Areca leaves were collected from various parts of Bangalore.Fibers were used for studying the strength and for preparing composites.These leaves were kept soaked in water for around 2-8 days.Soaking process of leaves loosens the fibers and it can be easily extracted.Using brush made of metal wire fibers were separated from the leaves.It is then kept in room temperature and dried.Extracted fibers are also called untreated fibers.
2.Basic raw materials
• Matrix material
• Reinforcing material
2.1 Matrix material
Matrix is the component which holds the reinforcements of composites together.Body and grips for the composite is provided by matrix.And these are usually lower in strength than the reinforcements.The matrix must possess capability of being forced about the reinforcements during the manufacture of composites.Reinforcing of fibers into matrix resins forms the composite.
Resins are organic polymers used as matrix to hold fibrous reinforcements in composite materials or as adhesives also.
The motives of matrix are to provide
i. Transferring load to fibers
ii. Dimensional ability
iii. Fiber support
v. Quality surface finish
• Lapox L-12(Epoxy)
These are liquid, unmodified epoxy resins of medium viscosities which can be able to use with various hardeners in order to make reinforced composites and laminates. The selection of hardeners depends on the method of processing and also on the required properties of the cured composites.
Table 1.1 - Properties of Epoxy Resins
Epoxy Resin (Lapox L-12)
Appearance ------ Clear liquid
Epoxy value Eq/kg 5.25-5.4
Hydrolysable chlorine % 0.1 max
Viscosity at 250 mPas 10000-12000
Volatile content % 0.55 max
These are low viscosity room temperature curative aliphatic amine curative agents.These are mostly employed in civil engineering systems where low viscosities and setting fast at ambient temperatures are desired.
Table: 1.2 - Properties of Hardener K-6
Appearance ------ Clear liquid
Viscosity at 250 mPas 10-23
Refractive Index ------ 1.4940-1.5000
Water content % 1 max
2.2 Reinforcing material
Fibrous materials which when bring together to polymer matrix produces dramatic progresses in the physical properties of composites. Reinforcements improves the total mechanical properties of matrix. For the fabrication of composites an extensive variety of chopped fibers of different lengths are used. 50mm, 30mm & 10mm are the fibers of various dimensions.
3.Fabrication: Hand lay-up technique
In this method resins are filled by hand into the fiber which is in the arrangement of casually distributed fabrics.Hand lay-up processes are accomplished by different types of rollers or brushes. composite plates form as the test samplings were fabricated by using traditional Hand lay-up method. It is a very common technique of composite fabrication, restricted by its capacity to produce simple profiles.
A plate comprising of Epoxy resins with small areca sheath fibers reinforcements were fabricated with addition of Hardeners. The plates were made with 60% of Epoxy resins and 40% of small areca sheath fibers by volume.
Succeeding fabrications of plates tangled with various fiber sizes which were followed by construction of plate with same resin.
4 Fabrication Steps
• Bottom slab of mould is carefully cleaned with the thinner, smoothen by the wax polish and the release film like Polyvinyl Alcohol solutions are spread on it.
• The same practice is followed for upper slab also.
• The hardeners and Epoxy mixed in the ratios of 1:10.
• The preliminary material preparation comprises getting the areca fibers cut to anticipated dimensions.
• Chopped fibers of diverse fiber lengths as 50mm, 30mm & 10mm.
• Chopped fibers were randomly spread over surfaces of the die.
• Weight of fibers are determined, in harmony with which the amount of resins to be used are decided in such a way that the finishing plates are made using approximate fibers and resins by weight.
• Curing additives are added in specific amounts and stirred thoroughly.
• Fibers are casually scattered on the plates and resins are applied.
• Detailed compactions are achieved to avoid air bubble entrapment. The moulds are closed by upper slab.
• Top block accounts of C-clamps which compresses lay-up to the anticipated thickness of 3.5mm to 4.0mm, which is preserved using suitable stoppers and lay-up is permitted to cure form 18-25hours beforehand it is recovered from the moulds.
• All the above given steps are reiterated to fabricate different Fiber lengths.
Fig:1.2-Die forming the mould Fig:1.3-Affixation of release
Fig: 1.4 - Stirring the matrix Fig: 1.5 - Curing stage
INTRODUCTION TO EXPERIMENTAL TEST
2.1 The key purposes of testing composites
• Evaluation and optimization of materials.
• For determining the special effects of equipments and tool designs.
• Evaluation and optimization of manufacturing processes that are available.
• For establishing engineering design informations.
• For measuring the qualities and reproducibilities of finish products.
• For ensuring the quality of raw material.
2.2 Types of conducted tests
• Tensile test
• Flexural test
2.2.1 Tensile test
Tensile tests are known to be the most important type of mechanical tests we can perform on any material.These tests are simple, comparatively less expensive, and entirely standardized. By pulling any specimens we can find the tensile strength of that material by evaluating its deformations. As we continues to pull the materials until it gets broke, we will be obtaining good and complete tensile profiles. A curve will show the results how it had reacted to the applied forces.And the Ultimate strengths are calculated founded on gross cross sectional areas.
• Hooke’s law
For almost all the tensile testings of materials,it is noticed in the initial portions of the graphs, the relationships between the applied forces, loads, and the elongations of the specimens are found to be linear. In these linear regions,lines obey the relationship known as “Hooke’s Law”. The ratios of stress to strain is constant according to Hooke’s law. The slopes of the lines (E) in these regions where the stress (σ) is found to be proportional to the strain (ε) and are termed as “Modulus of Elasticity”.
• Modulus of elasticity
It is the measure of stiffness of a material. But it is only applied in the linear regions of the curve. If any specimens are loaded within these linear regions, the materials will be returning to its precise same conditions when the loads are removed. Hooke’s Law will be no more applied and more or less permanent deformations occurs in the specimens at a point where the curves are no more linear and when deviates from straight line relationships. These points are known as “proportional or elastic limit”. Behaviour of materials under loads are calculated by Young’s modulus. For example, the extent a fiber will lengthen under tension can be calculated by Young’s modulus, or in which load a thin column buckles under compressions. Some calculations also requires the use of other material properties, such as the shear modulus, density or Poisson’s ratio.
The internal distributions of forces per unit areas which balances and reacts to the external loads that applied to any body. Stresses are often broken down to its shear and usual components as all these have its unique physical significances.
...(download the rest of the essay above)