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51.
《Strain》2018,54(4)
When a crack initiates and grows in a metal or composite structure, for example, due to high cycle fatigue, the crack propagation gives rise to acoustic emissions (AE)—ultrasonic waves travelling through the structure. Because the presence and rate of growth of any cracks are important pieces of information about the condition or health of the structure, the monitoring of AE activity using sensors mounted on its surface is a potentially useful technique of structural health monitoring. In tests, acoustic emissions are often simulated by breaking a pencil lead against the surface of the structure in a standardised way (a "Hsu‐Nielsen" source), but the forces that this imparts are not well understood at present. The current paper proposes a new evolutionary optimisation‐based approach to source characterisation. The principle is to introduce a parametrised representation of a general source and then identify the parameters that allow the source to best match responses measured elsewhere on the structure. The predicted responses are modelled using a local interaction simulation approach (LISA) algorithm to simulate the propagation of the ultrasonic waves. The approach is validated here using experiments on AE propagation in thin plate‐like structures, where the ultrasound propagates as Lamb waves. Three separate case studies are proposed here. In the first case, an idealised point source is simulated using laser‐generated ultrasound, and the optimisation algorithm uses a two‐dimensional LISA model. A differential evolution optimisation scheme is used to find the optimal profile of forcing to match the simulation with experiment. In the second case, the two‐dimensional LISA approach is used to characterise the forces associated with standard pencil lead breaks. The final study addresses the full three‐dimensional wave propagation. Because of the computational expense of the latter calculation, the LISA algorithm is implemented using a CUDA graphics card computer system. 相似文献
52.
Dongfang Hu Guodong Han Musango Lungu Zhengliang Huang Zuwei Liao Jingdai Wang Yongrong Yang 《Advanced Powder Technology》2017,28(9):2306-2316
Bubble and particle motion behaviors are investigated experimentally in a gas solid fluidized bed with liquid spray on the side wall. The particles used in the experiment are classified as Geldart B particles. The results reveal that when the fluid drag force is less than the liquid bridge force between particles, liquid distribute all over the bed. Bubble size increases as the increase of inter-particle force, then decreases owing to the increase of particle weight with increasing liquid flow rate. When the fluid drag force is greater than the liquid bridge force, liquid mainly distribute in the upper part of the bed. And it is difficult for the wet particles to form agglomerates. Bubble size decreases with increasing liquid flow rate due to the increasing of minimum fluidization velocity. Besides, the acoustic emission (AE) measurements illustrate that the liquid adhesion and evaporation on particles could enhance the particles motion intensity. Consequently, the bubble and particle behaviors change due to the variation in fluidized gas velocity and liquid flow rate should be seriously considered when attempting to successfully design and operate the side wall liquid spray gas solid fluidized bed. 相似文献
53.
Xiaokang Pan Filippo Berto Xiaoping Zhou 《Fatigue & Fracture of Engineering Materials & Structures》2022,45(1):302-322
This work discusses the results from tests conducted to investigate the uniaxial compression and creep behavior of red sandstone. An original untreated sample and an 800°C treated sample were selected to carry out the experiments. High temperature had an obvious influence on the mechanical properties of the red sandstone. The relationship between creep strain and instantaneous strain, as well as the instantaneous deformation modulus and creep viscosity coefficient, was analyzed. High temperature reduced the ability of the red sandstone to resist instantaneous deformation and creep deformation. Acoustic emission (AE) technology was also used in the loading process of uniaxial compression and creep tests, providing a powerful means for damage evolutionary analysis of the red sandstone. 相似文献
54.
55.
Dynamic destabilization analysis based on AE experiment of deep-seated, steep-inclined and extra-thick coal seam 总被引:1,自引:1,他引:0
No. 5 coal seam in Huating Coal Mine is a deep-seated, steep-inclined extra-thick coal seam where excavation disturbance is quite frequent. The maximum and minimum principal stresses differ widely. During mining, dynamical destabilization happens frequently and induce tragedies. Based on the comparison between the acoustic emission (AE) experiment on dynamical destabilization of coal rock and the related in situ testing results, this article provides comprehensive analysis on the regular quantificational AE patterns (energy rate, total events) of coal rock destabilization in complex-variable environment. The comparison parameters include dynamic tension energy rate, deformation resistance to compression, and shear stress. 相似文献
56.
Study of electromagnetic and acoustic emission in creep experiments of water-containing rock samples
Based on biaxial shear creep tests conducted on rock samples with different water contents, we present the results of our study on the regularities of electromagnetic and acoustic emission during the process of creep experiments in which we have ana-lyzed the contribution of water to the occurrence of electromagnetic radiation. The result shows that in the creep-fracturing course of rock samples, when the water content increases, the initial frequency and amplitude of electromagnetic and acoustic emission also increases, but at a decreasing growth rate caused by loading stress. This can be used as a criterion for the long-term stability of rock masses under conditions of repeated inundation and discharge of water. 相似文献
57.
Unlike the previous single (dual) satellite observation, the four Clusterll satellites make it possible to directly compute
the continuous field-aligned current (FAC) density according to the magnetic data from them and to enable the investigation
of the relationship between the FAC and geomagnetic activity. This paper analyzes the observation data when the Cluster satellites
crossed the plasma sheet boundary layer (PSBL) in the magnetotail during the two magnetic storms in August to October 2001.
According to the data, during the magnetic storms the relationship between the variations of FAC and AE index turned out to
be: 1) FAC was obviously increasing during the storms; 2) FAC density was approximately negatively correlated with AE index
from the sudden commencement to the early main phase of the storm; 3) they were approximately positively correlated during
the late main phase and early recovery phase; 4) they were no apparent correlation during the late recovery phase.
Supported by the CAS International Partnership Program for Creative Research Teams and the National Natural Science Foundation
of China (Grant Nos. 40621003, 40674091 and 40390150 相似文献
58.
This paper investigates the tensile response of damaged glass/epoxy composite laminates repaired using hybrid external patches. Hybrid external patches based on glass and Kevlar woven fabrics bonded on both faces of the damaged parent laminate were considered. Five different kinds of plain weave woven fabrics with a different ratio between glass and Kevlar fibers (100/0, 75/25, 50/50, 25/75 and 0/100) were used as the external patches. The intention of using these hybrid patches was to combine the excellent tensile stiffness of Kevlar fiber with the superior resin adhesion property of glass fiber. The virgin and damaged specimens were taken as the reference specimens for comparison of residual mechanical properties and damage mechanisms. Damage evolution and the failure progression of the repaired glass/epoxy specimens were monitored using real-time Acoustic Emission (AE) monitoring technique. The Acoustic Emission (AE) results depict different damage profiles and link them with mechanical test results to reveal the load to a change in failure mechanisms during mechanical loading concerning the influence of each hybrid patches on the performance of repaired glass/epoxy specimens. Good correlation of the acoustic emission results with the photographic images of fractured specimens was obtained. Specimens repaired with the equal volume fraction of glass and Kevlar fibers in the external patches presented the most favorable residual tensile response by effectively releasing the stress concentration in the damaged area. 相似文献
59.
刘浩 《岩石力学与工程学报》2001,20(4):518
ACOUSTIC EMISSION AND CRACK DEVELOPMENT IN ROCKS@刘浩$香港合东中国育限公司 相似文献
60.
M. Cai H. Morioka P.K. Kaiser Y. Tasaka H. Kurose M. Minami T. Maejima 《International Journal of Rock Mechanics and Mining Sciences》2007,44(4):538-549
Most back-analyses in geotechnical engineering are based on methods that utilize field displacement monitoring data. In the present study, a novel method is developed to back-calculate rock mass strength parameters from AE (acoustic emission) monitoring data in combination with FEM stress analysis. The method is based on the important concept of generalized AE initiation threshold of rock masses, established from comprehensive data analysis of laboratory test and underground monitoring programs using AE and microseismic (MS) techniques. An easy-to-use Wizard is developed in Microsoft Excel™ to assist site engineers to perform the back-analysis. The efficient solver in Excel is utilized to reach the optimization solution of an objective function with constraints. The Wizard allows the user to complete the analysis process in an interactive fashion. One example is given to demonstrate the back-analysis process using AE monitoring data recorded from a cavern site. The rock mass strength parameters identified from this approach compare well with field test data, suggesting that the tool can be used effectively to back-calculate rock mass strength parameters from AE monitoring data. 相似文献