Sonic Tests Research Articles

On a Sonic Non-destructive Testing of Refractory Bricks

On a Sonic Non-destructive Testing of Refractory Bricks

Sound Source for ASD Sonic Test Facility

The sound source for the ASD Sonic Test Facility now under construction consists of two banks of independently controlled sirens designed to give sinusoidal output over a range of operating pressures. The main fixed bank of sirens (frequency range 50 to 2000 cps) employs 25 sirens, each using a 24-in. rotor; a second movable bank (frequency 500 to 10 000 cps) employs nine sirens each using a 12-in. rotor. Each siren employs a modulator which permits random or coherent amplitude modulation of the acoustic output at modulation frequencies from 0 to 25 cps for the large sirens and from 0 to 50 cps for the smaller sirens. Maximum acoustic power output of the fixed bank of sirens is expected to exceed 106 w in the midfrequency region from 200 to 800 cps. Finite amplitude limitations will be discussed. (Sponsored by Aeronautical Systems Division, Air Force Systems Command, U. S. Air Force.)

Generation of Intense Audio Sound Fields Utilizing Arrays of Multiple-Driver Horns

There are several major applications for intense audio sound fields: the outdoor propagation of speech and of warning signals, and the sonic fatigue testing of missile and aircraft components. In these applications, several factors combine to make it necessary to limit the portion of the frequency spectrum covered by any one loudspeaker unit. In order to provide adequate power capacity, selection is required between the alternatives of (a) using a large number of identical drivers, (b) using a plurality of drivers each especially designed for a selected portion of the frequency range, and (c) using combinations of these arrangements. In an array currently being used for sonic-fatigue testing, a plurality of large open cone loudspeakers is used for low frequencies, and a plurality of horns is used for middle and high frequencies. Each horn is driven by several drivers. The driver voice coil and diaphragm proportions have been optimized to withstand fatigue stresses under the thermal conditions encountered. The driver is rated at 50-w input for program material. Horn assemblies are available having throat arrays for mounting 6, 12, or 24 drivers. Various applications will be illustrated.

Some Structural Design Features of the WADD Sonic Fatigue Test Facility

Construction of a large high-intensity sonic fatigue facility is under way at Wright-Patterson Air Force Base, Dayton, Ohio. No previous large structure has been required to withstand long term intense excitation at all frequencies in a wide band, so that structural design of this facility was faced with some unprecedented problems. The present paper outlines the test chamber size and performance requirements and how these led to the present design. The present structure is described, and design of viscoelastically damped configurations is discussed. The sizes and design stress levels of typical beams and panels in this structure are compared to those encountered in conventional structures. Some interesting details of the structure are pointed out.

Generation of Intense Audio Sound Fields Utilizing Arrays of Multiple-Driver Horns

There are several major applications for intense audio sound fields: the outdoor propagation of speech and of warning signals, and the sonic fatigue testing of missile and aircraft components. In these applications, several factors combine to make it necessary to limit the portion of the frequency spectrum covered by any one loudspeaker unit. In order to provide adequate power capacity, selection is required between the alternatives of (a) using a large number of identical drivers, (b) using a plurality of drivers each especially designed for a selected portion of the frequency range, and (c) using combinations of these arrangements. In an array currently being used for sonic fatigue testing, a plurality of large open-cone woofers is used for low frequencies, and a plurality of horns is used for middle and high frequencies. Each horn is driven by several drivers. The driver voice coil and diaphragm proportions have been optimized to withstand fatigue stresses under the thermal conditions encountered. The driver is rated at 50-w input for program material. Horn assemblies are available having throat arrays for mounting 6, 12, or 24 drivers. Various applications will be illustrated.

Sonic Fatigue Testing of Flight Vehicle Structures—Facilities and Techniques

The structural fatigue problems caused by engine noise and aerodynamic boundary layer turbulence necessitate the laboratory testing of specimens that are typical of the flight vehicle's structure. Generally, specimens of panel configuration are tested to facilitate a comparison of the test results. The present noise source in the laboratory that is capable of generating the required sound pressure levels for such testing is the discrete frequency siren. This may employ either the normal or grazing incidence technique. The siren discussed herein uses the grazing incidence, plane-wave tube principle. Specimens of up to 14 ft long and 4 ft wide can be accommodated and tested to sound pressure levels of 170 db (re 0.0002 microbar) at frequencies between 50 cps and 1000 cps. A siren plenum chamber of 6-ft diameter with a rotor of 3-ft diameter is utilized to obtain these sound pressure levels. The testing techniques used in the operation of this facility are described.

Rapid Method for Evaluation and Design of Structures with Viscoelastic Interlayers

A simple method is presented for rapid approximate determination of stress-vs-frequency and power absorbed-vs-frequency curves for plate and beam structures incorporating viscoelastic shear damping. The utility of this method is illustrated by applying it to the design of damping for the wall structures of the Wright Air Development Division sonic fatigue test facility. Some conclusions are drawn concerning damping material properties desirable for obtaining favorable stress-vs-frequency trends. (Results presented grew out of studies supported by the U. S. Air Force. Wright Air Development Division.)

Equipment Testing to Sonic Environments—Facilities and Techniques

A general description, along with details, for the equipment qualification sonic testing facility at North American Aviation, Inc.. Columbus. Ohio, is presented. Methods of sound generation, control, and monitoring and testing techniques are described. A unique method of generating noise at the open end of a large catenoidal horn (11 ft at the open end, 10 ft long, and 3 ft at the throat) and concentrating such noise at the throat to increase SPL is utilized in this facility.

Electronically Modulated Air Valve

A new design of an electronically modulated air valve on the dynamic principle, which will generate acoustic power in excess of 1.5 kw for small electrical input, will be discussed in detail. Applications of this device for generation of high intensity random noise will be described. Measurements in reverberant environment, free field, and for sonic fatigue tests of structures will be presented. A number of new applications, some of which may involve speech, such as in disaster warning systems, signal systems, communication systems, and psychological warfare are suggested.

A sonic spalling test : J. F. Clements and W. R. Davis, British ceramic society, Transactions, v. 57, Oct. 1958, p. 624–644

A sonic spalling test : J. F. Clements and W. R. Davis, British ceramic society, Transactions, v. 57, Oct. 1958, p. 624–644

Multichannel Swept Sonic Tester for Casting Quality Control

Automatic, production-type, sonic inspection based on the measurement of the fundamental vibrating frequency and/or decrement of a mechanically shocked casting has been in operation in our foundries for several years. The method has been suitable for the detection of cracks, voids, porosity, mottle, shrink, etc., on many of the parts having simple geometries. However, the more complex castings can vibrate in many basic modes and these modes upon shock excitation may interact indistinguishably. Swept-frequency, continuous-wave, forced vibration obviates mode interaction and permits casting evaluation by comparison of the sonic energy absorption spectra. Center frequencies, bandwidths, and amplitudes of certain of the absorption peaks usually establish overall quality. The multichannel Swept Sonic Tester evaluates a given casting by determining the presence of a response within each of several preselected bands. These channels have very sharp limits which are established by active, tunable, twin-T networks. Each channel is self-contained permitting the system to be extended to accommodate any degree of casting complexity by adding channels in building block fashion. The spectrum sweep, having an adjustable sweep width, sweep rate, and starting frequency, is accomplished by heterodyning a crystal oscillator with a reactance-controlled frequency-swept oscillator and approximately follows the derived ideal frequency vs. time characteristic for conserving inspection time.

MEDICAL JURISPRUDENCE ON THE PLEA OF INSANITY IN CRIMINAL TRIALS

We are able to say, with comnplete confidence and earnest sincerity, that the legal test for the irresponsibility of the insane is wrong in theory, false in fact, cruel in its metaphysical conception, and unreliable in its practical application. If, however, the law, admitting its errors, asks medical men to supply sonic new test of irresponsibility capable of general application, it is asking an impossibility. Insanity is not a result of metaphysical definition; it is a matter of physical brain disease. There is no single test of insanity; there caii be no single test for the irresponsibility of the insane. Some insane are responsible for certain, if not all of their criminal acts; others are completely irresponsible, and there are gradations of responsibility varying with the nature of the act and the state of the insane person. Every case must be considered by its own facts. As well might a medical man ask the law to lay down the test for typhoid fever when an area is declared infected and when all cas...