Composite dome

Composite materials have variety of application due to their advantages over using singular materials such as impact resistance, strength, corrosion resistance and good performance-to-weight ratio. In this laboratory, glass-fibre epoxy composite is constructed using glass fibre sheets and e-proxy resin through prepreg lay-up technique. The prepregs consist of 4 layers of glass fibre, which are partially cured with epoxy resin. E-glass is the most widely used type of glass fibre; it consists of silicon dioxide and metallic oxide and produced by drawing molten glass through a small orifice. The most common applications of glass-fibre epoxy composite are fishing rods, storage tanks and aircraft parts (i.e. fuselage) due to its excellent tensile strength, light weight and low cost.

This laboratory has two objectives. Firstly to construct a single circular E-glass epoxy composite dome that consists 4 layers of E-glass fabric and epoxy resin using a vacuuming process. These 4 layers of glass have different fibre arrangements (biaxial plain weave and tri-axial fibre) and within the composite are aligned to provide maximised strength in several directions. The aim is to create as high a quality composite part as possible. The second objective is to take a note on each step of process, accurately recording data such as the weight of each E-glass layer and the amount of resin consumed by each individual layer of fibre sheet.
The final product produced will be analysed for faults and compared to what would be expected in the industry or what could theoretically be better done.

Measuring and cutting the fibers

The direction of the fiber was marked and placed carefully on the dome mould.

During construction, great care is taken to ensure the individual fibres are not damaged. This is done by radially working the roller on the fibre sheets and avoiding over working any particular section. If too many fibres are damaged, then when the part is put under load the fibres could pull out resulting in failure closer to the failure point of the matrix meaning the fibres have not improved the part as desired.

Resin was applied on the fibers.

An important step in the manufacture of composites is to ensure the matrix material incorporates all the fibres. This is so all forces applied to the composite are properly transferred to all of the fibres. In the lab, it was attempted to ensure this occurs by saturating each fibre layer with resin before applying to the mould. This amount of saturation is determined when the fibre sheet becomes more transparent; but this can be hard to judge and does not absolutely ensure saturation. If there are sections of poorly saturated fibre in the final part than there may be fibres that are not bearing load when the part is put under force, reducing the total strength of the part.

The removal of air bubbles before vacuuming process.

Air was pumped out by vacuum pump.

As the process of preparing each sheet took a considerable amount of time, the resin reservoir progressively hardened and became increasingly difficult to spread. This may lead to issues such as voids of resin where saturation has not occurred but probably has a more pronounced impact on how each layer adheres to each other. If a lamina is not correctly bonded to its surrounding lamina then the matrix material between them could fail under load and the laminate could come apart. Avoiding this issue was attempted by working quickly, but it was still needed to mix additional resin as the first batch hardened before completion of the layering process.

Weight constant

Portion number	Cup (g)	Resin base (g)	Resin hardener (g)	Total resin (g)
1	10.9	242.7	47.1	289.8
2	19.5	57.3	12.8	70.1

Table 1: Weight constant used in the experiment

Weight data

Layer no.	Type	Dry weight of plastic sheet (g)	Dry weight of Fiber (g)	Remaining resin Weight (g)
1	Tri-axial	17.6	75.3	9.1
2	Biaxial	21.1	70.8	14.2
3	Tri-axial	17.6	80.6	16.1
4	Biaxial	23.1	78.6	26.7

Table 2: The weight data obtained from the experiment

Portion number

Cup (g)

Resin base (g)

Resin hardener (g)

Total resin (g)

1

10.9

242.7

47.1

289.8

2

19.5

57.3

12.8

70.1

Layer no.

Type

Dry weight of plastic sheet (g)

Dry weight of

Fiber (g)

Remaining resin

Weight (g)

1

Tri-axial

17.6

75.3

9.1

2

Biaxial

21.1

70.8

14.2

3

Tri-axial

17.6

80.6

16.1

4

Biaxial

23.1

78.6

26.7