摘要:

The rapid changes in technology, the changes in the national and global economy and the emergence of many new nations that acquire an increasing competence to innovate is presenting us with new issues and opportunities. In particular, it affects the innovation system of the country, namely the scientific and technological infrastructure, the workforce and the policy environment in which government, industry, and academia operates. From a sequential or serial model we are moving or have moved to a dynamic, interactive one that encompasses more stakeholders in a realtime way. Of late, the work of the Council on Competitiveness has focused on the capacity for innovation as a pre-requisite for national competitiveness. This talk will discuss the results from its report “Going Global: The New Shape of American Innovation” and its “Findings from the Innovation Index” and assess the forces that affect the future. The main conclusion will be that the changes we have and will be facing are irreversible and require the active and positive participation of the technical professional and technical institutions. It also requires new relationships between the main participants of the innovation system. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306029

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Developments in engineering education for the last five decades are briefly reviewed. Particular attention is given to the period for 1985 to the present, which was a period of unprecedented study of engineering education with many in-depth reports issued. These reports tend to have a common theme focusing significantly on the global engineering enterprise. Because of increasing globalization of industry, engineering education in the United States is undergoing major reform. Pressure from industry to revisit certain aspects of engineering education has been a major factor in changes currently underway in the U.S. engineering education program accreditation process. I am not a futurist, but I dare to make some projections of the challenges and changes for engineering education during the period from the year 2000 onward, focusing on the next two to three decades. One dominant factor driving these predicted changes is the fast growing developments in information technology and the rate that information can be transmitted globally. Another among the several I mention is that much of engineering will move more and more toward the molecular level. As a result, engineering education must include biology along with the traditional chemistry and physics as the basis for the practice of engineering. Finally, I enumerate some of the challenges that the engineering professors will face in the next century. We will see unrelenting pressure for changes in engineering education and if professors are to be successful they will have to adopt a culture of rapid change—something rather difficult to imagine in the past. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306030

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

In this shrinking world, what happens in an industry in one country can significantly affect the same industry elsewhere around the globe. In April 1986, a nuclear accident destroyed Unit 4 of Ukraine’s Chernobyl nuclear power plant, focusing worldwide attention on the dozens of Soviet-designed reactors still in operation. The Chemobyl accident led to public concerns about all operating nuclear power plants and, in some countries (e.g., Italy and Sweden), to proposals for nationwide plant closures or moratoriums on new construction. However, for most former Soviet Union countries, plant shutdown was and still is not a viable option—the plants produce a significant percentage of each nation’s total electricity, and those countries do not have sufficient economic resources to develop alternative power sources. In cooperation with similar programs initiated in Canada, Japan, and western European countries, the U.S. Department of Energy (DOE) is conducting a comprehensive effort to reduce risks at Soviet-designed nuclear power plants until they can be shut down or brought into compliance with international standards. This paper describes DOE-supported initiatives with participating host countries to: • improve reliability and accuracy of nondestructive evaluation equipment used for in-service inspection • transfer technologies and infrastructure to improve in-service inspections • enhance management systems for training and certifying host-country in-service inspection personnel The goal of these initiatives to enhance the use of international standards (ASME, ASNT, European Standards EN, and ISO) in operating and regulatory practices at Soviet-designed nuclear power plants. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306031

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Experiments indicate that the radiating near zone of a compressional circular transducer directly coupled to a homogeneous and isotropic solid has the following structure: there are geometrical zones where one can distinguish a plane compressional wave and toroidal waves, both compressional and shear, radiated by the transducer rim. As has been shown previously the modern diffraction theory allows to describe these explicitly. It also gives explicit asymptotic description of waves present in the transition zones. In case of a normal incidence of a plane compressional wave the explicit expressions have been obtained by Achenbach and co-authors for the fields diffracted by a penny-shaped crack. We build on the above work by applying the uniform GTD to model an oblique incidence of a plane compressional wave on an elliptical crack. We compare our asymptotic results with numerical results based on the boundary integral code as developed by Glushkovs, Krasnodar University, Russia. The asymptotic formulas form a basis of a code for high-frequency simulation of ultrasonic scattering by elliptical cracks situated in the vicinity of a compressional circular transducer, currently under development at our Center. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306032

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Understanding the nature of ultrasonic propagation, scattering effects and mode conversation for crack diffraction in materials is critical to the effectiveness of ultrasonic characterization and sizing cracks and defects in structures. Thus far, a complete solution for the diffraction of an ultrasonic pulse of arbitrary shape at a crack of arbitrary shape has not yet been achieved. In this work, diffraction of a thermoelastic laser-generated ultrasonic line source at a semi-infinite half-plane is examined using rigorous diffraction theory. Directivity patterns are calculated for a laser line source, for diffraction of a plane wave at a semi-infinite half-plane and for diffraction of an ultrasonic shear wave generated by a laser line. Experimental validation of the theory is performed using laser-generated ultrasonic diffraction of a shear wave at a slot and its subsequent detection with an EMAT receiver sensitive to shear displacements. Results from calculations and experiments show that the directivity of a laser line source is identical to a laser point source in two dimensions if thermal conduction and subsurface optical penetration effects are neglected. Calculations of the directivity pattern for diffraction of an ultrasonic shear wave at a semi-infinite half-plane show that the majority of the diffracted energy propagates in the direction of the incident plane wave with a smaller portion diffracted at all angles. Diffraction of a laser-generated line source at a semi-infinite half-plane shows similar results. Both models indicate that there will not be a sharp shadow boundary for ultrasonic diffraction at a crack. Experiments performed on an aluminum half-cylinder milled with an EDM slot along the radius verify that ultrasonic signals appear in the shadow zone of the crack. Surface scans using the hybrid laser/EMAT system on aluminum plates milled with slots of different sizes show that crack diffraction is a frequency dependent process. Lower frequencies are found to dominate in the shadow zone. These results indicate that crack sizing may be aided by filtering the signals or similar signal processing methods. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306033

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A complete ultrasonic nondestructive testing situation involving a transmitting transducer, scattering from a defect and a receiving transducer is modeled. The defect is taken to be a smooth rectangular crack in an otherwise homogeneous, isotropic, elastic solid. The crack may be located close to a free surface. To solve the scattering problem, an integral equation method is employed. Starting from an integral representation of the displacement field an integral equation for the crack opening displacement is derived. To solve the equation, the crack opening displacement is expanded in a conveniently chosen set of functions with the correct square-root behavior at the crack tips. The transmitting probe is modeled by prescribing the traction on the area of contact. To model the receiver an electromechanical reciprocity argument is utilized which determines the change in signal response due to the presence of the defect. Some numerical results for the signal response are presented for various combinations of the relevant parameters (transducer type, frequency, crack location and orientation). The results are compared to previously obtained results for scattering from a strip-like crack. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306034

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A Boundary Element Method (BEM) is one of the most frequently used techniques for numerical simulation of ultrasonic nondestructive testing. In simulating a pulse-echo flaw detection test by a BEM, it is desirable that both transmission and reception points of ultrasound are included in the analysis model. However, numerical simulation with that model takes enormous computational time because the scale of the problem is characterized by the distance between these two points compared to the wave length and it is very large in this case. The objective of this study is to develop an efficient numerical method to carry out the simulation which covers the whole process of pulse-echo method concerning mechanical wave propagation. The approach adopted here is to use elastodynamic ray theory in addition to the conventional BEM. In this method, the reflection and propagation of waves in a defect-free region are evaluated by the ray theory and the scattered wave induced by defects by BEM. In this study, the combined method of BEM and ray theory is applied to reflection and scattering problems of 2D time harmonic SH waves in a thick plate model. Both BEM and ray analysis are conducted in the frequency domain and the results obtained are transformed into time-domain solutions when it is needed. Numerical examples show that the combined method can give as accurate solutions as the conventional BEM with less number of boundary elements and the proposed method is very efficient. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306035

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

This paper presents a theoretical investigation into the scattering of a Rayleigh wave by a surface-breaking crack subjected to a compressive stress. The boundary conditions at the partially contacting crack surfaces are modelled according to the quasi-static approximation. Following the results of recent investigations on the subject, the ratio between in transverse and the normal stiffness constants of two rough surfaces in contact is assumed to be 0.55. The model allows for arbitrary distributions of the interfacial stiffness constants in order to simulate the effect of applied compressive stress fields having arbitrary shape along the crack faces. Results are presented to illustrate the behavior of the reflection and transmission coefficients, as well as the dependence of the total energy radiated into the bulk, as functions of a) the ratio between the crack depth and the Rayleigh wavelength, and b) the interfacial stiffness constants. At high frequency, the model predicts an surprising initial increase of the reflection coefficient as the interface stiffness increases, followed by the expected decrease below the value typical of an open crack. It is also shown that the relative variation of reflection coefficient from cracks having the same interfacial stiffness depends on the depth-to-wavelength ratio.—This work was funded by the 5thFramework Program of the European Commission. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306036

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

Experiments indicate that the radiating near zone of a compressional circular transducer directly coupled to a homogeneous and isotropic solid has the following structures: there are geometrical zones where one can distinguish a plane compressional wave and toroidal waves, both compressional and shear, radiated by the transducer rim. As we have shown previously, the modern diffraction theory allows to describe these explicitly. It also gives explicit asymptotic description of waves present in the transition zones. A lot of work has been done by other authors in calculating the fields obtained as the result of a plane wave incident on a plane crack. Here, we present calculations which have been carried out in the framework of Geometrical Elastodynamics and pertain to scattering of toroidal waves by an infinite plane crack. We demonstrate that when the incident wave is toroidal shear there are gaps in the portion of the crack which at a given moment in time contribute to the scattered compressional waves. Using the uniform Keller’s GTD our results may be extended to modeling diffraction of the toroidal waves by elliptic cracks and included in the code for high-frequency simulation of ultrasonic scattering in such cracks situated in the vicinity of a compressional circular transducer, currently under development at our Center. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306037

出版商:AIP    

年代:1900

数据来源: AIP

摘要:

A mathematical model is developed to describe the scattering of a plane wave incident at an arbitrary angle on a transversely isotropic cylinder imbedded in a solid elastic matrix. The model is based on the normal mode expansion method, and accommodates both compression and shear waves, polarized in any direction. The geometry is a good model for a composite material featuring a single reinforcing fiber encased in an elastic matrix. The sensitivity of the system to perturbations in the cylinder’s elastic constants in explored, as revealed by changes in the scattered wave spectrum. The results indicate several system resonances, each sensitive to perturbations in certain elastic constants of the cylinder. Also, dispersive pseudo-Stoneley waves that travel on the matrix-cylinder interface lead to resonances in the scattered wave spectrum that would be good indicators of deficiencies in the integrity of the interface. ©2000 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1306038

出版商:AIP    

年代:1900

数据来源: AIP