| 1. |
- Lundberg, Bengt, et al.
(författare)
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Analysis of elastic waves in non-uniform rods from two-point strain measurement
- 1990
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Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 137:3, s. 483-493
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Tidskriftsartikel (refereegranskat)abstract
- A method is established which permits evaluation of the histories of normal force and particle velocity at an arbitrary cross-section E of a non-uniform linearly-elastic rod from measured strain histories at two different cross-sections, A and B. Other quantities at E, such as stress, strain, displacement, acceleration and power transmission, can be determined in terms of the evaluated normal force and particle velocity. The method is an extension of that developed by Lundberg and Henchoz for uniform rods. Theoretical results, based on one-dimensional elastic wave theory, are provided for the general case as well as for cases of piecewise constant characteritic impedance. Experimental tests with different configurations of non-uniform rods and strain gauges show that the normal force histories determined at E with the present method (from measured strains at A and B) agree well with those obtained through direct strain measurement at E.
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| 2. |
- Aidanpää, Jan-Olov, et al.
(författare)
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Periodic and chaotic behaviour of a threshold-limited two-degree-of-freedom system
- 1993
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 165:2, s. 305-327
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Tidskriftsartikel (refereegranskat)abstract
- A two-degree-of-freedom impact oscillator with proportional damping is considered. The maximum displacement of one of the masses is limited to a threshold value by a rigid wall, which gives rise to a non-linearity in the system. Impacts between the mass and the wall are described by a coefficient of restitution. The behaviour of the system is rich and includes features like period doublings, period havings, jumps, chaos, etc. Periodic motions of the system are studied by analytical methods. The influence of system parameters such as damping, coefficient of restitution, distribution of masses and clearance, etc., is studied for some extreme values of these parameters. The stability of a class of periodic motions is investigated. Parameter ranges which result in stable periodic multiple impacts are identified. Application of the results to the design of impact tools is discussed.
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| 3. |
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| 4. |
- Lundberg, Bengt, et al.
(författare)
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In Situ Determination Of The Complex Modulus From Strain Measurements On An Impacted Structure
- 1993
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 167:3, s. 413-419
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Tidskriftsartikel (refereegranskat)abstract
- A method is proposed for in situ determination of the complex modulus of a member of an impact-loaded structure. The modulus was obtained in terms of strains measured at three different cross-sections of a uniform part of the member, by using one-dimensional theory. The potential of the method was examined for a cylindrical polypropylene bar mounted as a member in each of two simple frame structures, and the modulus was obtained in the frequency range of 500 Hz to 3 kHz. For comparison, the modulus was also determined from tests on the same member, dismounted from the structures, by using a different method based on measurement of end-point accelerations. The results obtained from the in situ tests on the two frame structures and from the tests on the dismounted member are in fair agreement. The larger scatter in the results of the in situ tests is probably explained by a lower signal-to-noise ratio due to the use of strain gauges rather than accelerometers and to differences in excitation.
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| 5. |
- Ödeen, Sven, et al.
(författare)
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Determination of complex modulus from measured end-point accelerations of an impacted rod specimen
- 1993
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 165:1, s. 1-8
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Tidskriftsartikel (refereegranskat)abstract
- A method is presented for determination of the complex modulus of a linearly viscoelastic material from measured end-point accelerations of an impact-loaded rod specimen. An iterative numerical scheme was used. An approximate analytical solution was also established for the case of small accelerometer mass relative to the specimen mass. Tests were carried out at room temperature for polypropylene, with relatively high losses, and polyamide 6, with relatively low losses. Tests were also performed at temperatures between 20 and 140°C for the former material. Valid results were obtained in the approximate frequency range of 400 Hz to 200 kHz with specimen diameters between 11 and 21 mm, and specimen lengths between 200 and 800 mm. For polypropylene these results are in good agreement with those obtained by using a different method developed by Blanc. For polyamide 6, however, there was some disagreement for the imaginary part of the complex modulus. The method was convenient to use at elevated temperatures as well as at room temperature. It should be suitable for fast routine testing of materials provided that the losses are not too low.
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