用共焦Fabry—Perot干涉仪探测激光超声信号的研究

本文给出一种非接触式接收激光超声信号的方法，利用自行研制的实验系统，探测到用ＰＺＴ换能器和脉冲激光产生的超声信号，其信噪比足以满足进一步的电子学信号处理要求。这是将该技术应用于ＮＤＴ中的基础     

Lamb wave scattering by a symmetric pair of surface-breaking cracks in a plate

The scattering problem of a Lamb wave incident on a symmetric pair of surface-breaking transverse cracks in a plate is considered. The Lamb wave is assumed to be obliquely incident on the crack plane. Since the cracks are part-through, the scattered field will contain reflected as well as transmitted waves. The energy of the incoming wave is partitioned into reflected and transmitted wave modes. Energy coefficients of the reflected and transmitted waves are calculated as a function of incident frequency and crack depth. The incidence angle of the incoming wave is also treated as a parameter. Both the reflected and transmitted wave fields are considered as linear superpositions of all real and complex wave modes in the plate. Decomposition of modes is achieved with the help of an orthogonality condition based on the principle of reciprocal work. Continuity of displacement and stress fields is imposed at the crack plane. Energy coefficients for reflection and transmission are obtained from the mode amplitudes. Energy coefficients are shown to be a strong function of incident frequency and crack depth. Experiments are conducted with a PZT transducer network interacting with a symmetric pair of machined cracks in an aluminum plate. Trends predicted by the analysis are reflected in the experimental results.     

Acoustoelastic determination of residual stress with laser doppler velocimetry

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.     

Acoustical birefringence and the use of ultrasonic waves for experimental stress analysis

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.     

连续信号激光—超声旋涡测量技术

介绍了一种新的激光超声测量技术-连续信号激光-超声旋涡测量技术。用连续波超声信号记录流场参数（速度）变化。其主要优点是：降低对超声换能器的要求;不需要高能量激光光源;可以对旋涡流场进行定量的非接触测量。     

Designing an all-purpose force transducer

Many design and analysis situations require the determination of loads being transmitted to a structure. Since it is not always possible to insert a load cell, it is proposed that the structure itself and a set of strain gages be used to determine each of the applied loads (forces and moments) responsible for the measured strains. In essence, the structure becomes the transducer.Although a set of loads will uniquely deform a structure, the measurements can only be made at a finite number of points. However, in most situations, these data are sufficient to reveal the combination of loads that caused the deformation.The development of a technique for determining these loads is described. Limitations of the technique are discussed along with the associated error estimates. A worked example is given at the end.Paper was presented at the 1990 SEM Spring Conference on Experimental Mechanics held in Albuquerque, NM on June 3–6.     

Nondestructive evaluation of the carbon content in steel

The aim of this work is to propose an experimental method to evaluate the steel carbon content by ultrasound. The sample is immersed in a water tank in order to analyze it under various incidences of sound waves. Longitudinal wave velocities are measured by immersion by using a 5-MHz frequency probe. Transverse wave velocities are measured in a contact mode by using a 4-MHz transverse wave transducer. The attenuation coefficients of ultrasonic longitudinal and transverse waves are deduced from three successive basic echoes through the sample. The effects of some heat treatments on ultrasonic parameters are also studied. The measurement of ultrasonic parameters in steel offers an interesting possibility of tracing the carbon content and, at the same time, provides information on the steel structure and its elasticity.     

Propagation of plane waves at the imperfect boundary of elastic and electro-microstretch generalized thermoelastic solids

The problem of reflection and transmission of plane waves incident on the contact surface of an elastic solid and an electro-microstretch generalized thermoelastic solid is discussed. It is found that there exist five reflected waves, i.e., longitudinal displacement （LD） wave, thermal （T） wave, longitudinal microstretch （LM） wave and two coupled transverse displacement and microrotational （CD（I） and CD（II）） waves in the electro-microstretch generalized thermoelastic solid, and two transmitted waves, i.e., longitudinal （P） and transverse （SV） waves in the elastic solid. The amplitude ratios of different reflected and transmitted waves are obtained for an imperfect boundary and deduced for normal force stiffness, transverse force stiffness, and perfect bonding. The variations of amplitude ratios with incidence angles have been depicted graphically for the LD wave and the CD（I） wave. It is noticed that the amplitude ratios of reflected and transmitted waves are affected by the stiffness, electric field, stretch, and thermal properties of the media. Some particular interest cases have been deduced from the present investigations.     

Investigation on the Design of Piezoelectric Actuator/Sensor for Damage Detection in Beam with Lamb Waves

Piezoelectric wafer type actuator/sensor is widely used to generate and sense Lamb waves for Structural Health Monitoring (SHM). However, multiple Lamb waves modes are generally excited with this type of transducer. As a result, there is some difficulty in using Lamb waves for damage detection. To selectively generate a single A₀/S₀ Lamb mode, the tuned excitation of Lamb waves has been studied by some researchers. This paper investigates the design of the PZT actuator/sensor bonded to beam-like structure for generating single A₀/S₀ Lamb mode. In the study it is found that some factors, including the bonding layer, the unknown material properties and dynamical characteristics of the beam, will influence the design of PZT actuator/sensor. Piezoelectric impedance technique is introduced to facilitate the design of PZT actuator/sensor. Crack detection in beam using the tuned A₀/S₀ Lamb waves is performed.     

Antiplane Shear Waves in Two Contacting Ferromagnetic Half Spaces

The problem of reflection and refraction of antiplane shear (or magneto-elastic) waves at the interface between two ferromagnetic half-spaces with slipping contact (vacuum gap) is studied for waves propagating normal to the direction of the applied external magnetic field which is assumed to be parallel to the interface. We show the existence of new waves that are localized near the interface between the two ferromagnetic media and accompany the reflected and the transmitted waves. We call the new waves as accompanying surface magneto-elastic (ASME) waves; their amplitudes depend upon values of magnetoelastic parameters of the two media and the intensity of the applied magnetic field. We derive closed-form expressions for magnitudes (coefficients) of the reflected, the refracted (transmitted) and the ASME waves. We show that for a range of values of the applied magnetic field the coefficient of the reflected wave increases and that of the transmitted wave decreases with an increase in the magnitude of the applied magnetic field; these coefficients eventually approach 1 and 0, respectively. That is, the applied external magnetic field can totally eliminate the transmitted wave, and can control energies of the reflected, the refracted and the ASME waves.     

Self-demodulation acoustic signatures for nonlinear propagation in glass beadsSignatures acoustiques de l'auto-démodulation basse fréquence lors de la propagation non linéaire dans des billes de verres

The present Note describes some experimental work related to the nonlinear propagation of acoustic waves in granular media such as unconsolidated glass beads. The studied nonlinear effect is a self-demodulation process performed with the operation of the so-called parametric transmitting antenna. The pump (or carrier) wave is generated by a high power ultrasonic broad-band transducer (100 kHz central frequency) which is LF (low frequency, i.e., a few kHz) amplitude modulated. As the attenuation of acoustic waves increases with frequency, only the LF demodulated wave can be transmitted. A parametric study is performed where the HF central frequency is monitored between 60 and 300 kHz. The LF demodulation profile versus the HF frequency is modified, its shape being temporally derived almost twice. A numerical analysis of the order of temporal derivation is done in the Fourier domain, its value varying from 1.25 to 2.7. Qualitative agreement with current theoretical models is described, and an advanced theoretical analysis by the same authors [Phys. Rev. E 66 (2002) 041303], taking into account absorption, nonlinearity, dispersion and scattering, is briefly discussed. To cite this article: V. Tournat et al., C. R. Mecanique 331 (2003).     

Determination of uniaxial stresses in steel structures by the laser-ultrasonic method

This paper describes the experimental implementation of the laser-ultrasonic method for diagnosing mechanical compression and tensile stresses in steel structures, based on the acoustoelasticity effect. The special laser-ultrasonic transducer that provides the laser excitation and highly sensitive piezoelectric detection of head (longitudinal subsurface) ultrasonic waves is developed. It is shown on the example of R65 rail samples of various quality that, regardless of the structural phase state of the rail, there is one and the same linear relationship between the relative variation of the velocity of head ultrasonic waves and the absolute value of uniaxial compression and tensile stresses acting in the rail.     

Quasi-P-waves at a corrugated interface between two dissimilar monoclinic elastic half-spaces

In this paper we have derived reflection and transmission coefficients of qP-waves at a corrugated interface between two different elastic half-spaces of monoclinic type. Using Rayleigh’s method, the expressions for reflection and transmission coefficients are derived in closed form for a specific interface and for the first order approximation of the corrugation. Numerical computations are performed for a specific model and the results obtained have been shown graphically. The variation of the modulus of reflection and transmission coefficients with the angle of incidence, frequency and corrugation of the interface are shown separately. These coefficients are found to be strongly influenced by the angle of incidence, frequency, elastic parameters and amplitude of the corrugation of the interface. It is found that (i) the modulus of reflection and transmission coefficients at the plane interface are independent of corrugation of the interface and that of frequency of the incident wave, (ii) the reflection and transmission coefficients of regularly reflected and transmitted waves are found to be greater than that of irregularly reflected and transmitted waves, (iii) the coefficients of irregularly reflected and transmitted waves are found to increase and decrease with increase of corrugation and frequency parameters respectively. The results of Singh and Khurana [Singh, S.J., Khurana, S., 2001. Reflection and transmission of P- and SV-waves at the interface two between monoclinic elastic half-spaces. Proc. Natl. Acad. Sci. India 71(A) (IV), 305–319] have been reduced from the present problem.     

Mesoscopic model to simulate the mechanical behavior of reinforced concrete members affected by corrosion

In this contribution, a finite element methodology devised to simulate the structural deterioration of corroded reinforced concrete members is presented. The proposed numerical strategy has the ability to reproduce many of the well-known (undesirable) mechanical effects induced by corrosion processes in the embedded steel bars, as for example: expansion of the reinforcements due to the corrosion product accumulation, damage and cracking patterns distribution in the surrounding concrete, degradation of steel–concrete bond stress transfer, net area reduction in the reinforcements and, mainly, the influence of all these mentioned mechanisms on the structural load carrying capacity predictions.At the numerical level, each component of the RC structure is represented by means of a suitable FE formulation. For the concrete, a cohesive model based on the Continuum Strong Discontinuity Approach (CSDA) is used. Steel bars are modeled by means of an elasto-plastic constitutive relation. The interface is simulated using contact-friction elements, with the friction degradation as a function of the degree of corrosion attack. Two different (and coupled) mesoscopic analyzes are considered in order to describe the main physical phenomena that govern the problem: (i) an analysis at the cross section level and (ii) an analysis at the structural member level.The resultant mechanical model can be used to simulate generalized reinforcement corrosion. Experimental and previous numerical results, obtained from the available literature, are used to validate the proposed strategy.     

Experimental analysis of contact for the indentation of a flat rounded punch

The ‘plane vs. plane’ contact involving flat punches has been the subject of many investigations, even in recent years, mainly due to the crucial role that such components play in phenomena, such as fretting fatigue and indentation tests. While the problem has been deeply approached from a theoretical point of view, there is a noteworthy lack of experimental verifications due to the limited number of laboratory techniques capable of supplying detailed information about contact parameters. In order to make a partial contribution towards gaining an understanding of such problems, this study proposes the investigation of flat rounded punch contact with an ultrasound-based technique, which exploits the properties of ultrasonic waves to be differently reflected by a contact interface depending on its stress state. A suitable setup was built in such a way as to ensure a good level of control of contact conditions, and the interface was scanned with a high-frequency ultrasonic transducer so as to acquire the reflection data. While the graphic processing of the ultrasonic coefficient of reflection may easily be displayed as a ‘contact map’, the quantitative accuracy of the method was also investigated by comparing experimental results with those obtained from a Finite Element model of the system. The results show a good level of agreement between the two approaches, thus confirming that the ultrasonic technique can be effectively employed to investigate many contact problems which to date have never (or scarcely) been experimentally validated.     

Ultrasonic field modeling in plates immersed in fluid

Distributed Point Source Method (DPSM) is a semi-analytical technique that can be used to calculate the ultrasonic field (pressure, velocity and displacement fields in a fluid, or stress and displacement fields in a solid) generated by ultrasonic transducers. So far the technique has been used to model ultrasonic fields in homogeneous and multilayered fluid structures, and near a fluid–solid interface when a solid half-space is immersed in a fluid. In this paper, the method is extended to model the ultrasonic field generated in a homogeneous isotropic solid plate immersed in a fluid. The objective of this study is to model the generation of guided waves in a solid plate when ultrasonic beams from transducers of finite dimension strike the plate at different critical angles. DPSM results for a solid half-space problem are compared with the finite element predictions to show the superiority of the DPSM technique. The predicted results are also compared with the experimental visualization of the mode patterns of Lamb waves propagating in a glass plate obtained from stroboscopic photoelastic method. Experimental and theoretical results show good qualitative agreement. The DPSM technique is then applied to study the mode patterns in aluminum plates immersed in water.     

Experimental and numerical studies of guided wave damage detection in bars with structural discontinuities

This paper deals with longitudinal and flexural wave propagations in steel bars with structural discontinuities. Numerical simulations were performed using the spectral element method and compared with experimental studies conducted on an intact bar as well as on bars with an additional mass, a notch and a grooved weld. To model longitudinal wave propagation including lateral deformations, special rod spectral elements in time domain (based on Love and Mindlin–Herrmann theories) were formulated. The effect of the three discontinuities on wave propagation is discussed, and the applicability of longitudinal and flexural waves to non-destructive damage detection is investigated.     

Using laser ultrasonics for nondestructive residual stress evaluation

A non-contact measuring technique of ultrasonic waves velocity is proposed, in which Rayleigh waves are detected by a laser Doppler velocimeter and the velocity is measured precisely by means of a sing-around unit and a digital oscilloscope. With the proposed technique, the acoustoelastic coefficient of Rayleigh waves in mild steel SS41 is obtained, which is in good agreement with that obtained by the contact method. Furthermore the non-contact technique is applied to evaluate the residual stress in a butt-welded steel plate, the result is reasonable.     

Wave-based defect detection and interwire friction modeling for overhead transmission lines

In this study, the feasibility of continuous, online monitoring of power lines using ultrasonic waves is considered. Local and global wave-based approaches for wire break detection in overhead transmission lines are presented. Both methods use a sending/receiving transducer to generate an ultrasonic, longitudinal, elastic wave in the cable. Defects in the cable cause a portion of the incident ultrasonic wave to be reflected back to the transducer, which when received, can be used to identify the presence of the defect. Although the transducers can only be attached to the surface of the cable, subsurface wires can also be interrogated since elastic energy spreads to these wires through friction contact. This study also explores how the elastic energy of a propagating wave becomes distributed among contacting rods via friction contact. This work focuses specifically on a two-rod system in which the wave energy from an excited “active” rod is transmitted to a neighboring “passive” rod through friction contact. An energy-based model is used to approximate the time average elastic wave power in the two rods as a function of propagation distance. Power predictions from the energy-based model compare well with experimental measurements and finite element simulations.     

Hysteretic linear and nonlinear acoustic responses from pressed interfaces

An analysis of the linear and nonlinear acoustic responses from an interface between rough surfaces in elastoplastic contact is presented as a model of the ultrasonic wave interactions with imperfect interfaces and closed cracks. A micromechanical elastoplastic contact model predicts the linear and second order interfacial stiffness from the topographic and mechanical properties of the contacting surfaces during a loading–unloading cycle. The effects of those surface properties on the linear and nonlinear reflection/transmission of elastic longitudinal waves are shown. The second order harmonic amplitudes of reflected/transmitted waves decrease by more than an order of magnitude during the transition from the elastic contact mode to the elastoplastic contact mode. It is observed that under specific loading histories the interface between smooth surfaces generates higher elastoplastic hysteresis in the interfacial stiffness and the acoustic nonlinearity than interfaces between rough surfaces. The results show that when plastic flow in the contacting asperities is significant, the acoustic nonlinearity is insensitive to the asperity peak distribution. A comparison with existing experimental data for the acoustic nonlinearity in the transmitted waves is also given with a discussion on its contact mechanical implication.