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The non-linear excitation of wind instruments generates higher harmonics of the playing frequency. These higher harmonics are coupled to resonances in the pipe. This is called mode locking. When the pipe modes are not harmonic, the playing frequency shifts away from the fundamental in order to maximize the output. It may go up or down, depending on the position of the modes and the amplitude. The effect is especially manifest for fork fingerings. Three fork fingerings on a clarinet were investigated. They were artificially blown between the threshold and extinction pressure. A time domain simulation was carried out based on a lumped model of the excitation coupled to an input impedance calculated from the instrument dimensions. At low amplitudes the fundamental frequency dominates and the playing frequency is governed by the position of the first peak in the input impedance spectra. At higher blowing pressures the playing frequency shifts. For both blowing and simulation this follows the same pattern. The frequencies predicted by the calculations are higher than the values found by blowing, which may be due to inadequacies in the model description, to uncertainties of the various parameters, as reed stiffness, moving reed area, and the properties of the slit flow.

Rubbers filled with high amounts of a hard inorganic filler still show the typical mechanical properties of a high polymer, viz. a glass-rubber transition region, a glassy state and a rubbery state. The influence of filler characteristics on the glass-rubber transition is discussed, chiefly on the basis of the course of shear modulus at constant frequency as a function of temperature.

Rubbers filled with high amounts of a hard inorganic filler still show typical mechanical properties of a high polymer, viz., a glass transition region, a glassy state and a rubbery state. Effects of filler characteristics on the glass transition are discussed, chiefly on the basis of the course of shear modulus at constant frequency as a function of temperature. Effect of volume content of filler on the glass transition of composite materials consists chiefly in a change of the levels of shear modulus in the glassy and in the rubbery state. This change may be described by a simple macroscopic model due to van der Poel. Predictions by this theory could be confirmed for rubbers filled with single filler fractions in the filler size range 30 to 500 µm, and in the range of filler content 0 to 50 vol%. At smaller particle sizes, an effect of filler size was observed, which points to increase in the transition temperature and to increase in the level of modulus in the rubbery state with decreasing filler size. Preparation of composite materials with high filler contents (>55 vol%) is only possible by using a filler with a bimodal size distribution. In this case, moduli depend on filler content and mixing ratio of coarse to fine filler fraction; the van der Poel theory then gives predictions which are too high in comparison with experimental results.

To make twist proportional to length, corrections must be applied to the free specimen length between the clamps. These corrections are determined experimentally by clamping a specimen of polymeric material over various lengths and extrapolating the torsion angle to zero length. For cylinders with ring-shaped clamps, a two-sided correction was found of 0·235 of the diameter. For rectangular specimens with flat-plate clamping at the ends, the correction varies between 0·20 (square cross section) and −0·55 (very slender cross section) of the greatest width. Results only partly correspond with theoretical predictions, since theoretical and experimental conditions are not identical.

A description is given of a method for measuringYoung's modulus up to 100 Hz and shear modulus up to 1000 Hz by means of attaching known moments of inertia at the ends of a specimen. The same specimen can be used for both types of measurements.

This paper describes a torsional pendulum and a torsional creep instrument. With the pendulum shear moduli between 106 and 1010N/m2 can be measured at frequencies from 0.1 to 20 Hz. The creep instrument is suitable for measurement of shear compliances lower than 10−7 m2/N in the time range from 1 to 105 seconds. In both instruments, specimens are kept at the right temperature by blowing heated nitrogen gas through a surrounding thermostatic chamber. The signal of a platinum resistance thermometer, provided in each chamber, automatically controls the heating of the gas. Temperatures from −180 to +300 °C can be maintained with an absolute accuracy of ±1 °C and a long term stability of ±0.05 °C. It is shown that one cannot directly compare one and the same shear property, calculated from the shear modulus as measured with the pendulum as well as from the shear compliance as measured with the creep instrument. This is due to differences in the temperature of one thermostatic chamber over against the other. Finally, the paper presents a method to reduce these differences to ±0.1 °C, although the absolute accuracy of temperature control remains ±1 °C.

A description is given of an instrument for the measurements of the dynamic shear modulus,G, and the corresponding damping, tanδ, of solid polymeric materials. The instrument is suitable for the measurement of moduli in the range from 106 to 1010 newton/m2, tanδ values from 0.005 to 3 and frequencies between 0.1 and 20 Hz. The temperature of the specimen can be adjusted to any value between −180 and + 300 ‡C. The obtained accuracy is better than 5%. The accuracy of the measurement considerably decreases when tanδ is higher than 0.3.

The mechanical properties of composite solid propellants depend essentially on the type of binder that is chosen. The viscoelastic behaviour of pure binders is discussed by demonstrating the variation of shear modulus, bulk modulus, Young's modulus, Poisson's ratio and thermal expansion with time, frequency and temperature for unfilled amorphous polymers. The strong frequency and time dependence of the shear properties in the glass—rubber transition region is shown by measurements over many decades in frequency at various temperatures. The validity of the time—temperature shift principle is discussed. The relationship between filler characteristics and mechanical properties of inert filled composite materials is treated in detail. At small deformations, the mechanical behaviour of composite materials is independent of filler size and is simply related to filler content. This relationship is discussed in the light of various existing theories for the description of composite materials. A theory due to Van der Poel is found to be most satisfactory. At high filler contents with multimodal size distributions, deviations from this theory are found. The ultimate properties of composite materials are very sensitive to the size of filler. This is demonstrated for two examples: stress—strain diagrams and tensile creep under high stresses. The relationship between strength, dewetting and creep at room temperature is elucidated.

Results are presented of stress-strain tests performed at various temperatures and strain rates on materials filled with various amounts of sodium chloride particles with a mean size of 0.1 mm. Stress and strain at rupture decreased with increasing filler content. For each material investigated it was possible to construct the well-known failure envelope by means of which the results could be described adequately. The dewetting of the particles in the rubbery matrix, sometimes resulting in a maximum in the stress-strain curve, is ascribed to failure of the rubber between the particles and not to failure of the rubber-salt bond, because the dewetting maximum was dependent on temperature and time in the same way as the rupture properties of the unfilled material. The results are compared with earlier investigations, e.g. high speed tensile tests and creep experiments, and a good agreement is found.

A device is described with which an axial rotation can be obtained proportional to the logarithm of the time over an arbitrary number of decades. The main parts of the apparatus are a synchronous motor, a mechanical counter and two gear-wheels with variable radii.