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Any material consisting of two or more components with different properties and distinct boundaries between the components can be referred as composite material. The idea of combining several components to produce a material with properties that are not attainable with individual components has been used by man for thousands of years.
To utilize high strength and stiffness of fibers, they are bound with a matrix material whose strength and stiffness are much lower than those of fibers. Matrix materials provide the final shape of the composite structure and govern the parameters of the manufacturing process.Optimal combination of fiber and matrix properties should satisfy a set of operational and manufacturing requirements.
The primary functions of resin are to transfer stress between the reinforcing fibers, act as a glue to hold the fibers together and protect the fibers from mechanical and environmental damage.
First of all, the stiffness of the matrix should correspond to the stiffness of the fibers and must be sufficient to provide uniform loading of fibers. The fibers are usually characterized with relatively high scatter of strength that could be increasing due to the damage of the fibers caused by the processing equipment. Naturally, fracture of the weakest or damaged fiber should not result in material failure. Instead, the matrix should evenly redistribute the load from the broken fiber to the adjacent ones and then load the broken fiber at a distance from the cross-section at which it failed. The higher is the matrix stiffness, the smaller is this distance, and the less is the influence of damaged fibers on material strength and stiffness. Moreover, the matrix should provide the proper stress diffusion.
Resins are divided into two major groups known as thermoset and thermoplastic. Thermoplastic resins become soft when heated, and may be shaped or molded while in a heated semi-fluid state and become rigid when cooled. Thermoset resins, on the other hand, are usually liquids or low melting point solids in their initial form.
When used to produce finished goods, these thermosetting resins are 'cured' by the use of aÂ catalyst, heat or a combination of the two. Once cured, solid thermoset resins cannot be converted back to their original liquid form.
Unlike thermoplastic resins, cured thermosets will not melt and flow but will soften when heated (and lose hardness) and once formed they cannot be reshaped.Â
Heat Distortion TemperatureÂ (HDT) and theÂ Glass Transition Temperature (Tg) are used to measure the softening of a cured resin. Both test methods (HDT and Tg) measure the approximate temperature where the cured resin will soften significantly to yield (bend or sag) under load.
The most common thermosetting resins used in the composites industry are unsaturated polyesters, epoxies, vinyl esters and phenolics. There are differences between these groups that must be understood to choose the proper material for a specific application.
Epoxy resins have a well-established record in a wide range of composite parts, structures and concrete repair. A major benefit of epoxy resins over unsaturated polyester resins is their lowerÂ shrinkage. Generally epoxies are cured by addition of an anhydride or an amine hardener as a 2-part system. DifferentÂ hardeners, as well as quantity of a hardener produce a different cure profile and give different properties to the finished composite.
Epoxies are used primarily for fabricating high performance composites with superior mechanical properties, resistance to corrosive liquids and environments, superior electrical properties, good performance at elevated temperatures, good adhesion to a substrate, or a combination of these benefits. Epoxy resins are used with a number of fibrous reinforcing materials, including glass, carbon and aramid. Epoxies are compatible with most composite manufacturing processes, particularly vacuum-bag molding, autoclave molding, pressure-bag molding, compression molding, filament winding and hand lay-up.
Thus, properties of any composite material are mainly dependent on the properties of fibers as well as the matrix used for them. If we can improve the existing matrix properties with respect to load transfer characteristics, matrix stiffness, thermal resistance, chemical resistance, crack corrosion etc. without affecting strength/weight ratio; then a lot of material, money and time can be saved without compromising the safety of humans.
CHAPTER 2: LITERATURE REVIEW
2. Present Theories and Practices:
Autar K. Kaw  emphasizes on overview of composites followed by their basic mechanical behavior. It introduces basic ideas about composites including importance in today's world. Other topics include types of fibers and matrices, manufacturing, applications, recycling and basic definitions used in the mechanics of composites. This book also gives review on experimental characterization of the mechanical properties of a lamina. Other mechanical design issues such as fatigue, environmental effects and impact are also introduced.
Robert Jones  gives detailed information regarding introduction, theory and testing on composites materials. Composites materials are ideal for structural applications where high strength to weight ratio are required. Aircraft and spacecraft are typical weight sensitive structures in which composite materials are cost effective. The studies of composite materials include manufacturing processes, anisotropic elasticity, strength and micromechanics.
BrahimAttaf  gives special focus on Sustainable materials and eco-design aspects, curing processes, modeling and testing of composites, Stress-strength analysis of adhesive joints, Characterization and thermal behavior in an eco-friendly manner which is very much essential in world's socio-economic well-being and living conditions for present and future generations. By adopting these principles of sustainable design,Specific recommendations
are to give much more focus and attention to the chemical substances used inthe manufacturing process, the amount of VOC emissions, the enhancement ofquality-health-environment performance, the amount of waste produced, expired materials and ways of recycling.
Daniel Gay, Suong V. Hoa, Stephen W. Tsai  presents an introduction to composite materials, the fabrication processes, the properties of a single ply, sandwich materials, conceptual design, assembly and applications of composites in the aerospaceand other areas. It also focuses on elastic anisotropic properties, the directional dependence of different properties and mechanical properties of thin laminates. It deals with the determination of mechanical properties of composite structures in different forms such as plates, tubes or composite components made using different processes such as hand-lay-up or filament winding.
L. Glas, P. S. Allan, T. Vu-Khanh, A. CervenkaAn overview is given of the mechanical performance (stiffness, strength, toughness, creep ...) of finite fiber length reinforced thermoplastics based on polypropylene and polyamide as the matrices and glass, carbon and Kevlar as the reinforcement. Different degrees of fiber orientation distribution and fiber attrition as produced by classical injection molding and multiple-live feed molding were evaluated. It shows that the simple test geometry used (injection molded plaques) resembled more a complicated structure than a material. Increased alignment of the fibers in a given direction affected all the mechanical properties, but the effect was largest for the tensile stiffness. A higher degree of fiber orientation was not accompanied by an increase in properties related to failure (ultimate stress, KIc).
Presently used resins for composite materials of aircrafts and automobiles are mostly made up from polymers or synthetic resins. But this newly developed matrix is composed of basic ingredients such as carbohydrates, proteins, natural gum & cotton fibers as reinforcing materials which are biodegradable or herbal in nature.
Newly developed glue has already been demonstrated for certain applications and has benefits in terms of ballistic application, high temperature withstanding capacity, high impact resistance, high unidirectional tensile strength etc. as tested at DRDO HYDRABAD. However till date it has not been evaluated scientifically to assess it applicability at par with existing matrix vis-à-vis epoxy matrix.
Thus the aim of this project is to study the mechanical behavior and analyze the characteristics of newly developed matrix which can be used for composite materials.
Extensive Literature Survey
Study of newly developed composite matrix (glue) and manufacturing methods.
Testing of Matrix properties and its comparison with Epoxy.
Feasibility study on manufacturing process for making laminate with carbon/glass fibers.
Making test specimen from laminate.
Analytical estimation of properties of composite test specimen with new matrix.
Validation through structural testing.
Expected completion date of work: June 2013
Literature review on composite materials.
Literature review on various manufacturing methods of composites.
Study of the manufacturing method of newly developed matrix 'BRAMHA RESIN'.
Literature review on various international codes & standards followed for testing of composite materials for characterization of resin.
Study of the basic mechanical properties that needs to be found out to characterize the 'BRAMHA RESIN'.
Selection of particular codes & standards for testing of resin under consideration.
Determination of physical properties of the resin.
Study of feasibility of carbon & glass fiber as reinforcement for Bramha resin.
Study of effect of fiber orientation on strength of composites.
Study of manufacturing methods that can be used for preparation of the specimens as per the selected standards & codes oftesting.
Preparation of molds for making specimen.
Preparation of specimen using carbon & glass fiber as reinforcement.
Extensive Literature Survey
Study of newly developed composite matrix (glue)
Study of various manufacturing methods
Feasibility study on manufacturing processes for glass/carbon fiber laminates
Making test specimen from laminates
Analytical estimation of properties of test specimen
Proposed work work completed work remained
CHAPTER 3: COMPOSITE MATERIALS
3.1 COMPOSITE MATERIAL: - BRAMHA RESIN
This material is a polymeric resin prepared from naturally available organic ingredients such as wheat, cereals, carbohydrates, proteins, natural gum etc. This material is selected for testing based upon its feasibility for following applications.
Bulletproof jackets & helmets
All the above mentioned are challenging applications & requires advanced materials of very high strength as well as low weight as possible i.e. high strength per unit weight. For this peculiar requirement carbon fibers and glass fibers are most suitable among all available options. Due to this reason this newly developed BRAMHA resin is reinforced with carbon & glass fibers to prepare the composite material.
Basically fiber reinforced composite materials are of 3 types:
Polymer based composites
Metallic based composites
Ceramic based composites
Since the Bramha resin is one kind of polymer, the materials produced form this resin falls under the category of polymer based composites.
FUNCTIONS OF THE MATRIX: -
The matrix binds the fibers together, holding them aligned in the important stressed directions. Loads applied to the composite are then transferred into the fibers, the principal load-bearing component, through the matrix enabling the composite to withstand compression, flexural and shear forces as well as tensile loads. The ability of composites reinforced with short fibers to support loads of any kind is dependent on the presence of the matrix as the load-transfer medium, and the efficiency of this load transfer is directly related to the quality of the fiber/matrix bond.
The matrix must also isolate the fibers from each other so that they can act as separate entities. Many reinforcing fibers are brittle solids with highly variable strengths. When such materials are used in the form of fine fibers, not only are the fibers stronger than the monolithic form of the same solid, but there is the additional benefit that the fiber aggregate does not fail catastrophically. Moreover, the fiber bundle strength is less variable than that of a monolithic rod of equivalent load-bearing ability. But these advantages of the fiber aggregate can only be realized if the matrix separates the fibers from each other so that cracks are unable to pass unimpeded through sequences of fibers in contact, which would result in completely brittle composites.
The matrix should protect the reinforcing filaments from mechanical damage (eg. abrasion) and from environmental attack. Since many of the resins which are used as matrices for glass fibers permit diffusion of water, this function is often not fulfilled in many GRP materials and the environmental damage that results is aggravated by stress. In cement the alkaline nature of the matrix itself is damaging to ordinary glass fibers and alkali-resistant glasses containing zirconium have been developed (Proctor & Yale, 1980) in an effort to counter this. For composites like MMCs or CMCs operating at elevated temperature, the matrix would need to protect the fibers from oxidative attack.
A ductile matrix will provide a means of slowing down or stopping cracks that might have originated at broken fibers. Conversely, a brittle matrix may depend upon the fibers to act as matrix crack stoppers.
Through the quality of its 'grip' on the fibers (the interfacial bond strength), the matrix can also be an important means of increasing the toughness of the composite.
By comparison with the common reinforcing filaments most matrix materials are weak and flexible and their strengths and moduli are often neglected in calculating composite properties. But metals are structural materials in their own right and in MMCs their inherent shear stiffness and compressional rigidity are important in determining the behavior of the composite in shear and compression.
3.2.1 Fiber Factors Contribute To The Mechanical Performance Of A Composite:
â€¢ Length: The ï¬bers can be long or short. Long, continuous ï¬bers are easy to orient and process, but short ï¬bers cannot be controlled fully for proper orientation. Long ï¬bers provide many beneï¬ts over short ï¬bers. These include impact resistance, low shrinkage, improvedsurface ï¬nish and dimensional stability. However, short ï¬bers provide low cost, are easy to work with and have fast cycle time fabrication procedures Short ï¬bers have fewer ï¬‚aws and therefore have higher strength.
â€¢ Orientation: Fibers oriented in one direction give very high stiffness and strength in that direction. If the ï¬bers are oriented in more than one direction, such as in a mat, there will be high stiffness and strength in the directions of the ï¬ber orientations. However for the same volume of ï¬bers per unit volume of the composite, it cannot match the stiffness and strength of unidirectional composites.
â€¢ Shape: The most common shape of ï¬bers is circular because handling and manufacturing them is easy. Hexagon and square-shaped ï¬bers are possible, but their advantages of strength and high packing factors do not outweigh the difficulty in handling and processing.
â€¢ Material: The material of the ï¬ber directly inï¬‚uences the mechanical performance of a composite. Fibers are generally expected to have high elastic moduli and strengths. This expectation and cost have been key factors in the graphite, aramids, and glass dominating the ï¬ber market for composites.
3.2.2 Matrix Factors Contribute To the Mechanical Performance of Composites:-
Use of ï¬bers by themselves is limited, with the exceptions of ropes and cables. Therefore, ï¬bers are used as reinforcement to matrices. The matrix functions include binding the ï¬bers together, protecting ï¬bers from the environment, shielding from damage due to handling, and distributing the load to ï¬bers. Although matrices by themselves generally have low mechanical properties compared to those of ï¬bers, the matrix inï¬‚uences many mechanical properties of the composite.
These properties include
Transverse modulus and strength
Shear modulus and strength
Inter laminar shear strength
Thermal expansion coefficient
Other than the ï¬ber and the matrix, other factors inï¬‚uence the mechanical performance of a composite include the ï¬ber-matrix interface. It determines how well the matrix transfers the load to the ï¬bers. Chemical, mechanical, and reaction bonding may form the interface. In most cases, more than one type of bonding occurs.
â€¢ Chemical bonding is formed between the ï¬ber surface and the matrix. Some ï¬bers bond naturally to the matrix and others do not. Coupling agents are often added to form a chemical bond.
â€¢ The natural roughness or etching of the ï¬ber surface causing inter-locking may form a mechanical bond between the ï¬ber and matrix.
â€¢ If the thermal expansion coefficient of the matrix is higher than that of the ï¬ber and the manufacturing temperatures are higher than the operating temperatures, the matrix will radially shrink more than the ï¬ber. This causes the matrix to compress around the ï¬ber. Reaction bonding occurs when atoms or molecules of the ï¬ber and the matrix diffuse into each other at the interface. This inter-diffusion often creates a distinct interfacial layer, called the interphase, with different properties from that of the ï¬ber or the matrix. Although this thin interfacial layer helps to form a bond, it also forms micro-cracks in the ï¬ber.These micro cracks reduce the strength of the ï¬ber and thus that of the composite.
3.3 DRAWBACKS AND LIMITATIONS IN USE OF COMPOSITES:
â€¢ High cost of fabrication of composites is a critical issue. For example a part made of graphite/epoxy composite may cost up to 10 to 15times the material costs. Improvements in processing and manufacturing techniques will lower these costs in the future. Already, manufacturing techniques such as SMC (sheet molding compound) and SRIM (structural reinforcement injection molding) are lowering the cost and production time in manufacturing automobile parts.
â€¢ Mechanical characterization of a composite structure is more complex than that of a metal structure. Unlike metals, composite materials are not isotropic, that is, their properties are not the same in all directions. Therefore, they require more material parameters. For example, a single layer of a graphite/epoxy composite requires nine stiffness and strength constants for conducting mechanical analysis. In the case of a monolithic material such as steel, one requires only four stiffness and strength constants. Such complexity makes structural analysis computationally and experimentally more complicated and intensive. In addition, evaluation and measurement techniques of some composite properties, such as compressive strengths, are still being debated.
â€¢ Repair of composites is not a simple process compared to that for metals. Sometimes critical ï¬‚aws and cracks in composite structures may go undetected. Composites do not have a high combination of strength and fracture toughness compared to metals. Metals show an excellent combination of strength and fracture toughness compared to composites.
CHAPTER 4: BRAMHA RESIN
4.1 MANUFACTURING METHOD ADAPTED FOR BRAMHA RESIN: -
The process of curing of conventional resin such as epoxy takes hours of time and thousands of temperature to cure prepegs or composite laminate. For the preparation of Brahma resin a novel method is adapted. In this method, wheat or any other material mentioned above is boiled continuously for minimum 40 minutes by mixing with water. Then the mixture is fed to the crushing machine where it is crushed continuously for 10 minutes.
After crushing, the mixture is then taken to the pressing machine where it is pressed so that the pure solvent or glue is separated from the solid or undissolved residue. This process is carried for nearly 10 minutes. Then the pure solvent separated from it which is semi liquid in state is taken to another pot. It is mixed with water & kept as it is for 1 day. The mixture is then again fed to the crushing so that thorough mixing occurs & finally we get the glue or resin as an extract.
THE LIQUID FOR 10 MINUTES
CRUSHING AGAIN TO CREATE POWDER
FOR 1 DAY
IN PLATE DRYER
EXTRACTED LIQUID FOR 30 MINUTES
PRESSING OF LIQUID TO SEPARATE
IN A CONTAINER FOR MIN.40 MINUTES
Fig.4.1 Block diagram of manufacturing method used for preparation of Bramha resin.
4.2 CARBON & GLASS FIBERS AS REINFORCEMENT: -
The theoretical strength of a given type of solid is determined by the strengths of the atomic or molecular bonds that hold the solid together. And although the practical strengths of solids are determined by the defects which they contain, it is necessary to seek materials with the strongest chemical bonds if we are to have the best chance of exploiting the principle of composite materials construction.
4.2.1 GLASS FIBERS: -
Glass fibers are manufactured by drawing molten glass into very fine threads and then immediately protecting them from contact with the atmosphere or with hard surfaces in order to preserve the defect-free structure that is created by the drawing process. Glass fibers are as strong as any of the newer inorganic fibers but they lack rigidity on account of their molecular structure. The properties of glasses can be modified to a limited extent by changing the chemical composition of the glass, but the only glass used to any great extent in composite materials is ordinary borosilicate glass, known as E-glass. The largest volume usage of composite materials involves E-glass as the reinforcement. S-glass has somewhat better properties than E-glass, including higher thermal stability, but its higher cost has limited the extent of its use.
Table 4.1 Chemical composition of E-glass & S-glass fibers
Chemical composition of E-glass & S-glass fibers
Comparison of Properties of E-Glass and S-Glass: -
Table 4.2 Properties of E-Glass and S-Glass
Ultimate tensile strength
Coefficient of thermal expansion
4.2.2 CARBON FIBERS: -
By oxidizing and pyrolysing a highly drawn textile fiber such as polyacrylonitrile (PAN), preventing it from shrinking in the early stages of the degradation process, and subsequently hot-stretching it, it is possible to convert it to a carbon filament with an elastic modulus that approaches the value we would predict from a consideration of the crystal structure of graphite, although the final strength is usuallywell below the theoretical strength of the carbon-carbon chain. The influence of strength-limiting defects is considerable, and clean-room methods of production can result in substantial increases in the tensile strength of commercial materials. Prior to sale, fibers are usually surface-treated by chemical or electrolytic oxidation methods in order to improve the quality of adhesion between the fiber and the matrix in a composite. Depending on processing conditions, a wide range of mechanical properties can be obtained, and fiber can therefore be chosen from this range so as to give the desired composite properties.
Fig. 4.2 Forms of available ï¬bers
Table4.3 Speciï¬c Modulus and Speciï¬c Strength of Typical Fibers, Composites and Bulk Metals
4.3 REASONS FOR USING FIBERS OF THIN DIAMETER: -
â€¢ Actual strength of materials is several magnitudes lower than the theoretical strength. This difference is due to the inherent ï¬‚aws in the material. Removing these ï¬‚aws can increase the strength of the material. As the ï¬bers become smaller in diameter, the chances of an inherent ï¬‚aw in the material are reduced. A steel plate may have strength of 100 ksi (689 MPa), while a wire made from this steel plate can have strength of 600 ksi (4100 MPa). Figure shows how the strength of a carbon ï¬ber increases with the decrease in its diameter.
For higher ductility and toughness and better transfer of loads from the matrix to ï¬ber, composites require larger surface area of the ï¬ber-matrix interface. For the same volume fraction of ï¬bers in acomposite, the area of the ï¬ber-matrix interface is inversely proportional to the diameter of the ï¬ber and is proved as follows.
Assume a lamina consisting of N ï¬bers of diameter D. The ï¬ber-matrix interface area in this lamina is
AI = N Ï€ D L .â€¦..(1)
If one replaces the ï¬bers of diameter D by ï¬bers of diameter d, then the number of ï¬bers, n, to keep the ï¬ber volume the same would be
n= N ..â€¦.(2)
Then, the ï¬ber-matrix interface area in the resulting lamina would be
AII = n Ï€ d L. â€¦â€¦(3)
This implies that, for a ï¬xed ï¬ber volume in a given volume of composite, the area of the ï¬ber-matrix interface is inversely proportional to the diameter of the ï¬ber.
Fibers able to bend without breaking are required in manufacturing of composite materials, especially for woven fabric composites. Ability to bend increases with a decrease in the ï¬ber diameter and is measured as ï¬‚exibility. Flexibility is deï¬ned as the inverse of bending stiffness and is proportional to the inverse of the product of the elastic modulus of the ï¬ber and the fourth power of its diameter; it can be proved as follows.
Bending stiffness is the resistance to bending moments. According to the Strength of Materials course, if a beam is subjected to a pure bending moment, M,
v = deï¬‚ection of the centroidal line (in. or m)
E = Young's modulus of the beam (psi or Pa)
I = second moment of area (in.4 or m4)
x = coordinate along the length of beam (in. or m)
The bending stiffness, then, is EI and the ï¬‚exibility is simply the inverse of EI. Because the second moment of area of a cylindrical beam of diameter d is
Flexibility âˆ â€¦â€¦(6)
For a particular material, unlike strength, the Young's modulus does not change appreciably as a function of its diameter. Therefore, the ï¬‚exibility for a particular material is inversely proportional to the fourth power of the diameter.
Fig. 4.3Fiber strength as a function of ï¬ber diameter for carbon ï¬bers
4.4 PREPARATION OF LAMINATES: -
For conventional composite material laminate preparation following methods are used mostly
Compression molding: -C:\Users\OMKAR\Desktop\compression molding.jpg
Fig.4.4 Compression molding
With compression molding, the counter mold will close the moldafter the impregnated reinforcements have been placed on the mold. The wholeassembly is placed in a press that can apply a pressure of 1 to 2bars.Thepolymerization takes place either at ambient temperature or higher.
Vacuum molding: -C:\Users\OMKAR\Desktop\vacuum molding.jpg
Fig. 4.5 Vacuum molding
This process of molding with vacuum is still called depression moldingor bagmolding. As in the case of contact molding one uses anopen mold on top of which the impregnated reinforcements are placed. In thecase of sandwich materials, the cores are also used. One sheetof soft plastic is used for sealing this is adhesively bonded to the perimeter of the mold. Vacuum is applied under the piece of plastic. Thepiece is then compacted due to the action of atmospheric pressure, and the airbubbles are eliminated. Porous fabrics absorb excess resin. The whole materialis polymerized by an oven or by an autoclave under pressure 7 bars in the caseof carbon/epoxy to obtain better mechanical properties. This process has applications for aircraft structures, with the rate of a few parts per day.
Resin injection molding: -C:\Users\OMKAR\Desktop\injection molding.jpg
` Fig. 4.6 Injection molding
With resin injection molding the reinforcements such as mats, fabrics are put in place between the mold and counter mold. The polyester or phenolicresin is injected. The moldpressure is low. This process can produce up to 30 pieces per day. The investment is less costly and has application in automobile bodies.
Filament winding: -C:\Users\OMKAR\Desktop\filament winding.jpg
Fig. 4.7 Filament winding
For pieces which revolve around their midpoint, winding is done on a mandrel.The process of filament windingcan be integrated into acontinuous chain of production and can fabricate tubes of long length. The rateof production can be up to 500 kg of composite per day. These can be used tomake missile tubes, containers, or tubes for transporting petroleum.The fiber volume fraction is high (up to 85%). This process is also used to fabricate components of high internal pressure, such as reservoirs and propulsion nozzles.
Apart from these, there are many other manufacturing methods available in the market.
4.5 LAMINATE PREPARATION BY USING BRAMHA RESIN: -
For preparation of laminates from Brahma resin, "hand layup", a simple & easy method is used. This method is used as we required only limited no. of specimen of fixed size & geometry. For making these specimens, molds are prepared from 10 mm thickness & 2 inch width aluminium plate. Aluminium plates are selected due to the reason that they do not get adhere to the glue or resin or the mold from which we are going to prepare the laminates & specimen can be removed easily from the mold after curing.
For making laminates, slots of the required size have been created on the aluminium plates by milling cutter so that fine surface finish can be also achieved. Additional 2 inches distance along length is added for easy handling, removal& proper gripping of specimen. Carbon & glass fibers are used in the form strips cut from mats. Molds are placed on perfectly horizontal surface so as to have uniform resin flow & continuity throughout the length of the specimen.
First, a thin layer of resin is placed uniformly in mold. Then 1st strip of fiber mat is placed above the resin. Then again 2nd layer of resin is placed over the 1st layer of fibers. 2nd strip of fiber mat is then placed over the 2nd layer of resin. This process is continued till required thickness is achieved. The top of the mold is then covered by another perfectly flat aluminium plate & a load of 10- 15 kg is applied on it so that perfectly compact specimen can be prepared & air cavities or bubbles get removed. Also additional glue is get removed.
F:\UTTAM PATIL PVT. LTD\prroojecta\some snaps\mold.jpg
Fig.4.8 Mould for specimen preperation
Fig.4.9 Hand layup method of specimen preparation
4.6 PHYSICAL PROPERTIES: -
RESIN CONTENT BY SOLVENT EXTRACTION: -
Objective: -The objective of this test is to determine the resin content in a cured laminate.
No. of specimen: - 3
Size of specimen: - 20mm Ã- 20mm.
Weight: - 1gm.
Materials required: - Conc. Sulphuric acid (sp. Gr. 1.83).
- Hydrogen peroxide
- Distilled water
- Precision balance
- Filtering crucible (15-40 microns)
Weigh the sample.
Place sample in flask containing about 25ml of concentrated sulphuric acid.
Heat the flask.
When resin begins to decompose add drop by drop H2O2(total amount 25-30 ml).
Keep adding H2O2till solution becomes transparent & fibers rise to the surface of liquid.
Allow the flask to cool down.
Weigh a clean crucible cooled after drying at 110Ëšc in a dryer.
Pour the content of the flask into the filtering crucible.
Rinse the fibers with acetone followed by distilled water.
Dry it in an oven at110Ëšc.
Take out crucible from oven & leave it to cool down.
After cooling, weigh the crucible immediately.
Analysis of results: -
Size of specimen- 10Ã-10Ã-1 mm
Weight of specimen- 1) 0.46 gm. 2) 0.43 gm. 3) 0.47 gm.
Weight of fibers after test- 1) 0.1270 gm. 2) 0.1034 gm. 3) 0.1173 gm.
Resin content- 1) 0.333gm 2) 0.3246 gm. 3) 0.3527 gm.
Resin %- 1)72.39 2)75.48 3) 75.04
Average resin content: - 74.30%
Fig.4.10 Resin content determination by solvent extraction
WEIGHT & DENSITY:-
Carbon Fiber Reinforced Specimen:-
Table 4.4 Density of carbon fiber specimen size 1"
Table 4.5 Density of carbon fiber specimen size Â½"
Glass fiber reinforced specimen: -
Table 4.6 Density of glass fiber specimen size 1"
Pure resin (without reinforcement): -
Table 4.7 Density of pure resin specimen
1" carbon fiber reinforced- 1.4Ã-103 (kg/m3).
Â½" carbon fiber reinforced- 1.57Ã-103 (kg/m3).
1" glass fiber reinforced- 1.41Ã-103 (kg/m3).
Pure resin- 1.82 (kg/m3).
WATER ABSORPTIVITY: -
As the material under consideration is an organic polymer, water absorbing capacity of the prepared specimen need to be checked.
No. of specimen tested: -3
Size of specimen: - 1/2"Ã-1" Ã-1mm
Weigh the specimen before testing.
Place the specimen in beaker containing 100 ml water for 72 hours approximately.
After 72 hours, take out the specimen from the beaker & clean them with dry cotton.
Weigh the specimen immediately after cleaning.
Weight of specimen before test: - (1) 0.7603 gm.
(2) 0.7814 gm.
(3) 0.7732 gm.
Weight of specimen after test: -(1) 0.7685 gm.
(2) 0.7884 gm.
(3) 0.7775 gm.
% of Water absorbed: - (1) 0.0082 gm. = 1.0780%
(2) 0.0070 gm. = 0.8958%
(3) 0.0043 gm. = 0.5561%
Similarly, the test is conducted for pure resin specimen.
Size of specimen:-2.5"Ã-2"Ã-0.5".
Weight of specimen before test: - 3.4882 gm.
Weight of specimen after test: - 3.5093 gm.
% of water absorbed: - 0.0211 gm. = 0.6048%.
CHAPTER 5: SPECIMEN PREPARATION
5.1 STANDARD USED FOR TENSILE TESTING
ASME D 3039/D 3039M-00
ASMEis standard used for structural properties of composite laminate. ASTM stands for American Society for Material Testing which is a well-known standard used worldwide. ASTM D3039/D3039M-00is standard test method for Tensile Properties of Polymer Matrix Composite Materials. Important particulars about the test are given below.
This test method determines the in-plane tensile propertiesof polymer matrix composite materials reinforced byhigh-modulus fibers. The composite material forms are limitedto continuous fiber or discontinuous fiber-reinforced compositesin which the laminate is balanced and symmetric withrespect to the test direction.
This test method is designed to produce tensile propertydata for material specifications, research and development,quality assurance, and structural design and analysis. Factorsthat influence the tensile response and should therefore bereported include the following: material, methods of materialpreparation and lay-up, specimen stacking sequence, specimenpreparation, specimen conditioning, environment of testing,specimen alignment and gripping, speed of testing, time and temperature, void content and volume, percent reinforcement. Properties in the test direction which may be obtained fromthis test method include the following:
1. Ultimate tensile strength,
2. Ultimate tensile strain,
3. Tensile chord modulus of elasticity,
4. Poisson's ratio
TEST SPECIMENS: -
SAMPLING-Test at least five specimens per test conditionunless valid results can be gained through the use of fewerspecimens, such as in the case of a designed experiment.
GEOMETRY-Design of mechanical test coupons, especially those using end tabs, remains to a large extent an artrather than a science, with no industry consensus on how to approach the engineering of the gripping interface. Each major composite testing laboratory has developed gripping methods for the specific material systems and environments commonly encountered within that laboratory. Comparison of these methods shows they differ widely, making it extremely difficultto recommend a universally useful approach or set of approaches. The specimen dimensions for balanced and symmetric fiber orientation are given in Table
Table5.1 Tensile Specimen Geometry Recommendations
Balanced and Symmetric
USE OF TABS-There are many materialconfigurations, such as multidirectional laminates, fabric-basedmaterials, or randomly reinforced sheet-molding compounds,which can be successfully tested without tabs. However, tabsare strongly recommended when testing unidirectional materials(or strongly unidirectional dominated laminates) to failure in the fiber direction. Tabs may also be required when testingunidirectional materials in the matrix direction to preventgripping damage.
TAB MATERIAL-The most consistently used bondedtab material has been continuous E-glass fiber-reinforcedpolymer matrix materials (woven or unwoven) in a [0/90]nslaminate configuration. The tab material is commonly appliedat 45Â° to the loading direction to provide a soft interface. Otherconfigurations that have reportedly been successfully usedhave incorporatedtabs made of the same materialas is being tested.
SPECIMEN PREPARATION-Control of fiber alignment is critical. Improper fiber alignment will reduce the measured properties. Erratic fiber alignment will also increase the coefficient of variation. The specimen preparation method shall be reported.
5.2 METHOD OF SPECIMEN PREPARATION AS PER THE STANDARD: -
Carbon fabric has been cut so precisely that no fiber in direction of length has brake. The carbon fiber has kept stretched while molding the specimen to avoid buckling or zigzag of fiber.
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Fig.5.1 Carbon fiber cutting for specimen
The manufacturing method that has used for specimens is hand molding. The mold is made from Aluminium, to avoid edge and cutting effect that might occur while cutting specimen from plates. Making specimen in mold eliminates precautions to avoid notches, undercuts, rough and uneven surfaces by inappropriate machining.
Fig.5.2 Carbon fibers cut from mat
PROVISION OF TABS-
As per ASTM standards, use of tabs is not strongly recommended. But, failure modes observed from some testing which is LAT (Lateral - At grip/tab - Top). The tabs are provided to the specimens. The material of tabs is glass/Brahma composite.
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Fig.5.3 Details of Specimen as Per ASTM D-3039
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Fig.5.4 Image of prepared specimen