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Showing papers by "Leif Kari published in 2008"


Journal ArticleDOI
TL;DR: In this article, the authors investigated the effect of varying the process parameters on the compacted material; the compactibility in the compaction bed, the uniformity of compacted surface, the pull-out phenomenon, the springback gradient, the stick-slip phenomenon and the homogeneity of the dispersions of nanoparticles in the polymer powders in the solid state.
Abstract: Compaction of polymer powders and polymer-based nanocomposites by uniaxial high-velocity cold compaction (HVC), by high-energy ball milling (HEBM) and using a novel technique, relaxation assists, was investigated with a focus on the process parameters, the compactibility characteristics, surface morphology and friction. The basic phenomena associated with HVC are explained and the general energy principle is introduced to explain the pull-out phenomenon, springback gradient, delay time, relative time of the pressure wave, and stick-slip phenomenon during the compaction process. Experimental results for different compaction profiles, different particle size distributions and different milling system for polymer-based nanocomposite are presented, showing the effect of varying the process parameters on the compacted material; the compactibility in the compacted bed, the uniformity of the compacted surface, the pull-out phenomenon, the springback gradient, the stick-slip phenomenon and the homogeneity of the dispersions of nanoparticles in the polymer powders in the solid state. It was found that the high-velocity compaction process is an interruption process and that the opposite velocity and pressure loss during the compaction process have a major influence on the quality of the compacted material. The relaxation assist device is a novel technique that has been successfully developed to improve the compaction process. The relaxation assists are parts of the piston and they are regarded as projectile supports. They are constructed of the same material as the piston, and the diameters are the same but the lengths are different. The relaxation assist device leads to an improvement in the compaction of powders, polymer powders and polymer-based nanocomposites by giving a more homogeneous opposite velocity and a better locking of the powder bed in the compacted form during the compaction process with less change in dimensions in the case of both homogeneous and heterogeneous materials. If the movement of the particles is restricted the powder bed attains a higher density and the total elastic springback is minimized. In addition, there is a more homogeneous dispersion of nanoparticles in the case of a heterogeneous material. A much better transfer of the pressure through the powder bed and a smaller loss of pressure lead to a more homogenous stick-slip of the particles and a higher sliding coefficient due to the overall friction during the compaction process.

26 citations


Journal ArticleDOI
TL;DR: In this paper, a magneto-sensitive rubber isolator inserted between a source and an infinite plate is modelled in the audible frequency range, and the energy flow into the plate with the rubber subjected to a magnetic field applied perpendicular to the axial displacement is calculated.
Abstract: A magneto-sensitive rubber isolator inserted between a source and an infinite plate is modelled in the audible frequency range, and the energy flow into the plate with the rubber subjected to a magnetic field applied perpendicular to the axial displacement is calculated. Subsequently the result is compared to the corresponding energy flow for zero magnetic induction; upon the application of an external magnetic field the rubber becomes stiffer, thus shifting the internal resonances of the isolator. This is a fast and reversible process enabling adaption of the isolator to rapidly changing audio frequency conditions by simply turning on and off a magnetic field. In the application example considered, the energy flow into the plate at the first internal dynamic peak stiffness frequency is reduced by approximately 7 dB—a large difference in a sound and vibration context—by inducing magnetic saturation of the rubber.

19 citations


Book ChapterDOI
08 Apr 2008

2 citations


01 Jan 2008
TL;DR: In this article, an indirect method for the dynamic stiffness of wire rope isolators in the audible frequency range, the stiffness dependence on static preload, vibration amplitude and frequency is resolved, and it is shown that although the stiffness is strongly dependent on the frequency, the peaks are rounded; indicating rather high damping.
Abstract: In presenting an indirect method for the dynamic stiffness of wire rope isolators in the audible frequency range, the stiffness dependence on static preload, vibration amplitude and frequency is resolved. It is shown that although the stiffness is strongly dependent on the frequency, the peaks are rounded; indicating rather high damping – contrary to those of ordinary steel springs – and, thus, is displaying similar behavior as rubber isolators. The main reason for the increased damping is the friction motion between the separate threads of the cable twist. Furthermore, the stiffness is independent on vibration amplitudes typically applied within the audible frequency range, while showing a substantially lower stiffness for significantly higher amplitudes, typically applied for low-frequency applications. Finally, the dynamic stiffness is displaying a strong static preload dependence; the higher the preload, the lower is the stiffness. In conclusion, wire rope isolators – typically applied for shock isolation and low-frequency applications – may also be suitable for noise and vibration applications within the audible frequency range, contrary to ordinary metal springs.

1 citations


Proceedings ArticleDOI
19 Jun 2008
TL;DR: In this article, a computer program is developed to analyze one-dimensional elasto-plastic wave propagation in nonlinear particle systems, where the system is modeled by a discrete element method where the particles exhibit elastic and plastic loading and elastic unloading during compaction.
Abstract: A computer program is developed to analyze one‐dimensional elasto‐plastic wave propagation in non‐linear particle systems The system is modeled by a discrete element method where the particles exhibit elastic and plastic loading and elastic unloading during compaction The particles system is set into motion by hitting a plunger at one end while the other end is blocked Results in form of elasto‐plastic wave front propagation versus time, its peak deformations and reflection from the blocked end are shown