A composite material is a combination of two materials with different physical and chemical properties..pptx

A composite material is a combination of two materials with different physical and chemical properties. When they are combined they create a material which is specialised to do a certain job, for instance to become stronger, lighter or resistant to electricity.

1. Composite Materials

2. Classification of Materials Materials used in the design and manufacture of products Plastics Wood Composites Ceramics Metals Fabrics

3. Introduction Contemporary composites resulting from research and innovation from past few decades have progressed from glass fiber for automobile bodies to particulate composites for aerospace and a range other applications. “ materials composed of two or more distinctly identifiable constituents ” are used to describe natural composites like timber, organic materials, like tissue surrounding the skeletal system, soil aggregates, minerals and rock Further, though composite constituents are often distinguishable from one another, no clear determination can be really made. To facilitate definition, the accent is often shifted to the levels at which differentiation take place viz., microscopic or macroscopic.

4. Definition of Composites A combination of two or more materials differing in form or composition on a macro scale. The constituents retain their identities, that is, they do not dissolve or merge completely into one another although they act in concert . Normally, the components can be physically identified and exhibit an interface between one another

5. Definition of Composites Composite materials, often shortened to composites, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or microscopic scale within the finished structure.

6. A judicious combination of two or more materials that produces a synergistic effect. A material system composed of two or more physically distinct phases whose combination produces aggregate properties that are different from those of its constituents.

7. Composites Concrete - - small rocks bonded (cement) in a sand matrix. Current technology also involves some fiber (and perhaps resin) introduction. Steel reinforced concrete can approach a fiber reinforced matrix. Automobile tyres - - cord (fibers - - metal, nylon, rayon, Kevlar) reinforced truncated rubber donut. Teeth - - enamel coated sub-structure Bone - - - osteone tubes surrounding blood vessels. Osteones composed of several plies of collogen fibers. The collogen fibers of each lamina are parallel and spiral about the axis of the osteones , the direction of spiral being reversed in each plie . Wood - - - cellulose chains embedded in lignin matrix Rock - - - many rock formations consist naturally of layered deposits of different (mechanical) properties and perhaps different anisotropy.

8. Soil - - - bedding often produces anisotropic material properties Asbestos Clad metal Laminated beams (wood or wood-metal) Plywood Honeycomb structures Paper and wallboard Asphalt mixes Sintered carbide tools “Shatter-proof” glass

9. 900 KW wind turbine with composite blades (Courtesy of GE Wind Energy, 2003)

10. 2002 Ford Thunderbird with composite body panels

11. Automotive Composites Consortium Focal Project 3 carbon fiber composite body-in-white (Courtesy of Automotive Composites Consortium)

12. Composite Leaf Springs for Automotive Suspension (Source: LiteFlex LLC)

13. Airport People Mover with Composite Cabins (Source: TPI Composites Inc.)

14. Installation of Composite Bridge Deck (Source: Hardcore Composites)

15. Plywood

16. From M.Shuart , NASA Langley, 2001

17. ADVANTAGES OF COMPOSITES High resistance to fatigue and corrosion degradation. High ‘strength or stiffness to weight’ ratio. As enumerated above, weight savings are significant ranging from 25-45% of the weight of conventional metallic designs. Due to greater reliability, there are fewer inspections and structural repairs. Directional tailoring capabilities to meet the design requirements. The fibre pattern can be laid in a manner that will tailor the structure to efficiently sustain the applied loads. Improved dent resistance is normally achieved. Composite panels do not sustain damage as easily as thin gage sheet metals. It is easier to achieve smooth aerodynamic profiles for drag reduction. Complex double-curvature parts with a smooth surface finish can be made in one manufacturing operation. Composites offer improved torsional stiffness. This implies high whirling speeds, reduced number of intermediate bearings and supporting structural elements. The overall part count and manufacturing & assembly costs are thus reduced. High resistance to impact damage.

18. ADVANTAGES OF COMPOSITES Composites are dimensionally stable i.e. they have low thermal conductivity and low coefficient of thermal expansion. Composite materials can be tailored to comply with a broad range of thermal expansion design requirements and to minimise thermal stresses. Manufacture and assembly are simplified because of part integration (joint/fastener reduction) thereby reducing cost. The improved weather ability of composites in a marine environment as well as their corrosion resistance and durability reduce the down time for maintenance. Close tolerances can be achieved without machining. Material is reduced because composite parts and structures are frequently built to shape rather than machined to the required configuration, as is common with metals. Excellent heat sink properties of composites, especially Carbon-Carbon, combined with their lightweight have extended their use for aircraft brakes. Improved friction and wear properties.

19. DISADVANTAGE OF COMPOSITES High cost of raw materials and fabrication. Composites are more brittle than wrought metals and thus are more easily damaged. Transverse properties may be weak. Matrix is weak, therefore, low toughness. Reuse and disposal may be difficult. Difficult to attach. Repair introduces new problems, for the following reasons: Materials require refrigerated transport and storage and have limited shelf life. Hot curing is necessary in many cases requiring special tooling. Hot or cold curing takes time. Analysis is difficult. Matrix is subject to environmental degradation.

20. Applications of composites However, proper design and material selection can circumvent many of the above disadvantages. In aircraft application, advanced fibre reinforced composites are now being used in many structural applications, viz. floor beams, engine cowlings, flight control surfaces, landing gear doors, wing-to-body fairings, etc., and also major load carrying structures including the vertical and horizontal stabiliser main torque boxes. Composites are also being considered for use in improvements to civil infrastructures, viz., earthquake proof highway supports, power generating wind mills, long span bridges, etc.

21. Composite materials The individual materials that make up composites are called constituents . Most composites have two constituent materials: a binder or matrix and reinforcement

22. Composite materials Primary phase-Matrix Forms the matrix within which the secondary phase is imbedded Any of three basic material types: polymers, metals, or ceramics Secondary Phase-Reinforcements Referred to as the imbedded phase or called the reinforcing agent Serves to strengthen the composite. (fibers, particles, etc.) Can be one of the three basic materials or an element such as carbon or boron

23. Functions of the Matrix Material (Primary Phase) Provides for the bulk form of the part or product made of the composite material Holds the imbedded phase in place, usually enclosing and often concealing it When a load is applied, the matrix shares the load with the secondary phase, in some cases deforming so that the stress is essentially born by the reinforcing agent

24. The Reinforcing Phase (Secondary Phase) Function is to reinforce the primary phase Imbedded phase is most commonly one of the following shapes: Fibers Particles Flakes In addition, the secondary phase can take the form of an infiltrated phase in a skeletal or porous matrix Example: a powder metallurgy part infiltrated with polymer

25. Figure 9.1 ‑ Possible physical shapes of imbedded phases in composite materials: (a) fiber, (b) particle, and (c) flake

26. The Interface There is always an interface between constituent phases in a composite material For the composite to operate effectively, the phases must bond where they join at the interface Figure 9.4 ‑ Interfaces between phases in a composite material: (a) direct bonding between primary and secondary phases

27. Interphase In some cases, a third ingredient must be added to achieve bonding of primary and secondary phases Called an interphase , this third ingredient can be thought of as an adhesive Figure 9.4 ‑ Interfaces between phases: (b) addition of a third ingredient to bond the primary phases and form an interphase

28. Figure 9.4 ‑ Interfaces and interphases between phases in a composite material: (c) formation of an interphase by solution of the primary and secondary phases at their boundary Another Interphase Interphase consisting of a solution of primary and secondary phases

29. One Possible Classification of Composite Materials Traditional composites – composite materials that occur in nature or have been produced by civilizations for many years Examples: wood, concrete, asphalt Synthetic composites - modern material systems normally associated with the manufacturing industries, in which the components are first produced separately and then combined in a controlled way to achieve the desired structure, properties, and part geometry

30. Classification of Composites Composites are generally classified based on type of matrix material which is one of the ingredients for making composites [ 6-8 ], Polymer Matrix Composites Metal Matrix composites Ceramic Matrix Composites Hybrid composite Reinforcements: Continuous & Discontinuous reinforcement Monofilaments Short fibers and long fibres Whiskers Particulates Dispersoids

31. Types of composites (MMC, PMC, CMC)

32. Matrix Material The matrix material serves two paramount purposes viz., binding the reinforcement phases in place and distribute the load or stresses among the constituent reinforcement materials under an applied force. The demands on matrices are many. They may need to adjust to temperature variations, be conductors or resistors of electricity, have moisture sensitivity etc. This may offer weight advantages, ease of handling and other merits which may also become applicable depending on the purpose for which matrices are chosen.

33. Functions of a Matrix Holds the fibres together. Protects the fibres from environment. Distributes the loads evenly between fibres so that all fibres are subjected to the same amount of strain. Enhances transverse properties of a laminate. Improves impact and fracture resistance of a component. Helps to avoid propagation of crack growth through the fibres by providing alternate failure path along the interface between the fibres and the matrix.

34. Desired Properties of a Matrix Material Reduced moisture absorption. Low shrinkage. Low coefficient of thermal expansion. Good flow characteristics so that it penetrates the fibre bundles completely and eliminates voids during the compacting/curing process. Reasonable strength, modulus and elongation (elongation should be greater than fibre ). Must be elastic to transfer load to fibres . Strength at elevated temperature (depending on application). Low temperature capability (depending on application). Excellent chemical resistance (depending on application). Should be easily processable into the final composite shape. Dimensional stability (maintains its shape).

35. Factors considered for Selection of Matrix The matrix must have a mechanical strength commensurate with that of the reinforcement i.e. both should be compatible. Thus, if a high strength fiber is used as the reinforcement, there is no point using a low strength matrix, which will not transmit stresses efficiently to the reinforcement. The matrix must stand up to the service conditions, viz., temperature, humidity, exposure to ultra-violet environment, exposure to chemic3l atmosphere, abrasion by dust particles, etc. The matrix must be easy to use in the selected fabrication process. Life expectancy. The resultant composite should be cost effective.

36. Matrix Material

37. Polymer Matrix Materials Polymers make ideal matrix materials as they Can be processed easily, Possess lightweight, and Posses desirable mechanical properties. It follows, therefore, that high temperature resins are extensively used in aeronautical applications.

38. Polymer Matrix Materials There are two types of Polymer Matrix Materials Thermosets Thermoplastics

39. Thermosets A thermosetting plastic, also known as a thermoset, is polymer material that irreversibly cures. The cure may be done through heat (generally above 200 °C (392 °F)), through a chemical reaction (two-part epoxy, for example), or irradiation such as electron beam processing. A cured thermosetting polymer is called a thermoset. Thermoset materials are usually liquid or malleable prior to curing and designed to be molded into their final form, or used as adhesives. They can be retained in a partially cured condition too over prolonged periods of time, rendering Thermosets very flexible. They are most suited as matrix bases for advanced conditions fiber reinforced composites. Thermosets find wide ranging applications in the form of chopped fiber composites particularly when a premixed or moulding compound with fibers of specific quality and aspect ratio happens to be starting material as in epoxy, polymer and phenolic polyamide resins. Aerospace components, automobile parts, defense system components etc ., use a great deal of this type of fiber composites. Epoxy matrix materials are used in printed circuit boards.

40. Thermosets Polyesters phenolic and Epoxies are the two important classes of thermoset resins.

41. Epoxy resins Epoxy resins are widely used in filament-wound composites and are suitable for moulding prepress. They are reasonably stable to chemical attacks and are excellent adherents having slow shrinkage during curing and no emission of volatile gases. The use of epoxies rather expensive. Also , they cannot be expected to be used beyond a temperature of 140ºC. Their use in high technology areas where service temperatures are higher, as a result, is ruled out.

42. Polyester resins Polyester resins on the other hand are quite easily accessible , cheap and find use in a wide range of fields. Liquid polyesters are stored at room temperature for months, sometimes for years and the mere addition of a catalyst can cure the matrix material within a short time. They are used in automobile and structural applications .

43. Polyester resins The cured polyester is usually rigid or flexible as the case may be and transparent. Polyesters withstand the variations of environment and stable against chemicals. Depending on the formulation of the resin or service requirement of application, they can be used up to about 75ºC or higher. Other advantages of polyesters include easy compatibility with few glass fibers.

44. Polyamide resins Aromatic Polyamides are the most sought after candidates as the matrices of advanced fiber composites for structural applications demanding long duration exposure for continuous service at around 200ºC-250ºC .

45. Thermoplastics Thermoplastic, also known as a thermo softening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently Thermoplastics have one- or two-dimensional molecular structure at an elevated temperature and show exaggerated melting point. Another advantage is that the process of softening at elevated temperatures can reversed to regain its properties during cooling, facilitating applications of conventional compress techniques to mould the compounds. Resins reinforced with thermoplastics now comprised an emerging group of composites. The theme of most experiments in this area is to improve the base properties of the resins and extract the greatest functional advantages from them in new avenues, including attempts to replace metals in die-casting processes.

46. Thermoplastics

47. Polymer T m Acrylonitrile butadiene styrene (ABS) Acrylic (PMMA) 130–140 °C Celluloid Cellulose acetate Cyclic Olefin Copolymer (COC) Ethylene-Vinyl Acetate (EVA) Ethylene vinyl alcohol (EVOH) Fluoroplastics ( PTFE , alongside with FEP, PFA, CTFE , ECTFE , ETFE ) Ionomers Kydex , a trademarked acrylic/PVC alloy Liquid Crystal Polymer (LCP) Polyoxymethylene (POM or Acetal) 166°C Polyacrylates (Acrylic) Polyacrylonitrile (PAN or Acrylonitrile) Polyamide (PA or Nylon) Polyamide-imide (PAI) Polyaryletherketone (PAEK or Ketone) Polybutadiene (PBD) Polybutylene (PB) Melting point and glass transition temperature of various thermoplastics

48. Different types of Thermosets and thermoplastic resins commonly in use are as follows:

49. Some of the significant differences between Thermosets and Thermoplastics

50. Metal Matrix Materials Metal matrix composites, at present though generating a wide interest in research fraternity, are not as widely in use as their plastic counterparts. High strength, fracture toughness and stiffness are offered by metal matrices than those offered by their polymer counterparts. They can withstand elevated temperature in corrosive environment than polymer composites. Most metals and alloys could be used as matrices and they require reinforcement materials which need to be stable over a range of temperature and non-reactive too. Light metals form the matrix for temperature application and the reinforcements in addition to the aforementioned reasons are characterized by high moduli . Most metals and alloys make good matrices. However, practically, the choices for low temperature applications are not many. Only light metals are responsive, with their low density proving an advantage. Titanium, Aluminium and magnesium are the popular matrix metals currently in vogue, which are particularly useful for aircraft applications. If metallic matrix materials have to offer high strength, they require high modulus reinforcements. The strength-to-weight ratios of resulting composites can be higher than most alloys.

51. The melting point, physical and mechanical properties of the composite at various temperatures determine the service temperature of composites.

52. Ceramic Matrix Materials Ceramics can be described as solid materials which exhibit very strong ionic bonding in general and in few cases covalent bonding. High melting points, good corrosion resistance, stability at elevated temperatures and high compressive strength render ceramic-based matrix materials a favourite for applications requiring a structural material that doesn’t give way at temperatures above 1500ºC. Naturally, ceramic matrices are the obvious choice for high temperature applications. High modulus of elasticity and low tensile strain, which most ceramics posses, have combined to cause the failure of attempts to add reinforcements to obtain strength improvement. This is because at the stress levels at which ceramics rupture, there is insufficient elongation of the matrix which keeps composite from transferring an effective quantum of load to the reinforcement and the composite may fail unless the percentage of fiber volume is high enough.

53. Addition of high-strength fiber to a weaker ceramic has not always been successful and often the resultant composite has proved to be weaker. Ceramics have a higher thermal expansion coefficient than reinforcement materials means, the resultant composite is unlikely to have a superior level of strength. In that case, the composite will develop strength within ceramic at the time of cooling resulting in micro cracks extending from fiber to fiber within the matrix. Micro cracking can result in a composite with tensile strength lower than that of the matrix.

54. Carbon Matrices Carbon and graphite have a special place in composite materials options, both being highly superior, high temperature materials with strengths and rigidity that are not affected by temperature up to 2300ºC. This carbon-carbon composite is fabricated through compaction of carbon or multiple impregnations of porous frames with liquid carboniser precursors and subsequent pyrolization . They can also be manufactured through chemical vapour deposition of pyrolytic carbon. Carbon-carbon composites are not be applied in elevated temperatures, as many composites have proved to be far superior at these temperatures. However, their capacity to retain their properties at room temperature as well as at temperature in the range of 2400ºC and their dimensional stability make them the oblivious choice in a range of applications related to aeronautics, military, industry and space. Components, that are exposed to higher temperature and on which the demands for high standard performance are many, are most likely to have carbon-carbon composites used in them.

55. Glass Matrices In comparison to ceramics glass matrices are found to be more reinforcement-friendly. The various manufacturing methods of polymers can be used for glass matrices. Glass matrix composite with high strength and modulus can be obtained and they can be maintained upto temperature of the order of 650ºC. Composites with glass matrices are considered superior in dimensions to polymer or metal system, due to the low thermal expansion behavior. This property allows fabrication of many components in intricate shapes and their tribological characters are considered very special. Since the elastic modulus of glass is far lower than of any prospective reinforcement materials, application of stress usually results in high elasticity modulus fiber that the tensile strength of the composite its considerably enhanced than that of the constituents, which is not case in ceramic matrices.

56. Reinforcement Materials

57. Fibers Fibers are the important class of reinforcements, as they satisfy the desired conditions and transfer strength to the matrix constituent, influencing and enhancing their properties as desired. Glass fibers are the earliest known fibers used to reinforce materials. Ceramic and metal fibers were subsequently found out and put to extensive use, to render composites stiffer more resistant to heat. The performance of a fiber composite is judged by its length, shape, orientation, composition of the fibers and the mechanical properties of the matrix. The orientation of the fiber in the matrix is an indication of the strength of the composite and the strength is greatest along the longitudinal directional of fiber. Optimum performance from longitudinal fibers can be obtained if the load is applied along its direction. The slightest shift in the angle of loading may drastically reduce the strength of the composite.

58. Types of fibers Organic and inorganic fibers are used to reinforce composite materials. Almost all organic fibers have low density, flexibility, and elasticity. Inorganic fibers are of high modulus, high thermal stability and possess greater rigidity than organic fibers and not withstanding the diverse advantages of organic fibers which render the composites in which they are used. Glass fibers, silicon carbide fibers, high silica and quartz fibers, aluminina fibers, metal fibers and wires, graphite fibers, boron fibers, aramid fibers etc. Among the glass fibers, it is again classified into E-glass, A-glass, R-glass etc.

59. Aramid fiber

60. Carbon fiber

61. Glass fiber

62. Boron fiber

63. Silicon carbide fiber

64. Metal fiber

65. Whiskers Single crystals grown with nearly zero defects are termed whiskers. They are usually discontinuous and short fibers of different cross sections made from several materials like graphite, silicon carbide, copper, iron etc. Typical lengths are in 3 to 55 N.M. ranges. Whiskers differ from particles in that, whiskers have a definite length to width ratio greater than one. Whiskers can have extraordinary strengths upto 7000 MPa .

66. Flake Flakes are often used in place of fibers as can be densely packed. Metal flakes that are in close contact with each other in polymer matrices can conduct electricity or heat, while mica flakes and glass can resist both. Flakes are not expensive to produce and usually cost less than fibers. But they fall short of expectations in aspects like control of size, shape and show defects in the end product. Flake composites have a higher theoretical modulus of elasticity than fiber reinforced composites. They are relatively cheaper to produce and be handled in small quantities.

67. Filled composite Fillers are inert substances added to reduce the resin cost and/or improve its physical properties, viz., hardness, stiffness and impact strength. Commonly used fillers are calcium carbonate, hydrated alumina and clay. Filled composites result from addition of filer materials to plastic matrices to replace a portion of the matrix, enhance or change the properties of the composites. The fillers also enhance strength and reduce weight. The skeleton could be a group of cells, honeycomb structures, like a network of open pores. The infiltrant could also be independent of the matrix and yet bind the components like powders or fibers, or they could just be used to fill voids. Fillers may be the main ingredient or an additional one in a composite. The filler particles may be irregular structures, or have precise geometrical shapes like polyhedrons, short fibers or spheres .

68. Particulate Reinforced Composites Microstructures of metal and ceramics composites, which show particles of one phase strewn in the other, are known as particle reinforced composites. Square, triangular and round shapes of reinforcement are known, but the dimensions of all their sides are observed to be more or less equal. The size and volume concentration of the dispersoid distinguishes it from dispersion hardened materials. The dispersed size in particulate composites is of the order of a few microns and volume concentration is greater than 28%. The mechanism used to strengthen each of them is also different. The dispersed in the dispersion-strengthen materials reinforces the matrix alloy by arresting motion of dislocations and needs large forces to fracture the restriction created by dispersion. In particulate composites, the particles strengthen the system by their hardness relative to the matrix.

69. Microspheres Microspheres are considered to be some of the most useful fillers. Their specific gravity, stable particle size, strength and controlled density to modify products without compromising on profitability or physical properties are its their most-sought after assets. Solid glass Microspheres, manufactured from glass are most suitable for plastics. Solid glass Microspheres are coated with a binding agent which bonds itself as well as the sphere’s surface to the resin. Hollow microspheres are essentially silicate based, made at controlled specific gravity. They are larger than solid glass spheres used in polymers and commercially supplied in a wider range of particle sizes. Commercially, silicate-based hollow microspheres with different compositions using organic compounds are also available. Microspheres, whether solid or hollow, show properties that are directly related to their spherical shape let them behave like minute ball bearing, and hence, they give better flow properties. They also distribute stress uniformly throughout resin matrices.

70. FIBER REINFORCED COMPOSITES The embedding of strong, stiff fibers in a softer material (matrix) results in a fiber reinforced composite material. Reinforcing fibers can be made of metals, ceramics, glasses, or polymers.

71. FIBER REINFORCED COMPOSITES Single-Layer Multi-Layer Laminates Hybrids Continuous-Fiber Reinforced Discontinuous-Fiber Reinforced Preferred Orientation Random Orientation Uni-directional Reinforcement Bi-directional Reinforcement

72. ORIENTATION Orientation determines the mechanical strength of the composite and the direction in which the strength is greatest. There are three types of fiber orientation: 1D, 2D & 3D. 1D orientation type has maximum composite strength and modulus in the direction of the fiber axis. The planar type or 2Dexhibits different strengths in each direction of fiber orientation. The 3D type is isotropic. The mechanical properties in any one direction are proportional to the amount of fiber by volume oriented in that direction. As fiber orientation becomes more random, the mechanical properties anisotropic.

73. Examples of reinforcement styles, combinations, orientations and configurations of fibers in composites

74. Lamina A lamina is a flat( or curved,as in as shell ) arrangement of unidirectional fibers or woven fibers in a matrix. Two typical laminae are shown in fig. The fibers ,or filaments , the main reinforcing or load carrying agent, are typically strong and stiff. The matrix may be organic, ceramic, or metallic. Its function is to support and protect the fibers and to provide a means of distributing load among the fibers and transmitting it between them.

75. Laminates A laminate is a stack of lamina having various orientations of principal material directions. The layers of a laminate are usually bound together by the same matrix material that is used in the lamina. Laminates can be composed of plates of different materials.

76. Fibre Reinforced Polymer (FRP) Laminated Composites Laminate Lay-up A structural laminate is designed to have a specific lay-up or ply arrangement, based on the various design criteria imposed on it. A laminate lay-up definition refers to the fiber orientation of successive plies in a laminate with respect to an established reference coordinate system.

77. Two or more layers bonded together in an integral piece Example: plywood in which layers are the same wood, but grains are oriented differently to increase overall strength of the laminated piece

78. Laminate Lay-up Code Laminate lay-up code must be able to specify the following: The orientation of each ply relative to the reference axis; Number of plies, with orientation; Exact geometric sequence of plies; Adjacent plies oriented at angles equal in magnitude but opposite in sign, appropriate positive or negative signs should be assigned.

79. Laminate Orientation Code

80. Total Lay-up code Fiber orientation of all the plies is sequentially written. Subscript ‘T’ outside the bracket denotes total laminate definition code, and ± sign denotes fiber orientation.

81. Symmetric Lay-up Code In a laminate with symmetric lay-up code, every ply above the mid-plane has an identical ply below the mid-plane. One half of the laminate, from the first ply to the mid-plane, is written sequentially within brackets. A subscript ‘S’ outside the bracket denotes symmetrical laminate definition code. When the laminate mid-plane divides a physical ply into case of symmetric laminate with odd number of plies.

82. Symmetric Lay-up Code

83. Hybrid Laminate Code A hybrid laminate includes plies of different materials within its lay-up. In this case, every ply is identified by its fiber orientation angle and a subscript on the angle identified the type or material.

84. Set Identification Code In this case, sets of plies repeat within a laminate lay-up. These are identified by including them within parenthesis. An integer prefix to the subscript ‘S’ refers to the laminate mid-plane.

85. Other Laminar Composite Structures Automotive tyres - consists of multiple layers bonded together FRPs - multi‑layered fiber reinforced plastic panels for aircraft, automobile body panels, boat hulls Printed circuit boards - layers of reinforced plastic and copper for electrical conductivity and insulation Windshield glass - two layers of glass on either side of a sheet of tough plastic

86. PREPREGS Ready to mold material in sheet form which may be cloth, mat or paper impregnated with resin and stored for use. The resin is partially cured to B-stage and supplied to the fabricator, who lays up the finished shape and completes the cure with heat and pressure. Thin plies of continuous fibers, unidirectional tape generally has cured ply thickness of 0.127mm to 0.254mm. Very thin plies of 0.06mm are also available for spacecraft applications, but are very expensive.

87. A typical set of steps in prepreg manufacturing

88. Sheet molding compound SMC prepreg is made from glass strands chopped to lengths of 25 or 50mm, sandwiched between two layers of film, onto which the resin paste has already been applied. The prepreg passes through a compaction system that ensures complete strand impregnation before being wound into rolls. These are stored for a few days before moulding , to allow the prepreg to thicken to a mouldable viscosity.

89. Bulk Molding Compound BMC is a in the form of a bulk prepreg . BMC is combination of chopped glass strands with resin suitable for either compression or injection moulding .

90. Honeycomb Sandwich Structure Sandwich structure is a layered construction consisting of two thin sheets between a thick layer. The two thin sheets are called “Face Sheets”. The Intermediate thick layer is called the sandwich “Core”.

91. Salient Advantages of Prepegs : Desired Fibre to Resin ratio with in close tolerances can be obtained. Easy to handle during the lay-up. Lay up time is less compared to wet lay up process. Lay-up process once standardized, can be automised to obtain the repeatability of component. More consistent and reproducible. Few rejections. Finest Quality material. Work area is neat and clean. Lower inventory since no resin or curing agents need to be stocked.

92. Sandwich Structure – Foam Core Consists of a relatively thick core of low density foam bonded on both faces to thin sheets of a different material

93. Sandwich Structure – Honeycomb Core An alternative to foam core Either foam or honeycomb achieves high strength‑to‑weight and stiffness‑to‑weight ratios

94. Sandwich Construction

95. Why Honeycomb Sandwich It has high stiffness to weight ratio. It has high strength to weight ratio. Flexibility to form complex contours. Uniform crushing under compression. Ease to obtain a very flat surface and hence dimensional control. By proper selection of material and geometry large weight savings can be achieved over conventional structure.

96. Constituents of Sandwich Structure The sandwich construction consists of : 1. Face Sheets : Are thin sheets Adhesively bonded to the core. The main function of face sheets is to resist all the bending and direct stress induced in the structure. The material of the face sheets may be selected as Aluminium, Magnesium, Steel, CFRP etc. Selection of Facing materials depends upon : - Where and how these structures are used. - The elevated temperature usage. - Strength. - Ease of formability. - Thermal and Electrical insulation properties etc.

97. 2. Core : Core is made of very thin Metallic / Non-metallic material. Metallic : Aluminium, Stainless steel, Titanium Non Metallic : Fiber glass, Nomex , Kraft Paper The low-density core used in sandwich construction has to resist the shear load and give rigidity to the facings. Must be stiff enough to resist shear stress induced when the panel is subjected to bending. Must also be stiff enough to keep the faces flat .

98. Classification of Composite Manufacturing Processes Open Mold Process Spray lay-up - Chopped roving and resin sprayed simultaneously, rolled. Hand lay-up - Lay-up of fibers or woven cloth, impregnate, no heat or pressure. Filament winding. Sheet molding compound. Expansion tool molding. Contact molding.

99. Classification of Composite Manufacturing Processes Closed Mold Process Compression molding – Load with raw material, press into shape. Vacuum bag, pressure bag, autoclave - Prepreg laid up, bagged, cured. Injection molding – Mold injected under pressure. Resin Transfer – Fibers in place, resin injected at low temperature. Continuous Process Pultrusion. Braiding.

100. Open Mold Processes Advantages Freedom of design Easy to change design Low mold and/or tooling cost Tailored properties possible High strength large parts possible On-site production possible

101. Open Mold Processes Disadvantages Low to medium number of parts Long cycle times per molding Not the cleanest application process Only one surface has aesthetic appearance Operator skill dependent

102. Spray Lay-up

103. Spray Lay-up Spray lay-up is an open mold process that uses mechanical spraying and chopping equipment for depositing the resin and glass reinforcement The fiber is chopped in a hand held gun and fed into a spray of catalyzed liquid resin directed at the mold. The sprayed, catalyzed liquid resin will wet the reinforcement fibers, which are simultaneously chopped in the same spray gun. The deposited materials are left to cure under standard atmospheric conditions.

104. Spray Lay-up In spray lay-up, the mold defines the shape of the outer surface, and the mold itself is usually made of reinforced plastic. The mold is first coated with a wax to ensure removal after curing. A layer of gel coat is then sprayed on to the mold to form the outermost surface of the products.  The gel coat is allowed to cure for several hours but remains tacky so subsequent resin layers adhere better

105. Spray Lay-up Layers are built up and rolled out on the mold as necessary to form the part.  The spray gun has separate resin and catalyst streams which mix as they exit the gun.  However, compared to hand lay-up, more resin is typically used to produce similar parts by spray lay-up because of the inevitable over spray of resin during application. Polyester resins designed for use in spray lay-up are promoted for cure at room temperature and usually are catalyzed with a liquid peroxide such as MEKP

106. Spray Lay-up Advantages Widely used from many years. Low cost way of quickly depositing fiber and resin. Low cost tooling. Disadvantages Laminates tend to be very resin-rich and, therefore, excessively heavy. Only short fibers are incorporated, which severely limits the mechanical properties of the laminate. Resins need to be low in viscosity to be sprayable . This generally compromises their mechanical/thermal properties.

107. Spray Lay-up Applications Simple enclosures, lightly loaded structural panels, e.g. caravan bodies, truck fairings, bathtubs, shower trays.

108. Spray Lay-up

109. Wet Lay-up or Hand Lay-up

110. Wet Lay-up or Hand Lay-up The hand (wet) lay-up is one of the oldest and most commonly used methods for manufacture of composite parts. Hand lay-up composites are a case of continuous fiber reinforced composites. Layers of unidirectional or woven composites are combined to result in a material exhibiting desirable properties in one or more directions. Each layer is oriented to achieve the maximum utilization of its properties. Layers of different materials (different fibers in different directions) can be combined to further enhance the overall performance of the laminated composite material. Resins are impregnated by hand into fibers, which are in the form of woven, knitted, stitched or bonded fabrics. This is usually accomplished by rollers or brushes. Laminates are left to cure under standard atmospheric conditions.

111. Wet Lay-up or Hand Lay-up Advantages Design flexibility. Large and complex items can be produced. Tooling cost is low. Design changes are easily effected. Sandwich constructions are possible. Semi-skilled workers are needed. Applications Standard wind-turbine blades, boats, Architectural moldings.

112. Wet Lay-up or Hand Lay-up Disadvantages Only one molded surface is obtained. Quality is related to the skill of the operator. Low volume process. Longer cure times required. Resins need to be low in viscosity to be workable by hand. This generally compromises their mechanical/thermal properties. The waste factor can be high. As the final result is directly depending on the skills of the operator, well-trained operators are a prerequisite. Operator costs constitute a large part of the total costs of this processing technique.

113. Continuous Lamination

114. Continuous Lamination Continuous Lamination  of reinforced plastics materials involves impregnating various reinforcements with resins on an in-line conveyor.  The resulting laminate is cured and trimmed as it passes through the various conveyor zones.  In this process, the resin mix is metered onto a bottom carrier film, using a blade to control thickness.  This film, which defines the panel's surface, is generally polyester, cellophane or nylon, and may have a smooth, embossed or matte surface. Chopped glass fibers free-fall into the resin mix and are allowed to saturate with resin, or "wet out".  A second carrier film is applied to the top of the panel before subsequent forming and curing.  The cured panel is then stripped of its films, trimmed, and cut to the desired length.  Principal products include translucent industrial skylights, and greenhouse panels, wall and ceiling liners for food areas, garage doors and cooling tower louvers.

115. Filament Winding Filament winding is automated processes for creating parts of simple geometry wherein continuous resin impregnated fibers are wound over a rotating male tool called mandrel. A continuous fiber roving passes through a shuttle, which rotates and the roving is wrapped around a revolving or stationary mandrel Two basic types of filament winding are in use - ( i ) the polar or planer method, and (ii) the high helical pattern winding.

116. Filament Winding

117. Filament Winding Polar or planer method The polar or planer method of winding utilizes a fixed mandrel and a shuttle that revolves around the longitudinal axis of the part to form longitudinal winding patterns. This type of winding is used if the longitudinal fibers are required with angle less than 25° to the mandrel axis.

118. Filament Winding High helical pattern winding In the high helical pattern winding, the mandrel rotates while the shuttle transverses back and forth. Both the mandrel rotation and shuttle movement are in the horizontal plane. By controlling the mandrel rotation and shuttle speed, the fibre angle can be controlled. Angles of 25°-85° to the mandrel rotation axis are possible.

119. Filament Winding High helical pattern winding

120. Filament Winding A tank being wound without resin

121. Filament Winding After completion of the winding, the filament wound structure is cured at room temperature or in an oven. The mandrel is removed after the curing. The mandrel, which determines accurate internal geometry for the component, is generally the only major tool. Low cost mandrel materials such as cardboard or wood can be used for winding low cost routine parts. For critical parts requiring close tolerances, expensive mandrels designed for long term use may be required. For high temperature cure 315°C (600°F), graphite mandrels with low thermal expansion may be advantageous.

122. Filament Winding Advantages Excellent mechanical properties due to use of continuous fibres . High degree of design flexibility due to controlled fibre orientation and lower cost of large number of composites. This is a very fast and economic method of laying down material. Resin content can be controlled by metering the resin onto each fibre tow through nips or dies.

123. Filament Winding Disadvantages Difficulty to wind complex shapes, which may require complex equipment. Poor external finish. The process is limited to convex shaped components. Fibre cannot easily be laid exactly along the length of a component. Mandrel costs for large components can be high. Low viscosity resins usually need to be used with lower mechanical properties.

124. Closed Mold Processes Compression Molding Compression molding is one of the oldest manufacturing techniques in the composites industry. The recent development of high strength, fast cure sheet molding compounds, bulk molding compounds and advancement in press technology is making the compression molding process very popular for mass production of composite parts. Fully formed parts are molded in matched metal compression molds that give the final part shape.

125. Compression Molding

126. Compression Molding This process utilizes large tonnage presses wherein the part is cured between two matched steel dies under pressure and high temperature. The moving platen is heated either by steam or electricity to promote thermal curing. Curing of the part is affected by the following factors: Size of platen, which determines the length and width of the part, which can be cured. Total tonnage of the press, which determines the pressure to be exerted on the projected surface area of the part.

127. Compression Molding After placing the laminate to be cured called the 'charge' in the core of the mold, the cavity is then closed at a rate of usually 4-12 mm/sec. In most cases the mold is heated to 150°C (302°F), which causes the charge viscosity to be reduced. With increasing mold pressure as the mold is closed, the charge flows towards the cavity extremities, forcing air out of the cavity. The molding pressure based on projected part area ranges from 0.7 to 9 MPa (100 to 1200 psi). Higher molding pressure causes sink marks, while lower pressure cause porosity. The curing time is usually between 25 sec to 3 minutes depending on several factors including' resin-initiator-inhibitor reactivity, part thickness, component complexity and mold temperature.

128. Vacuum Bag Molding Vacuum bagging techniques have been developed for fabricating a variety of aerospace components and structures. The process is principally suited to prepreg materials. This method utilises a flexible film or rubber bag that covers the part lay-up. The bag permits evacuation of the air to apply vaccum or atmospheric pressure.

129. Vacuum Bag Molding

130. Vacuum Bag Molding Bag sealant Temporarily bonds vacuum bag to tool Vacuum fitting and hardware Exhausts air, provides convenient connection to vacuum pump Bagging film or vacuum bag Encloses part, allows for vacuum and pressure used to contain any vacuum pressure applied application of the vacuum bag extremely critical bag perforation must be prevented no sharp edges on tool properly sealed on edge no bridging (requires folds in bag) folds must be properly made or undesirable wrinkles may occur in part

131. Vacuum Bag Molding Breather mat or film Allows air or vacuum transfer to all of part loosely woven fabric Perforated release film Allows flow of resin or air without adhesion placed on top of or under the laminate and peel ply (if used) allows volatiles to escape from laminate and excess resin to be bled from the laminate into the bleeder plies during cure porous or perforated Peel ply placed immediately on top of or under the composite laminate removed just before bonding or painting operations to provide clean, bondable surface woven fabric (nylon, polyester, or fiberglass) treated with nontransferable release agent Imparts a bondable surface to cured laminate

132. Vacuum Bag Molding Laminate Glass bleeder ply absorb excess resin from the laminate during cure (resulting in desired fiber volume) fiberglass fabric or other absorbent materials amount of bleeder used is a function of absorbency of material resin content finished part fiber volume desired Barrier film between bleeder plies and breather Non-perforated, non-adhering (release) film Stacked silicon edge dam Forces excess resin to flow vertically, increasing fluid pressure located peripherally to minimize edge bleeding may be integral part of tool or rubber, metal bars, etc.

133. Vacuum Bag Molding A vacuum is drawn on the lay-up, which helps in eliminating entrapped air. A maximum pressure of about 104 kPa (15 psi) is achieved in this method. The removal of excess resin results in higher fibre content and improved mechanical properties. The lay-up is usually allowed to cool at room temperature. To reduce the cure time, oven is preferred.

134. Autoclave Molding Autoclave molding is similar to vacuum bag process except that the lay-up is subjected to greater pressures and compact parts are produced. Primary disadvantage is high initial and recurring operating cost. The advantage is to produce parts with complex configuration and very large sizes.

135. Injection Molding Injection molding refers to a process that generally involves forcing or injecting a fluid plastic material into a closed mold. It is differentiated from compression molding, in which plastic materials in a soft but not fluid condition are formed by transferring them into an open mold, which is then forcibly closed. This method is not normally used in polymeric matrix compound processes due to fiber damage in the barrel.

136. Injection Molding The molding compound is fed into injection chamber through the feed hopper. The molding compound is heated in the injection chamber wherein it changes into liquid form. It is forced into the injection mold by the plunger.

137. Resin Transfer Molding (RTM) Resin transfer molding is a closed mold low pressure process that allows the fabrication of composites ranging in complexity from simple, low performance to complex, high performance parts and in size from small to large

138. Resin Transfer Molding (RTM)

139. Resin Transfer Molding (RTM) The fibre reinforcement, which may be pre-shaped, is placed into a tool cavity, which is then closed. A tube connects the closed tool cavity with a supply of liquid resin, which is pumped or transferred into the tool to impregnate the reinforcement for subsequent curing. Injection pressure is normally less than 690 kPa (100 psi). The displaced air is allowed to escape through vents to avoid dry spots. Cure cycle is dependent on part thickness, type of resin system and the temperature of the mold and resin system. The part cures in the mold, normally heated by controllers.

140. Resin Transfer Molding (RTM) Advantages Parts can be made with better reproducibility than with wet lay-up. Reinforcement and combination of reinforcements can be used to meet specific properties. Production cycles are much faster than with wet lay-up. Using matched tools for the mold, one can improve the finish of all the surfaces. Mechanical properties of molded parts are comparable to other composite fabrication processes. Large and complex shapes can be made efficiently. Volatile emissions are low because RTM is a closed mold process. The skill level of operator is less critical. Mold surfaces can be gel coated to improve surface performance.

141. Resin Transfer Molding (RTM) Disadvantages The mold design is critical and requires good tools or great skill. Reinforcement movement during resin injection is sometimes a problem. Control of flow pattern or resin uniformity is difficult. Radii and edges tend to be resin rich.

142. Resin Film Infusion (RFI) In resin film infusion process, dry fabrics are laid up interleaved with layers of semi-solid resin film supplied on a release paper. The lay-up is vacuum bagged to remove air through the dry fabrics, and then heated to allow the resin to first melt and flow into the air-free fabrics followed by curing.

143. Pultrusion

144. Pultrusion

145. Closed mold Continuous Processes -Pultrusion Pultrusion is an automated process used to create shapes by pulling rovings through a shaped and heated die. Practical applications are limited to constant cross-section parts. Pultrusion is used to manufacture constant cross-section shapes, viz., I-beam, box, channels, tubings , etc.

146. Pultrusion The Pultrusion process machine consists of six different parts namely, the creel, the resin bath, the forming die, the heated curing die, the pullers and the cut-off saw. The creel is the beginning of the Pultrusion process and is the material storage system from which the fibres and mat or fabric are drawn in the correct sequence to match the design requirements of the structural shape. All Pultrusion processes utilise a resin impregnation bath to facilitate the impregnation of the resin into the fibre structure. The use of pre-impregnated fibres eliminates the resin bath.

147. Pultrusion Two types of dies are used in Pultrusion process, namely, the forming and the heating or curing die. Forming is done immediately after the impregnation process. Forming dies are normally attached to the heating or curing die in order to provide the correct relationship between the forming and the heated curing step. The rovings go through a heated die that represents the cross-section of finished part. Curing is accomplished by heating the die. The product continuously pulled out and as it comes out of the puller mechanism, it is cut to desired length by an automatic saw.

148. Pultrusion Advantages Production is continuous. Material scrap rate is low. The requirement for support material is eliminated i.e., breathers. bleeder, cloth, separator film, bagging film, edge tape, etc. Labour requirements are low. Disadvantages Limited to constant or near constant cross-section components. Heated die costs can be high.

149. Pultrusion

150. Pultrusion

151. Pultrusion

152. Pultrusion

153. Pultrusion

154. Pultrusion

155. Thermoforming Thermoforming is a process of shaping flat thermoplastic sheet which includes two stages: softening the sheet by heating, followed by forming it in the mold cavity. Elastomers and Thermosets can not be formed by the Thermoforming methods because of their cross-linked structure as they do not soften when heated.

156. Thermoforming Vacuum Thermoforming

157. Thermoforming

158. Defects in composites Sources of defects commonly introduced to composite materials during manufacture, processing and machining, include : Inclusions – e.g. backing paper, peel ply etc, accidentally included in material during manufacture, can have degrading effect on mechanical properties. Disbonds – can occur because of poor consolidation or as a result of an inclusion. Fibre breakage – either due to cutting or can be because of excessive fibre curvature at sharp radii corners. Improper fibre splicing/ply joining . Fibre wrinkling/defects – can form when producing pre-forms i.e. tight radii corners, material inability to drape etc. Fibre misalignment, distortion, knots/whorls – especially prevalent in low fibre volume fraction materials.

159. Defects in composites Sources of defects commonly introduced to composite materials during manufacture, processing and machining, include : Incorrect stacking sequence – resulting in incorrect mechanical properties and possibly warpage . Voidage (porosity) – due to inclusion of air, solvents or other contamination during mixing of resin. Can act as stress concentrations and will have an effect on some of the mechanical properties i.e. lower transverse and through-thickness tensile, flexural, shear and compression strengths. Resin starved areas – due to poor resin application, inadequate wetting out of fibres / fibre preforms or poor resin flow (incorrect cure process). Delaminations – this type of defect can occur during manufacturing and in-service, and can have a severe detrimental effect on mechanical properties, particularly in compression.

160. Defects in composites Sources of defects commonly introduced to composite materials during manufacture, processing and machining, include : Imperfections due to incorrect cure process ( under cure, non uniform cure or heat damage ) – may be a result of the size of the component being fabricated i.e for thick sections one may get thermal or degree of cure gradients within the component resulting in inhomogeneous material. Tooling installation and removal problems. Imperfections due to machining – operations such as hole drilling and trimming can introduce defects such as delaminations , interlaminar cracking, and damage to fibres and matrix if not performed correctly. Residual stresses – presence and nature influenced by cure/processing history. Effects laminate mechanical properties and can cause warping, fibre buckling, micro-cracking of the matrix and delaminations .

161. In-Service Phenomena Defects sustained  Vibration/fatigue/creep  Impact/shock/high rate loading  Lightning strike  Environmental cycling (heat, humidity etc)  Loading history  Bacterial/chemical degradation  Galvanic corrosion  Poor maintenance (e.g. tool drop) and repair     Fibre fracture   Fibre debond  Matrix cracking  Dents, abrasions, scratches, punctures     Delaminations / debonds  Sandwich core crushing  Sandwich skin delamination   In-Service Phenomenon and Resulting Defect Types

162. Delamination Delamination refers to situations in which failure (or inadequate adhesion) occurs on a plane between adjacent layers within a laminate. This type of failure is dominated by the properties of the matrix and since matrix strengths and toughness tend to be relatively low, laminated composites are prone to the development of delaminations . In many types of composite structure (e.g. aircraft, marine, etc.) delaminations are the most common form of defect/damage.

163. Cracking Cracking is a common form of damage in composites and other materials arising in manufacture or under service conditions.      In manufacture, cracking can occur as part of the curing process under the thermal or residual stresses induced. This is most common around stress concentrators such as bolt holes, attachments or where changes in cross section occur. Operations such as hole drilling and trimming can introduce inter-laminar cracking   in composites.  In-service cracking can occur from impact damage

164. Disbond A disbond refers to the situation in composite sandwich structures decohesion has occured of a bonded layer.  This may be the consequence of poor adhesion, service loading or impact damage.  The disbond may not be visible externally

165. Void Voids and porosity can occur in manufacture due to volatile resin components or air not properly controlled during cure. Single or isolated large air bubbles are referred to as voids or voidage . These are large enough to be of structural significance and can also be individually detected and measured by ultrasound. Where large planar voids occur at the interfaces between the plies these are referred to as delaminations .

166. Impact damage Impact damage is an important damage mechanism in composite materials that can occur in-service or as a result of handling during or following manufacture. This can give rise to surface indentations and other damage below the surface such as cracking, delamination or disbonding . Characteristically there is a conical area of damage below the surface containing small microcracks and delaminations . Damage is usually most extensive sub-surface and may be difficult to ascertain on visual examination of the surface itself.

167. Porosity Porosity can be described as a large number of microvoids , each of which is too small to be of structural significance or to be detected individually by a realistic inspection technique, but which collectively may reduce the mechanical properties of the components to an unacceptable degree. It is usually produced during the curing cycle from entrapped air, moisture or volatile products. Porosity is most likely following manufacturing by hand lay-up. 

168. Erosion Erosion of the composite surface  can occur in service, particularly in composite process vessels or pipework from the effects of material flow or impact of particulates.  A precursor is the localised breakdown of the gel coat or chemical liner in the case of process vessels. This mechanism may give rise to broad defects or to finer scale pin-hole damage. Erosion can facilitate further environment ingress and damage to the composite material. The localised loss of wall thickness will impact on the integrity of the material.

169. Matrix microcracking Matrix microcracking refers to intralaminar or ply cracks that traverse the thickness of the ply and run parallel to the fibres in that ply. Their existence does not necessarily mean catastrophic failure of the composite as they can be present only in certain plies (usually those transverse to the main loading direction) and while the fibres (which carry most of the load) remain intact. Matrix microcracks can develop under tensile loading, fatigue loading, thermal loading and impact conditions.

170. Fiber Breakage Fibre defects . The presence of defects in the fibres themselves is one of the ultimate limiting factors in determining strength of composite materials, and sometimes faulty fibres can be identified as the sites from which damage growth has been initiated. These defects are present in fibres as supplied, are always likely to be present and probably must be considered as one of the basic material properties.

171. Environmental Ingress Composites like any materials can degrade in the environment to which they are exposed.  This can give rise to a variety of damage mechanisms and a general reduction in strength and toughness with time. Chemical vessels not protected by an internal polyethylene or polypropylene liner can be particularly affected, or where protective liners have broken down.  Erosion or damage to protective gelcoats can also initiate damage to the composite material. 

172. FibreWrinkling or waviness FibreWrinkling or waviness refers to the in-plane kinking of the fibres in a ply.  Waviness or wrinkling of the fibres can seriously affect laminate strength.  This type of defect is particularly of concern in high integrity aerospace and defence components

173. Fibre and Ply Misalignment Fibre misalignment refers to local or more extensive misalignment of fibres in the composite material.  This causes local changes in volume fraction by preventing ideal packing of fibres . Ply misalignment refers to the situation where a whole or part of a ply or layer of the composite is misaligned. This is produced as a result of mistakes made in lay-up of the component plies. This alters the overall stiffness and strength of the laminate and may cause bending during cure. The properties of the resulting component will be affected.

174. Incorrect Cure Incomplete cure refers to the situation where the matrix has been Incompletely cured matrix due to incorrect curing cycle or faulty resin material.  This may be localised or affect the whole component.  The result will be reduced strength and toughness.  Incomplete cure is also an issue in adhesive processes using resin based adhesives affecting the integrity of end-fittings and adhesive joints.

175. Excess Resin Fabrication methods for composites are designed to provide a uniform distribution of fibres in a resin matrix.  properties depend on the fibre volume fraction . Load transfer across the fibre matrix interfaces are a key feature giving rise to the good strength and toughness characteristics of composites.  It is a natural consequence of manufacturing methods that local variations in fibre or resin content will occur . Where the resin content is above design limits this is referred to as excess resin . In engineered components such as those produced by filament winding, higher fibre levels may be deliberately introduced in key areas where enhanced performance is required.