| 1. |
- Wittmer, M., et al.
(author)
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Mechanical properties of liquid-phase-bonded copper-ceramic substrates.
- 1982
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In: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 65:3, s. 149-153
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Journal article (peer-reviewed)abstract
- Liquid-phase bonding of copper foils to ceramic substrates is a very attractive technique for the fabrication of metallized substrates for hybrid power electronics applications. The design and reliability considerations of such substrates necessitate the knowledge of their mechanical properties. Therefore, stresses and strains in the copper and in the ceramic of bonded substrates were investigated. Theoretical calculations are presented to support the experimental results.
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| 2. |
- Boström, Anders E, 1951, et al.
(author)
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Propagation of elastic surface waves along a cylindrical cavity and their excitation by a point force
- 1982
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In: Journal of the Acoustical Society of America. - 1520-8524 .- 0001-4966. ; 72, s. 998-1004
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Journal article (peer-reviewed)abstract
- The existence of surface wave modes, propagating along on infinite cylindrical cavity in an elastic medium, is established for every integer m, where m is the azimuthal mode number. These waves are analogous to the Rayleigh wave on a half-space, being confined to the immediate vicinity of the cavity. The modes exhibit dispersion and have a cutoff frequency that increases with m, except for the flexural (m=1) mode which exists at all frequencies. At cutoff the phase velocity is equal to that of the shear waves and decreases, with increasing frequency, to that of the Rayleigh wave. We present results for the group velocities and displacement and stress fields of the modes and also exhibit the effect of various point forces acting near the cavity. In the vicinity of the cavity, not too near the point force, the surface wave contribution dominates the total displacement field.
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| 3. |
- Boström, Anders E, 1951
(author)
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Surface waves on the periodic boundary of an elastic half space
- 1982
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In: Applied Scientific Research. - 0003-6994. ; 39, s. 129-142
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Journal article (peer-reviewed)abstract
- The existence of free surface waves on the periodic boundary of an elastic half space is established. These waves are a generalization of Rayleigh waves, and they can propagate both along and - at low frequencies and small profile heights - normal to the ridges of the periodic surface (periodic in one direction and constant in the other). It is shown how the wave number depends on the height and shape of the periodic surface, the frequency, and the direction of propagation. To give a further insight into the behaviour of the surface waves some computations of surface displacements are given
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| 4. |
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| 5. |
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| 6. |
- Gudmundson, Peter
(author)
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The dynamic behaviour of slender structures with cross-sectional cracks
- 1983
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In: Journal of the mechanics and physics of solids. - : Elsevier BV. - 0022-5096 .- 1873-4782. ; 31:4, s. 329-345
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Journal article (peer-reviewed)abstract
- A dynamic model for beams with cross-sectional cracks is discussed. It is shown that a crack can be represented by a consistent, static flexibility matrix. Two different methods for the determination of the flexibility matrix are discussed. If the static stress intensity factors are known, the flexibility matrix can be determined from an integration of these stress intensity factors. Alternatively, static finite element calculations can be used for the determination of the flexibility matrix. Both methods are demonstrated in the present paper. The mathematical model was applied to an edge-cracked cantilevered beam and the eigenfrequencies were determined for different crack lengths and crack positions. These results were compared to experimentally obtained eigenfrequencies. In the experiments, the cracks were modelled by sawing cuts. The theoretical results were, for all crack lengths, in excellent agreement with the experimental data. The dynamic stress intensity factor for a longitudinally vibrating, centrally cracked bar was determined as well. The results compared very well with dynamic finite element calculations. The crack closure effect was experimentally investigated for an edge-cracked beam with a fatigue crack. It was found that the eigenfrequencies decreased, as functions of crack length, at a much slower rate than in the case of an open crack.
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| 7. |
- Gudmundson, Peter
(author)
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Tuning of turbine blades : a theoretical approach.
- 1983
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In: Journal of engineering for power. - : ASME International. - 0022-0825. ; 105:2, s. 249-255
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Journal article (peer-reviewed)abstract
- A perturbation method is described which predicts the changes in eigenfrequencies resulting from geometrical changes of a structure. This dependence is represented by dimensionless functions, one for each eigenfrequency, which vary over the surface of the structure. The functions are presented for each eigenfrequency as isoline plots. The method was applied to a turbine blade and a rectangular beam.
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| 8. |
- Hoffelner, W., et al.
(author)
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A fracture mechanics analysis of ultrasonic fatigue
- 1982
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In: Engineering Fracture Mechanics. - 0013-7944 .- 1873-7315. ; 16:3, s. 365-371
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Journal article (peer-reviewed)abstract
- The method of ultrasonic fatigue finds increasing interest in materials science. Especially, fatigue crack growth rates near the threshold stress intensity range, Δ”K0, can be determined with this method in reasonable times providing no frequency and corrosion effects exist. But for an accurate application of this technique it is necessary to improve the testing systems and also the determination of the dynamic cyclic stress intensity range, Δ”K. In this paper, fatigue crack growth experiments at ultrasonic frequencies with different mean stresses and also the calculation of the dynamic stress intensity range with finite elements are treated. On this basis fatigue crack growth curves at room temperature of the alloys Hastelloy X and IN 800 were measured and compared with results obtained at low frequencies. No significant influence of frequency could be found in these materials.
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| 9. |
- Andersson, L-E, et al.
(author)
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Some fundamental transmission properties of impedance transitions
- 1984
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In: Wave motion. - : Elsevier BV. - 0165-2125 .- 1878-433X. ; 6:4, s. 389-406
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Journal article (peer-reviewed)abstract
- Reflection and transmission of waves by impedance transitions from a constant input to a constant output characteristic impedence are considered. Several fundamental properties are explored, primarily for impedance transitions with piece-wise constant characteristic impedance in an arbitrary number N of intervals of equal length. For example, the following properties are shown: (i) The relative momentum transmission depends only on the ratio of output to input characteristic impedance. (ii) For a given impedance transition there are at most, and generally exactly, 2N different transitions, including the original one, with identical transmission properties. (iii) For monotoneous impedance transitions the efficiency of energy transmission is minimized by one with an abrupt change in characteristic impedance. (iv) There exists an optimal impedance transition, with a certain antisymmetry, which maximizes the efficiency of energy transmission for a given incident wave of finite duration and energy. Several of the results can be extended to more general classes of impedence transitions. Simple illustrative examples are given.
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| 10. |
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