clusters during mechanical tests. The negative influence of high temperatures on the polymer matrix degradation, leading to a decrease in the ability of the matrix to effectively distribute internal stresses over the PCM volume due to the adhesion corruption with the reinforcing material, has been established.

Abstract: This paper demonstrates a simple technique to detect vibration-induced fatigue cracks using a hybrid method by vibration and acoustic emission techniques. A thin aluminum plate of 6082-T6 was excited using a vibration shaker to achieve a bending mode where the maximum stress exhibited at the plate mid-span. To simulate crack formation, a sharp notch was created. This systematic setup allows mode I crack propagation through plate thickness. The development of cracks over time changed the natural frequency of the plate which leads to the reduction of vibration amplitudes. This experimental technique facilitates the identification of acoustic emission waves during the onset of damage in the presence of noise due to dynamic motion. The effect of crack development on Lamb waves was investigated. The acoustic emission signals were cross-correlated with a Gaussian window of a central frequency of 250kHz. The results show a reduction in the fundamental wave A₀, whilst an increase in S₀ wave amplitudes at some stages during crack extension. The current experimental work can be an alternative technique for vibration-induced fatigue test evaluation.

Abstract: The article discusses the experimental substantiation of predicting the operational properties of elastic elements by the acoustic emission (AE) method, as well as the use of the non-destructive method of acoustic emission as an element of digital certification of critical mechanical and instrument engineering products.

Abstract: The article examines the process of crystallization of Wood alloy using the ultrasonic method. The dependence of the determination of the speed of sound in three aggregate states of the alloy (liquid, solid, transition (liquid-solid)) was derived. The relation-ship with the amplitude values of the sound signal, a single pulse in determining the speed of sound, as well as in determining the state of the alloy is carried out. The data obtained allow us to analyze the state of the alloy and the measurement time and the specified frequency range directly in the process of crystallization.

Abstract: The development of weight-efficient reusable launch systems has increased the urgency of problems associated with ultra-low-cycle fatigue. In this paper, one-sided three-point bending cyclic tests of GFRP specimens were performed. Parallel to the cyclic tests, registration of acoustic emission signals has been performed to identify the main damage mechanisms underlying ultra-low-cycle fatigue of fabric-reinforced composites. The obtained displacement-time diagrams showed a noticeable effect of creep on the deformation process. It was found that fiber fracture is the main mechanism of microdamage accumulation. A phenomenological three-element model based on the Norton-Bailey law and the Masing structural model was proposed. The model allowed describing both the deformation process of the specimens in time and their durability at different load levels. An optimization algorithm based on the deformable polyhedron method was used to find the optimal set of the model parameters.

Abstract: Information on deformation of coatings at different loading levels during peeling is given. It is shown that the deformations of the organosilicon coating appear already at the initial stages of loading, and the obtained data correlate with the data on acoustic emission. For a polyvinyl acetate coating at low loading levels, equal to 0.3-0.4 R, the release of acoustic signal energy is not observed. The absence of signals with a large amplitude at loading levels up to 0.7-0.8 R indicates the development of plastic deformations in the contact zone of the coating with the substrate. It was found that early localization of bond breaking in the contact zone, leading to the formation of a fracture focus, occurs in organosilicon coatings KO-168. For PVAC coatings, an abrupt growth of cracks is characteristic, which is preceded by its slow growth. The pseudoplastic mechanism of destruction of PVAC coatings has been established. The influence of the nature of the substrate on the change in the nature of the peeling of the coatings is considered.

Abstract: The strength of materials is determined by their atomic molecular structure and the process of decay of atomic molecular bonds, which must be taken into account when optimizing materials strength control technologies. The fracture photomicrograph of metal microdamage of welded joint at various moments of time, a multilevel model of flow of acoustic emission signals of materials are presented. The physical meaning, the scale level of parameters included in the model are revealed. The structure of the mathematical model of the flow of AE signals with components of its informative elements of different scale level by strength characteristics of structural materials and resource of technical objects is shown. The multilevel model of the AE signal flow is hierarchically structured, obtained by generalizing deterministic-statistical variability. It describes the process of randomly recording deterministic accumulated damages in the material both before and after the formation of a crack at the stage of waiting for its next leap. It is shown that the proposed nanotechnology of strength control of materials is reduced to non-destructive determination of parameters of prognostic homogeneous destruction, identification of which is based on multilevel modeling of time dependence of micro-crack formation, formulation of criterion of strength homogeneity, registration of AE parameters related to the model of a specific product, which can be automated processing of registration results and determination of universal strength nanoconstants from already published reference data of fatigue tests of standard material samples.