超声纯横波法测试45#钢的内部应力

声各向同性的金属材料在应力作用下,材料表现出声各向异性,这是用声弹性法分析材料内部应力的基础。本文用垂直于应力方向传播的超声纯横波对45#钢进行测试,测试时横波的偏振化方向分别平行和垂直于应力方向。实验结果表明:材料在拉、压应力作用下,相互正交的两超声纯横波的声速都发生了变化,且声各向异性因子与应力成线性关系。利用此关系可测试材料内部应力,提供了一种无损测试材料内部应力的方法,另外本实验方法也可以对材料内部残余应力进行评估。实验中利用回振法测量声速,可测量声速的微小变化,精度高。     

Stress measurement using vertically polarized shear waves

This paper proposes a method to evaluate surface stresses in orthotropic materials by the use of vertically polarized shear waves (SV waves). It is assumed that the normal to the surface coincides with one of the axes of anisotropy, and that the material anisotropy is not necessarily small. The speeds of the waves are expressed in terms of the material properties, the stress, the rigid body rotation and the propagation direction. From the expressions, and for the following two cases: (1) the rigid body rotation is known, (2) the anisotropy is weak, it is possible to determine the components of the surface stress by measuring the speeds of SV waves propagating in several directions. When the anisotropy is weak, the acoustoelastic birefringence for SV waves is also derived, to separate the material anisotropy and the difference of the principal stresses. The theory can be applied to stress evaluation by using ultrasonic Lamb waves whose speeds are nearly equal to those of SV waves.     

Acoustoelastic determination of stress in slightly orthotropic materials

A method is proposed to determine stresses in acoustoelasticity by making use of orthotropic stress-acoustic relations and the equations of equilibrium. It is derived theoretically that shear stress is determined ny ultrasonic data ofB and ?, which denote a magnitude of acoustic birefringence and its principal direction, respectively. Other stress components are obtained by numerical integration of the equilibrium equation with the shear stress thus determined. Experiments were carried out to show the validity and usefulment of the method. This method was applied to the measurement of stress field on a plate with a circular hole subjected to axial tension. Ultrasonic measurements were made by a Y-cut quartz transducer with 5-MHz fundamental frequency. The specimen was cut out from 1100 aluminum plate of 4-mm thickness, which shows a slight orthotropy due to roll working. The values ofB and ? were measured in both stressed and unstressed state. Then, stress distributions were determined by the method proposed here, and are compared with the known theoretical distributions.     

A device for measuring the velocity of ultrasonic waves: An application to stress analysis

In this paper we present a device for the practical application of an ultrasonic critical-angle refractometry (UCRfr) technique. UCRfr is a technique for measuring the velocity of longitudinal, shear and Rayleight waves, developed to improve the traditional ultrasonic methods for measuring the stress level in materials by means of acousto-elasticity. The technique consists of relating the variations in wave propagation velocity to variations in the angle of refraction at the interface with a second medium. Variations in the angle of refraction are determined on the basis of delay in receiving of the same wave at two different points. The study deals with the measurements of velocity changes of longitudinal wave due to uniaxial stress. In the present work the effects of stress on aluminum and steel specimens have been studied. Experimentation has show the potential of the technique for stress measurement; on the other hand, when the applied stress is known, it allows the measurement of the acoustoelastic constants of longitudinal waves. As regards measuring variations in velocity induced by stress, using this method it is possible, with a suitable choice of the material the device is made of, to isolate the effects of stress on velocity from the possible effects of temperature.     

Application of ultrasonic-pulse-spectroscopy measurements to experimental stress analysis

We apply the technique of ultrasonic pulse spectroscopy to measure the interference effects between two shear waves propagating in specimens loaded in uniaxial compression. We show that the power spectrum of an echo containing both fast and slow components of a shear wave will exhibit periodic minima. The periodicity exhibited in the spectrum is 1/Δτ, where Δτ is the difference in arrival time between the fast and slow waves. A change in the state of stress which produces a change in the two shear velocities results in a stress-dependent change in wave-arrival times. Because of this velocity change, the frequency at which a particular minimum occurs in the spectrum changes, and this can be used to indicate the state of stress in the material. Our results indicate that, if the spectrum minima frequencies could be resolved to within 10 kHz, the principal-stress differences within 36 psi (0.251 MPa) could be measured in specimens of aluminum 1 in. (2.54 cm) thick. Inherent in analyzing and measuring echo-interference effects is a single-echo requirement. Thus, transducer coupling effects are minimized and measurements in highly attenuating materials or at high frequencies in normal attenuating materials are possible. This technique shows considerable promise as a means of measuring and monitoring the applied stresses in materials.     

An electromagnetic shear-stress gage for large-amplitude shear waves

In many materials, especially plastics, ceramics and rocks, large-amplitude shear-wave propagation studies could provide valuable information for the development of constitutive equations. A newly developed electromagnetic-gage configuration provides an output voltage which is directly related to the dynamic shear stress in the material. The electromagnetic shear-stress gage has been used to make direct measurements of shear-wave stresses in PMMA and Solenhofen limestone. Large-amplitude shear waves were obtained with a new plate-impact technique which generates shear waves by a controlled-reflection process. The configuration of the stress gage permits it to be used simultaneously with more conventional electromagnetic velocity gages, thus providing both types of data in one experiment.     

Direct measurement of static yield properties of cohesive suspensions

A technique of yield stress investigation based upon the combined use of two devices (an applied stress rheometer and an instrument for measuring the propagation velocity of small amplitude, torsional shear waves) is described. Investigations into the low shear rate rheological properties of illitic suspensions are reported for shear rates, typically, in the range 10^–4— 10^–1 s^–1 under applied stresses in the range 0.01 — 10 Nm^–2 and involving shear strains between 10^–1 and 10^–4. Results are presented which demonstrate that the technique does not invoke the excessive structural disruption of material associated with applied shear rate based methods (direct and otherwise) and the widely encountered problem of wall slip at the surface of rotational measuring devices is avoided using miniature vane geometries. Results are compared with those obtained using smooth-walled cyclindrical measuring devices in both applied stress and applied shear rate instruments.Yield measurements are considered in relation to the structural properties of the undisturbed material state and shear moduli obtained by studying the propagation of small amplitude (10^–5 rad), high frequency (~ 300 Hz) torsional shear waves through the test materials are reported. Experimental techniques and instrument modifications to permit these measurements are described.     

The Physical Fundamentals of the Ultrasonic Nondestructive Stress Analysis of Solids

Theoretical and experimental works on acoustoelasticity are briefly generalized. Studies conducted and scientific results obtained at the S. P. Timoshenko Institute of Mechanics and E. O. Paton Institute of Electric Welding of the National Academy of Sciences of Ukraine are highlighted. Special features of these works and their difference from those of other authors are pointed out. The basic principles and laws governing the propagation of longitudinal, shear, and surface waves in bi- and triaxially stressed bodies are briefly stated with regard for the orthotropy and nonlinear properties of the material. The experimentally proven principles and laws for elastic waves propagating in initially stressed bodies are formulated. The physical fundamentals of the ultrasonic nondestructive technique for determining bi- and triaxial stresses in solids are described. The determination of bi- and triaxial residual stresses in specimens and structural members is demonstrated by examples. The basic principles of the related (dielectric and electromagnetic) methods for stress analysis of polymeric materials are stated. The application of the electromagnetic method to the stress analysis of some polymeric materials is considered     

Acoustoelastic stress analysis of residual stress in a patch-welded disk

The acoustoelastic stress analysis is based on the fact that an initially isotropic material becomes anisotropic under stress. The birefringent effect for polarized ultrasonic shear waves in the stressed material will then be similar to the photoelastic effect in which a light wave and a transparent model specimen are used. In this paper, the velocity differences of acoustical, perpendicularly polarized waves are measured directly by a ‘sing-around’ method using a 5-MHz shear-type transducer. The residual-stress distribution in a mild-steel circular plate with a concentrically patch-welded joint is measured by this method. The acoustoelastic coefficient is obtained separately by uniaxial testing of the base material. The results show that the acoustical stress measurement, carried out nondestructively, agrees well with those obtained by conventional destructive methods as well as with theoretical predictions.     

Stress evaluation by pulse-echo ultrasonic longitudinal wave

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.     

压应力对压剪裂纹扩展的影响研究

本文针对压剪裂纹的启裂及扩展问题,研究了脆性材料中裂纹面压应力变化对其扩展的影响规律.借助双轴加载试验机可自由调节两个轴位移和力的优势,设计了一种单边对称双裂纹压剪试样.试验中,施加裂纹面压应力至不同的预设值后,使剪应力单调增大直至裂纹启裂及扩展,得到不同预设压应力下压剪裂纹启裂及扩展规律. 随着预设压应力增大,启裂角增大,裂纹扩展路径与初始裂纹的偏角也增大.但随着压应力增大,启裂角增大至一定值后趋于稳定,实验发现,依据裂纹是否闭合,压应力对压剪裂纹扩展的作用大致可分为两个阶段:闭合前,压应力对裂纹启裂载荷及启裂角、扩展路径均有影响,预设压应力增大,裂纹启裂载荷增大、启裂角增大,扩展路径愈来愈偏离初始裂纹方向;闭合后,压应力虽然增大,启裂角和临界压剪应力比始终恒定,压应力对临界剪力和扩展路径存在一定影响.研究表明,裂纹启裂角与启裂时的压剪应力比存在一定的对应关系.启裂时的压剪应力比增大,启裂角增大,启裂时的压剪应力比恒定,启裂角不变.      

Propagation behavior of Love waves in a functionally graded half-space with initial stress

The propagation behavior of Love waves in a functionally graded material layered non-piezoelectric half-space with initial stress is taken into account. The Wentzel–Kramers–Brillouin (WKB) technique is adopted for the theoretical derivations. The analytical solutions are obtained for the dispersion relations and the distributions of the mechanical displacement and stress along the thickness direction in the layered structure. First, these solutions are used to study the effects of the initial stress on the dispersion relations and the group and phase velocities, then the influences of the initial stress on the distributions of the mechanical displacement and shear stresses along the thickness direction are discussed in detail. Numerical results obtained indicate that the phase velocity of the Love waves increases with the increase in the magnitude of the initial tensile stress, while decreases with the increase in the magnitude of the initial compression stress. The effects on the dispersion relations of the Love wave propagation are negligible as the magnitudes of the initial stress are less than 100 MPa. Some other results are obtained for the distributions of field quantities along thickness direction. The results obtained are not only meaningful for the design of functionally graded structures with high performance but also effective for the evaluation of residual stress distribution in the layered structures.     

结构中微裂纹与超声波的混频非线性作用数值仿真研究

针对结构中微裂纹检测难题,本文对结构中微裂纹与超声波的混频非线性作用进行了数值仿真研究。基于经典非线性理论,得到了两列超声纵波相互作用产生混频效应的理论条件。通过有限元仿真,研究了两列纵波与微裂纹相互作用产生混频的条件,并分析了界面处静应力、摩擦系数和裂纹方向对混频效应的影响。研究发现,超声波与微裂纹相互作用产生混频非线性效应的发生条件仍符合经典非线性理论下的混频产生条件。裂纹界面处施加的静应力对差频横波幅值有明显影响;当施加静应力与无裂纹模型得到的最大应力值接近时,混频非线性效应最强;裂纹界面的摩擦系数对超声波的混频非线性效应影响较小;透射差频横波传播方向与经典非线性理论预测的理论差频分量方向基本一致,且几乎不受裂纹方向变化的影响,而反射差频横波的传播方向随裂纹方向的改变而有所不同。本文研究工作为微裂纹检出及方向识别做了有益探索。     

Experimental analysis of rolling contact stresses in a viscoelastic strip

An experimental approach to two-dimensional, viscoelastic, steadily moving rolling contact is described. The photoviscoelastic technique is employed for the analysis of rolling contact stresses between a viscoelastic plate and a rigid rolling cylinder in which the principal axes of stress, strain and birefringence are not coincident with each other. Using an elliptically polarized white light, the distribution of isochromatic fringe order and the principal axes of birefringence at an instant are determined from a single photoviscoelastic image. The time variations of the differences of the principal stresses and strains, as well as their directions, are obtained by use of the optical constitutive equations of photoviscoelasticity. The experimental results involving the time variation of the stresses around the contact surface and their distributions are analyzed.     

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.     

定向断裂控制爆破的空孔效应实验分析

采用新型数字激光动态焦散线实验系统, 对爆炸荷载作用下空孔周围的动应力场分布及空孔对爆生主裂纹扩展行为的影响进行了研究。研究结果表明, 在空孔周围强应力场的影响下, 2条相向扩展的爆生主裂纹逐渐向空孔处偏转, 并在空孔处贯通; 空孔附近的主应力方向与炮孔连心线夹角基本稳定在约12°, 增大空孔尺寸对空孔附近的主应力方向影响不明显; 爆炸应力波与空孔相互作用, 产生反射拉伸波, 改变了主裂纹尖端的应力场, 降低了主裂纹的扩展速度, 且空孔直径越大, 主裂纹的扩展速度越低; 当爆生主裂纹扩展到空孔附近时, 主裂纹尖端动态应力强度因子再次出现上升的趋势。     

Ultrasonic nondestructive material evaluation method and study on texture and cross slip effects under simple and pure shear states

Ultrasonic wave velocities propagating in a plastically deformed medium are known to depend upon its microstructural material properties. Therefore, the authors have proposed the theoretical modeling of an ultrasonic nondestructive method to evaluate plastically deformed states. In the present paper, we verify the proposed theoretical modeling of an ultrasonic nondestructive method and examine its accuracy by comparing the experimental results with the simulated subsequent yield surfaces, the longitudinal and transverse wave velocities under combined stress states of an aluminum alloy using internal state variables of an anisotropic distortional yield model which were determined to achieve a good fit for the experimental results of the longitudinal and transverse wave velocity changes under uniaxial tension test. As a special case, the velocity changes of longitudinal wave under pure shear state subjected to the combinations of tension and compression are also studied, it shows a different result compared with that of longitudinal wave velocity under torsional tests of thin thickness cylinders, i.e., simple shear state. The effects on ultrasonic wave velocity changes due to texture and cross slip under simple and pure shear states are studied via a finite element polycrystal model (FEPM).     

Torsional surface waves in heterogeneous anisotropic half-space under initial stress

The present paper is concerned with the propagation of torsional surface waves in a heterogeneous anisotropic half-space under the initial compressive stress. The heterogeneity in the half-space is caused by the linear variation in rigidity, initial compressive stress and density. The solution part of the problem involves the use of Whittaker function. The dispersion equation has been obtained in a closed form, which shows the variation of phase velocity with corresponding wave number. Effects of anisotropy and initial stress have been shown by the means of graphs for different anisotropic materials. It has found that the phase velocity of torsional waves decreases with increment in initial stress and inhomogeneity. Obtained phase velocity of torsional surface wave is found to be less than the shear wave velocity, which agrees with the standard result.     

The Potential of Ultrasonic Non-Destructive Measurement of Residual Stresses by Modal Frequency Spacing using Leaky Lamb Waves

This paper investigates the potential of ultrasonic non-destructive measurements of residual stresses using the modal frequency spacing method based on the interference spectrum of leaky Lamb waves as an alternative to the commonly used flight-time approach in ultrasonic methods. Extensive experiments were carried out to verify the viability and robustness of the technique using an instrumented leaky Lamb wave setup with uniaxial stressed samples and welded steel samples. To improve the signal-to-noise ratio, multiple sets of raw signals of specularly reflected and leaky Lamb waves were acquired and then averaged in the time domain. The acquired data in the time domain were then transformed into the frequency domain to form the interference spectrum of leaky Lamb waves with a good repeatability. The acoustoelastic coefficient of carbon steel is then derived from the measured relationship of wave velocity and applied stress. Finally, a welded steel plate was examined and residual stress was evaluated. The current work demonstrates the feasibility and the potential of the proposed method in measuring residual stresses in welded plates and thin-walled structures.     

Evaluation of an applied plane-stress tensor distribution using ultrasonic shear waves

Most acoustoelastic stress measurements using shear waves that have been carried out so far are strongly related to photoelastic experiments: the velocity difference of the birefringent waves is evaluated. Absolute time-of-flight measurements potentially give more information about stresses but are also likely to be inaccurate. A technique is developed enabling time-of-flight and polarization angle measurements in an aluminum plate that are reproducible within 1/3 ns and one-deg respectively. Based on a previous calibration of the acoustoelastic effect, a plane-stress tensor field caused by applying a load to an aluminum 2024-T351 compact-tension specimen is evaluated. The results are compared to those of a finite-element analysis.