Table of contents |Fulltext|
1. Introduction
2. An approximative model for the ultrasonic inspection
3. The model on a separat page!
4. Practical applications and experimental veriffication of the model
   • 4.1 Inclined notches
   • 4.2 Inner crack
   • 4.3 Crack within a Turbine shaft
5. Summary
6. References

1. Introduction

Endorsed by the wide spread availability of powerful computer technology the manual ultrasonic inspection e. g. on welds is to an increasing amount replaced by mechanized automatic inspections. The standard presentation of a result from an automatic inspection is a picture of indications either in a direct presentation of the basic datas received by the ultrasonic inspection device (e.g. C-Scans or B-Scans produced by combining A-scan- and probe position data) or derived from the primary datas with more or less sophisticated transformation procedures (SAFT, Holography etc.). Due to the imagelike presentation of the results, the operator has to apply special acceptance criteria which are not only derived from the echo amplitude. They should ruthermore be based on typical patterns corresponding to special defect situations. Theoretical modeling of such patterns represents therefore a stringent need for a reliable automatic ultrasonic inspection and for the training of operators. This contribution tries to describe a kind of approximative modeling for the practical application at ultrasonic inspections for some typical cases. Figure 1 shows a schematic of a procedure for the developement of solutions for a new inspection task for an NDT method.

The selection of the best method for the inspection, the optimization of the method, the qualification and the evaluation of the results can successfully be executed and accellerated by the appropriate use of theoretical modeling. But the practical use of modeling requires the on line availability of results and the possibility to change rapidly the interesting parameters of a modeled situation, that means e.g. to play with different hypothesis of possible defects etc. This leads at present to a certain preference for approximative methods, because they are the only ones being fast enough on the basis of the mainly applied personal computers. Powerfull workstations will in future also be present in many laboratories and service companies, but they certainly require higher qualified personal, which is usually not available on site. Some problems with the approximations and their limitations will be discussed at the end of this contribution.

The simulation of an NDT situation by computers can contribute to the training of operators and to the solution of different problems: e.g. it seems to be possible to predict the reliability of certain inspection methods, the direction of optimization procedures can be defined and the comparison of a given result with a theoretically calculated defect image can enhance the qualitative and quantitative evaluation of the results.

Author

Hermann Wüstenberg, Anton Erhard
Bundesanstalt für Materialprüfung BAM
ZfP Ultrasonic Laboratory VIII.4, D-12205 Berlin
Tel. + 49 (0) 8104-0, Fax + 49 (0) 8112029
E-mail: Hermann.Wuestenberg@bam-berlin.de
Home Page: http://trappist.kb.bam-berlin.de/dept8.html

Presented on the Application Workshop in May '97