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161.
Ultrasonic critical angle reflectivity method is used to measure the phase velocity of generalized Lamb waves in cadmium and
zinc platings. In addition to the free propagating modes, leaky-wave modes are also observed. Leaky waves are considered using
principles familiar from the discussion of surface waves in anisotropic media and a relatively good agreement is obtained
between the theoretical computations and measured data. 相似文献
162.
The elastic constants of single crystal galena have been determined from the measured ultrasonic velocities down to liquid
helium temperature. A cryostat incorporating an arrangement to inject the liquid bonding material at low temperature is described.
At 5 K, the values of elastic constants are C11=14.90, C12=3.51 and C44=2.92×1010 N/m2. 相似文献
163.
A plastic-clad optical fibre system has been examined as a delivery system of pulsed laser energy for the generation of ultrasound. The onset of significant optical damage caused by the laser has been investigated. By using multimode fibres of 1 m length with 600 μm core size, it was found that laser power densities from the fibre were sufficient to produce ultrasonic waveforms corresponding to both the thermoelastic and plasma generation regimes. Out-of-plane acoustic displacements of >250 pm can be achieved through 2.5 cm thick aluminium test samples, showing that fibre optical delivery systems may be considered in systems using laser-generated ultrasound for non-destructive testing applications. 相似文献
164.
165.
In order to reduce the amount of sample to be collected and the time consumed in the analytical process, a broad range of analytes should be preferably considered in the same analytical procedure. A suitable methodology for pesticide residue analysis in soil samples was developed based on ultrasonic extraction (USE) and gas chromatography–mass spectrometry (GC–MS). For this study, different classes of pesticides were selected, both recent and old persistent molecules: parent compounds and degradation products, namely organochlorine, organophosphorous and pyrethroid insecticides, triazine and acetanilide herbicides and other miscellaneous pesticides. Pesticide residues could be detected in the low- to sub-ppb range (0.05–7.0 μg kg−1) with good precision (7.5–20.5%, average 13.7% R.S.D.) and extraction efficiency (69–118%, average 88%) for the great majority of analytes. This methodology has been applied in a monitoring program of soil samples from an intensive horticulture area in Póvoa de Varzim, North of Portugal. The pesticides detected in four sampling programs (2001/2002) were the following: lindane, dieldrin, endosulfan, endosulfan sulfate, 4,4′-DDE, 4,4′-DDD, atrazine, desethylatrazine, alachlor, dimethoate, chlorpyrifos, pendimethalin, procymidone and chlorfenvinphos. Pesticide contamination was investigated at three depths and in different soil and crop types to assess the influence of soil characteristics and trends over time. 相似文献
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Detection of kissing bonds by Lamb waves 总被引:6,自引:0,他引:6
Closed cracks under compressive normal stresses are difficult to detect by the conventional ultrasonic techniques. When the crack surfaces stay in very close contact with each other then the bond between the two surfaces of the crack is called a ‘kissing bond’. This is a very dangerous bond. Catastrophic failures can result if the system is subjected to crack opening normal stresses or shear stresses. When the crack surfaces are smooth then kissing bonds cannot transmit shear stress very well but can carry compressive normal stress, these bonds are called ‘slip bonds’. Conventional P-wave scans (C-scan or A-scan) are based on the assumptions that P-waves are reflected by the defective interface. However, an interface subjected to a large compressive stress cannot reflect P-waves effectively, hence these bonds remain invisible to the conventional P-wave based C-scan or A-scan techniques. In this paper it is shown that the kissing bonds can be effectively detected by some leaky Lamb mode. Theoretical and experimental results are presented to show that using the Lamb waves is an effective way of detecting kissing bonds. 相似文献
170.