缺陷识别反问题的研究状况与若干进展

简要回顾了缺陷识别反问题的发展状况,评述了几类典型识别方法:基于势函数理论的电学法,静态ＢＥＭ优化迭代法,射线法,Ｔ矩阵法,Ｂｏｒｎ近似法,边界积分方程及边界元法．介绍了作者建立的裂纹及夹杂识别的迭代优化法．指出了缺陷识别反问题需要研究的主要问题．      

Whole-field experimental displacement analysis of composite cylinders

The lack of a quick, nondestructive method of flaw detection in composite materials is a hindrance to their use. Optical methods of determining displacements hold promise as a method of detection of these flaws. This paper illustrates the use of digital-image-processing equipment to determine the displacement fields in an internally pressurized composite cylinder. Included are results of actual experiments performed by the authors on both a Plexiglas and a composite cylinder.     

Time-of-Flight Diffraction Measurement Using Laser Ultrasound

We developed a new time-of-flight diffraction (TOFD) method based on laser ultrasound, which can use not only longitudinal waves but also shear waves. This method is more advantageous than the conventional TOFD method, because it enables us to obtain flaw depths accurately without knowing the longitudinal or shear wave velocity in the specimen or the distance between the transmitter and receiver, which are not easily obtained in complex-shaped objects. We applied the proposed method to estimate slit depths in aluminum alloy plates. The times of flight of the lateral wave, diffracted waves and the mode-converted shear wave at the flaw tip were measured and used to estimate the slit depth. As a result, an accurate estimation of flaw depth was achieved.     

Nuclear reactor pressure vessel-specific flaw distribution development

Vessel intergrity predictions performed through fracture mechanics analysis of a pressurized thermal shock event have been shown to be significantly sensitive to the overall flaw distribution input. It has been shown that modern vessel in-service inspection (ISI) results can be used for development of vessel flaw distribution(s) that are more representative of U.S. vessels. This paper describes the development and application of a methodology to analyze ISI data for the purpose of flaw distribution determination. The resultant methodology considers detection reliability, flaw sizing accuracy and flaw detection threshold in its application. Application of the methodology was then demonstrated using four recently acquired U.S. PWR vessel inspection data sets. Throughout the program, new insight was obtained into several key inspection performance and vessel integrity prediction practice issues that will impact future vessel integrity evaluation. For example, the potential application of a vessel-specific flaw distribution now provides at least one method by which a vessel-specific reference flaw size applicable to pressure-temperature limit curves determination can be estimated. This paper will discuss also the development and application of the methodology and the impact to future vessel integrity analyses.     

Stress-strain state of an anisotropic plate with curved cracks and thin rigid inclusions

We solve the bending problem for an anisotropic plate with flaws like smooth curved nonoverlapping through cracks and rigid inclusions. The problem is solved by the method of Lekhnitskii complex potentials specified as Cauchy type integrals over the flaw contours with an unknown integrand density function. We use the Sokhotskii—Plemelj formulas to reduce the boundary-value problem to a system of singular integral equations with the additional conditions that the displacements in the plate are single-valued when going around the cut contours and the equilibrium conditions for stress-free rigid inclusions. After the singular integrals are approximated by the Gauss-Chebyshev quadrature formulas, the problem is reduced to solving a system of linear algebraic equations. We study the local stress distribution near flaw tips. We analyze the mutual influence of flaws on the stress distribution character near their vertices and compare the well-known solutions for isotropic plates with the solutions obtained by passing to the limit in the anisotropy parameters (“weakly anisotropic material”) and by using the method proposed here.     

A method of finding the principal modes of nonlinear vibration systems and their stabilities

This paper presents a new method of finding the principal modes of nonlinear vibration systems, by means of which the problem of finding principal modes of nonlinear systems is transferred to the problem of finding real roots of a set of algebraic equations. The method is applicable to various kinds of nonlinear vibration systems with many degrees of freedom, and is simple in calculation. The paper presents another new method of analyzing the stabilities of principal modes of nonlinear systems.     

An introduction to dynamic photoelasticity

The general area of elastodynamics is divided into four more limited topics including, stress-wave propagation, vibration and impact, fracture propagation and quasi-static transients. The application of dynamic photoelasticity to each topic is discussed. Recording methods used in dynamic photoelasticity which are reviewed include the high-speed framing camera, the Cranz-Schardin system, Q-switched ruby lasers, and a stopaction strobe system. Advantages and disadvantages of each method of recording are covered. Analysis procedures used in interpreting the dynamic isochromatic-fringe patterns are described. Examples are illustrated where separation of the principal stresses is possible and a calibration method for determining the dynamic material-fringe valuef _σ ^* is reviewed. Finally, four applications of dynamic photoelasticity to problems arising in geophysics, fracture mechanics, flaw detection and mining are briefly reviewed to show the versatility of the dynamic photoelastic method are described.     

Comparative holographic interferometry: A nondestructive inspection system for detection of flaws

Comparative holographic interferometry addresses a key problem of nondestructive evaluation: comparison of the resistance to strength in real time of two nominally identical specimens. After outlining the basis of comparative holography in flaw detection, the present paper reports on some new and complementary developments in comparative holographic interferometry. The proposed systems stand out by their ability to store the master displacement field in the interferometric setup. The integration of the storage capacity in the instrument considerably augments its potential in nondestructive routine inspection tasks. The visual display of the fringes contouring the difference in mechanical response is shown to improve considerably with the addition of auxiliary phase difference satisfying certain conditions. Methods for the generation of corresponding fringes are considered and their localization investigated in brief. Particular attention is devoted to the formation of the holographic moiré fringes. The influence of system misalignment on the moiré fringe interpretation is examined. A potential application of comparative holography to the quantitative evaluation of fatigue is described. Experimental evidence supporting the operational feasibility of the technique along with the results obtained in application to flaw detection are finally presented.     

Diagrams of critical equilibrium for brittle bodies with sharp flaws

Certain forms of the stress-intensity factors close to the tips of sharp flaws (plane problem) are used as the basis of a method for plotting critical equilibrium diagrams for brittle bodies with flaws in the form of pointed cavity-cracks [5]. Concrete examples are discussed, mainly in the context of such diagrams, for a brittle body weakened by a circular cavity flaw with a crack leaving the edge of the flaw. Determination of the stress-intensity factors for this problem is based on approximate solution of an integral equation by the method of collocations. Plots of some familiar diagrams are also analyzed.Translated from Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, Vol. 11, No. 3, pp. 98–104, May–June, 1970.     

管道及管路系统流固耦合振动问题的研究动态

对管道及管路系统流固耦合振动问题在近二十年来的进展作了综述。根据问题特点，将本课题分为三个分支，即从紊流到振动噪声源的研究，流－弹耦合振动的研究和声－弹耦合振动的研究。在分别总结这三个分支的研究成果的同时指出了尚需进一步研究的某些问题。