Non-Metallic Aircraft Materials PDF

**NON-METALLIC AIRCRAFT MATERIALS** **Mid 1950s** Magnesium, Plastic, and Fabric **80% to 15%** Wood, and Aluminum 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 **WOOD**...

**NON-METALLIC AIRCRAFT MATERIALS** **Mid 1950s** Magnesium, Plastic, and Fabric **80% to 15%** Wood, and Aluminum 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 **WOOD** - Today, very little is used in aircraft construction except for: - restorations - homebuilt aircraft Aircraft made of wood: de Havilland Mosquito  TRANSPARENT PLASTICS - used in aircraft canopies, windshields, windows classified into two according to reaction to heat: - **Thermoplastic** - will soften when heated and harden when cooled. - **Thermosetting** - harden upon heating, and reheating has no softening effect. **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. - **Stretched Acrylic** - A new development in transparent plastics - It is pulled in both directions to rearrange its molecular structure before being shaped. **COMPOSITE MATERIALS** - In the 1940s, the aircraft industry began to develop **synthetic fibers** to enhance aircraft design. - Combination of reinforcement such as a fiber, whisker, or particle, surrounded and held in place by a resin, forming a structure. Advantages - High strength to weight ratio - Fiber-to-fiber transfer of stress - Modulus 3.5 to 5 times that of - steel or aluminum - Higher corrosion resistance - Tensile strength 4 to 6 times - that of steel/aluminum - Greater design flexibility - Bonded construction - eliminates joints and fasteners - Easily repairable **DISADVANTAGES** Cost, very expensive processing equipment **Fiber Reinforced Materials** - The purpose of reinforcement in reinforced materials are 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. **Laminated Structures** - Strong and stiff but heavy **Sandwich Structure** - With a core center, equal in strength, less weight **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. **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. **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. **Natural Rubber** - It has better physical properties: flexibility, elasticity, tensile strength, tear strength, and low heat buildup due to flexing (hysteresis). Limited because of its inferior resistance **Synthetic Rubber** - Synthetic rubber is available in several types, each of which is compounded of different materials to give the desired properties. to give the desired properties. The most widely used are the **butyls,** **Buna-S**, and **neoprene.** **Butyl** - A hydrocarbon rubber with superior resistance to gas permeation and deterioration (oxygen, vegetable oils, animal fats, alkalies, ozone, and weathering). **Buna-S** - It has good resistance to heat, but only in the absence of severe flexing. poor resistance to gasoline, oil concentrated acids, and solvents. Normally used for tires and tubes **Buna-N** - It is highly resistant to hydrocarbons and solvents, with good performance in temperatures up to 300°F and down to -75°F. Commonly used in oil and gasoline hoses, tank linings, gaskets, and seals. **Neoprene** - More durable, excellent resistance to ozone, sunlight, heat, and oil, though itstensile strength and tear resistance are slightly lower. **Thiokol** - excellent resistance to deterioration and chemicals like petroleum and gasoline but has low physical properties, including tensile strength, elasticity, and tear abrasion resistance. **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. **Silastic** - excellent dielectric properties **SEALING COMPOUNDS** - **One-Part Sealant** - pre-prepared - **Two-part Sealant** - require separate packaging of a base compound and an accelerator, typically equal by weight to ensure proper curing and material quality. **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 the1960s.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** - Composite materials combine distinct components to achieve superior structural properties, with individual materials remaining physically identifiable. **Applications of composites on aircraft include:** 1. Fairings 2. Flight control surfaces 3. Landing gear doors 4. Leading and trailing edge panels on the wing 5. and stabilizer 6. Interior components 7. Floor beams and floor boards 8. Vertical and horizontal stabilizer primary 9. structure on large aircraft 10. Primary wing and fuselage structure on new 11. generation large aircraft 12. Turbine engine fan blades 13. Propellers **Isotropic material** - Uniform in all directions **Anisotropic materials** - properties that differ according to direction of measurement - 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. **Composite Laminate** - including stiffness, stability, and strength, are influenced by the **stacking sequence of its plies.** **FIBER ORIENTATION**- 0 (axial), ±45° (shear), and 90°(side) addressing specific load types. 2 types of fiber orientation: **Unidirectional materials** - have strength in one direction. **Bidirectional materials** - Have strength in two directions but not necessarily equally. **Quasi-isotropic layups** - use a combination of orientations to mimic isotropic properties. **Warp clocks** - are used to indicate fiber directions, with default orientation assumed if the clock is not provided. **FIBER FORMS** - start with spooled unidirectional raw fibers, where individual fiber 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. Fibers can be supplied as dry fiber requiring resin impregnation or as prepreg materials with pre-applied resin. **Rovings** - All filaments are in the same direction and they are nots twisted. **Unidirectional (Tape)** - Unidirectional prepreg tapes, commonly used in aerospace, are made by impregnating raw drystrands with hot melted thermosetting resins through heat and pressure of the impregnation machine. **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. 2 types of bidirectional weave: 1. **Plain weave** - each fiber alternating over and then under each intersecting strand. 2. **Satin weave** - fiber bundles traverse both in warp and fill directions changing over/under position less frequently. **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. **TYPES OF FIBER** **FIBERGLASS** - in secondary aircraft structures and helicopter rotor blades. 1. **E-glass** - for electrical applications because it has high resistance to current flow. 2. **S-glass** - for structural strength. **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: 1. Kevlar® 49 - high stiffness 2. Kevlar® 29 - lower stiffness The main disadvantage of aramid fibers is their general weakness incompression and hygroscopy (absorbing moisture). **CARBON/GRAPHITE** - Advantages: Carbon fiber is highly strong and corrosion-resistant, making it suitable for structural aircraft applications. - Disadvantages: It has lowerconductivity than aluminum, necessitating lightning protection, and is expensive; it also poses a risk of galvanic corrosion when used with metallic fasteners. **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. **CERAMIC FIBERS** - Ceramic fibers are used for high-temperature applications, such as turbine blades in a gas turbine engine. Can be used at temperatures up to 2 200 °F. **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. **MATRIX MATERIAL** **THERMOSETTING RESINS** - Thermoseting resins, which cure into insoluble solids and serve as effective adhesives and bonding agents, are versatile, easily shaped, and compatible with various materials. **TYPES OF RESINS:** 1. **Polyester Resin** - inexpensive, fast-processing 2. **Vinyl Ester Resin** - good corrosion resistance and mechanical properties 3. **Phenolic Resin** - low smoke and flammability characteristics 4. **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. 5. **Polyimides** - excel in high-temperature environments where their thermal resistance, oxidative stability, low coefficient of thermal expansion, and solvent resistance benefit the design. 6. **Polybenzimidazole(PBI)** -extremely high temperature resistant and is used for high temperature materials. 7. **Bismaleimide (BMI**) - has a higher temperature capability and higher toughness than epoxy resins, and it provides excellent performance at ambient and elevated. **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. **Semicrystalline thermoplastics** - possess properties of inherent flame resistance, superior toughness, good mechanical properties at elevated temperatures and after impact, and low moisture absorption. **Amorphous thermoplastics** - noted for their processing ease **Polyether Ether Ketone (PEEK)** - This aromatic ketone material **Thermosetting resins** use a chemical reaction to cure. **CURING STAGES OF RESINS:** **A STAGE**- chemical reaction has not started. **B STAGE**- chemical reaction has started. **C STAGE** -- fully cured **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. - 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.