ABSTRACT

The increasing use of adhesives in automotive manufacture has brought about the need for robust methods for non-invasive quality assurance (QA) of adhesively bonded components. Ultrasonic methods are already widely used in the aerospace industry and it is reasonable to try and apply these to automotive structures. Ultrasound offers a rugged technology which is safe, easy to use and can be implemented using standard `of the shelf' instrumentation, suitable for a factory setting. This paper describes the development of a high frequency pulse-echo method for NDT of adhesively bonded structures which offers a degree of quantitative assessment which may not be possible with conventional low frequency techniques, particularly when the dimensions of the structure are not known. A theoretical model of the wave system excited in a multi-layer bond is briefly described and it is shown that the model can be used to investigate the effects of varying sample dimension, absorption in the adhesive, transducer coupling and the presence of paint layers. It is demonstrated that pulse overlapping and interference make analysis of the received signal difficult such that standard methods of pulse gating and level triggering are not possible. In this paper a method based on an adaptive digital filter is described which overcomes this problem and results of pulse-echo measurements on adhesively bonded lap joints are presented. It is shown that for steel and aluminium substrates bonded with structural adhesive it is possible to detect front and back face disbonds and to quantify the substrate and bond-line thicknesses. The techniques described in this paper have formed the basis of algorithms for an intelligent NDT instrument for QA of adhesively bonded structures.

Table of contents |Fulltext|
1. Introduction
2. The wave system
3. The thin layer reverberation problem
4. Results
5. Limits of testability
6. Bond dimension and substrate type
   • Table 6a. Limits of testability for a bottom substrate disbond for steel substrates
   • Table 6b. As table 6a but for aluminium substrates.
   • (ii) Adhesive absorption
   • (iii) Paint coatings
   • (iv) Coupling
7. Conclusions and future work
8. References
9. All Figures on one Page

Authors

Dr. Richard J. Freemantle and R. E. Challis
Ultrasonics and Digital Signal Processing Laboratory, Dept. Physics, Keele
University, Staffs., ST5 5BG, UK.
Tel. +44 1782 583457, Fax. +44 1782 711093.
Email udsplab.elec.keele.ac.uk
Homepage http://udsplab.elec.keele.ac.uk

The Paper was presented on the UTonline Application Workshop in May '97