International Journal of Adhesion & Adhesives 22 (2002) 129–137
On the precision of the wedge-opened double cantilever beam method
for measuringthe debondingtoughness of adhesively bonded plates
Jean-Yves Sener
a,b
, Thierry Ferracin
a
, Laurence Caussin
a
, Francis Delannay
a,
*
a
D
!
epartement des sciences des mat
!
eriaux et des proc
!
ed
!
e-PCIM, Universit
!
e Catholique de Louvain, Place Sainte Barbe 2,
B-1348 Louvain-la-Neuve, Belgium
b
R&D Cockerill-Sambre Groupe Usinor, Domaine Universitaire du Sart-Tilman B57, B-4000 Li
"
ege, Belgium
Accepted 17 August 2001
Abstract
The paper aims at contributingto a better appraisal of the wedge-opened double cantilever beam method for testingthe
debonding toughness of adhesively bonded plates. The test specimens consisted of two plates of either hot-dip galvanized low carbon
steel or alloy Al-6082-T6 bonded with an epoxy-based adhesive. The classical method of crack length measurement by visual
observation of the crack tip alongthe side of the specimen is compared with a method makinguse of displacement sensors for
continuously monitoringthe deflection of the plates. The variation of toughness with debondingrate was derived from the evolution
of the debond length either with respect to a static wedge or with respect to a wedge advancing at a constant rate. The paper
enlightens the uncertainty arising from the anticlastic effect and compares the experimental reproducibilities provided by the
different test procedures. r 2002 Elsevier Science Ltd. All rights reserved.
Keywords: A. Epoxide; B. Metals; C. Wedge test; Anticlastic effect
1. Introduction
The wedge-opened double cantilever beam (DCB) test
is one of the simplest methods for the application of
fracture mechanics to the testingof crack extension in
adhesive joints or composite laminates [1,2]. The
simplicity of the test rests on the facts that the debond
extension is intrinsically stable and that no load cell is
needed. The principle of the test is sketched in Fig. 1.
Two plates, taken in the present case as havingthe same
thickness, h; are bonded face to face with an adhesive
layer of thickness e: The width, w; of the plates can be
larger than the width, b; of the bonded area. A wedge of
thickness D inserted between the plates induces the
extension of a decohesion crack up to a distance a from
the wedge. If the plates remain purely elastic, the
‘‘debondingtoughness’’ of the bond, which we will
designate by the symbol G; is equal to the strain energy
release rate G: If we assume that the assembly is free of
residual stresses and that the contribution of the
adhesive layer to the strain energy of the system can
be neglected, G can be expressed on the basis of a simple
beam bendingmodel as
G ¼
3u
2
Eh
3
w
16a
4
b
; ð1Þ
where E is the plates Young’s modulus and the
displacement at the wedge is u ¼ D À e [1–4]. Several
more refined expressions of G have been proposed in the
literature. They will be considered in the Section 4 of this
paper.
The larger the plate thickness, the larger the
maximum toughness that can be measured without the
occurrence of plastic dissipation in the plates. Using
again a simple beam bending model, the condition of
applicability of relation (1) for this symmetrical DCB
configuration is [5]
Gp
hs
2
Y
w
3Eb
; ð2Þ
where s
Y
is the plates yield stress.
It has been widely demonstrated in the literature that,
duringdebond extension in a DCB specimen, the actual
debond front is not straight but ‘‘thumb nail’’ shaped,
i.e. the local debond length aðzÞ decreases when the
*Correspondingauthor. Tel.: +32-10-47-24-26; fax: +32-10-47-40-
28.
E-mail address: delannay@pcim.ucl.ac.be (F. Delannay).
0143-7496/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0143-7496(01)00046-X