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Nov 1989

Volume 86, Issue S1, pp. S1-S125

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back to top Session Z. Structural Acoustics and Vibration III: Damping in Structural Systems
Contributed Papers
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Dynamic modulus measurements made with the dynamic mechanical thermal analyzer (A)

R. J. Deigan and J. J. Dlubac

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S63-S63 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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Polymer Laboratories' dynamic mechanical thermal analyzer (DTMA) measures the dynamic Young's or shear modulus and loss factor of viscoelastic materials. The DMTA infers the modulus and loss factor by measuring the response of a small sample to forced vibrations in a small material sample. An optimal sample geometry is selected for a given Young's modulus range by considering effects such as thermal stress, shear deflection in short beams, and system compliance. The goal is to minimize these combined errors in the dynamic Young's modulus and loss factor measurement over the full madulus range. As a result of this analysis recommended DMTA test procedures are presented.
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Dynamic mechanical properties of neoprene rubber blends (A)

W. M. Madigosky

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S63-S63 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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Blends of neoprene with other elastomers can be used to provide certain properties that are not obtainable with either elastomer alone. Although the effect of blending on the physical properties of neoprene blends has been investigated, the effect of blending on the dynamic mechanical properties has not been investigated to the same extent. Neoprene is compatible with natural rubber, SBR, NBR, polysulfide rubber, and has limited compatibility with butyl rubber. Seventy different blends were prepared and the physical properties measured. The dynamical mechanical properties are being measured on a Polymer Laboratories DMTA and frequency shifted using the WLF equation. This paper presents data and an analysis of the samples measured thus far.
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Structural damping measurements of polymer composites with laser Doppler vibrometry (A)

Martin J. Pechersky and Michael T. Gerusky

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S63-S64 (1989); (2 pages)

Online Publication Date: 13 Aug 2005

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Damping loss factors of three commercially available composites up to a frequency of 12 kHz have been performed. A resonance dwell technique was used in which both the excitation and measurement were non‐contact. The excitation was accomplished electromagnetically and the driving point admittance was measured with a laser vibrometer. The 25‐era‐long slender beam specimens were seismically supported at two nodes for each resonance by a combination of soft springs and silk thread. The mode shapes to determine the nodes of each beam were measured prior to the damping measurements. Metallic specimens were also measured to determine the limit on the accuracy of the measurement. The damping factors for the composites (Q−1) were found to be about two orders of magnitude larger than the metallic beam and all of the composite damping factors were found to increase monatomically with the excitation frequency over the range tested. Loss factors of the composites ranged from 1 to 4 × 10−3 at the lower frequencies to about 3 to 16 × 10−3 at the higher frequencies.
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Dynamic finite element analysis of a compressionally loaded viscoelastic cylinder (A)

R. W. Harrison

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S64-S64 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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A nonlinear finite element program utilizing the Mooney‐Rivlin strain‐energy tensor was used to obtain the static deflection of a compressionally loaded viscoelastic cylinder. The deformed coordinates and the mass and stress tensors were then passed to a complementary dynamic finite element program where the vibration isolation as a function of the applied vibrational frequency and the impedance of the top surface were calculated. The predictions of the finite element programs were verified with both Instron and accelerometer data. The calculations show the effect of compressional loading on the vibration absorption response and indicate possible geometrical modifications to enhance this absorption for application in the theory of motor mount isolation.
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Prediction of the loss factor of a double pipe damping system (A)

Meng Li and Robert G. White

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S64-S64 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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It is well known that increasing the damping of machinery structures will reduce noise radiation due to ringing vibration. Damping in industrial pipes can be increased by various damping techniques. This study was motivated by the need to decrease the noise radiation and vibration of pipework in power plants, particularly at elevated temperatures. Based upon the physical phenomenon of the air film damping of two parallel plates, a double pipe damping system with a very small air gap was investigated. In analysis, the Flugge shell equations of motion and the Navier‐Stokes equation for viscous fluid were employed. First, a traveling wave‐type solution was taken for shell and fluid. Then, from the interface conditions between the shell and fluid, the solution for the fluid medium was expressed in terms of shell displacements. Finally, solving the fluid equation of motion gave the fluid velocity profiles and stresses in the clearance between two cylindrical shells. From the definition of energy dissipated in the fluid, the equation of loss factor of the whole system was derived. The analytical results showed a very good qualitative agreement with the experiment. The study showed that different shell modes had a different contribution to the squeezing film damping, and the optimal design of the double pipe damping system can be deduced. The theory has been extended to studying the squeezing film damping system with various kinds of viscous fluid, such as lubrication oil, etc.
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Obtaining internal and coupling loss factors by a transient test method (A)

K. Sato and N. Lalor

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S64-S64 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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Statistical energy analysis (SEA) is taking an increasing role in determining energy flow and predicting noise reduction of machine structures. In order to set up the SEA model it is necessary to obtain the internal and coupling loss factors of each substructure either from theory or from measurement. The conventional measurement technique, in which steady‐state input power is supplied by a shaker to each subsystem in turn, is very time consuming. Moreover, it is not always possible to attach the shaker in the best position due to space limitations. This paper describes a transient method of loss factor measurement, using an instrumented hammer, which overcomes the above‐mentioned difficulties. The technique uses the point and transfer inertance data for the structure to calculate input powers and subsystem energies. Results obtained by this method are compared with those obtained conventionally and good agreeement is demonstrated.
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Theoretical and experimental investigation of high‐temperature damping treatment using ceramic‐fiber interlayer between plates (A)

L. C. Chow and R. J. Pinnington

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S64-S64 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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The damping techniques available for high‐temperature applications, such as in power generating plants, are very limited. As part of the investigation of high‐temperature damping work being carried out in ISVR, this paper describes the theoretical and experimental assessment of damping of plates using ceramic‐fiber material as an interlayer. An experimental rig that is used to measure the ceramic‐fiber material dynamic properties at elevated temperature will also be described.
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