Rheology of zirconium adipate sol

Summary Employing aStormer viscosimeter, cup and rotor type, the rheological behaviour of gel yielding zirconium adipate sol has been investigated. Application of Staudinger's viscosity relation _sp =K _m Mc, gives the extent of aggregation during sol-gel transformation. In the gelling region a sharp rise in specific viscosity, nearly forty fold is observed. Rheological data is used in determining the gelling time and compares favourably well with values obtained by other methods.

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Zusammenfassung Mit Hilfe einesStormer-Viskosimeters vom koaxialen Zylindertyp wurde das rheologische Verhalten von Zirkonium-Adipat-Sol, das gelieren kann, untersucht. Die Anwendung der Staudinger Beziehung _spez=K _m M. c gibt das Ausmaß der Aggregierung während der SolGel-Umwandlung wieder. Im Gelierungsgebiet wird eine starke Zunahme in der spezifischen Viskosität — beinahe auf das 40fache — beobachtet. Rheologische Daten werden verwendet, um die Gelierzeit zu bestimmen, und sie können mit den Resultaten anderer Methoden gut verglichen werden.

     

Experimental investigation of the fatigue behavior of thread-type projections

In this paper the effect of flank angle, root radius and pitch on the fatigue life of thread-type projections is determined. Projections simulating threads with flank angles of 7, 20 and 30 deg, root radii ranging from 0.030 to 0.078 in. and pitches of 1/4, 3/8 and 1/2 in. were tested. Predictions of maximum fillet stresses were made by Heywood's method for correlation with measurements taken with miniature strain gages in the specimen thread fillets. A graph of the percent increase in load vs. percent decrease in life for the 3/8 in. pitch specimens is included.     

Stress and deformation analysis from reduced-scale plastic-model testing

The use of scale models, which are made from plastic material, for stress and deformation analysis of missile nose-cone structures is discussed. The special strain-gage application and testing techniques, which are required because of the use of plastic materials, are detailed.The utilization of relatively inexpensive simplified models for the investigation of two specific design conditions is cited. The first case is a stress and deformation study of a thin, constant-thickness, shallow spherical shell which is supported by a circumferential line reaction and subjected to uniform external pressure. Comparisons are made with a recently published theoretical analysis of the problem.The second case is a particular design problem which is concerned with the determination of the stress and deformation in a variable-thickness, shallow spherical shell with several various-size cutouts. The shell is loaded with a varying external-pressure load which is reacted by a circumferential line load at the periphery. Influence curves for both stress and deformation are given.Some limitations of plastic-model testing are reviewed, and guides to successful use of the method are given.Paper was presented at 1959 SESA Spring Meeting held in Washington, D. C. on May 20–22.     

Experimental investigation on tunnel sonic boom

Upon the entrance of a high-speed train into a relatively long train tunnel, compression waves are generated in front of the train. These compression waves subsequently coalesce into a weak shock wave so that a unpleasant sonic boom is emitted from the tunnel exit. In order to investigate the generation of the weak shock wave in train tunnels and the emission of the resulting sonic boom from the train tunnel exit and to search for methods for the reduction of these sonic booms, a 1300 scaled train tunnel simulator was constructed and simulation experiments were carried out using this facility.In the train tunnel simulator, an 18 mm dia. and 200 mm long plastic piston moves along a 40 mm dia. and 25 m long test section with speed ranging from 60 to 100 m/s. The tunnel simulator was tilted 8° to the floor so that the attenuation of the piston speed was not more than 10 % of its entrance speed. Pressure measurements along the tunnel simulator and holographic interferometric optical flow visualization of weak shock waves in the tunnel simulator clearly showed that compression waves, with propagation, coalesced into a weak shock wave. Although, for reduction of the sonic boom in prototype train tunnels, the installation of a hood at the entrance of the tunnels was known to be useful for their suppression, this effect was confirmed in the present experiment and found to be effective particularly for low piston speeds. The installation of a partially perforated wall at the exit of the tunnel simulator was found to smear pressure gradients at the shock. This effect is significant for higher piston speeds. Throughout the series of train tunnel simulator experiments, the combination of both the entrance hood and the perforated wall significantly reduces shock overpressures for piston speeds ofu _p ranging from 60 to 100 m/s. These experimental findings were then applied to a real train tunnel and good agreement was obtained between the tunnel simulator result and the real tunnel measurements.     

Ein interaktives Verfahren zur Auswertung von Kaustiken an Trennflächenrissen

Übersicht In diesem Beitrag wird eine auf der interaktiven numerisch/graphischen Bildverarbeitung beruhende Methode zur Ermittlung der Spannungsintensitätsfaktoren, für Trennflächenrisse in Verbundmaterialien vorgestellt. Eine Anzahl von detenpunkten entlang der experimentell aufgezeichneten Kaustik wird als Eingabe verwendet. Das Verfahren überprüft die Genauigkeit und Zuverlässigkeit der Ergebnisse selbst, indem die auf der Basis des Resultats numerisch generierte Kaustik mit der experimentellen verglichen wird.

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An interactive method for data processing from crack tip caustics at interfaces

Summary An interactive numerical-graphical image processing method for the evaluation of stress intensity factors at interface cracks in composites will be presented. Based on a set of experimental data points suitably chosen along the caustic the multipoint overdeterministic data reduction technique provides reliable and rapidly coverging results by cross-checking experimental caustics with numerically generated iterative caustics.

     

A reflection-type oil-film skin-friction meter

Tanner has shown analytically that the slope characteristics of a thin oil-film lying in contact with a surface on which an aerodynamic boundary-layer is developing are explicitly related to the local skin-friction. Unlike many conventional methods of measuring skin-friction, the oil-film method is absolute in nature, requires no calibration and in principle, can be universally applied. In all existing forms of the meter, however, interferometry is used to make measurements of the oil film. In the present contribution, the technique has been simplified by completely eliminating interferometry. This has been achieved by making direct and dynamic measurements of the oil-film slope by directing a reflected beam of light off the top of the oil film to a small position sensing photodiode. The raw data now is very different from that in the interferometric method and consequently, new methods of determining skin-friction from measured oil-film slope histories have been developed. The reflection method has been verified in incompressible flat plate turbulent boundary-layers. The standard of deviation of the measurements is about 10% of the mean. The present version of the meter is compact and simple.     

Micro-interferometry for measurement of thermal displacements at fiber/matrix interfaces

A micro-interferometric technique for measuring out-of-plane thermal displacements on a scale commensurate with the dimensions of the fiber/matrix unit cell is described. A scanning micro-interferometer is used to image surface displacements of samples containing a single-pitch-based carbon fiber embedded in an epoxy matrix. The interferometer design gives the necessary resolution to detect small changes in thermal displacements in the fiber/matrix interface region. The samples were heated electrically through the fiber to create radially symmetric temperature and displacement fields. Repeatable displacement measurements were obtained on a radial line across the interface region with an accuracy of ±25 Å. A sharp expansion of the matrix surrounding the fiber was observed with each heating. Overall, the experiments demonstrate the utility of micro-interferometry for measuring submicron displacements.     

Flow near the rear end of a slender axisymmetric body

The steady flow of a viscous incompressible fluid at high Reynolds numbers near a body of revolution of finite length whose radius coincides in order of magnitude with the thickness of the boundary layer is considered. The structure of the boundary layer in the neighborhood of the rear end of the body is investigated on the assumption that it has a power-law shape with values of the exponent n 1/2. A solution is also obtained for the near wake.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 10–18, September–October, 1990.     

Effect of different initial conditions on a turbulent round free jet

Velocity measurements were made in two jet flows, the first exiting from a smooth contraction nozzle and the second from a long pipe with a fully developed pipe flow profile. The Reynolds number, based on nozzle diameter and exit bulk velocity, was the same (䏪,000) in each flow. The smooth contraction jet flow developed much more rapidly and approached self-preservation more rapidly than the pipe jet. These differences were associated with differences in the turbulence structure in both the near and far fields between the two jets. Throughout the shear layer for x<3d, the peak in the v spectrum occurred at a lower frequency in the pipe jet than in the contraction jet. For x́d, the peaks in the two jets appeared to be nearly at the same frequency. In the pipe jet, the near-field distributions of f(r) and g(r), the longitudinal and transverse velocity correlation functions, differed significantly from the contraction jet. The integral length scale L_u was greater in the pipe jet, whereas L_v was smaller. In the far field, the distributions of f(r) and g(r) were nearly similar in the two flows. The larger initial shear layer thickness of the pipe jet produced a dimensionally lower frequency instability, resulting in longer wavelength structures, which developed and paired at larger downstream distances. The regular vortex formation and pairing were disrupted in the shear layer of the pipe jet. The streamwise vortices, which enhance entrainment and turbulent mixing, were absent in the shear layer of the pipe jet. The formation of large-scale structures should occur much farther downstream in the pipe jet than in the contraction jet.     

Modulus, Fracture Strength, and Brittle vs. Plastic Response of the Outer Shell of Arc-grown Multi-walled Carbon Nanotubes

The fracture strengths and elastic moduli of arc-grown multi-walled carbon nanotubes (MWCNTs) were measured by tensile loading inside of a scanning electron microscope (SEM). Eighteen tensile tests were performed on 14 MWCNTs with three of them being tested multiple times (3×, 2×, and 2×, respectively). All the MWCNTs fractured in the “sword-in-sheath” mode. The diameters of the MWCNTs were measured in a transmission electron microscope (TEM), and the outer diameter with an assumed 0.34 nm shell thickness was used to convert measured load-displacement data to stress and strain values. An unusual yielding before fracture was observed in two tensile loading experiments. The 18 outer shell fracture strength values ranged from 10 to 66 GPa, and the 18 Young's modulus values, obtained from a linear fit of the stress–strain data, ranged from 620 to 1,200 GPa, with a mean of 940 GPa. The possible influence of stress concentration at the clamps is discussed.