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Zawartość zarchiwizowana w dniu 2019-03-12

NON-DESTRUCTIVE EVALUATION OF CERAMIC MATERIALS BY ULTRASONIC METHODS AT HIGH FREQUENCIES.

Cel

DEVELOPMENT OF AN ACOUSTIC SYSTEM FOR NON-DESTRUCTIVE TESTING OF CERAMIC COMPONENTS WITH FREQUENCIES BEYOND 100 MHZ.
In order to evaluate the loadability, to estimate lifetime and to examine defects and damages with respect to the failure of components, the knowledge of the stress state is a mandatory preassumption.

The setup enables an automated and nondestructive evaluation of stress states in the surface, in a surface layer up to about 6-10 mm deep and in the bulk of metallic and ceramic semiproducts and components.

Continuous measurements during the scanning of the component result in the evaluation of stess distribution and in the localization of stress inhomogeneities. Measurements using stationary probes lead to continuous surveillances of mechanical and thermal treatments. Thus, a variety of process optimizations can be performed (eg screw connections, stress relief treatments, hardening processes and press and sinter processes). The ultrasonic techniques represent an important complement to the techniques already applied, such as X-ray techniques with analysing depths of some 10 um and the partially destructive bore hole and toroid core techniques.

These techniques which are, in comparison with the ultrasonic techniques, time (and money) consuming and which only give small spot analyses, can be replaced by ultrasonic techniques in many cases of application.

The accuracy of the evaluated stresses (to better than 10%) and the resolution (to better than 30 MPa) depend on the material and on the geometry of the component.
IN CERAMIC COMPONENTS THE CRITICAL DEFECT SIZE CAN BE AS SMALL AS 10 MICRON.
THIS REQUIRES - BESIDES OTHER POSSIBLE TECHNIQUES - ULTRASONIC INSPECTION SYSTEMS WHICH USE FREQUENCIES > 100MHZ BECAUSE THE ACOUSTIC WAVELENGTH IS THEN OF THE ORDER OF 10-100 MICRON, AND THEREFORE COMPARABLE TO THE SIZE OF THE DEFECTS ENSURING THEIR MAXIMAL DETECTABILITY.

THE EXPERIMENTAL EFFORTS WILL FIRST BE DIRECTED TO THE EXTENSION AND OPTIMIZATION OF THE ALREADY EXISTING LABORATORY SET-UP WHICH PRESENTLY WORKS UP TO 200 MHZ. IN PARTICULAR, INSTEAD OF USING SHORT RECTANGULAR PULSES AS IS COMMONLY DONE, SHORT BURST WILL BE USED IN ORDER TO ACHIEVE A HIGHER RF-SIGNAL STRENGTH AT THE FREQUENCIES DESIRED. THE TRANSDUCER NECESSARY FOR THIS WORK WILL BE MADE OUT OF SPUTTERED ZNO LAYERS, AND THE DELAY LINES USED WILL BE MATCHED IN THEIR ACOUSTIC IMPEDANCE TO THE MATERIAL BEING EXAMINED.
WILL BE MATCHED IN THEIR ACOUSTIC IMPEDANCE TO THE MATERIAL BEING EXAMINED.
THE RESULTS OF THIS WORK SHOULD LEAD TO THE "KNOW-HOW" FOR THE CONSTRUCTION OF AN INDUSTRIAL PROTOTYPE.

BESIDES THE MERE DETECTION OF A DEFECT BY ULTRASOUND, IT IS ALSO POSSIBLE TO DETERMINE ITS SIZE AND THE TYPE OF THE DEFECT BY ANALYZING THE MAGNITUDE OF THE SCATTERED SIGNALS AS A FUNCTION OF FREQUENCY. THIS METHOD HAS BEEN EMPLOYED UNTIL NOW ONLY IN A RETRICTED NUMBER OF CASES. THEREFORE, PARTICULAR EMPHASIS WILL BE GIVEN TO ITS FURTHER VERIFICATION, AND TO ITS EXTENSION TO DEFECTS GEOMETRIES OTHER THAN SPHERES.

FOR PRACTICAL APPLICATIONS IT IS DESIRABLE TO DEVELOP PROCEDURES AND METHODS WHICH CAN BE USED IN A SIMPLE MANNER. CONSEQUENTLY, IT IS NECESSARY TO MAKE ALL MATHEMATICAL HANDLING OF THE EXPERIMENTAL DATA BY COMPUTER PROGRAMS WHICH ARE THE FIRST STAGE OF AN AUTOMIZED ULTRASONIC INSPECTION SYSTEM EMPLOYING HIGH ACOUSTIC FREQUENCIES.

Temat(-y)

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Zaproszenie do składania wniosków

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System finansowania

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Koordynator

FRAUNHOFER-GESELLSCHAFT ZUR FOERDERUNG DER ANGEWANDTEN FORSCHUNG E.V.
Wkład UE
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Adres
Universitaet, Gebaeude 37
66123 SAARBRUECKEN
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