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  • Articles  (42)
  • YBa2Cu3O7  (18)
  • ultrasonics  (13)
  • fault simulation  (11)
  • 1990-1994  (30)
  • 1985-1989  (12)
  • 1960-1964
  • 1950-1954
  • Electrical Engineering, Measurement and Control Technology  (42)
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  • Articles  (42)
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  • 1
    Electronic Resource
    Electronic Resource
    Phonon structures in tunneling conductance of superconducting YBa2Cu3O7 (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 367-369 
    Details
    ISSN: 1572-9605
    Keywords: Tunneling conductance ; second derivative ; phonon structure ; YBa2Cu3O7
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We report on measurements of the tunneling conductance structures above the superconducting gap energy using YBa2Cu3O7 polycrystalline junctions. The measured second derivative data are reproducible among the junctions, and the intensities of the common structures at the biases of 37–38, 47–53, 67–77, and 94–95 mV are strong enough to be assigned. These structures are in agreement with those in the neutron phonon density of states in whole energy regions when the energies are measured from the gap edge of 26±1 meV. This correspondence indicates that the electron-phonon interaction contributes to the pairing mechanism of this superconductor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724570
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  • 2
    Electronic Resource
    Electronic Resource
    Raman scattering studies of ultrathin-layer YBa2Cu3O7/PrBa2Cu3O7 superlattices (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 213-216 
    Details
    ISSN: 1572-9605
    Keywords: Raman scattering ; superlattice ; YBa2Cu3O7 ; PrBa2Cu3O7 ; phonon renormalization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We present Raman scattering studies ofc-oriented ultrathin-layer superconducting (YBa2Cu3O7) m /(PrBa2Cu3O7) n superlattices. For the superlattice with (m=2,n=1) sequence, Raman spectra reveal a new line in the spectral region around 320 cm−1. It is interpreted as a mode representing a combination of IR optical phonons of the Y-sublayers with an admixture of aB 1g type Raman active vibration in the Pr sublayers. This new line, which is similar to those from the interior of the Brillouin zone of the original lattice, does not exhibit superconductivity-induced self-energy effects, although its counterpart in the pure substance does. No additional line is found in the (m=1,n=2) superlattice in the same region, supporting our interpretation for the (m=2,n=1) sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730397
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  • 3
    Electronic Resource
    Electronic Resource
    High-quality YBa2Cu3O7 films on 4-in. Wafers of sapphire, gallium arsenide, and silicon (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 231-233 
    Details
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; thin films ; large-area deposition ; semiconductor substrates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Our technique of reactive thermal co-evaporation has been extended to fabricate large films (up to 4 in.) of YBa2Cu3O7 with high quality. A rotating substrate holder is used to separate the deposition and oxidation processes. This allows free access of the metal vapors. As large substrate wafers we use Al2O3, Si, and GaAs with buffer layers of CeO2, YSZ, and MgO, respectively. On all substrates, the uniformity of thickness and composition was better than 2%. Inductively measuredT c andj c (77 K) were 87.5±0.2 K and 〉1×106 A/cm2, respectively, across the full wafer area. This holds also for GaAs substrates due to a new procedure of capping by Si3N4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730401
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  • 4
    Electronic Resource
    Electronic Resource
    Temperature dependence of the infrared optical properties of YBa2Cu3O7: A plasmon damping model (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 481-483 
    Details
    ISSN: 1572-9605
    Keywords: High-T c superconductors ; YBa2Cu3O7 ; infrared ; plasmon ; resistivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The temperature dependence observed in the mid- and near-infrared optical properties of YBa2Cu3O7 is explained in terms of the Drude model for free charge carriers. In the Drude model, the linear temperature dependence of the dc resistivity arises from the free charge carriers having a temperature-dependent mean free path. This temperature dependence results in the plasmon contribution to the dielectric constant having a damping coefficient which also varies linearly with temperature. We find that the temperature dependence which is observed in the absorption and reflection spectra of YBa2Cu3O7 is consistent with this simple model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724594
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  • 5
    Electronic Resource
    Electronic Resource
    Theoretical study of isotope effect in La-doped Y-123 (1993)
    Springer
    Journal of superconductivity 6 (1993), S. 19-25 
    Details
    ISSN: 1572-9605
    Keywords: Isotope effects ; YBa2Cu3O7 ; Cooper pairing interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The recent oxygen isotope effect measurement made in the system YBa2-x La x Cu3O7 (0≤x≤0.5) is analyzed using the “two-carrier” model which describes a superconducting system as a mass anisotropic system consisting of charge carriers with two different masses as a result of lattice defects or oxygen deficiency. The extent to which Ba, Cu, and O atoms participate in the phonon-mediated Cooper pairing interaction is elucidated. The relationship between the theoretically deduced mass anisotropic factor andT c agrees closely with the experimental results of Uemuraet al. [28]. Furthermore, the superconducting energy gap toT c ratio is found to be close to 3.5. Excellent agreement is also achieved between the theoretically calculated oxygen isotopic constant and the experimental results of Bornemann and Morris [12].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618501
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  • 6
    Electronic Resource
    Electronic Resource
    Film thickness dependence of critical current density for YBa2Cu3O7 films post-annealed at a low oxygen partial pressure (1993)
    Springer
    Journal of superconductivity 6 (1993), S. 37-41 
    Details
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; critical current density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The variation of critical current density at 77 K as a function of film thickness was studied for YBa2Cu3O7 films on (100) LaAlO3 substrates. Film thicknesses were in the range 0.2–1.6μm. The films were deposited by co-evaporation and post-annealed under conditions which have previously resulted in high-quality films (750°C and an oxygen partial pressure of 29 Pa). The critical current density at 77 K exceeds 1 MA cm−2 for the thinner films, and decreases with increasing film thickness in excess of about 0.4μm. The decrease is in rough agreement with a switch fromc-axis toa-axis growth at about this critical thickness. A good anticorrelation was found between room temperature resistivity and critical current density at 77 K. The results are compared to those obtained before by post-annealing at 850°C in 1 atm of oxygen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618503
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  • 7
    Electronic Resource
    Electronic Resource
    Ultrasonic beam propagation through a bimetallic weld—A comparison of predictions of the Gauss-Hermite beam model and finite element method (1993)
    Springer
    Journal of nondestructive evaluation 12 (1993), S. 151-158 
    Details
    ISSN: 1573-4862
    Keywords: Beam propagation ; bimetallic weld ; Gauss-Hermite beam model ; finite element method ; ultrasonics ; anisotropic medium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In this paper, predictions of two models for the propagation of ultrasonic beams through a two-dimensional, bimetallic weld geometry are compared. The finite element method can predict beam propagation through quite general geometry with high accuracy. This model, however, requires significant computational time. On the other hand, the approximate Gauss-Hermite model offers considerably greater computational speed, but has lower accuracy in certain regions and cannot treat the most general geometries and inhomogeneities in material properties. This paper compares the performances of the two models for the case of the two-dimensional, bimetallic weld consisting of multiple layers, some of which have anisotropic properties. It is found that the results of the two models are in good agreement in the vicinity of the central ray, and that the deviation increases as one moves away from the axis. Also, as the beam propagates through multiple interfaces, the accuracy of the Gauss-Hermite solution decreases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00567571
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  • 8
    Electronic Resource
    Electronic Resource
    Delay fault simulation of sequential circuits (1993)
    Springer
    Journal of electronic testing 4 (1993), S. 131-135 
    Details
    ISSN: 1573-0727
    Keywords: Gate delay fault ; fault simulation ; robust test ; sequential circuit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This article proposes a 7-valued logic appropriate for test generation and fault simulation, in the area of robust tests for gate delay faults, and a straightforward simulation strategy for sequential circuits. It is shown that a purely qualitative logic of robust testing is inadequate for circuits with edge-triggered flip-flops. The relation between the 7-valued logic and the similar logic proposed before by Smith, Schulz et al., and Lin and Reddy are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00971642
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  • 9
    Electronic Resource
    Electronic Resource
    A fault simulation method: Parallel pattern critical path tracing (1993)
    Springer
    Journal of electronic testing 4 (1993), S. 255-265 
    Details
    ISSN: 1573-0727
    Keywords: Critical path tracing ; fault simulation ; parallel pattern simulation ; single fault propagation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We present a fast fault simulation algorithm for combinational circuits which combines parallel pattern evaluation and critical path tracing. When the number of faults is large, our algorithm exploits the full advantages of critical path tracing. As fault dropping progresses, the overhead for critical path tracing surpasses its advantages. On the other hand, the efficiency of Parallel Pattern Single Fault Propagation (PPSFP) increases rapidly since relatively few undetected faults remain, and they tend to be inactive. To avoid the overhead of critical path tracing and achieve the advantages of PPSFP, dynamic update of node classes is used to produce a smooth transition from critical path tracing to PPSFP. By using this approach, we get high performance for both small and large numbers of test patterns. Also, preprocessing related to structure analysis is avoided while achieving almost all of its advantages.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00971974
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  • 10
    Electronic Resource
    Electronic Resource
    A comparative study of transient waves in random (polycrystalline) media (1992)
    Springer
    Journal of nondestructive evaluation 11 (1992), S. 9-17 
    Details
    ISSN: 1573-4862
    Keywords: Casuality ; effective medium ; ultrasonics ; polycrystalline medium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The paper investigates the transient response of a random medium as predicted by two methods, a perturbation scheme and a causal approach. It is shown by direct computation of a pulse propagation that the perturbation scheme yields an “advanced” response inconsistent with the physical realizability of the medium. The causal model as well as a modified perturbation scheme exhibit a physically reasonable behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566013
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  • 11
    Electronic Resource
    Electronic Resource
    Ultrasonic flaw classification in weldments using probabilistic neural networks (1992)
    Springer
    Journal of nondestructive evaluation 11 (1992), S. 69-77 
    Details
    ISSN: 1573-4862
    Keywords: Welds ; flaw classification ; ultrasonics ; neural networks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A probabilistic neural network is used here to classify flaws in weldments from their ultrasonic scattering signatures. It is shown that such a network is both simple to construct and fast to train. Probabilistic nets are also shown to be able to exhibit the high performance of other neural networks, such as feed forward nets trained via back-propagation, while possessing important advantages of speed, explicitness of their architecture, and physical meaning of their outputs. Probabilistic nets are also demonstrated to have performance equal to common statistical approaches, such as theK-nearest neighbor method, while retaining their unique advantages.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00568290
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  • 12
    Electronic Resource
    Electronic Resource
    Analysis of nonlinearly viscoelastic behavior of adhesive bonds (1992)
    Springer
    Journal of nondestructive evaluation 11 (1992), S. 221-226 
    Details
    ISSN: 1573-4862
    Keywords: Nonlinear viscoelastic behavior ; adhesive layers ; ultrasonics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The purpose of this paper is to provide a theoretical framework to study the nonlinear viscoelastic behavior of adhesive layers. The stress-strain behavior of the adhesive material in shear is assumed to have a nonlinear elastic part and a linear viscoelastic part, i.e., σ yx =f(ε yx )+K mεyx. To measuref(ε yx ) andK m by an ultrasonic technique, it is proposed to prestress the adhesive layer in the nonlinear range and to superimpose a small amplitude ultrasonic signal. The reflected field is used to obtain the wave speed and hencedf(ε yx )/dε yx as a function of the pre-stress. The viscoelastic parameter is obtained from the amplitude decay. By repeating this procedure for various values of prestress and using numerical integration, the stress-strain behavior of the adhesive layer can be reconstructed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566412
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  • 13
    Electronic Resource
    Electronic Resource
    Dynamic effects in the detection of bridging faults in CMOS ICs (1992)
    Springer
    Journal of electronic testing 3 (1992), S. 197-205 
    Details
    ISSN: 1573-0727
    Keywords: Bridging faults ; fault models ; fault simulation ; test invalidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Dynamic effects in the detection of bridging faults in CMOS circuits are taken into account showing that a test vector designed to detect a bridging may be invalidated because of the increased propagation delay of the faulty signal. To overcome this problem, it is shown that a sequence of two test vectors 〈 T 0, T 1 〉, in which the second can detect a bridging fault as a steady error, can detect the fault independently of additional propagation delays if T0 initializes the faulty signal to a logic value different from the fault-free one produced by T 1. This technique can be conveniently used both in test generation and fault simulation. In addition, it is shown how any fault simulator able to deal with FCMOS circuits can be modified to evaluate the impact of test invalidation on the fault coverage of bridging faults. For any test vector, this can be done by checking the state of the circuit produced by the previous test vector.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00134730
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  • 14
    Electronic Resource
    Electronic Resource
    Vapor pressures of Y, Ba, Cu precursors for the growth of YBa2Cu3O7 by MOVPE (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 119-125 
    Details
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; MOVPE ; vapor pressures ; β-diketonates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The vapor pressures of theβ-diketonates Y(THD), Ba(THD), and Cu(THD), commonly used as precursors for MOVPE of YBa2Cu3O7, and Y(MCP) were measured at different temperatures. A time-resolved static method recording the pressure vs. time at constant temperature was used, permitting us to deduce the vapor pressure even if the materials tend to decompose. The values of the constants of the Clausius-Clapeyron equation log10p(T)/p 0=A-B/T are,A=11.7, 8.7, 8.27, 16.6 andB=4359, 2654, 3602, and 6453 K for Y(THD), Y(MCP), Ba(THD), and Cu(THD), respectively withp 0= 1 Pa and temperatureT in K. The thermal stability of the sources was measured and are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618055
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  • 15
    Electronic Resource
    Electronic Resource
    Critical current density and microstructure of YBa2Cu3O7 thin films post-annealed at a low oxygen partial pressure (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 143-147 
    Details
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; critical current density ; microstructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Post-annealing of thin films of YBa2Cu3O7 (YBCO) has been performed at 29 Pa and 750°C. For films 0.6 μm thick, a critical current density 〉1 MA cm−2 is obtained at 77 K, with a sharp eddy current response at 25 MHz. Microstructural investigation of these films by crosssectional and planar transmission electron microscopy reveals that the YBCO film has thec-axis normal to the plane of the substrate in a continuous sheet of varying thickness, frequently covering the entire thickness of the film. Mutually perpendicular rods with thec-axis in the plane of the LaAlO3 substrate are also seen. The microstructure and critical current density of these films are compared with those of previously reported films post-annealed in atmosphericpressure oxygen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618058
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  • 16
    Electronic Resource
    Electronic Resource
    Process monitoring during post-annealing of YBa2Cu3O7 thin films containing fluorine (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 167-170 
    Details
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; post-annealing ; process monitoring
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The post-annealing method of producing thin films of YBa2Cu3O7 (YBCO) has taken on a new impetus due to the recent work showing that films of the highest quality can be made by using low partial pressures of oxygen during the annealing cycle. Here it is shown that for films produced by using BaF2 as a source material, the post-annealing procedure can be closely controlled by monitoring the F that evolves due to the water vapor reaction with BaF2. The use of an ion-sensitive electrode allowed small F evolution rates (about 1 ng s−1) to be detected above background, sufficient to measure the F evolution rate from even the smallest samples used. The time interval during which F evolves was found to increase with increasing YBCO film area being annealed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618062
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  • 17
    Electronic Resource
    Electronic Resource
    Elastic wave propagation with kinematic discontinuity along a non-ideal interface between two isotropic elastic half-spaces (1991)
    Springer
    Journal of nondestructive evaluation 10 (1991), S. 39-53 
    Details
    ISSN: 1573-4862
    Keywords: Elastic wave propagation ; nondestructive evaluation ; ultrasonics ; bonded material inspection ; adhesive bonds ; interfaces
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The problem of wave propagation along the interface between two elastic, isotropic, and homogeneous half-spaces is studied when the half-spaces are coupled through a vanishingly thin layer of Voigt material. It is assumed that the separation, 2H, between the half-spaces, and the complex rigidity-modulus, μ, of the layer are both vanishingly small, but the complex quantity μ/2H remains finite. In a series of experiments in which two blocks of elastic materials with or without lubricant/couplant at the interface are subjected to an external load normal to the interface, the variation of the speed and attenuation of interfacial waves, generated and detected by piezoelectric transducers, was measured as a function of external load. Assuming a nonlinear relation between external load and μ/2H, the experimental data is interpreted theoretically, and the best-fit parameters of the nonlinear relation are determined. For the 13 cases of interfaces studied, with or without lubricant/couplant, satisfactory agreement was found between experiment and theory, except in one case. Even in this case, the agreement is satisfactory in the lower range of load. It is hoped that this study will be useful in developing nondestructive methods of testing the bonding conditions at an interface between elastic materials by means of interfacial wave properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00568099
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  • 18
    Electronic Resource
    Electronic Resource
    On the boundary conditions for ultrasonic transmission by partially closed cracks (1991)
    Springer
    Journal of nondestructive evaluation 10 (1991), S. 139-149 
    Details
    ISSN: 1573-4862
    Keywords: Closed cracks ; ultrasonics ; reflection and transmission ; coefficients ; effective boundary conditions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The probability of detecting crack-like defects using ultrasonic techniques can be severely reduced if the crack is closed by a static background pressure. In this paper, we model the contacting faces of a partially closed crack by an array of circular spot-welds randomly distributed over an infinite plane. We give an exact derivation of the reflection and transmission coefficients for a plane elastic wave at such a boundary in terms of the mean interfacial stresses. The latter are estimated in the limit when the contact radius is much smaller than the wavelength and the contacts are sparsely distributed. This calculation is then related to a distributed spring model of the interface. The latter replaces the real interface by an effective homogeneous linear boundary condition which relates the crack opening displacement to the boundary stresses by effective stiffnesses. These unknown parameters are chosen to ensure that the model condition predicts the exact values of the mean interfacial stresses and the reflection and transmission coefficients in the limit already described. Our results are consistent with and complement those of Baik and Thompson(1) who introduced the distributed spring model in this and a number of other contexts. Our analysis provides a systematic assessment of the range of validity of the model and suggests ways in which the present estimates may be improved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00567096
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  • 19
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    Fault simulation for general FCMOS ICs (1991)
    Springer
    Journal of electronic testing 2 (1991), S. 181-190 
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    ISSN: 1573-0727
    Keywords: bridging faults ; CMOS circuits ; critical path analysis ; fault simulation ; stuck-open faults
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This work presents a technique to correctly deal with non-stuck-at faults in FCMOS circuits making use of complex macrogates. This method can be applied to any gate-level fault simulator providing, for each line of the circuit, the observability status that is directly related to that of individual devices in the actual macrogate implementation. Conductance conflicts are correctly solved to detect bridgings and transistors stuck-on. Fault coverage results are presented and discussed for two typical FCMOS circuits. Results obtained on all ISCAS benchmarks show that the time required for the fault simulation of CMOS faults is comparable to that of stuck-ats.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00133502
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  • 20
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    On behavior fault modeling for digital designs (1991)
    Springer
    Journal of electronic testing 2 (1991), S. 135-151 
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    ISSN: 1573-0727
    Keywords: behavior model ; fault coverage correlation ; fault model ; fault simulation ; stuck-at fault
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A critical aspect of digital electronics is the testing of the manufactured designs for correct functionality. The testing process consists of first generating a set of test vectors, then applying them as stimuli to the manufactured designs, and finally comparing the output response with that of the desired response. A design is considered acceptable when the output response matches the desired response and is rejected otherwise. Fundamental to the process of test vector generation is the assumption of an underlying fault model that is a model of the failures introduced during manufacture. The choice of the fault model influences the accuracy of testing and the computer CPU time required to generate test vectors for a given design. The most popular fault model in the industry today is the single stuck-at fault at the gate level that requires exorbitantly large CPU times for moderately complex digital designs. This article introduces new high-level behavior fault models that are associated with high-level hardware descriptions of digital designs. The derivation of these faults is based on the failure modes of the language constructs of the high-level hardware description language. Behavior faults include multiple input stuck-at faults and this article also reasons the nature of test vectors for such faults. The potential advantages of behavior fault modeling include early estimates of fault coverage in the design process prior to the synthesis of the gate-level representation of the design, faster fault simulation, and results that may be more comprehensible to the high-level architects. The behavior-fault-modeling approach is evaluated through a study of correlation of the results of behavior fault simulation of several representative digital designs with the results of gate-level single stuck-at fault simulation of equivalent gate-level representations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00133499
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  • 21
    Electronic Resource
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    Fault simulation using small fault samples (1991)
    Springer
    Journal of electronic testing 2 (1991), S. 191-203 
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    ISSN: 1573-0727
    Keywords: Bayesian estimation ; confidence level ; fault simulation ; sampling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This article emphasizes simulation-based sampling techniques for estimating fault coverage that use small fault samples. Although random testing is considered to be the primary area of application of the technique it is also suitable for estimating the fault coverage of nonrandom tests based on specific fault models. Especially for fault coverages exceeding 95%, it is shown that a precise estimate can be obtained using a fault sample of only 500 faults. The estimation is based on a binomial approximation of the probability density of the sample fault coverage. Using Bayes statistics an estimate is obtained whose accuracy is a linear function of the sample size if the fault coverage approaches 100%. The sample size is independent of the circuit size, thus making fault sampling particularly interesting for the fault simulation of ULSI designs due to the resulting reduction of the time complexity of fault simulation from O(N 2) to O(N).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00133503
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  • 22
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    A characterization of robust test-pairs for stuck-open faults (1991)
    Springer
    Journal of electronic testing 1 (1991), S. 275-286 
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    ISSN: 1573-0727
    Keywords: fault simulation ; robust tests ; stuck-open faults ; test generation algorithms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Tests for stuck-open faults in static CMOS circuits consist of a sequence of two input vectors. Such test-pairs may be invalidated by delays in the circuit. Test-pairs that are not invalidated by delays in the circuit are known as robust test-pairs. We present a six-valued logic system Ω = {0, 1, r, f, 0h, 1h}. We show how Ω differs from a number of other logic systems that have been proposed for test generation. This logic system abstracts the important aspects of the transition behavior of the circuit, on application of an input pair, that is necessary to characterize robust test-pairs for stuck-open faults. This characterization of robust test-pairs is used to derive: (i) an algorithm for determining if a given test-pair is a robust test-pair for a given stuck-open fault or not; and (ii) a simplified algorithm for computing a robust test-pair for a stuck-open fault. The resulting algorithm for computing robust tests for stuck-open faults can be implemented by minor modifications to test generation algorithms for stuck-at faults.
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    URL: http://dx.doi.org/10.1007/BF00136316
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    Reproducibility of transition temperature and critical current density of thin films of YBa2Cu3O7 on (100) LaAlO3 (1991)
    Springer
    Journal of superconductivity 4 (1991), S. 61-65 
    Details
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; critical current ; LaAlO3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Submicrometer epitaxial films of YBa2Cu3O7(YBCO) on (100) LaAlO3 were made by coevaporation and furnace annealing. Samples from more than a dozen runs are used in this study. The zero resistance transition temperature (T c) is high (89 or 90 K) if the film composition is phase pure (Ba/Y=2, Cu/Y=3) or if it is enriched in Ba and Cu. For these compositions the critical current density (J c) at 77 K has an average value of 2×105 A cm−2, with a tendency for decreasingJ c with increasing film thickness (0.2 to 0.8μm). Variations inJ c are not correlated with deviations from ideal stoichiometry. Steeper slopes of the resistance-temperature curves above 100 K and lower values of the room-temperature resistivity are associated with high values ofJ c. If the film composition is enriched in Y relative to Ba and Cu,T c decreases by several degrees.
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    URL: http://dx.doi.org/10.1007/BF00618299
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    Microwave properties of highly oriented YBa2Cu3O7-δ superconducting thin films (1991)
    Springer
    Journal of superconductivity 4 (1991), S. 253-257 
    Details
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; microwave properties ; R s
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have performed millimeter-wave frequency (94 GHz) measurements on high-quality YBa2Cu3O7-δ superconducting films on yttrium-stabilized (100) ZrO2 and MgO substrates. The ∼0.2μm thin films fabricated by magnetron sputteringin situ with the YBa2Cu3O7-δ powders as target exhibit superconducting transition temperatures up to 88 K. The critical current density of 6×105 A/cm2 at 77 K and the X-ray diffraction spectrum as well as scanning electron microscope photographs indicate these thin films are fullyc-axis oriented, extremely high in density, and universally homogeneous. Millimeter-wave surface resistances have been measured on a hemisphere open resonator in the temperature range of 20 K toT c and beyond. The surface resistance at 94 GHz and 77 K for these films is found to be about 30 mΩ, nearly 1/4 that for copper, and a drop of two orders in the surface resistance within 4 K is observed, which indicates that these films are good materials for applications in the millimeter-wave range, especially for fabricating microwave devices. We observed such low surface resistance in these thin films due to the near absence of grain and phase boundaries coupled with a high degree of crystalline orientation.
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    URL: http://dx.doi.org/10.1007/BF00618145
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    Optimization of annealing temperature for YBa2Cu3O7 thin films post-annealed at a low oxygen partial pressure (1991)
    Springer
    Journal of superconductivity 4 (1991), S. 279-282 
    Details
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; annealing temperature ; LaAlO3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Post-annealing of YBa2Cu3O7 (YBCO) thin films is usually performed at 850–900°C in atmospheric-pressure oxygen. In this study, coevaporated YBCO films on LaAlO3 were post-annealed in an oxygen partial pressure of 29 Pa at temperatures in the range 700–825°C. Zero resistance transition temperatures were 89–90 K. Both d.c. (room-temperature resistance and critical-current density) and a.c. parameters (extracted from eddy-current response measurements at 25 MHz) were monitored. The optimum temperature is close to 750°C, which is on the YBCO thermodynamic stability line at this low oxygen partial pressure.
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    URL: http://dx.doi.org/10.1007/BF00618149
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    Laser-based ultrasonics on Gr/epoxy composite (1990)
    Springer
    Journal of nondestructive evaluation 9 (1990), S. 229-238 
    Details
    ISSN: 1573-4862
    Keywords: Thermo-elasticity ; noncontact NDE ; photo-acoustics ; composite ; Gr/epoxy ; ultrasonics ; cscan ; array
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Critical issues are examined in the application of laser generation and detection of ultrasound to the inspection of large area air-frame composites. Among these issues are surface roughness, signal-to-noise ratio, insensitivity to the path length between the part and detector, and wide band vs. narrow-band generation. Demonstrated is the feasibility of transmission C-scans of 150 ply Gr/epoxy panels containing simulated delaminations. Waveforms having a signal-to-noise ratio of greater than 40 dB in 15-mm thick Gr/epoxy were obtained with generating laser powers well below the ablation limit for the graphite epoxy. Detection was shot-noise limited with a detector noise figure of about 5–10 dB.
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    URL: http://dx.doi.org/10.1007/BF00565641
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    Differential fault simulation for sequential circuits (1990)
    Springer
    Journal of electronic testing 1 (1990), S. 7-13 
    Details
    ISSN: 1573-0727
    Keywords: fault simulation ; sequential circuits ; test generation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A new fast fault simulation algorithm called differential fault simulation, DSIM, for synchronous sequential circuits is described. Unlike concurrent fault simulation, for every test vector, DSIM simulates the good machine and each faulty machine separately, one after another, rather than simultaneously simulating all machines. Therefore, DSIM dramatically reduces the memory requirement and the overhead in the memory management in concurrent fault simulation. Also, unlike serial fault simulation, DSIM simulates each machine by reprocessing its differences from the previously simulated machine. In this manner, DSIM is more efficient than serial fault simulation. Experiments have shown that DSIM runs 3 to 12 times faster than an existing concurrent fault simulator. In addition, owing to the simplicity of this algorithm, DSIM is very easy to implement and maintain. An implementation consists of only about 300 lines of “C” language statements added to the event-driven true-value simulator in an existing sequential circuit test generator program, STG3. Currently DSIM uses the zero-delay timing model. The addition of alternative delay models is under development.
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    URL: http://dx.doi.org/10.1007/BF00134011
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    Hierarchical multi-level fault simulation of large systems (1990)
    Springer
    Journal of electronic testing 1 (1990), S. 139-149 
    Details
    ISSN: 1573-0727
    Keywords: fault simulation ; multilevel simulation ; testing ; VLSI design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract This article discusses an approach for hierarchical multilevel fault simulation for large systems described at the transistor, gate, and higher levels. The approach reduces the memory requirement of the simulation drastically, thus allowing the simulation of circuits that are too large to simulate at one flat level on typical engineering workstations. This is achieved by exploiting the regularity and modularity found in a hierarchical circuit description that contains many repeated substructures. The hierarchical setup also allows flexible multilevel simulation: behavioral models can replace subcircuits at any level of the hierarchy for accelerated simulation. The simulation algorithms are at the switch level so that general MOS digital designs with bidirectional signal flow can be handled, and both stuck-at and transistor faults are treated accurately. The approach has been implemented in the hierarchical logic and fault simulation system, CHAMP, that runs under UNIX on SUN-3 and SUN-4 workstations. It has been used successfully for simulating and fault grading a large commercial microprocessor.
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    URL: http://dx.doi.org/10.1007/BF00137390
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    Extended selection of switching target faults in CONT algorithm for test generation (1990)
    Springer
    Journal of electronic testing 1 (1990), S. 183-189 
    Details
    ISSN: 1573-0727
    Keywords: D-algorithm ; fault simulation ; fault target switching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We describe an extended selection of switching target faults in the CONT algorithm. The main difficulty in test generation is the conflict that arises in the process of determining the signal values due to reconvergent fanouts. Conventional approaches for test generation change a signal value, which causes conflicts to another possible choice for backtracking. In the CONT algorithm, a strategy of switching target fault was proposed as a new backtracking mechanism. In this method, the target fault is switched to a new target fault instead of making an alternative assignment on the primary input value when a conflict occurs. A disadvantage of the CONT algorithm is that unjustified lines exist in the process of test generation. These unjustified lines make the procedure of switching targets complicated and restrict the possible choice in selecting the new target fault. In the new version of CONT, called CONT-2, we have removed the unjustified lines in the process of test generation and have extended to two target-fault types for switching targets. Implementing CONT-2 by a Fortran program, ISCAS85 benchmark circuits are examined. Experiments on a combined system with fault simulation followed by CONT-2 are also presented.
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    URL: http://dx.doi.org/10.1007/BF00153855
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    Extended selection of switching target faults in CONT algorithm for test generation (1990)
    Springer
    Journal of electronic testing 1 (1990), S. 183-189 
    Details
    ISSN: 1573-0727
    Keywords: D-algorithm ; fault simulation ; fault target switching
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract We describe an extended selection of switching target faults in the CONT algorithm. The main difficulty in test generation is the conflict that arises in the process of determining the signal values due to reconvergent fanouts. Conventional approaches for test generation change a signal value, which causes conflicts to another possible choice for backtracking. In the CONT algorithm, a strategy of switching target fault was proposed as a new backtracking mechanism. In this method, the target fault is switched to a new target fault instead of making an alternative assignment on the primary input value when a conflict occurs. A disadvantage of the CONT algorithm is that unjustified lines exist in the process of test generation. These unjustified lines make the procedure of switching targets complicated and restrict the possible choice in selecting the new target fault. In the new version of CONT, called CONT-2, we have removed the unjustified lines in the process of test generation and have extended to two target-fault types for switching targets. Implementing CONT-2 by a Fortran program, ISCAS85 benchmark circuits are examined. Experiments on a combined system with fault simulation followed by CONT-2 are also presented.
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    URL: http://dx.doi.org/10.1007/BF00938681
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    The low magnetic field properties of superconducting bulk yttrium barium copper oxide-sintered versus partially melted material (1989)
    Springer
    Journal of superconductivity 2 (1989), S. 427-461 
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    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; a.c. susceptibility ; magnetic field effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A comparison of the low magnetic field properties of sintered (990°C) and partially melted samples (1050°C) has been performed. Changes in the microstructure produced by recrystallization from the melt result in a significant increase in flux pinning at 77 K. Low-frequency (10–100 Hz), low-a.c. magnetic field (0.01–9.0 Oe) a.c. susceptibility data show that gross changes in the a.c. loss component accompanies the observed changes in microstructure. The effects of applied d.c. magnetic fields (10–220 Oe) on the a.c. responses of these microstructures have also been probed. Data are analyzed and critically discussed in terms of current models appropriate for granular superconductors and in terms of older models appropriate for metallic alloys and compounds. Particular attention is given to published interpretations of the in-phase or loss component of the a.c. magnetic susceptibility and to the possible roles which minority phases and sample inhomogeneities may play in determining the detailed a.c. responses of these high-T coxides.
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    Analysis of electronic structure and charge density of the high-temperature superconductor YBa2Cu3O7 (1988)
    Springer
    Journal of superconductivity 1 (1988), S. 111-141 
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    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; electronic band structure ; LAPW method ; density of states ; Fermi surface ; Coulomb potential ; charge density ; electron-phonon interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Self-consistent linearized augmented plane wave (LAPW) method calculations of the band structure, density of states, Fermi surface, Coulomb potential, charge density, core-level shifts, and electron-phonon interaction are presented for Y1Ba2Cu3O7. The calculated Sommerfield parameterγ is 4.35 mJ(mole Cu)−1 K−2, roughly about a factor of 2 smaller than experimentally deduced values of the enhanced valueγ=(1 + λ)γ0, suggesting that the Fermi surface mass enhancement is of the order of unity. The crystal charge density is best represented by overlapping spherical ionic densities when the Cu and O ions are assigned charges of +1.62 and −1.69, respectively, corresponding to about 0.3 holes per oxygen atom. Core-level energies for the inequivalent atoms differ by as much as 0.45 eV for Cu and 0.7 eV for O, amounts which may be detectable by core-level spectroscopies. These results provide important information on the character and magnitude of ionic contributions to bonding in these materials. Within the rigid muffin-tin approximation, calculated McMillan-Hopfield parameters yield estimates for the electron-phonon strength λ that appear to be too small to account for the observedT c. We point out an unusual band of oxygen-derived chain states below, but within 0.1 eV of, the Fermi level.
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    URL: http://dx.doi.org/10.1007/BF00617955
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    Ultrasonic reflection by a planar distribution of cracks (1988)
    Springer
    Journal of nondestructive evaluation 7 (1988), S. 123-129 
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    ISSN: 1573-4862
    Keywords: Diffusion bonds ; reflection ; ultrasonics ; cracks ; stress-intensity factors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Ultrasonic wave reflection and transmission by planar crack distributions is considered. General expressions for the reflection and transmission coefficients are derived for incident longitudinal and transverse time harmonic plane waves. For low frequencies, closed-form algebraic expressions are given in terms of the geometrical parameters, the material constants, and the incident wavefield. The results have been extended to statistical distributions, and reflection coefficients for equivalent statistical and deterministic distributions of penny-shaped cracks are compared. It is also shown that the Mode-I stress-intensity factor for a distribution of equal-sized cracks can be directly related to reflection data.
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    URL: http://dx.doi.org/10.1007/BF00565997
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    Interfacial phenomena and microstructural connectivity in explosively fabricated Y-Ba-Cu-O superconductors (1988)
    Springer
    Journal of superconductivity 1 (1988), S. 3-19 
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    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; explosive consolidation ; SEM ; TEM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Measurements of supercurrent transport and current density in explosively fabricated superconducting prototypes have been erratic, with current densities measured to be in excess of 103 A/cm2. This erratic behavior appears to be related to the degree of consolidation achieved for Y-Ba-Cu-O powders and, more specifically, to the connectivity or interfacial structure at individual, contacting, superconducting particles. We have used SEM and TEM to characterize and illustrate some of these features in preliminary superconducting prototypes composed of Y-Ba-Cu-O powder channels consolidated and encapsulated in copper and aluminum matrices by explosively generated shock waves. Observations of grain boundaries and interface phase regions cast some light on the prospects for producing good connectivity through optimizing the consolidation process and process parameters as well as the elimination of surface reactions on particles prior to consolidation, or thermal effects during consolidation.
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    URL: http://dx.doi.org/10.1007/BF00617947
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    Processing of single-phase ceramic 123 YBaCu-oxide superconductor by hot pressing (1988)
    Springer
    Journal of superconductivity 1 (1988), S. 45-52 
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    ISSN: 1572-9605
    Keywords: YBa2Cu3O7 ; hot pressing ; electrical resistivity ; critical current density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract High-quality, single-phase, polycrystalline samples of high-temperature superconducting 123 YBaCu-oxide have been processed by hot pressing of specially prepared charge material at elevated temperatures. The samples are orthorhombic with unit cell dimensionsa = 3.824(1) Å,b = 3.888(1) Å, andc = 11.679(2) Å. They exhibit: (i) densities up to 82% of the theoretical value; (2) a sharp phase transition between the normal and superconducting states at 91.6 K; (3) a reduced dependence on thermal cycling effects and on excitation currents in resistivity measurements; and (4) a reduction in surface deterioration due to water, air, and acid attack. The hot-pressed samples supported current densities at least two orders of magnitude greater than those found in cold-pressed samples measured under similar conditions.
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    URL: http://dx.doi.org/10.1007/BF00617950
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    Effects of the structure of the Fermi surface on the normal and superconducting parameters of the high-Tc oxide superconductors (1988)
    Springer
    Journal of superconductivity 1 (1988), S. 143-151 
    Details
    ISSN: 1572-9605
    Keywords: La1.8Sr0.2CuO4 ; YBa2Cu3O7 ; Fermi surface ; multiband structure ; coherence length ; effective mass ; Fermi energy ; Fermi velocity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have described the major features of the Fermi surfaces of the high-Tc cuprates. The description in momentum space and use of Fermiology allows us to analyze the large anisotropy and multiband structure of the new materials. These properties are crucial because of the extremely small values of the coherence length. The Fermi surface can be reconstructed with the use of experimental data. Based on this method, we have evaluated the parameters such as effective mass, Fermi energy, Fermi velocity, and coherence length and estimated them for La1.8Sr0.2CuO4 and Y1Ba2Cu3O7 with the use of heat capacity and Hall effect measurements.
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    Microwave absorption in high-T c superconductors (1988)
    Springer
    Journal of superconductivity 1 (1988), S. 165-174 
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    ISSN: 1572-9605
    Keywords: microwave ; surface impedance ; highT c ; La2CuO4 ; YBa2Cu3O7
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We have investigated the 9- and 10-GHz microwave properties of bulk samples of strontium and barium substituted La2CuO4 and YBa2Cu3O7 and one YBa2Cu3O7 MBE film on SrTiO3. Anomalous microwave absorption is seen especially for poorly compacted bulk ceramic samples. Transitions were generally broadened nearT c and the residual losses were high. The real part of the surface impedance could be fit belowT c to the empirical equation with an added term linear in temperature. The microwave response of the film was masked by paraelectric absorption and acoustic resonances in the substrate.
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    ORCHID—A computer simulation of the reliability of an NDE inspection system (1987)
    Springer
    Journal of nondestructive evaluation 6 (1987), S. 23-31 
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    ISSN: 1573-4862
    Keywords: NDE ; inspection systems ; reliability ; probability of detection ; computer simulation ; eddy current ; ultrasonics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract CANDU pressurized heavy water reactors contain several hundred horizontally-mounted zirconium alloy pressure tubes. Following a pressure tube failure, a pressure tube inspection system called CIGARette was rapidly designed, manufactured and put in operation. Defects called hydride blisters were found to be the cause of the failure, and were detected using a combination of eddy current and ultrasonic scans. A number of improvements were made to CIGARette during the inspection period. The ORCHID computer program models the operation of the delivery system, eddy current and ultrasonic systems by imitating the on-reactor decision-making procedure. ORCHID predicts that during the early stage of development, less than one blistered tube in three would be detected, while less than one in two would be detected in the middle development stage. However, ORCHID predicts that during the late development stage, probability of detection will be over 90%, primarily due to the inclusion of axial ultrasonic scans (a procedural modification). Rotational and axial slip could severely reduce probability of detection. Comparison of CIGARette's inspection data with ORCHID's predictions indicate that the latter are compatible with the actual inspection results, though the numbers are small and data uncertain. It should be emphasized that the CIGARette system has been essentially replaced with the much more reliable CIGAR system.
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    URL: http://dx.doi.org/10.1007/BF00566694
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    Concrete strength ultrasonic digital tester (1986)
    Springer
    Journal of nondestructive evaluation 5 (1986), S. 157-160 
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    ISSN: 1573-4862
    Keywords: NDE of concrete ; ultrasonics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract This paper describes the design and construction of a concrete strength ultrasonic digital meter. The method depends on the transmission and reception of two ultrasonic sinusoidal signals. These two signals are so processed so as to yield a digital output number representative of the speed of propagation through the concrete specimen. This velocity figure can be related to the applications on finding the concrete crush strength, concrete crack depth, as well as the concrete behavior with electrical curing temperature. The electronic system employs Complementary-Oxide Semiconductor logic circuits and hybrid conversion circuits. It consumes such a little power, which makes such a design transportable and hence a battery operated device.
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    URL: http://dx.doi.org/10.1007/BF00570624
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    Ultrasonic characteristics of graphite/epoxy composite material subjected to fatigue and impacts (1986)
    Springer
    Journal of nondestructive evaluation 5 (1986), S. 119-131 
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    ISSN: 1573-4862
    Keywords: graphite/epoxy ; composites ; ultrasonics ; stress wave factor ; fatigue life ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Fiber-reinforced composites, because of their superior specific strengths and stiffnesses, are used in many aircraft components. However, in this application these composites are subjected not only to fatigue loading, but to occasionally high velocity impact due to the bird injection, hail, dust, and rain. Thus, it is important to evaluate the residual life and degradation due to combined fatigue and impact loadings. Unidirectional graphite epoxy composites (MA8276-Tiger) which are used in the aerospace industry were impacted by a free falling weight at energy levels of 0.567j, 1.134j, and 1.571j [impact energy toughness (j/cm3); 0.12, 0.24, 0.34], respectively. The subsequent changes/degradation in elastic moduli, strength, toughness, and fatigue properties were measured after different number of impacts. It was found that for all energy levels these properties vary linearly with the number of impacts. Furthermore, attenuation changes is not a good ultrasonic parameter for degradation estimation, since it does not incorporate the micro- and macrocracks beyond the impact point. However, these micro- and macrocracks have significant effect on the mechanical properties. In contrast to the attenuation, the stress wave factor, which indicates the efficiency of wave propagation along the specimen, correlates very well with degradation, and it can be used effectively to measure the residual strength after impact. Ultrasonic characteristic on specimens subjected to combined fatigue and impact were also studied. Based on these experiments, it is concluded that the loss in fatigue residual life due to impact loads may be predicted by measuring the effects of the impact load on attenuation and stress wave factor. It was found that the reduction in fatigue life is proportional to sudden changes in attenuation and stress wave factor. Damage accumulation models based on Coffin-Manson equation, was suggested for impact and combined fatigue and impact. It was found that residual properties and fatigue life can be estimated from these models.
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    Ultrasonic crack characterization via a constrained inversion algorithm (1985)
    Springer
    Journal of nondestructive evaluation 5 (1985), S. 37-43 
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    ISSN: 1573-4862
    Keywords: Kirchhoff approximation ; crack scattering ; ultrasonics ; NDE ; inverse scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The Kirchhoff approximation is used to show that the time domain impulse response of an isolated flat crack can be given a simple geometrical interpretation in terms of the derivative of a projected length function. For an elliptical crack, this derivative can be obtained explicitly to yield the two edge-diffracted waves which originate from the “flashpoints” of the crack. An explicit coordinate invariant expression is obtained from this elliptical crack solution which relates the time difference, Δt, between the arrival of these edge-diffracted waves and the crack size and orientation. Previously, we have proposed that this expression, together with Δt measurements in different scattering directions, could be used in a regression analysis as the basis for performing a constrained inversion of crack scattering data (i.e., where we attempt to obtain the “best” equivalent flat elliptical crack that fits the scattering measurements). Here we will demonstrate some results of applying the proposed algorithm using “noisy” synthetic data. The sensitivity of the results to both, number of measurements and transducer orientation, will be discussed.
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    Characterization of flaws using the zeroes of the real and imaginary parts of the ultrasonic scattering amplitude (1985)
    Springer
    Journal of nondestructive evaluation 5 (1985), S. 57-68 
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    ISSN: 1573-4862
    Keywords: Flaw sizing ; inverse Born approximation ; nondestructive evaluation ; ultrasonics ; zeroes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A new method for determining the size of flaws, such as cracks and voids, in structural materials is reported. The method is based on the observation that, for a wide class of flaws, the zeroes in the real and imaginary parts of the scattering amplitude occur at characteristic frequencies which depend on the flaw size. The method of reconstruction using the zeroes is simpler than the inverse Born approximation because the flaw sizes are extracted directly from the characteristic frequencies. The new method employs the same data input as the inverse Born algorithm and has certain common limitations. Following a theoretical treatment, experimental results are presented for a number of different types of flaws.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566956
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