AVI III Lesson 4-1 PDF

AVI-111 AIRCRAFT MATERIALS LESSON 4 Topic: Composite and Non-Metallic  OBJECTIVES By the end of this class, students will be able to: 1. Identify the key properties and applications of non-metallic and advanced composite materials in aviation. 2. Differentia...

AVI-111 AIRCRAFT MATERIALS LESSON 4 Topic: Composite and Non-Metallic  OBJECTIVES By the end of this class, students will be able to: 1. Identify the key properties and applications of non-metallic and advanced composite materials in aviation. 2. Differentiate between various fiber forms, types, and matrix materials used in composite structures. 3. Understand the curing stages of resin and the significance of pre-impregnated products in the manufacturing process. NON-METALLIC AIRCRAFT MATERIALS NON-METALLIC AIRCRAFT MATERIALS i.e. reinforced plastics and advanced composites. Replaced the following materials: magnesium mid-1950s plastic fabric wood aluminum 80% to 15% NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: 1. Wood 2. Plastics 3. Transparent Plastics 4. Composite Material 5. Reinforced Plastic 6. Rubber 7. Sealing Compounds NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: WOOD Today, very little is used in aircraft construction except for: restorations homebuilt aircraft NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: PLASTICS used in many applications throughout modern aircraft. structural components of thermosetting plastics reinforced with fiberglass decorative trim of thermoplastic materials to windows NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: TRANSPARENT PLASTICS used in aircraft canopies, windshields, windows classified into two according to reaction to heat: thermoplastic thermosetting NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: TRANSPARENT PLASTICS Thermoplastic will soften when heated and harden when cooled. Thermosetting harden upon heating, and reheating has no softening effect. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: TRANSPARENT PLASTICS manufactured in two forms: monolithic - solid laminated - made from transparent plastic face sheets bonded by an inner layer material. It has shatter resistant qualities. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: TRANSPARENT PLASTICS Stretched Acrylic A new development in transparent plastics It is pulled in both directions to rearrange its molecular structure before being shaped. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: COMPOSITE MATERIALS In the 1940s, the aircraft industry began to develop synthetic fibers to enhance aircraft design. Synthetic fibers are made of polymers that do not occur naturally, and are produced entirely in the laboratory. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: COMPOSITE MATERIALS A mixture of different materials. The composition of composite materials is a combination of reinforcement, such as a fiber, whisker, or particle, surrounded and held in place by a resin, forming a structure. Eg: Concrete = Gravel + Cement  COMPOSITE MATERIALS ADVANTAGES DISADVANTAGES High strength to weight ratio Cost, Very expensive processing Fiber-to-fiber transfer of stress equipment Products often toxic and hazardous Modulus 3.5 to 5 times that of Great variety of materials, steel or aluminum processes, and techniques Longer life than metals Inspection methods difficult to Higher corrosion resistance conduct Tensile strength 4 to 6 times Lack of long term design database that ofsteel/aluminum Lack of standardized system of methodology Greater design flexibility Lack of standardized methodology Bonded construction for construction and repairs eliminates joints and fasteners General lack of repair knowledge Easily repairable and expertise NON-METALLIC AIRCRAFT MATERIALS COMPOSITE MATERIALS Fiber Reinforced Materials The purpose of reinforcement in reinforced materials is to provide most of the strength. Three main forms: particles - square piece whiskers - crystalline, longer than it is wide fibers - filaments, longer than they are wide. NON-METALLIC AIRCRAFT MATERIALS COMPOSITE MATERIALS Laminated Structures Strong and stiff, but heavy. Composites can be made with or without an inner core of material. Sandwich Structure - with a core center, equal in strength, less weight NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: REINFORCED PLASTIC A thermosetting material used in the manufacture of radomes, antenna covers, and wingtips, and as insulation for various pieces of electrical equipment and fuel cells. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: REINFORCED PLASTIC It has excellent dielectric characteristics, high strength-to- weight ratio, resistance to mildew, rust, and rot, and ease of fabrication. Formed of either solid laminates or sandwich-type laminates. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: REINFORCED PLASTIC Solid laminates Constructed of three or more layers of resin impregnated cloths "wet laminated" together to form a solid sheet facing or molded shape. Sandwich-type laminates Constructed of two or more solid sheet facings or a molded shape enclosing a fiberglass honeycomb or foam-type core. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: RUBBER It is used to prevent the entrance of dirt, water, or air, and the loss of fluids, gases, or air. It is also used to absorb vibration, reduce noise, and cushion impact loads. It includes not only natural rubber, but all synthetic and silicone rubbers. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: RUBBER Natural Rubber It has better physical properties: flexibility, elasticity, tensile strength, tear strength, and low heat buildup due to flexing (hysteresis). Its suitability for aircraft use is somewhat limited because of its inferior resistance to most influences that cause deterioration. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: RUBBER Synthetic Rubber Synthetic rubber is available in several types, each of which is compounded of different materials to give the desired properties. The most widely used are the butyls, Buna-S, and neoprene. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: SYNTHETIC RUBBER Butyl A hydrocarbon rubber with superior resistance to gas permeation and deterioration (oxygen, vegetable oils, animal fats, alkalies, ozone, and weathering). It has a low water absorption rate and good resistance to heat and low temperature. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: SYNTHETIC RUBBER Buna-S resembles natural rubber both in processing and performance characteristics. It has good resistance to heat, but only in the absence of severe flexing. Generally has poor resistance to gasoline, oil concentrated acids, and solvents. It is normally used for tires and tubes as a substitute for natural rubber. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: SYNTHETIC RUBBER Buna-N It is highly resistant to hydrocarbons and solvents, with good performance in temperatures up to 300°F and down to -75°F. However, it has poor resilience in solvents at low temperatures and only fair resistance to tear, sunlight, and ozone. It offers good abrasion resistance and is commonly used in oil and gasoline hoses, tank linings, gaskets, and seals. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: SYNTHETIC RUBBER Neoprene It is more durable than natural rubber, with excellent resistance to ozone, sunlight, heat, and oil, though its tensile strength and tear resistance are slightly lower. It is commonly used in weather seals, oil-resistant hoses, and carburetor diaphragms, but has poor resistance to aromatic gasolines. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: SYNTHETIC RUBBER Thiokol Thiokol, or polysulfide rubber, offers excellent resistance to deterioration and chemicals like petroleum and gasoline but has low physical properties, including tensile strength, elasticity, and tear abrasion resistance. It is commonly used in oil hoses, tank linings for aromatic aviation gasolines, gaskets, and seals. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: SYNTHETIC RUBBER Silicone rubbers Silicone rubbers, made from silicon, oxygen, hydrogen, and carbon, offer excellent heat stability and flexibility across a wide temperature range from -150°F to 600°F, making them ideal for gaskets and seals. However, while they resist oils, they react poorly to both aromatic and nonaromatic gasoline. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: SYNTHETIC RUBBER Silastic Silastic, a well-known silicone, is used to insulate electrical and electronic equipment due to its excellent dielectric properties across a wide temperature range. It remains flexible without cracking and is also used for gaskets and seals in specific oil systems. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: SEALING COMPOUNDS Aircraft areas are sealed to withstand pressurization, prevent fuel leaks, block fumes, and protect against weather- related corrosion. Sealants typically involve multiple ingredients, with some requiring mixing before use, while others are ready to apply straight from the package. NON-METALLIC AIRCRAFT MATERIALS Listed in order from least to most commonly used: SEALING COMPOUNDS One-Part Sealant - These are pre-prepared by the manufacturer and ready to use, though their consistency can be adjusted with a manufacturer-recommended thinner if needed. Two-part Sealant - These require separate packaging of a base compound and an accelerator, which must be mixed in prescribed ratios, typically equal by weight, to ensure proper curing and material quality. ADVANCED COMPOSITE MATERIALS ADVANCED COMPOSITE MATERIALS These are increasingly used in aerospace structures for their weight savings compared to aluminum, with applications including fairings, spoilers, and flight controls developed since the 1960s. Modern large aircraft feature composite fuselage and wing structures, which require specialized knowledge for repair. Its primary advantages are high strength, low weight, and corrosion resistance. LAMINATED STRUCTURES LAMINATED STRUCTURES Composite materials combine distinct components to achieve superior structural properties, with individual materials remaining physically identifiable. Advanced composites typically consist of fibrous materials embedded in a resin matrix, laminated with fibers oriented in alternating directions for enhanced strength and stiffness. LAMINATED STRUCTURES Applications of composites on aircraft include: Fairings Flight control surfaces Landing gear doors Leading and trailing edge panels on the wing and stabilizer Interior components Floor beams and floor boards Vertical and horizontal stabilizer primary structure on large aircraft Primary wing and fuselage structure on new generation large aircraft Turbine engine fan blades Propellers MAJOR COMPONENTS OF A LAMINATE Isotropic materials, like aluminum and titanium, have uniform properties in all directions Anisotropic materials, such as fiber-reinforced composites, vary in strength and stiffness based on fiber orientation. Fibers in composites are the main load carriers Matrix supports and bonds the fibers, transfers loads, and provides environmental resistance. Although composites can be designed to optimize mechanical properties, they do not achieve the true isotropy of metals. MAJOR COMPONENTS OF A LAMINATE Anisotropic materials Isotropic materials STRENGTH CHARACTERISTICS The structural properties of a composite laminate, including stiffness, stability, and strength, are influenced by the stacking sequence of its plies. With more plies with chosen orientations, the number of possible stacking sequences increases significantly, such as the 24 sequences possible for a symmetric eight-ply laminate with four different orientations. STRENGTH CHARACTERISTICS FIBER ORIENTATION The strength and stiffness of a composite depend on the ply orientation and sequence, with different configurations like 0° (axial), ±45° (shear), and 90° (side) addressing specific load types. STRENGTH CHARACTERISTICS FIBER ORIENTATION Unidirectional materials have strength in one direction. Pre-impregnated (prepreg) tape Bidirectional materials have strength in two directions but not necessarily equally. Plain weave fabric FIBER ORIENTATION Quasi-isotropic layups use a Warp clocks are used to combination of orientations to indicate fiber directions, with mimic isotropic properties. default orientation assumed if the clock is not provided. FIBER FORMS FIBER FORMS Composite materials typically start with spooled unidirectional raw fibers, where individual fibers are called filaments, and bundles are known as tows, yarns, or rovings. Fibers can be supplied as dry fiber requiring resin impregnation or as prepreg materials with pre- applied resin. FIBER FORMS Rovings All filaments are in the same direction and they are not twisted. FIBER FORMS Unidirectional (Tape) Unidirectional prepreg tapes, commonly used in aerospace, are made by impregnating raw dry strands with hot melted thermosetting resins through heat and pressure of the impregnation machine. Tape products have high strength in the fiber direction and virtually no strength across the fibers. FIBER FORMS Bidirectional (Fabric) Bidirectional fabrics offer greater flexibility for the layup of complex shapes compared to unidirectional tapes and can be impregnated with resin through solution or hot melt processes. For aerospace structures, tightly woven fabrics are usually the choice to save weight, minimizing resin void size, and maintaining fiber orientation during the fabrication process. FIBER FORMS Bidirectional (Fabric) The more common fabric styles are plain or satin weaves. Plain weave - each fiber alternating over and then under each intersecting strand Satin weave - fiber bundles traverse both in warp and fill directions changing over/under position less frequently. Bidirectional (Tape) FIBER FORMS Nonwoven (Knitted or Stitched) Knitted or stitched fabrics can provide many benefits similar to unidirectional tapes, with fibers held in place by stitching with fine yarns or threads rather than weaving. These fabrics offer versatile multi-ply orientations and may enhance interlaminar shear and toughness properties, although they may add some weight and slightly reduce ultimate reinforcement fiber properties. TYPES OF FIBER TYPES OF FIBER 1. Fiberglass 2. Kevlar 3. Carbon/Graphite 4. Boron 5. Ceramic Fibers 6. Lightning Protection Fibers TYPES OF FIBER FIBERGLASS Fiberglass is used in secondary aircraft structures and helicopter rotor blades. E-glass - for electrical applications because it has high resistance to current flow. S-glass - for structural strength. TYPES OF FIBER FIBERGLASS Advantages: Lower cost, corrosion resistance, and non-conductivity, and is available in both dry fiber fabric and prepreg forms. TYPES OF FIBER KEVLAR (DuPont) Kevlar® aramid fibers are yellow, lightweight, strong, and tough, making them ideal for impact- prone areas. Two types of aramid fiber are used in the aviation industry: Kevlar® 49 - high stiffness Kevlar® 29 - lower stiffness TYPES OF FIBER KEVLAR (DuPont) The main disadvantage of aramid fibers is their general weakness in compression and hygroscopy (absorbing moisture). They are difficult to drill and cut, require special tools. Commonly used in military ballistic and body armor applications. TYPES OF FIBER CARBON/GRAPHITE Carbon and graphite fibers both stem from graphene (hexagonal) layer networks in carbon. Graphite fibers have a well- ordered three-dimensional structure and require more extensive processing, making them more expensive. TYPES OF FIBER CARBON/GRAPHITE Carbon fibers only have a two- dimensional structure. They are highly stiff and strong; and used in structural aircraft components like floor beams, stabilizers, and fuselage. Gray or black in color. TYPES OF FIBER CARBON/GRAPHITE Advantages: Carbon fiber is highly strong and corrosion-resistant, making it suitable for structural aircraft applications. Disadvantages: It has lower conductivity than aluminum, necessitating lightning protection, and is expensive; it also poses a risk of galvanic corrosion when used with metallic fasteners. TYPES OF FIBER BORON Boron fibers are very stiff, with high tensile and compressive strength, and are typically used in prepreg tape form with an epoxy matrix. However, they are expensive, difficult to apply to contoured surfaces, and can be hazardous to handle, making them mainly suitable for military aviation applications. TYPES OF FIBER CERAMIC FIBERS Ceramic fibers are used for high- temperature applications, such as turbine blades in a gas turbine engine. The ceramic fibers can be used at temperatures up to 2 200 °F. TYPES OF FIBER LIGHTNING PROTECTION FIBERS Carbon fibers are 1,000 times more resistive than aluminum to current flow, and epoxy resin is 1,000,000 times more resistive. As such, composite components often require a conductive surface layer, such as nickel-coated graphite cloth or conductive paints, for lightning protection. TYPES OF FIBER LIGHTNING PROTECTION FIBERS Repairs on these components must restore electrical conductivity, typically verified with an ohmmeter, and only approved materials from authorized vendors should be used for repairs. MATRIX MATERIALS MATRIX MATERIAL Resin refers to the polymer that significantly impacts the processing, fabrication, and properties of composite materials. MATRIX MATERIAL THERMOSETTING RESINS Thermosetting resins, which cure into insoluble solids and serve as effective adhesives and bonding agents, are versatile, easily shaped, and compatible with various materials. MATRIX MATERIAL THERMOSETTING RESINS Polyester Resin - inexpensive, fast-processing Vinyl Ester Resin - good corrosion resistance and mechanical properties Phenolic Resin - low smoke and flammability characteristics MATRIX MATERIAL THERMOSETTING RESINS Epoxy - offers high strength, modulus, and excellent adhesion with low volatiles and good chemical resistance, but they are brittle and have reduced properties when exposed to moisture. MATRIX MATERIAL THERMOSETTING RESINS Polyimides - excel in high- temperature environments where their thermal resistance, oxidative stability, low coefficient of thermal expansion, and solvent resistance benefit the design. MATRIX MATERIAL THERMOSETTING RESINS Polybenzimidazole (PBI) - extremely high temperature resistant and is used for high temperature materials. Bismaleimide (BMI) - has a higher temperature capability and higher toughness than epoxy resins, and it provides excellent performance at ambient and elevated temperatures. MATRIX MATERIAL THERMOPLASTIC RESINS Thermoplastic resins can be repeatedly softened and hardened with temperature changes, allowing for fast processing and shaping through molding or extrusion without chemical curing. MATRIX MATERIAL THERMOPLASTIC RESINS Semicrystalline thermoplastics - possess properties of inherent flame resistance, superior toughness, good mechanical properties at elevated temperatures and after impact, and low moisture absorption. MATRIX MATERIAL THERMOPLASTIC RESINS Amorphous thermoplastics - noted for their processing ease and speed, high temperature capability, good mechanical properties, excellent toughness and impact strength, and chemical stability. MATRIX MATERIAL THERMOPLASTIC RESINS Polyether Ether Ketone (PEEK) - This aromatic ketone material offers outstanding thermal and combustion characteristics and resistance to a wide range of solvents and proprietary fluids. CURING STAGES OF RESINS CURING STAGES OF RESINS Thermosetting resins use a chemical reaction to cure. There are three curing stages, which are A, B, and C. CURING STAGES OF RESINS A STAGE B STAGE C STAGE During a wet layup The chemical reaction The resin is fully cured. procedure, the has started. The resin Some resins cure components of the thickens and becomes at room temperature resin (base material tacky. It stays in the B and others need an and hardener) have stage when frozen at elevated been mixed but the 0°F and cures once temperature cure chemical reaction has warmed after removal cycle to fully cure. not started. from the freezer. CURING STAGES OF RESINS PRE-IMPREGNATED PRODUCTS (PREPREGS) PRE-IMPREGNATED PRODUCTS (PREPREGS) Prepreg material combines matrix and fiber reinforcement, available in unidirectional or fabric forms. The resin is in the B stage for improved handling and must be stored in a freezer below 0 °F to delay curing. PRE-IMPREGNATED PRODUCTS (PREPREGS) Prepregs are cured with elevated temperatures (such as 250 °F or 350 °F) using autoclaves, ovens, or heat blankets, and are typically purchased and stored on rolls in sealed plastic bags to prevent moisture contamination. PRE-IMPREGNATED PRODUCTS (PREPREGS) ANY QUESTIONS? THANK YOU FOR LISTENING