JEC COMPOSITES MAGAZINE - Issue #116 - October 2017 - 58

TECHNOLOGY

58
63

NDT

Non-destructive evaluation of the mechanical strength
of a TA6V4/composite bond using LASAT
Efficiency

Cost-efficient preforming using tailored textiles

TECHNOLOGY NDT

Non-destructive evaluation of the mechanical
strength of a TA6V4/composite bond using LASAT

Simon Bardy, CEA, DAM, DIF
mathieu ducouSSo, Safran Tech
tomaS Bergara, Rescoll
Laurent Berthe, Laboratoire Procédés et Ingénieries en Mécanique et
Matériaux, CNRS, Arts et Métiers
Paris Tech
Laurent Videau, CEA, DAM, DIF
Frédéric JenSon, Safran Tech
nicoLaS cuViLLier, Safran Tech

In the current context of aircraft weight reduction and considering the trend for
lowering production and maintenance costs, the aeronautics industry is promoting the use of adhesive bonds to replace mechanical fasteners. However,
the main limitation of structural bonding in the aircraft industry is the ability to
certify the good quality of a structural bond in a non-invasive way, i.e. to certify
that the bond can resist up to a predefined strength value.

onventional non-destructive testing (NDT) techniques
(Ultrasonics, radiography, shearography,...) allow disbonding detection but are inefficient to evaluate the mechanical strength of
bonds, i.e. detect weak bonds. A manufactured bonded part is not validated with 100% fiability with NDT technique. So, it is a huge lock for
a wide use of bonding in structural bonding where maximal fiability is
required. Thus, some industrials choose additionnal assembly process
to bonding such as bolding, riveting,...
Bonding is a compex process, divided into steps which has all to be
fully-controled. Production defaults come from a lack of adhesion
or a lack of adhesive cohesion due to various origins (pollution, micro-voids, uncomplete adhesive curing,...). Most of this defaults are
nowadays not detected and detectable imposing a perfect bonding
process control. That is why structural adhesives are hardly qualified
in aeronautics. Laser Adhesion test (LASAT) opens a new way for
NDT quantitative evaluation of bonded joints mechanical properties
answering to industrial issue in bonding technology.
This process is based on the use of high energy laser which can generate stresses localized in the bonding area.

jec composites magazine / N°116 October 2017

The results presented were realized in the frame of Compochoc project which aims to develop an automatic device to perform LASAT
inspection on industrial bonding.
The Compochoc plateform which will be hosted by Rescoll in september 2018 and industrials will be able to perform NDT testing with
LASAT process.
The LASer Adhesion Test [1] is seen as a promising alternative to
traditional NDT techniques to reveal these weak bonds in a reproducible and automated way. This test consists in applying calibrated
mechanical stresses to a given bonded assembly using laser-induced
shock waves. This calibrated configuration should lead to disbonding of the joint/substrate interface in case of a weak bond while not
damaging a healthy bond. Previous studies demonstrated the ability
of the LASAT technology to characterize the quality of composite/
composite bonded assemblies for typical operational thicknesses [2].
In the present work, LASAT is used to test two levels of adhesive bond
mechanical strength for a TA6V4 titanium alloy/3D woven carbon/
epoxy composite assembly. The potential of this technology for such a
configuration is demonstrated as well.

LASAT principle
The LASAT technique is based on the following principle: a high-en-

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #116 - October 2017