Thesis (M. E.)--University of Canterbury, 2008. / Typescript (photocopy). "December 2008." Includes bibliographical references (p. [99]-103). Also available via the World Wide Web.

No description available.

The split Hopkinson pressure bar has been used to study the acoustic isolation that can be achieved by inserting a compliant element into the sound path in an elastic system, and to study the dynamic response of the material comprising the compliant element. The specimens were inserted between two steel transducer bars. The incident stress pulse, of about 100 microsecond duration, was produced by striking the free end of one of the transducer bars by a round-headed striker bar. The incident pulse in the first bar and the transmitted pulse in the second bar were sensed by strain gages and displayed on an oscilloscope. The comparison of computed Fourier transforms (within the acoustic frequency range) of both the incident and transmitted pulses showed that in general a greater reduction in transmission of vibration across a specimen is achieved: i) by increasing the length of the specimen; ii) by using a material with a higher attenuation constant or higher viscous damping; iii) by increasing the impedance mismatch between the specimen and the steel transducer bars. Also, it was found that isolation is greater at high frequencies than at low frequencies. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

A theory for predicting the dynamic response of earth structures subject to earthquake forces as presented herein. The proposed theory essentially introduces a stress limit into the viscoelastic shear-slice or shear-beam analogy and thus, in essence, the structure is modelled by a multidegree of freedom system which responds in an elastic-viscoplastic manner. The stress limit may be varied with both the magnitude of displacement and the number of stress cycles so that, in practice, a complex stress-strain relationship can be considered in the analysis. The method allows the dynamic displacements, velocities, and accelerations within the structure to be calculated at any time, t, when the base is subjected to a known acceleration. If magnitude of displacements is considered the criterion for earthquake design, then the proposed method of analysis gives a direct measure of these displacements. The analysis is applied to a number of earth structures using a base acceleration corresponding to the 0-10 secs. of El Centro, 1940 earthquake. Displacements, velocities and accelerations are calculated at discreet time intervals. Results are compared with those obtained from a viscoelastic dynamic analysis and it is found that plastic action causes larger displacements and smaller accelerations. The location of plastic yield is dependent on the strength properties of the material. For material of uniform strength, yield will occur essentially at the base of the structure, while for ideal frictional material, yield will take place throughout the structure but will be greatest at the top. Lateral force or seismic,coefficients from viscoelastic and elastic-viscoplastic are compared. Results suggest that the common practice of allowing for plastic-action by assuming some high viscous damping factor such as 20% of critical in a viscoelastic analysis is unlikely to give correct results. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Viscoelastic properties of ferrofluid - Study of normal stresses differences Master Thesis Hana Šustková Abstract: Since 1960, a liquid becoming strongly magnetized in the presence of a mag- netic field, called ferrofluid, is known. This colloidal liquid made of ferro- or ferrimagnetic nanoparticles, with diameter in range 10-20 nm, suspended in a carrier fluid. This work focuses on the study of the viscoelastic properties of a selected ferrofluid - the steady-state and dynamic properties of the fluid with comparison to a standard fluid (basis fluid, etc.) and a MR fluid. Rheological measurements are carried out using a commercial rheometer. A magnetic cell for this rheometer is designed and built. In this magnetic cell the experiments are realized, the whole system is calibrated and the experiments performed. The ferrofluid APG513a, MR-fluid and reference fluid were used. Study of normal stresses differences (N1,N2) in liquids is carried out. Ac- cording to derived theoretical model, the course of N1 and N2 should be strongly dependent on the field - this was studied directly by measuring of the normal forces or indirectly applying the Laun's rule. A good accordance of theory and experiment was found and an anisotropic behaviour of ferrofluid was studied. The shear-thinning ability of the ferrofluid in normal direction...

Much of the work done on active and passive constrained layer beams is done with mathematical models proposed by Kerwin and extended by DiTaranto, Mead and Markus, and others. The mathematics proposed by these early researchers was tailored to fit the damping treatments in use at that time: thin foil damping tapes applied to panels for noise reduction. A key assumption was that all layers had identical transverse displacements. While these assumptions are reasonable when the core layer, normally a soft viscoelastic material(VEM), is thin and the constraining layer is weak in bending, there are many situations in industry and in the literature where the ``Mead and Markus'' (MM) assumptions should be questioned. An important consequence of the MM modeling assumptions is that the strain energy in the VEM core is dominated by shear strain, and this in turn means that only the shear modulus is of primary importance. This is fortunate since only the shear modulus is available to engineers for viscoelastic materials used for layered damping treatments. It is a common practice in industry and academia to simply make an educated guess of the value of Poisson's ratio. It is shown in the dissertation that this can result in erroneous predictions of damping, particularly in partial-coverage configurations. Finite element analysis is used to model both the MM assumptions and a less-restrictive approach commonly used in industry. Predictions of damping from these models are compared against models with elements from C0 elements and a C1-capable element that matches tractions at material interfaces. It is shown that the time-honored modal strain energy method is a good indicator of modeling accuracy. To assess the effects of the MM assumptions on an active PZT used as a constraining layer, closed-loop damping versus gain is determined using both the MM and higher order elements. For these analyses, the time-dependent properties of the viscoelastic material are represented by a Maxwell model using internal variables. Finally, the basic MM premise that all layers share the same transverse displacement is disproved by experiment. / Ph. D.

No description available.

No description available.

No description available.

No description available.