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Unconventional measurement techniques in experiments on masonry
Published in Jan Kubica, Arkadiusz Kwiecień, Łukasz Bednarz, Brick and Block Masonry - From Historical to Sustainable Masonry, 2020
When cracking occurs in a material, elastic waves are emitted and propagate. Piezoelectric sensors on the surface can detect them in the form of Acoustic Emission (AE) signals. These are pre-amplified, pass-band filtered, amplified, sent to a data logger, and processed. AE events are considered as the portion of the acoustic wave above a minimum amplitude threshold associated with background noise. An AE event is characterized by its amplitude (peak of the signal, detected in μV and converted in dBAE), count (number of times the signal rises and crosses the threshold), energy (area under the envelope of the AE event), duration, and waveform. The AE technique has already been widely used for the condition assessment and structural health monitoring of reinforced concrete and steel structures (Holford 2009), whereas its application to masonry is very limited due to the difficulties in detecting AE signals, which rapidly attenuate as a consequence of the heterogeneity of masonry (Royles 1991, Melbourne & Tomor 2006, Carpinteri & Lacidogna 2007).
Acoustic Emission Principles
Published in Don E. Bray, Roderic K. Stanley, Nondestructive Evaluation, 2018
Don E. Bray, Roderic K. Stanley
Acoustic emission is a passive inspection technique that uses the elastic waves generated by moving dislocations, cracks, fiber breaks, disbonds, etc. for defect detection and analysis in solids. In metals and concrete, the waves are generated by local stress redistributions associated with the motion of dislocations and cracks (both microscopic and macroscopic cracks). In composites, the stress waves are generated by a variety of actions involving cracking and separation in the fibers and the matrix. Material strain, induced by stress or some other stimulus, is required to release or generate the emissions. Longitudinal and transverse transient displacement elastic waves can be excited by the action of an abrupt local force. A general listing of typical AE sources, classified by material, is as follows:
Quality Control and Characterization
Published in B. T. Åström, Manufacturing of Polymer Composites, 2018
The Kaiser-effect stipulates that once loaded to a given stress level, a component should not emit any more noise upon reloading to the same stress level. The Felicity ratio, defined as the stress level where noise is emitted again upon reloading divided by the previous maximum stress level experienced, thus should be slightly larger than unity. Failure to obey the Kaiser-effect, i.e. exhibiting a Felicity ratio less than unity, indicates component damage and if noise is continuously emitted at a constant stress level there is reason to suspect ongoing crack propagation [13]. Acoustic emission is used in quality control of, for example, pressure vessels and pipes. To avoid permanent macroscopic damage during loading for acoustic emission inspection it is recommended that [13]: Testing is performed at stress levels well below the design loadThe total number of acoustic events is kept below a specified numberOnly few acoustic events above a specific amplitude are permittedThe Felicity ratio is kept close to unity
Structural health assessment techniques for in-service timber poles
Published in Structure and Infrastructure Engineering, 2023
Sahan Bandara, Pathmanathan Rajeev, Emad Gad
Acoustic emission is also a non-destructive testing technique which detects the release of ultrasonic stress waves from localised sources when a material deforms under stress. The failure of material is characterised by sudden release of energy at fracture and this energy is dissipated in the form of sound waves, which can be detected by acoustic sensors. Arrival time of sound waves can be used to determine the location of fracture. This system requires permanent data acquisition and mostly used for monitoring steel fractures (e.g. Hillemeier & Walther, 2007). There is no published work on the application of this technique to timber poles. However, it can be useful for the condition monitoring of timber structures (e.g. Kurz & Boller, 2015).
Influence of temperature on deformation failure and acoustic emission characterisation of asphalt concrete under uniaxial compression
Published in International Journal of Pavement Engineering, 2022
Hui Wei, Jue Li, Bing Hu, Feiyue Wang, Jianlong Zheng
Acoustic emission (AE) is widely used as a type of passive non-destructive testing technology in engineering fields, such as composite material detection, structural health inspection and rock fracture analysis (Aggelis et al., 2013, Hohl et al., 2018, Pang et al., 2018). In contrast to X-ray and ultrasonic non-destructive testing technology, the AE testing device does not need a wave source because it receives stress waves released inside the detected component in real-time which can be converted into electrical signals (Saeedifar and Zarouchas, 2020). By analysing the signal parameters, the occurrence and expansion of microcracks inside the structure can be monitored continuously in real-time to identify the location of potential damage (Wisner et al., 2019). Recent studies found that the AE technology has a great advantage in studying the law of instability and fracture evolution of materials, especially in continuously and real-time monitoring of the generation and propagation of internal microcracks under load (Wei et al., 2020). Some researchers have used the AE features to describe the low-temperature performance of asphalt mixtures, such as creep behaviour (Liu et al., 2020), fatigue damage (Jiao et al., 2019) and self-healing ability (Arnold et al., 2014). The results suggest that the fracture distribution and extension process could be tracked dynamically by establishing mathematical relationships between AE energy and macromechanical behaviour. Thus, the AE technology provides a scientific and effective approach to completely understand the deformation mechanism and fracture evolution of asphalt mixtures during the compression damage of asphalt pavements, which is also the objective of this study.
Experimental study on tensile strength and acoustic emission characteristics of shale exposure to supercritical CO2
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2021
Chao Qin, Yongdong Jiang, Zhipeng Kang, Xiao Song, Hao Liu
Acoustic emission technology is a non-destructive testing method for assessing material properties or structural integrity by receiving and analyzing acoustic emission signals of materials (Evans and Linzer 1974). In this experiment, the acoustic emission signals generated in shale were monitored in real time by the DISP series of all-digital acoustic emission monitors in the process of Brazilian splitting test before and after supercritical CO2 treatment. The results are shown in Figure 5, it can be seen that the stress–time curves and the acoustic emission–time curves under different supercritical CO2 treatment conditions are in good agreement. The cumulative acoustic emission absolute energy curves show a “smooth-steep increased” pattern, and the shale splitting shows a tensile failure mode before and after supercritical CO2 treatment (Zhang et al. 2017). Comparing Figure 5a–c, it can be found that the acoustic emission signals generated during the splitting process of all shale specimens are mainly concentrated in the “steep increase” stage (ie, the shale specimens were damaged completely). In addition, fewer acoustic emission signals generated in the untreated shale specimens during the entire splitting process, while the relatively dense acoustic emission signals generated in the treated specimens in the stage of pore and fracture compaction and elastic deformation. This indicates that the energy release pattern of shale was changed during shale splitting after supercritical CO2 treatment. The main reason for this is that the supercritical CO2 fluid has the properties of low viscosity, high diffusibility and strong solubility, the pore structure, and the primitive interaction force between minerals in shale are transformed after supercritical CO2 treatment.