Application of a microprocessor for acquisition of load,strain and acoustic-emission data

This paper describes an automatic system for acquisition, logging and analysis of stress, strain and acoustic-emission data. The complete system is a combination of several standard items of equipment and a newly developed intelligent data logger which has the capability to send data directly to a large-scale computer for reduction and plotting. The data logging and all interfacing with peripheral equipment are accomplished using digital electronics. The heart of the system is a four-bit microprocessor and digital cassette-tape unit. The system, which is controlled by instructions from a cathode-ray-tube terminal, has the capability to transmit data from the cassette unit to a large computer via a time-sharing aption. Typical results are presented for acoustic-emission count rate and total-count curves superimposed on stress-strain diagrams for boron/epoxy advanced composites.     

Thermohydrodynamic conditions at the peak flux of horizontal heaters in superfluid liquid helium II at zero net mass flow

Measurements of the peak flux (at the onset of film boiling) in He II are used as a diagnostic tool to investigate the non-classical thermohydrodynamics of superfluid liquid helium for horizontal heaters at zero net mass flow. Data for the single horizontal cylinder in a large pool of He II are approximately accounted for by a power law describing the dimensionless nonclassical superfluid transport number as a function of the fourth root of the dimensionless thermo-mechanical driving potential. Results for transport in narrow vertical cylinders (with insulated walls and lower end closed) are approximately described on the basis of the Gorter-Mellink transport equations. The saturation hypothesis is used which postulates local onset of boiling when vapor-liquid equilibrium is reached at the heater.     

Extremalprinzipe der Thermodynamik und Mechanik für stabile Gleichgewichtslagen von Kontinua

Übersicht In dieser Arbeit soll der Zusammenhang zwischen den Extremalprinzipien der Thermodynamik und der Mechanik für stabile Gleichgewichtszustände eines Kontinuums studiert werden. Als Nebenprodukt ergeben sich dabei zwanglos Verallgemeinerungen der klassischen Extremalprinzipe der Elastizitätstheorie (des Minimum-Energie-Prinzips und des Prinzips von Castigliano) auf multipolare und chemisch reagierende Materialien.

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Summary The aim of this paper is to study the relations between the variational principles of thermodynamics and mechanics for stable equilibrium states of a deformable body. As a by-product one obtains generalisations of the classical principles of elasticity-theory (the minimum-energy-principle and Castigliano's theorem) to multipolar and chemically reacting materials.

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Herrn Prof. Dr.-Ing. K. Klotter zum siebzigsten Geburtstag gewidmet.     

The contact stress in a bolted joint with a threaded bolt

The contact stress of a bolted joint, in which a clamped part was fastened to a body with a threaded bolt, was measured using sensitive pins, sensitive films and ultrasonic waves. The contact stress distribution was analyzed as a contact problem by an axisymmetrical theory of elasticity. Numerical calculations were performed. The experimental results were in fairly good agreement with the analytical results.Paper was presented at the 1992 SEM International Congress held in Las Vegas on June 9, 1992.     

Effect of measurement volume size on turbulent flow measurement using ultrasonic Doppler method

This paper presents the results of an investigation on the effects of measurement volume size on the mean velocity profile and the Reynolds stress for fully developed turbulent pipe flows. The study employs the ultrasonic velocity profile method, which is based on the ultrasonic Doppler method. The ultrasonic Doppler method offers many advantages over conventional methods for flow rate measurement in the nuclear power plant piping system. This method is capable of measuring the instantaneous velocity profile along the measuring line and is applicable for opaque liquids and opaque pipe wall materials. Furthermore, the method has the characteristic of being non-intrusive. Although it is applicable to various flow conditions, it requires a relatively large measurement volume. The measurement volume of the present method has a disk-shape determined by the effective diameter of the piezoelectric element and the number of the wave cycles of the ultrasonic pulse. Considering this disk-shaped measurement volume and expressing the time-averaged velocity in a truncated Taylor series expansion around the value at the center of the measuring control volume, the value of the velocity can be obtained. The results are then compared with the data obtained from DNS and LDA measurements. The result shows that the effect of the measurement volume size appears in the buffer region and viscous sublayer.     

Temperature spectra from a turbulent thermal plume by ultrasound scattering

This paper reports the results of a study on temperature inhomogeneities conducted on a thermal plume by using ultrasound scattering as a non-intrusive measurement technique. The plume rises from a metallic disk which can be heated up to 800 °C. The working fluid is air at atmospheric pressure. In the measurement technique, an incoming ultrasound wave is emitted towards the thermal plume. The incident wave is scattered because of non-linear couplings with the flow instabilities present in the measurement region. The scattered wave carries information about those flow instabilities. The technique allows for the retrieving of this information. The shape of the obtained spectrum of temperature fluctuations as a function of wave vector modulus is consistent with previous theoretical analysis. Three qualitatively different regions were identified: first, a production region characterized by a q² law; secondly, a region with behavior as per q⁻³ associated with a buoyancy region and; finally, a dissipation region associated with a q⁻⁷ law. These spectral regions characterize the energy transfers mechanisms among the length scales of flow investigated here. A coefficient of anisotropy γ was defined to analyze anisotropic features of the flow.     

The relaxation of linear flexible polymers which are slightly poly-disperse

The relaxation of slightly poly-disperse linear flexible polymers has been expressed in a simplified blending rule which is presumed to be a weighted linear superposition of the relaxation spectra of mono-disperse components which constitute the blend. Discrete components are characterized by their molecular weight M _i,weight fraction w _i,and relaxation time spectrum H _i(). ). In contrast to broadly distributed blends in which the small molecules mobilize the large ones and vice versa, we introduce the term slightly polydisperse for blends with molecular weight distributions narrow enough to have very little change in the longest relaxation times of each molecular weight component. The properties of this blending rule are analyzed and dynamic data is calculated for slightly poly-disperse polystyrene. As an application, the blending rule is used to determine the characteristic mono-disperse parameters (BSW parameters) of two materials, poly (vinyl methyl ether) and polycarbonate, for which we could not determine their BSW parameters directly since they were not available in nearly monodisperse form. The proposed blending rule can only be applied to systems in which all components are above the entanglement molecular weight, i.e. M _iM _c.Dedicated to the memory of Professor Tasos C. Papanastasiou