M6 Material & Hardware (DGCA)

Cheatsheet Content

### Introduction to Materials and Hardware - **Purpose:** Understanding the properties, selection, and maintenance of materials and hardware used in aircraft construction and repair is crucial for airworthiness. - **DGCA Relevance:** This module covers topics essential for aircraft maintenance engineers (AMEs) as per DGCA regulations. ### Material Properties - **Strength:** Ability to withstand applied loads without permanent deformation or failure. - **Tensile Strength:** Resistance to pulling forces. - **Compressive Strength:** Resistance to pushing forces. - **Shear Strength:** Resistance to forces parallel to the surface. - **Torsional Strength:** Resistance to twisting forces. - **Hardness:** Resistance to indentation, scratching, or abrasion. - **Toughness:** Ability to absorb energy and plastically deform without fracturing. (Area under stress-strain curve). - **Ductility:** Ability to be drawn into a wire or stretched without breaking (e.g., copper). - **Malleability:** Ability to be hammered or pressed into shape without breaking (e.g., gold). - **Elasticity:** Ability to return to original shape after deformation when load is removed. - **Plasticity:** Ability to retain deformed shape after load is removed. - **Brittleness:** Tendency to fracture with little or no plastic deformation (e.g., glass, cast iron). - **Fatigue:** Weakening of material due to repeated or cyclic loading. - **Creep:** Time-dependent deformation under constant stress at elevated temperatures. - **Corrosion Resistance:** Ability to resist degradation due to chemical or electrochemical reactions. ### Ferrous Metals - **Definition:** Metals containing iron as a primary component. - **Steel:** Iron alloyed with carbon (up to 2%). - **Low Carbon Steel (Mild Steel):** 0.60% C. Hard, brittle. Used for springs, cutting tools. - **Alloy Steels:** Steel with added elements (Cr, Ni, Mo, V, Mn) to improve properties. - **Stainless Steel:** Contains Chromium (>10.5%) for corrosion resistance. - **Austenitic (300 series):** Non-magnetic, excellent corrosion resistance (e.g., 304, 316). - **Martensitic (400 series):** Magnetic, heat-treatable, good strength (e.g., 410, 420). - **Ferritic (400 series):** Magnetic, good corrosion resistance, not heat-treatable (e.g., 430). - **Nickel Steel:** High strength, toughness. - **Chrome-Molybdenum Steel (4130):** High strength-to-weight ratio, weldable. Common in aircraft structures. - **Cast Iron:** Iron alloy with > 2% Carbon. Brittle, good damping properties. Not typically used for primary aircraft structures. ### Non-Ferrous Metals - **Definition:** Metals that do not contain iron as a primary component. - **Aluminum and its Alloys:** - **Properties:** Lightweight, good strength-to-weight ratio, corrosion resistance (due to oxide layer), good electrical and thermal conductivity. - **Alloy Designations (e.g., 2024, 6061, 7075):** - **1xxx series:** Pure Aluminum (>99%). Excellent corrosion resistance, low strength. - **2xxx series (Al-Cu):** High strength, poor corrosion resistance (e.g., 2014, 2024 - widely used in airframes). Often clad with pure aluminum (Alclad) for corrosion protection. - **5xxx series (Al-Mg):** Good corrosion resistance, weldable. Used for fuel tanks, marine applications. - **6xxx series (Al-Mg-Si):** Medium strength, good formability, weldable. Used for general structures (e.g., 6061). - **7xxx series (Al-Zn-Mg-Cu):** Highest strength, good fatigue resistance (e.g., 7075 - high-stress airframe components). - **Titanium and its Alloys:** - **Properties:** High strength-to-weight ratio, excellent corrosion resistance (especially at high temperatures), good fatigue resistance. - **Uses:** High-temperature applications (engine components, firewall), structural parts where weight saving is critical. - **Magnesium and its Alloys:** - **Properties:** Extremely lightweight, good strength-to-weight ratio. Poor corrosion resistance, highly flammable (fire risk). - **Uses:** Gearbox casings, wheels (with protective coatings). - **Copper and its Alloys:** - **Properties:** Excellent electrical and thermal conductivity, ductile, corrosion resistant. - **Brass (Cu-Zn):** Fittings, bushings. - **Bronze (Cu-Sn):** Bearings, gears. ### Heat Treatment of Metals - **Purpose:** To alter the physical and mechanical properties of metals (e.g., hardness, strength, ductility). - **Processes:** - **Hardening:** Heating to critical temperature, then rapid quenching (water, oil, air) to increase hardness and strength. (e.g., steel). - **Tempering:** Reheating hardened steel to a lower temperature, then cooling. Reduces brittleness and internal stresses while retaining sufficient hardness. - **Annealing:** Heating to critical temperature, then slow cooling (furnace). Makes metal softer, more ductile, relieves internal stresses. - **Normalizing:** Heating above critical temperature, then cooling in still air. Produces a uniform, fine-grained structure, reduces internal stresses. - **Solution Heat Treatment (Aluminum Alloys):** Heating to dissolve alloying elements, then quenching to "freeze" them in solution. This makes the alloy soft and workable. - **Precipitation Heat Treatment (Aging - Aluminum Alloys):** After solution heat treatment, the alloy is held at room temperature (natural aging) or elevated temperature (artificial aging) to allow alloying elements to precipitate, increasing strength and hardness. ### Composite Materials - **Definition:** 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 level within the finished structure. - **Components:** - **Matrix:** Binds the fibers together, protects them, transfers load (e.g., Epoxy, Polyester, Thermoplastics). - **Reinforcement (Fibers):** Provides strength and stiffness (e.g., Carbon Fiber, Glass Fiber, Aramid Fiber - Kevlar). - **Types of Composites:** - **Fiber-reinforced Composites:** Most common in aircraft. - **Carbon Fiber Reinforced Plastic (CFRP):** High strength-to-weight, high stiffness, good fatigue resistance. Used for primary structures (wings, fuselage). - **Glass Fiber Reinforced Plastic (GFRP):** Good strength, low cost, good electrical insulation. Used for fairings, radomes. - **Aramid Fiber Reinforced Plastic (AFRP - Kevlar):** High impact resistance, good tensile strength. Used for cargo liners, ballistic protection. - **Sandwich Structures:** Two thin, strong face sheets separated by a lightweight core (e.g., honeycomb, foam). Provides high bending stiffness with low weight. - **Advantages:** High strength-to-weight ratio, design flexibility, corrosion resistance, fatigue resistance. - **Disadvantages:** High cost, complex manufacturing, difficult repair, susceptibility to impact damage, delamination. - **Damage and Repair:** Inspect for delamination, disbonds, impact damage, fiber breakage. Repairs often involve patch repairs or scarf repairs. ### Aircraft Hardware - **Fasteners:** - **Rivets:** Permanent fasteners. - **Solid Rivets:** AN/MS standards. Driven (bucked) to form a second head. Materials: Aluminum alloys (1100, 2117-T4, 2017-T4, 2024-T4, 5056). - **Blind Rivets:** Used when only one side is accessible (e.g., CherryMax, Olympic-Lok, Huck). - **Special Rivets:** Hi-Shear, Jo-Bolt, Lockbolt. - **Bolts:** Removable fasteners. - **Aircraft Bolts (AN/MS):** High strength, close tolerance. Identify by head markings (e.g., AN standard, material). - **Close Tolerance Bolts:** Used in critical applications where shear strength and fit are paramount. - **Clevis Bolts:** Used for shear loads only. - **Eyebolts:** Used to attach cables or turnbuckles. - **Nuts:** - **Self-locking Nuts:** Prevent loosening due to vibration (e.g., Nylon insert, all-metal). - **Castle Nuts/Slotted Nuts:** Used with cotter pins for positive locking. - **Plain Nuts:** Require separate locking device (e.g., lock washer, secondary nut). - **Screws:** Used for non-structural or lightly loaded panels. - **Machine Screws:** Used with nuts or tapped holes. - **Self-tapping Screws:** Create their own threads. - **Structural Screws:** High strength, used in specific structural applications. - **Washers:** Distribute load, prevent damage to surface, act as shims. - **Plain Washers:** Flat, distribute load. - **Lock Washers:** Prevent loosening (e.g., split-ring, star). Not suitable for critical applications. - **Control Cables:** - **Materials:** Carbon steel or stainless steel. - **Construction:** 7x7 (flexible, small diameter), 7x19 (very flexible, larger diameter). - **Terminology:** Turnbuckles (tension adjustment), Swaged fittings (permanent end fittings), Fairleads (guide cables), Pulleys (change direction). - **Inspection:** Fraying, corrosion, tension. - **Pipes and Hoses:** - **Materials:** Aluminum alloy, stainless steel (rigid pipes). Rubber, synthetic rubber, Teflon (flexible hoses). - **Identification:** Color coding, markings. - **Fittings:** AN (Army-Navy) and MS (Military Standard) flared fittings, B-nuts, O-rings. - **Bearings:** Reduce friction and support rotating parts. - **Plain Bearings:** Bushings. - **Anti-friction Bearings:** Ball bearings, roller bearings (tapered, cylindrical, needle). - **Inspection:** Smoothness, play, lubrication. ### Corrosion and its Control - **Definition:** Deterioration of a material, usually a metal, due to a chemical or electrochemical reaction with its environment. - **Types of Corrosion:** - **Surface Corrosion:** Uniform etching or pitting on the surface. - **Pitting Corrosion:** Localized attack, forming small holes or pits. Very dangerous, hard to detect. - **Intergranular Corrosion:** Attack along grain boundaries of the metal. Often seen in improperly heat-treated aluminum alloys. - **Exfoliation Corrosion:** Advanced intergranular corrosion, lifting layers of the metal. - **Stress Corrosion Cracking (SCC):** Cracking caused by the combined effect of tensile stress and a corrosive environment. - **Fatigue Corrosion:** Cracking caused by the combined effect of cyclic stress and a corrosive environment. - **Fretting Corrosion:** Occurs at contact areas between two vibrating surfaces under load. - **Galvanic Corrosion:** Occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte. (Electrochemical series). - **Factors Affecting Corrosion:** Moisture, temperature, dissimilar metals, stress, pollutants (salt, industrial fumes). - **Corrosion Control:** - **Material Selection:** Using corrosion-resistant materials (e.g., stainless steel, aluminum alloys, composites). - **Protective Coatings:** Paint, primers (zinc chromate), anodizing (aluminum), cladding (Alclad). - **Sacrificial Protection:** Using a more active metal (e.g., zinc primers) to corrode instead of the base metal. - **Environmental Control:** Cleaning, drying, proper drainage. - **Design Considerations:** Avoiding moisture traps, ensuring proper ventilation. - **Regular Inspection and Maintenance:** Early detection and removal of corrosion. ### Non-Destructive Testing (NDT) - **Purpose:** To inspect materials or components for defects without causing damage. - **Methods:** - **Visual Inspection:** Most basic and common. Requires good lighting and magnification. - **Dye Penetrant Inspection (DPI/PT):** Detects surface-breaking flaws (cracks, porosity). Liquid penetrant seeps into flaws, then developer draws it out. - **Magnetic Particle Inspection (MPI/MT):** Detects surface and sub-surface flaws in ferromagnetic materials. Magnetic field applied, iron particles accumulate at flaw. - **Eddy Current Inspection (ECI):** Uses electromagnetic induction to detect surface and near-surface flaws, measure conductivity, and inspect for heat damage. - **Ultrasonic Inspection (UT):** Uses high-frequency sound waves to detect internal flaws, measure thickness. - **Radiographic Inspection (X-ray/Gamma Ray):** Uses penetrating radiation to detect internal flaws, assembly errors. Image captured on film or digital detector. ### Electrical Bonding and Shielding - **Bonding:** Electrically connecting metallic components to ensure a continuous low-resistance path for current flow. - **Purpose:** Static discharge, lightning protection, EMI/RFI shielding, return current path. - **Requirements:** Low resistance (