The Influence of Plasma Surface Treatment on the Fracture Toughness Peel Ply Prepared Bonded Composite Joints

The increasing use of composite materials in various
industries, such as aerospace, automotive and renewable
energy generation, has driven a need for a greater understanding
of the fracture behaviour of bonded composite
joints.
An important prerequisite for the adhesive bonding of
composites is the existence of a uniform surface free from
contaminants and mould release agents. While there are
several ways in which this may be achieved, the use of
peel plies has emerged as the preferred choice for many
industries due to the repeatable nature of the resulting surface,
particularly in the highly regulated aerospace industry.
The use of peel plies can present some problems. It is
possible that contamination from the peel ply can be transferred
to the composite substrate and adversely affect the
adhesive joint [1].
Plasma treatments have been shown to improve the
fracture toughness of adhesively bonded composite joints
[2] and can be used to remove contaminants, such as
mould release agents, from the surface [3].
The aim of this work is to evaluate the influence of
various peel ply treatments on the mode I fracture toughness
of different aerospace grade bonded composite joints
and to assess the subsequent benefits of employing an atmospheric
pressure plasma (APP) surface treatment prior
to adhesive bonding in each case.