The sound diffraction by a semi-infinite plane screen with a knife-edge was measured by AC-pulse of 2ms duration with freguency ranging from 5 to 40 kcs. The result is shown approximately by one curve of sound reduction vs. the Fresnels zone number N by the screen, (Fig. 4). This curve shows a few dB lower values than that of Kirchhoff's diffraction theory. Noise reduction by a concrete screen 2m high on the ground was measured by pure tones ranging from 250c/s to 4kcs and 1/3 octave band noises, from a speaker set on, or 1m above, the ground at 2m distance from the screen. The receiving point was moved on horizontal and vertical lines in the shadow zone of the screen, and recorded the sound pressure level distribution by a high speed level recorder. The results of the measurement are as follows; 1)From the practical point of view, the measured values showed good agreement with the culculated values which the reflected wave from the ground, at receiving side of the screen, was added to the diffracted direct sound wave as if the ground reflects perfectly. 2)The addition of the sound energy of reflected sound to the energy of the direct wave, shows reasonable agreement with measured values of band noises. On the other hand the calculated interference pattern for pure tone does not agree with measured pattern caused by the irregurarity of the boundaries. 3)The calculation should be based on the sound level at the top of the screen when the screen is absent. And the experimental curve in Fig. 4 mentioned above can be used as a designing chart for estimating the sound level at any point in the shadow zone of the screen. 4)Also when the source is above the ground, the same calculation method is applicable by means of the equivalent point source approximately. 5)The limiting condition for application of this calculation is that the vertical sound distribution at the brank plane above the screen was decaying off from the top of the screen. 6)The shielding effect of the screen is variable by the directional characteristics of the sound source.
This report is concerned with the analysis of the performance of Langevin type transducer with end metals, which have stepped or linearly tapered variation on cross sectional area perpendicular to direction of vibration. The analysis was made by the assumption that only plane wave exists along the direction of length in these transducers, and consequently by analogy of the four terminal transmission network theory. As result of this analysis, it was clarified that the equations of resonant condition in these transducers, and the mathematical expressions of equivalent lumped constants, force factor and stress distribution along the direction of length at resonance, could be acquired in simple forms. Thus a method of design of these transducers was obtained. Furthermore, on basis of the above mentioned solutions, the universal design charts for the transducer with the stepped end metals were drawn. These charts can be also applied to the transducer with the linearly tapered end metals where the slopes of tapers are gentle.
Applications of resonace method and supersonic pulse technique to the non-destructive testing of refractory bricks are studied. Elastic properties of bricks are measured by means of these sonic methods. In this parer, as the fundamental experiment, Young's modulus, sound velocity, apparent porosity and true porosity of schamotte brick specimen which is made under various manufacturing conditions or of various particle-size distributions are measured and correlationships between these physical quantities are analyzed.
Most important physical properties of refractory bricks are porosity and mechanical strength, however they are measured only by destructive test. Considering the result of the fundamental experiment in the previous paper, it is to be expected that porosity or strength can be nondestructively estimated from sound velocity of Young's modulus respectively. We have statistically analyzed them in order to know the influences of manufacturing condition or particle packing fluctuations on this regression estimate. Analysis of convariance was done in two-way layout of the forming pressure and the firing temperature or the forming pressure and the particle-size distribution. Practically, porosity or strength of schamotte brick has been found to be well estimated by sonic non-destructive testing mentioned above.
Several methods have been used as resistance test for thermal shock of refractory bricks. Thermal shock resistance is customarily judged from the physical appearance or spalled weight percent of specimen when rapid heating and cooling are repeated. They remain generally qualiative. Spalling is based on intrinsic weakness for thermal shock stress. In this experiment, decrease of Young's modulus of refractory brick on thermal shock is measured by supersonic pulse technique and analyzed. The decreasing tendency has been statistically showed to be logarithmic to thermal shock repeating frequency (from room temperature to 1200C and vice versa). We have introduced spalling index by decreasing constant of Young's modulus. This method is considered to be successful in expressing the spalling character for schamotte bricks.