共查询到10条相似文献,搜索用时 156 毫秒
1.
针对接地网圆钢杆腐蚀检测问题,本文进行了接地网圆钢杆高频纵向超声导波无损检测方法研究。首先对埋地环境下圆钢杆中纵向导波传播特性进行理论研究,分析了不同模态导波的群速度和衰减频散特性。研究发现,高阶纵向模态导波在衰减最小和群速度最大对应的频率处,在圆钢杆中传播能力强,是适合进行地埋圆钢杆导波检测试验的频率范围。在此基础上,进行了埋地圆钢杆高频纵向超声导波无损检测试验研究。结果发现,利用优选的检测参数可以很好地实现埋地圆钢杆中腐蚀缺陷检测。研究工作为接地网运行状态评价提供了很好的技术支撑。 相似文献
2.
The main object of this study is to develop a new technique for stress nondestructive measurement. A noncontact measurement
technique of ultrasonic wave velocity is proposed. In the measurement system, a laser Doppler velocimeter, which is noncontact,
is used to detect wave motions due to Rayleigh waves instead of a piezoelectric transducer. The noncontact measurement technique
is applied to determine the stress-acoustic coefficient of Rayleigh waves for aluminum 5052 and a structural steel, and the
results are in good agreement with those obtained using knife-edge piezoelectric transducers. The technique is also used to
evaluate residual stress existing in an H-section rolled beam of the structural steel. The distribution of residual stress
is reasonable. 相似文献
3.
This paper presents the results of an investigation on the effects of measurement volume size on the mean velocity profile and the Reynolds stress for fully developed turbulent pipe flows. The study employs the ultrasonic velocity profile method, which is based on the ultrasonic Doppler method. The ultrasonic Doppler method offers many advantages over conventional methods for flow rate measurement in the nuclear power plant piping system. This method is capable of measuring the instantaneous velocity profile along the measuring line and is applicable for opaque liquids and opaque pipe wall materials. Furthermore, the method has the characteristic of being non-intrusive. Although it is applicable to various flow conditions, it requires a relatively large measurement volume. The measurement volume of the present method has a disk-shape determined by the effective diameter of the piezoelectric element and the number of the wave cycles of the ultrasonic pulse. Considering this disk-shaped measurement volume and expressing the time-averaged velocity in a truncated Taylor series expansion around the value at the center of the measuring control volume, the value of the velocity can be obtained. The results are then compared with the data obtained from DNS and LDA measurements. The result shows that the effect of the measurement volume size appears in the buffer region and viscous sublayer. 相似文献
4.
This paper presents a nondestructive stress evaluation technique using the ultrasonic interference spectrum of leaky Lamb
waves. By using a specific pitch-catch ultrasonic setup, the symmetric and antisymmetric modes of Lamb waves in a finite plate
are decoupled, leading to simple relationships between the modal frequency spacing of two adjacent modes in the interference
spectrum and the acoustic wave velocities that are functions of stress. As a result, the stress in the plate can be determined
by measuring the modal frequency spacing instead of the relative flight times to calculate the acoustic wave velocity. Extensive
experiments were carried out to verify the viability and robustness of the new technique using a simple testing system. It
has been demonstrated that the new technique is about 25 times more accurate than existing flight-time approaches using the
same testing system. The experimental results agree well with the results obtained by other ultrasonic methods using expensive
equipment. 相似文献
5.
压剪联合冲击下K9玻璃中的失效波 总被引:1,自引:0,他引:1
对K9玻璃进行了冲击速度为150~400 m/s,倾斜角为10、15的纵剖试样斜撞击实验。结果表明,在加载剪切横波(S+)和卸载纵波(P-)之间有波速超过了纵波波速的波阵面存在,此波的存在对卸载纵波和卸载横波的幅值有一定的影响。由于失效波的产生与材料的表面性质密切相关,为消除纵剖试样中间界面的影响,模拟VISAR的实验条件,进行了冲击速度为70~300 m/s、倾斜角为10的横剖试样斜撞击实验。可以确定在此冲击范围失效波的波速在0.98~1.4 km/s,产生失效波的临界状态为:压应力0.86~1.01 GPa,对应剪应力0.053~0.071 GPa。表明剪应力的存在极大降低了失效波产生的阈值。在此基础上初步分析了撞击面的动摩擦因数和相对滑移速度。 相似文献
6.
Nelson N. Hsu 《Experimental Mechanics》1974,14(5):169-176
Stress-induced optical birefringence in transparent materials has long been a common technique of stress analysis. Although
stress-induced acoustic birefringence was discovered more than 20 years ago, its development and actual applications are still
limited. This paper will look at the similarities and differences between the propagation of light waves in photoelastic materials
and the propagation of ultrasonic waves in deformed solids. Critical comparisons of the experimental methods employed in photoelasticity
with those available in modern ultrasonic measuring technique show why previous studies on ultrasonic measurement of stresses
were not very successful.
A new experimental technique is devised for using ultrasonic waves for stress analysis. The technique employs a single rotatable
10-MHz shear transducer as the transmitter and receiver of ultrasonic pulses. The enlarged display of the 10-MHz modulated-pulse
pattern of reflected echoes provides a convenient way to determine the directions of principal axis of the stress within ±3
deg. The pulse-echo-overlap method is used to measure the absolute velocities of the two principal shear waves. The difference
in principal stresses is then calculated from the velocity measurements. Test results of common structural-aluminum and steel
specimens under uniaxial compression show a linear relation between the velocity changes and the applied stress. Ultrasonic
measurements of stress distribution in a 6.35-cm diameter, 1.9-cm-thick aluminum disk under diametric compression are also
reported.
Paper was presented at Third SESA International Congress on Experimental Mechanics held in Los Angeles, CA on May 13–18, 1973. 相似文献
7.
8.
P. Rizzo 《Experimental Mechanics》2006,46(3):297-306
In recent years methods based on guided ultrasonic waves gained increasing attention for the nondestructive evaluation and
the health monitoring of multi-wire strands used in civil structures as prestressing tendons and stay cables. The study of
wave propagation properties in such components has been challenging due to the load-dependent inter-wire contact and the helical
geometry of the peripheral wires. The present paper addresses an experimental investigation on the ultrasonic wave propagation
in seven-wire strands loaded at different stress levels. Wafer piezoelectric sensors are employed in a through transmission
configuration for the generation and detection of stress waves. The response of the lowest-order longitudinal mode is studied
at different levels of load. Those ultrasonic features, associated with the transmitted ultrasonic energy, sensitive to the
variation of applied load are identified and discussed as possible means of a load monitoring. 相似文献
9.
《International Journal of Solids and Structures》2006,43(7-8):1991-2013
Wave propagation in a porous elastic medium saturated by two immiscible fluids is investigated. It is shown that there exist three dilatational waves and one transverse wave propagating with different velocities. It is found that the velocities of all the three longitudinal waves are influenced by the capillary pressure, while the velocity of transverse wave does not at all. The problem of reflection and refraction phenomena due to longitudinal and transverse wave incident obliquely at a plane interface between uniform elastic solid half-space and porous elastic half-space saturated by two immiscible fluids has been analyzed. The amplitude ratios of various reflected and refracted waves are found to be continuous functions of the angle of incidence. Expression of energy ratios of various reflected and refracted waves are derived in closed form. The amplitude ratios and energy ratios have been computed numerically for a particular model and the results obtained are depicted graphically. It is verified that during transmission there is no dissipation of energy at the interface. Some particular cases have also been reduced from the present formulation. 相似文献
10.
Stress evaluation by pulse-echo ultrasonic longitudinal wave 总被引:3,自引:0,他引:3
D. Vangi 《Experimental Mechanics》2001,41(3):277-281
In this paper, an activity aimed at developing an ultrasonic technique for evaluation of states of stress, and in the presence
of gradients deriving from local effects of concentrated stress, is presented. The approach is based on the acoustoelastic
effect in which ultrasonic wave propagation speed is linked to the magnitude of the stresses present. The technique developed
calls for the use of longitudinal waves in pulse-echo technique that propagate in a direction perpendicular to the surface
of the work piece. The technique has been applied in different experimental configurations on test specimens with concentration
of stresses deriving from notches and fatigue cracks and has furnished encouraging results that highlight the potentiality
of the method. 相似文献