JEC COMPOSITES MAGAZINE - Issue #81 - May/June 2013 - 70

NDT

Damage and harmfulness of defects
There is a growing awareness of environmental issues across
the world. At the same time, changing lifestyles are increasing the need for greater and faster means of transportation.
Faced with this paradox, manufacturers in the transport
sector (such as the aerospace and automotive industries)
are left with no choice but to reduce the weight of structures
while improving their reliability. In this context, the use of
composite materials is one of the key solutions that can be
considered.

By
Thomas Jollivet, Materials Engineer
Henri Walaszek, NDE Technical
and Innovation Manager
Nicolas Terrien, Composite NDT
Application Manager
CETIM

he aerospace sector has been
using composite materials for a
long time, and they now make
up 50% of the weight of a new airliner.
The automotive industry is also going
to incorporate more and more composite materials into structural parts,
which represent a significant proportion of a vehicle’s overall weight.
Destructive control and non-destructive testing (NDT) can characterize
defects and damage relatively well, but
their harmfulness is an essential issue.
In the aerospace sector, this has been
studied and treated for a long time. In
the automotive industry, the question
arises for structural parts that require
optimized sizing. How can defects be
taken into account with new materials
and processes? Some answers are provided in this article, that focuses on
organic matrix composites with continuous fibres: thermosetting matrix
composites (TSCs) and thermoplastic
matrix composites (TPCs).

Effect of defects
The manufacture of composite material parts has a special and unique
feature compared to metallic materials: the material and the part are made
simultaneously. During this single
operation, it is necessary to control
the positioning of the reinforcement
fibres, the curing or melting/crystallization of the matrix and the part’s
geometry. Controlling the processing
of composite parts is therefore a prerequisite for claiming to achieve the
desired high levels of performance.
The whole list of terms for defects
in organic matrix composites has not
yet been established. Standardization work is currently being carried
out at the European level to align the

vocabulary used by constructors in
the aerospace field.
Figure 1 shows examples of commonplace imperfections: poor positioning
of the reinforcement in the plane of
the plies or, outside the plane of the
plies, porosities, lack of impregnation,
etc. The defects observed on TSCs or
TPCs are sometimes different in origin, so their morphology and harmfulness are different.
Culturally speaking, the transition
from metal to composites requires a
different way of looking at the inspection and design of parts. The cost of
manufacturing a composite part free
from imperfections would be prohibitive. Furthermore, the number of

Fig. 1: (a) waviness of the UD reinforcement at the failure point of a racing sailboat mast; (b) porosity in an
aerospace composite; (c) lack of impregnation at the core of tow in a thermoplastic composite

70 jec composites magazine / No81 May - June 2013

JEC COMPOSITES MAGAZINE - Issue #81 - May/June 2013

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #81 - May/June 2013