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Optical detection of defects in piezoelectric ultrasonic transducers
Abstracts from the First Danish-Israeli Symposium on Nondestructive Evaluation Acoustic emission characterization of fracture and deformation in composite materials and structures
How can NDE contribute to the better understanding of the manufacturing process of products?
I. Roman
K. Rudich
The Hebrew University of Jerusalem, Graduate School of Applied Science and Technology
Quafity Assurance and Reliability, Technion, Haifa 32000, Israel
The characterization of acoustic emission (AE) from composite materials and structures is becoming a useful tool for damage and failure mode analysis. However, the current state of the analysis of AE for this purpose has not yet advanced to the stage where a single acceptable method of analysis is available. Among the different approaches for processing AE, the analysis of different characteristics of the peak amplitude (PA) of AE signals was found to be a most useful tool for distinguishing different failure modes in many composite systems.
Quality control of advanced materials requires the development of adequate quantitative nondestructive measurement methods. The measured parameters should be correlated to the mechanical features of the materials. The achievement of this goal calls for close cooperation of all disciplines involved from the design up to the in-service inspection.
This paper summarizes some of our studies on Kevlar-epoxy, carbon-epoxy, and Kevlar-carbon-epoxy composites in which we have employed traditional and new approaches for the analysis of AE. The results enabled the establishment of a correlation between the relevant different failure modes and an AE parameter.
Interdisciplinary work poses many organizational, as well as technological, problems that have to be solved. In the present contribution, we discuss the approach taken by our group at the Technion towards interdisciplinary cooperation. Cases from our experience will be discussed to demonstrate the problem in defining the parameters to be measured, the importance of detailed knowledge about the products and the manufacturing process.
PC-based NDT procedure generators
Optical detection of defects in piezoelectric ultrasonic transducers
J. Larsen
P.N. Larsen
SVEJJE Centralen, Denmark Establishment of NDT-procedures can be rather time-consuming depending on the NDT-standard, the object to be tested, the available equipment and the experience of the NDT-expert who has to write the procedure. As a result of this, the procedures may be written to cover a broader scope of objects than desirable: the procedures are less specific than they should be. In order to minimize this problem, The Danish Welding Institute has initiated the development of personal computer based software tools called NDT-procedure generators. At present, procedure generators are established for X-ray examination according to ISO 1106/1 and 1106/3 and for scanner calculations in connection with the ultrasonic P-scan equipment also developed by the institute. The rules for the examination are integrated in the software tools and ensure that the generated procedures fulfil the specified requirements or that deviations are mentioned in the procedure. The procedures generated automatically have many advantages: • • • • •
Uniform NDT-procedure descriptions Easy to produce Reliable calculations Notes of non-conformance to the standards No need for the operator to test different techniques due to less specific NDT-procedures.
The Industrial Acoustics Laboratory, Technical University of Denmark, Building 425, DK-2800 Lyngby, Denmark Transmitting ultrasonic transducers in the MHz-range are used for many applications, especially in the medical field. The basic design of such transducers is a disc of piezoelectric ceramics glued to a backing cylinder. The disc is coated on two parallel surfaces with an electrical conductor, to which electric cords are soldered. During manufacturing of the transducers many defects may occur, including: the use of too much tin solder (creates a small lump), bad gluing to the backing material, cracks in the coating and defects in the backing material. This paper describes an optical technique which is able to distinguish between a perfect transducer and a transducer with a defect. For some of the defects the technique is also able to detect the particular type of defect. The theoretical background for the technique is the theory of light diffraction by ultrasonic fields, first formulated by Raman and Nath. The experimental set-up uses a 5 mW He-Ne laser, low costs optics and a light intensity meter. The data processing is performed using a standard personal computer. The optical technique has been applied on 4.5 MHz, 25 mm diameter transducers with introduced characteristic defects, and very promising results have been obtained.
0 3 0 8 - 9 1 2 6 / 8 8 / 0 6 0 4 5 3 - 0 6 © 1988 Butterworth & Co (Publishers) Ltd NDT International Volume 21 Number 6 December 1988
453
How can NDE contribute to the better understanding of the manufacturing process of products?
I. Roman
K. Rudich
The Hebrew University of Jerusalem, Graduate School of Applied Science and Technology
Quafity Assurance and Reliability, Technion, Haifa 32000, Israel
The characterization of acoustic emission (AE) from composite materials and structures is becoming a useful tool for damage and failure mode analysis. However, the current state of the analysis of AE for this purpose has not yet advanced to the stage where a single acceptable method of analysis is available. Among the different approaches for processing AE, the analysis of different characteristics of the peak amplitude (PA) of AE signals was found to be a most useful tool for distinguishing different failure modes in many composite systems.
Quality control of advanced materials requires the development of adequate quantitative nondestructive measurement methods. The measured parameters should be correlated to the mechanical features of the materials. The achievement of this goal calls for close cooperation of all disciplines involved from the design up to the in-service inspection.
This paper summarizes some of our studies on Kevlar-epoxy, carbon-epoxy, and Kevlar-carbon-epoxy composites in which we have employed traditional and new approaches for the analysis of AE. The results enabled the establishment of a correlation between the relevant different failure modes and an AE parameter.
Interdisciplinary work poses many organizational, as well as technological, problems that have to be solved. In the present contribution, we discuss the approach taken by our group at the Technion towards interdisciplinary cooperation. Cases from our experience will be discussed to demonstrate the problem in defining the parameters to be measured, the importance of detailed knowledge about the products and the manufacturing process.
PC-based NDT procedure generators
Optical detection of defects in piezoelectric ultrasonic transducers
J. Larsen
P.N. Larsen
SVEJJE Centralen, Denmark Establishment of NDT-procedures can be rather time-consuming depending on the NDT-standard, the object to be tested, the available equipment and the experience of the NDT-expert who has to write the procedure. As a result of this, the procedures may be written to cover a broader scope of objects than desirable: the procedures are less specific than they should be. In order to minimize this problem, The Danish Welding Institute has initiated the development of personal computer based software tools called NDT-procedure generators. At present, procedure generators are established for X-ray examination according to ISO 1106/1 and 1106/3 and for scanner calculations in connection with the ultrasonic P-scan equipment also developed by the institute. The rules for the examination are integrated in the software tools and ensure that the generated procedures fulfil the specified requirements or that deviations are mentioned in the procedure. The procedures generated automatically have many advantages: • • • • •
Uniform NDT-procedure descriptions Easy to produce Reliable calculations Notes of non-conformance to the standards No need for the operator to test different techniques due to less specific NDT-procedures.
The Industrial Acoustics Laboratory, Technical University of Denmark, Building 425, DK-2800 Lyngby, Denmark Transmitting ultrasonic transducers in the MHz-range are used for many applications, especially in the medical field. The basic design of such transducers is a disc of piezoelectric ceramics glued to a backing cylinder. The disc is coated on two parallel surfaces with an electrical conductor, to which electric cords are soldered. During manufacturing of the transducers many defects may occur, including: the use of too much tin solder (creates a small lump), bad gluing to the backing material, cracks in the coating and defects in the backing material. This paper describes an optical technique which is able to distinguish between a perfect transducer and a transducer with a defect. For some of the defects the technique is also able to detect the particular type of defect. The theoretical background for the technique is the theory of light diffraction by ultrasonic fields, first formulated by Raman and Nath. The experimental set-up uses a 5 mW He-Ne laser, low costs optics and a light intensity meter. The data processing is performed using a standard personal computer. The optical technique has been applied on 4.5 MHz, 25 mm diameter transducers with introduced characteristic defects, and very promising results have been obtained.
0 3 0 8 - 9 1 2 6 / 8 8 / 0 6 0 4 5 3 - 0 6 © 1988 Butterworth & Co (Publishers) Ltd NDT International Volume 21 Number 6 December 1988
453