Dixon, S. (1994) The analysis of aerospace adhesively bonded aluminium plates using electromagnetic acoustic transducers (EMATs). PhD thesis, University of Warwick.

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Abstract

This Thesis describes techniques used in the analysis of aerospace adhesively bonded
sandwich joints using radially polarised shear wave EMATs, together with an analysis of
the general performance of the EMAT systems used in the investigation.
It is generally accepted that to date there is no satisfactory technique for the detection of
defect types commonly encountered in adhesively bonded aerospace samples. This has
limited the use of adhesives for joining components on critical parts, where no additional
fixing techniques are used. Consequently, if a test procedure could be developed to
accurately monitor post production defects and in-service degradation then there would be
great benefits in terms of weight saving and strength in joined components which were held
together by adhesive bonds alone. Ultrasonics is a technique commonly applied to the
assessment of bond quality and readily lends itself to the probing of media which support
the propagation of acoustic waves. The principal is that the propagation of sound through
a medium gives some indication of the mechanical properties of that medium, and in terms
of an adhesive layer could measure the strength of the adhesive bulk itself- cohesion. The
efficiency of propagation of sound from one medium to another depends on the physical
properties of each medium, and possibly on how well the surfaces of each medium are
joined together - adhesion. Adhesion is the more difficult property to monitor as it is not just
a case of mechanically keying one medium to another on a nanometre scale, but other
interactions occur between the media similar to a Van der Walls type force that also
contribute to adhesion.
It has been extensively reported in the literature that the most sensitive ultrasonic wave to
use would be ashearwave at normal incidence to the adherent-adhesive interface. Radially
polarised shear wave EMATs have been used to generate the shear waves that induce a shear
stress at an adherent-adhesive interface. Some of the work involved in this project has
concentrated on the design, construction and characterisation of these EMATs and the
supporting hardware such as current pulser circuits and the necessary low noise-high
bandwidth preamplifiers. The experimental work is presented in chapters 3-7. Chapter 3
covers the performance of the EMAT systems, chapter 4 discusses the EMAT operation on
birefringent aluminium plates, chapters 5 and 6 cover the results and analysis used in the
adhesive bonds and chapter 7 describes a technique to monitor adhesive cure using EMATs
which monitor changes at an adherent-adhesive interface and within the adhesive bulk
itself.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QC Physics T Technology > TA Engineering (General). Civil engineering (General)
Library of Congress Subject Headings (LCSH):	Adhesion -- Measurement, Plates, Aluminum, Ultrasonics, Shear waves, Aerospace engineering
Official Date:	September 1994
Dates:	Date Event September 1994 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Shaw, Stephen ; Palmer, Stuart B.
Sponsors:	Great Britain. Defence Research Agency
Extent:	xviii, 107 leaves
Language:	eng

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