Full-ﬁeld assessment of the damage process of laminated
composite open-hole tensile specimens. Part I: Methodology
, Ben Green
, Michael R. Wisnom
Laboratoire de Me
canique et Proce
s de Fabrication, Ecole Nationale Supe
rieure d’Arts et Me
tiers, Rue Saint-Dominique, BP 508,
lons-en-Champagne Cedex, France
Department of Aerospace Engineering, University of Bristol, Queen’s Building, University Walk, BS8 1TR Bristol, UK
Received 21 June 2006; received in revised form 2 January 2007; accepted 4 January 2007
The present paper is the ﬁrst part of a study dedicated to the assessment of the damage taking place in composite open-hole tensile
specimens using full-ﬁeld strain measurements. It concentrates on the thorough validation of the methodology used to process the full-
ﬁeld data. First, the grid method used to provide the two components of the in-plane displacement ﬁeld at the surface of the test spec-
imens is described. Then, the data processing procedure to obtain the displacement maps during the test is discussed. The main part of
the paper is dedicated to the derivation of strains from displacements, investigating two procedures: local diﬀerentiation and polynomial
ﬁtting. The eﬀect of the grid is also investigated. Finally, successful experimental results are presented.
Ó 2007 Elsevier Ltd. All rights reserved.
Keywords: B. Optical properties/techniques; B. Mechanical properties; B. Transverse cracking; Open-hole tension
The mechanical behaviour of laminated composites has
been extensively studied since the start of their introduction
in aerospace applications in the sixties. Nevertheless, the
complexity of their behaviour arising from their speciﬁc
features like heterogeneity and anisotropy has made this
task a diﬃcult one, even when very simple mechanical tests
are performed . When more complex tests are per-
formed, containing cracks and/or notches, the analysis is
even more diﬃcult because of the strain gradients that
combine with the materials features to produce very com-
plex damage processes.
In order to address the experimental assessment of the
damage process of complex composites tests, it is clear that
it is of primary importance to obtain more extensive
experimental information than that of a few strain or dis-
placement measurements through strain gauges or extens-
ometers. Full-ﬁeld optical measurements represent an
excellent alternative to get access to a great amount of data.
There have been a number of studies in the literature
using full-ﬁeld measurements to examine the mechanical
response of a composite plate with a hole, because of the
signiﬁcance of such tests to aerospace applications where
bolts and rivets are used for joining purposes. For instance,
full-ﬁeld measurements are very interesting to validate the
strain distribution in a pin-loaded specimen, where it is
dependent on the local contact between pin and hole
aﬀected by friction and clearance. Lanza di Scalea et al.
compared the strain distribution obtained by a ﬁnite ele-
ment model and speckle interferometry measurements .
In the same spirit but using the grid method, Pierron
et al. validated their ﬁnite element simulation of the eﬀect
of clearance on the strain distribution in a pin-loaded plate
. Another interesting paper concerns the measurement of
the strain ﬁeld in an open-hole tensile test on a composite
interferometry. The data are then used in con-
junction with an inverse procedure to retrieve the material
elastic stiﬀness components . However, these studies
1359-835X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
Corresponding author. Tel.: +33 3 26 69 91 86; fax: +33 3 26 69 91 76.
E-mail address: firstname.lastname@example.org (F. Pierron).
Available online at www.sciencedirect.com
Composites: Part A 38 (2007) 2307–2320