Self-Healing: Glass Fibre Reinforced Plastic
The need for self-repair in the space environment
Composite structures operating in the space environment are vulnerable
to impact damage resulting from collisions with micrometeoroids
and orbital debris. The relative velocity of man-made debris ranges
from zero, for objects in the same orbit, to approximately 11 km/s
for objects in retrograde orbits. In comparison, collisions with
meteoroid particles take place with an average velocity of 19km/s.
The damage to the brittle composite structures consists of penetration
holes with adjacent surface damage and some internal ply delamination.
Space composite laminates can also suffer from internal matrix
microcracking. Microcracking damage can occur within the lifetime
of the composite structure due to its exposure to the repeated thermal
cycling within the space environment.
The aim of this research has been to characterise the form of self-healing
required within a space composite laminate to be able to repair
damage resulting from collisions with micrometeoroids and orbital
debris or damage arising from thermal cycling.
 
Fig. 1 Self-healing sequence
Self-healing repair of space composite
structures
Firstly the damage formation within the composite laminate must
be correctly characterised. A cross section of the damaged laminate
(when viewed parallel and normal to the 0 fibre orientation) is
illustrated in Fig. 2.
1400N Load point
1400N Load point
Fig. 2: Damage formation in [0/+45/90/-45]2s
laminate manufacture from pre-impregnated E-glass and epoxy 913
subjected to a 1400N three-point bend test.
Secondly, the locations of the self-healing layers
must be determined. To do this, a composite laminate was manufactured
from pre-impregnated E-glass and 913 epoxy with single plies of
self-healing fibres (placed in the 90 fibre direction) were located
at the key damage interfaces, i.e. the +45/90 interface above the
mid-plane and in the -45/90 below the mid-plane of the specimen.
The sample was damage with a 1400N 'impact' load and then allowed
to heal at 90 C for 1 hour. A cross section of the healed laminate
under UV light is shown in Fig. 3.
1400N Load point
Fig.3: Impact damaged cross-section
of [0/+45/90/-45]2s composite laminate containing healing filaments
at the +45/90 and -45/90 interfaces containing Cycom 823 and UV
dye
Fig. 3 clearly illustrates the extent of the infiltration
by the healing resin into the damage zone when viewed along the
0 fibre direction. This result compares favourably with the damage
observed in Fig. 2 and would suggest that the four self-healing
locations are ideally placed within the complex damage network to
fully infuse the damage site.
The result in Fig. 3 has illustrated the success of the Cycom 823
epoxy resin system at infusing the impact damage site from four
key locations. Due to the successful infusion trial, this system
has been selected for further evaluation under a pseudo-space environment,
i.e. thermal cycling and outgassing performance. This research is
still ongoing.
The image above is time lapse photography showing Cycom 823 epoxy
resin and hardener with UV dye infiltrating 1400N damage site in
16 ply [0°/45°/90°/-45°]2s E-glass/913 epoxy with
self-healing plies located at [+45/90] interface above the mid-plane
and in the [-45/90] interface below the mid-plane of the specimen.
Thermal cycling and outgassing assessment of the self-healing composite laminates for the space enviornment have been undertaken by http://www.ts-space.co.uk
A summary of the test results and a general introduction into the ESA funded research on self-healing has been included in the following pdf file - a copy of the presentation given at the 15th International Conference on Composite Materials presented in Durban, South Africa on 27 June to 01 July 2005.
Click here to download the ICCM presentation PDF .
Author: Dr Richard Trask
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