Current Issue : July - September Volume : 2020 Issue Number : 3 Articles : 5 Articles
A series of multistage creep tests under different confining pressures with acoustic emission monitoring have been performed to\ninvestigate the deformation characteristic and failure process of cracked granite during creep. The critical axial strain of cracked\nsample showed an increasing tendency with the increase of confining pressure. In contrast, critical lateral strain experienced a\nprocess of descending first at low confinement and then remaining nearly constant at high confinement. Compared with loadingcracked\nspecimen, smaller critical axial strain, greater critical lateral strain, and higher lateral creep strain rate were found for\nunloading-cracked specimen. Based on the spatial and temporal distribution of acoustic emission events, the cracking process\nduring creep was analysed. The AE events with high energy are mainly concentrated at the final fracture area of the specimen. The\nhigher the confining pressure, the more the AE events with low energy. Compared with the loading-cracked specimen, the\npercentage of AE events with high energy is relatively small for the unloading-cracked specimen....
A method is proposed for estimating the acoustic power output of ultrasound transducers\nusing a two-port model with electrical impedance measurements made in three different propagation\nmedia. When evaluated for two high-intensity focused ultrasound transducers at centre frequencies\nbetween 0.50 and 3.19 MHz, the resulting power estimates exceeded acoustic estimates by 4.5%â??21.8%.\nThe method was shown to be valid for drive levels producing up to 20 MPa in water and should\ntherefore be appropriate for many HIFU (high-intensity focused ultrasound) applications, with the\nprimary advantage of employing relatively low-cost, non-specialist materials and instrumentation....
In this work, C-Scan Acoustic Scanning Microscopy (ASM) is used to map the\ndefects of three SiC samples. The acoustic images indicate that numerous defects\nwith different shapes and area sexist in the wafers. Some of the defects\nhave areas of more than 100,000 microm2. The number of defects ranges from 1 to\n50 defects/wafer. Defect mapping is essential for defect repairing or avoidance.\nThis work shows that ASM can locate the precise positions of the crystallographic\ndefects, which enables defects repair and yield enhancement....
We describe here a time resolved pump-probe laser techniqueâ??picosecond\ninterferometryâ??which has been combined with diamond anvil cells (DAC). This method enables the\nmeasurement of the longitudinal sound velocity up to Mbar pressure for any kind of material (solids,\nliquids, metals, insulators). We also provide a description of picosecond acoustics data analysis\nin order to determine the complete set of elastic constants for single crystals. To illustrate such\ncapabilities, results are given on the pressure dependence of the acoustic properties for prototypical\ncases: polycrystal (hcp-Fe-5 wt% Si up to 115 GPa) and single-crystal (Si up to 10 GPa)....
Recently, a new method, called the extended sampling method (ESM), was proposed for the inverse scattering problems. Similar to\nthe classical linear sampling method (LSM), the ESM is simple to implement and fast. Compared to the LSM which uses fullaperture\nscattering data, the ESM only uses the scattering data of one incident wave. In this paper, we generalize the ESM for the\ninverse acoustic source problems. We show that the indicator function of ESM, which is defined using the approximated solutions\nof some linear ill-posed integral equations, is small when the support of the source is contained in the sampling disc and is large\nwhen the source is outside. This behavior is similar to the ESM for the inverse scattering problem. Numerical examples are\npresented to show the effectiveness of the method....
Loading....