44
2
? Example 2.1 How will you repair 5-mm-wide, 6-mm-deep, and
100-mm-long crack on a fuselage of a cargo aircraft? The
composite is made out of S-glass-reinforced epoxy resin, and
thickness of the section is 15 mm.
v Answer
The repair plan will have the following steps:
5 Step 1. The crack is assessed for its dimension and extent of
damage by analyzing its depth and area of delamination
using pulse-echo ultrasound sonographic testing.
5 Step 2. The affected area is marked by adding a 25 mm width
with a marker pen.
5 Step 3. The number of layers of glass fabric affected is counted
(say n number). At the location of the crack, a clean cut up to
n + 2 layers deep and 10 mm wide is made.
5 Step 4. Now from this cut, every lamina is cut to form steps
leading up to the top of composite. The width of each step is
measured as Width of every step = (total marked width –
10 mm)/no. of laminae
5 Step 5. For this stepped profile, S-glass prepreg or S-glass
fabric impregnated with an epoxy resin matching the
thickness of lamina is placed stepwise in the repair area so
that the prepared profile is completely packed.
5 Step 6. One extra layer is placed on the top in order to exert
positive pressure during curing.
5 Step 7. The entire assembly is prepared for vacuum-assisted
curing.
5 Step 8. After curing, the top layer is filed or emeried to match
the profile of the fuselage, and a final coat of resin is applied
and cured.
5 Step 9. The assembly is checked for any flaw using another
pulse-echo ultrasound flaw detector.
5 Step 10. If no flaw is found, the assembly is ready for use.
9. The experience and intuition gained over the years about the
behaviour of metallic materials do not apply to composite
materials.
10. Carbon fibre-reinforced composites have negative linear
coefficient of thermal expansion.
11. The raw materials of composites must be dried before
processing because all resin matrices and some fibres absorb
moisture.
12. The curing of some composites poses health hazards.
13. Carbon fibre-based composites are inherently black in colour.
Therefore, they cannot be pigmented.
14. Monitoring the overall health of composites and prediction of
their lifespan are a complex task. In November 1999, the
America’s Cup boat ‘Young America’ broke in two due to the
debonding face/core in the sandwich structure.
15. Even after several years of emphasis on composites as the
‘material of the future’ , economies of scale are still not well
Chapter 2 · Advantages and Applications of Polymeric Composites
2
? Example 2.1 How will you repair 5-mm-wide, 6-mm-deep, and
100-mm-long crack on a fuselage of a cargo aircraft? The
composite is made out of S-glass-reinforced epoxy resin, and
thickness of the section is 15 mm.
v Answer
The repair plan will have the following steps:
5 Step 1. The crack is assessed for its dimension and extent of
damage by analyzing its depth and area of delamination
using pulse-echo ultrasound sonographic testing.
5 Step 2. The affected area is marked by adding a 25 mm width
with a marker pen.
5 Step 3. The number of layers of glass fabric affected is counted
(say n number). At the location of the crack, a clean cut up to
n + 2 layers deep and 10 mm wide is made.
5 Step 4. Now from this cut, every lamina is cut to form steps
leading up to the top of composite. The width of each step is
measured as Width of every step = (total marked width –
10 mm)/no. of laminae
5 Step 5. For this stepped profile, S-glass prepreg or S-glass
fabric impregnated with an epoxy resin matching the
thickness of lamina is placed stepwise in the repair area so
that the prepared profile is completely packed.
5 Step 6. One extra layer is placed on the top in order to exert
positive pressure during curing.
5 Step 7. The entire assembly is prepared for vacuum-assisted
curing.
5 Step 8. After curing, the top layer is filed or emeried to match
the profile of the fuselage, and a final coat of resin is applied
and cured.
5 Step 9. The assembly is checked for any flaw using another
pulse-echo ultrasound flaw detector.
5 Step 10. If no flaw is found, the assembly is ready for use.
9. The experience and intuition gained over the years about the
behaviour of metallic materials do not apply to composite
materials.
10. Carbon fibre-reinforced composites have negative linear
coefficient of thermal expansion.
11. The raw materials of composites must be dried before
processing because all resin matrices and some fibres absorb
moisture.
12. The curing of some composites poses health hazards.
13. Carbon fibre-based composites are inherently black in colour.
Therefore, they cannot be pigmented.
14. Monitoring the overall health of composites and prediction of
their lifespan are a complex task. In November 1999, the
America’s Cup boat ‘Young America’ broke in two due to the
debonding face/core in the sandwich structure.
15. Even after several years of emphasis on composites as the
‘material of the future’ , economies of scale are still not well
Chapter 2 · Advantages and Applications of Polymeric Composites