JEC COMPOSITES MAGAZINE - Issue #113 - June 2017 - 71

Smart restoration of internal defects in damaged composite aerostructures

This healant has low viscosity properties that aid infiltration into the
damaged area. Several repair methods such as dripping repair, resin
injection with a vacuum chamber system and double bagging were
developed to this end. Strategic drilling of vent holes in the damaged
zone was experimented to study the optimum number of vent holes
to achieve high repair efficiency. As the Nano-Force 100 healant was
discovered later, the Epo-Tek 301 from Epoxy Technology Inc. which
composition is Bisphenol A Diglycidyl Ether Resin was used to implement the various repair techniques.

tive technique can be used for the following types of repairs:
- Filling up cracks in the matrix material with healants;
- In case of delamination between the laminates, bonding the laminates back together with healants;
- In case of fibre fracture, bonding (only) the aligned fibre segments
back together with healants;
- Repairing pulled out fibres with healants. The healant should be
carefully injected into the internal cracks using a low-pressure injection technique with a specific in-house developed device.

Following a compression-after-impact (CAI) test, the resin injection
with the vacuum chamber system repair method and 4 vent holes
drilled produced the highest repair efficiency as compared to the other
repair methods and numbers of vent holes. A series of specimens using the same repair mode were produced using the Nano-Force 100
healant and an average repair efficiency of 81.4% was achieved. These
damaged and repaired specimens were evaluated using non-destructive
testing methods such as ultrasonic C-scan flaw detection and thermography to study the crack architecture and the infiltration of the healant.

The unique selling points and technical recommendations for this
composite repair method are as follows:
- The repair can be conducted in two simple, less labour intensive stages, corresponding to the repair of internal and external damages;
- Application of healing agents into the damaged region without the
assistance of a thermal source to facilitate resin flow;
- After several mechanical strength assessments, particularly CAI
tests, it was found that resin injection using a vacuum chamber and
the Nano-Force 100 healant was the most effective method for the
repair of composite internal cracks and damages;
- An average repair efficiency of 81.5% was achieved on 16-ply composite specimens using the resin injection repair method and a vacuum chamber system, drilling 4 vent holes and injecting the NanoForce 100 healant;
- Among all the low-viscosity healants tested, the Nano-Force 100
carbon nanotube premix allows recovering the highest compression
strength in repaired prepreg samples;
- This mixed healant has an ideal density and viscosity that aid the
infiltration into the damaged internal area of the composite plates;
- Special drilling steps are required to create centre holes and vent
holes;
- After CAI, the composite damaged area is within 25mm from the
damage centre;
- The optimum number of vent holes to achieve the highest repair efficiency is 4.
After the BVD repair, the surface repair is carried out to restore the
surface back to its original condition in order to minimise unwanted
aerodynamic disturbances. The innovation in the composite surface repair includes an improved resin infusion technique that uses a thin layer
of low-viscosity resin injected under a thick double-sealed bag with a

Experimental investigations
Overall, the research and experimental investigations involved quantifying the resin healing effect and repair quality through the measurement of mechanical strength properties such as tensile strength, torsional strength, flexural strength, interlaminar fracture toughness and
fatigue. Experimental assessments were carried out in the laboratory
under tightly regulated extreme environmental conditions, namely
-57°C and 65°C, to simulate the differential temperatures experienced
by the aircraft when it takes off, during cruising and when it lands.
The main benefits of the solution/product are:
- Less labour intensive as no skilled workers are required;
- Faster repair, as the proposed method can handle both the internal
and external structure at the same time;
- No need to remove the "good" area, which could further damage
the structure and take it further away from the objective of achieving
strength recovery of the materials close to their pristine conditions.
The solution involves the development of a smart and sustainable repair technique to restore structural integrity. Specifically, this innova-

Fig. 1: Vacuum chamber
with resin injection system
for composite repair

No113 June 2017

/ jec composites magazine

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Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #113 - June 2017
