Lightweight Materials & Design

Lightweight Materials

• Lightweighting involves designing and manufacturing components with less weight
  • It uses advanced materials and engineering techniques

Achieving Lightweighting

• Material optimization: Utilizing alternative lightweight materials
  • These materials maintain a sufficient strength-to-weight ratio
  • This delivers incremental gains
• Design/structural changes: Making fundamental changes to the design for improved performance

Benefits of Lightweighting

• Increased fuel efficiency
• Reduced emissions
• Improved performance due to increased range and payload capacity
• Lower operating costs

Metal Alloys

• Aluminum alloys are important for aerospace structural weight
  • It is still more significant than that of composites
• Aerospace-grade aluminum has high strength to weight ratio, corrosion resistance, and electrical conductivity

Aluminum Alloys

• Alloy 5052 is a non-heat treatable alloy that is strong, ductile, and corrosion resistant
  • Ideal for aerospace applications because of these qualities
• Alloy 2219 aluminum alloy offers maximum strength at high temperatures
  • Successfully used for first space shuttle Columbia's external fuel tank, and has good weldability
• Alloy 7050 has high corrosion resistance and strength in wide sections
  • Used in wing skins and fuselage, especially in military crafts
  • Offers high resistance to fractures

Titanium Alloys

• Titanium alloys in aerospace are used in airframe and engine components
  • Making up 7% and 36% of the weight
• Features of titanium alloys: high strength to weight ratio, excellent corrosion resistance, elevated operational temperature range, and superior fatigue strength

Types of Titanium Alloys

• Alpha alloys: Non-heat treatable and weldable with low to medium strength
  • Exhibits good notch toughness, decent ductility
  • Shows excellent properties at cryogenic temperatures
  • Provides high temperature creep strength and oxidation resistance
• Alpha-Beta alloys: Heat treatable to varying extents
  • Mostly weldable but can lose some ductility in the weld area
  • Medium to high strength
  • Hot forming qualities are good but cold forming often presents difficulties
  • Creep strength isn't as good as in most alpha alloys
• Beta alloys: Readily heat treatable and generally weldable
  • High strength up to intermediate temperature levels
  • Solution treated condition provides excellent cold formability

Stainless Steel Alloys

• Stainless Steel is the lowest cost aerospace material
• High-strength steels are employed in gearing, bearings, and undercarriage applications
• Steel alloys offer extremely high strength and stiffness, low cost, and good dimensional properties at high temperatures

Types of Steel Alloys

• 300 Series (Austenitic Stainless Steels) offers excellent ductility, formability, and corrosion resistance
  • Has good weldability
  • Grade 321 is an austenitic chrome-nickel stainless, titanium added
    • For parts intermittently heated to between 800/1650°F (427/899°C)
    • Designed to eliminate intergranular corrosion in the as-welded condition
• 400 Series (Martensitic and Ferritic Stainless Steels) are chromium stainless steels with varied carbon levels
  • They are work hardenable.
  • Grade 410 is a hardenable martensitic stainless alloy used for highly stressed parts
    • Needing good corrosion resistance and strength
    • Can be heat-treated to obtain high-strength properties with good ductility

Composite Materials

• Composite materials combine different materials on a macroscopic scale
  • This creates a resultant material with properties of the components
• "Composites" is a broad term for materials like fiber-reinforced polymer composites - carbon fiber, glass fiber, and aramid fiber, with epoxy

Advantages of Composite Materials

• Increased strength and stiffness
• Reduced weight and part count
• Greater fatigue limits and corrosion resistance
• Can be tuned for specific applications

Fiber Reinforcement

• Fiber reinforcement makes provides strength and stiffness based on fiber alignment
• The three most common forms of fiber are carbon fiber, glass fiber, and aramid fiber

Carbon Fiber

• Carbon fiber is constituted from thin, strong crystalline filaments of carbon, and atoms carbon bonded in long chains
• Carbon fiber offers high stiffness and stiffness-to-weight ratio, high tensile strength and strength-to-weight ratio
  • Has high-temperature tolerance with special resins, low thermal expansion and high chemical resistance

Glass Fiber

• Glass fiber are thin strands of silica-based or other formulation glass extruded into fibers
  • These fibers have small diameters suitable for textile processing
• It is not as rigid as carbon fiber but it is much cheaper and less brittle
• Glass fiber features great heat and electrical insulation, as well as high stiffness

Aramid Fiber

• Aramid fiber, also known as Aromatic Polyamide, is made from long-chain synthetic polyamides
• This polymer has alternating benzene rings and amide groups, and a rigid, rod-like structure.
• Aramid fiber displays high tensile strength, high melting point (>500 degree celsius), is flame resistant, and has high durability under extreme tension and bending

Matrix Composites

• Matrix is a percolating alloy/metal/polymer/plastic/resin/ceramic material for composites, and into which other constituents are embedded
• Matrix binds the fiber reinforcement, gives the composite component its shape, and influences its surface quality

Types of Matrix Composites

• Metal matrix composites (MMCs) consist of a metallic matrix, like aluminum, magnesium, or titanium, reinforced by materials like silicon carbide, boron, or carbon fibers
  • Usually for high mechanical strength and thermal stability.
  • Shows higher strength and thermal stability than polymer-based composites
• Polymer matrix composites (PMCs) can are divided into thermosets and thermoplastics
  • Thermosets require a curing agent to harden and they can't be reheated
    • Thermoplastics can be reheated and reformed
    • High resistance to abrasion and corrosion
  • High stiffness and strength
• Carbon matrix composites -also known as carbon-carbon (C/c) composites - are made by embedding carbon fibers within a carbon matrix
  • Composites can be categorized based on reinforcement types and manufacturing processes.
  • Utilized in spacecraft components like thermal protection systems and rocket nozzles
    • The material withstands extreme conditions
    • Missile nose cones and heat shields use these as defense because of the lightweight and heat-resistant properties.

Composite Materials

• Fiberglass Reinforced Polymers (GFRP) are lightweight, strong and less brittle
• Kevlar – for strength and heat resistance
  • It is a combination of aramid fiber and epoxy

Lattice Structure

• Refers to a repeating grid pattern of intersecting ribs or stiffeners
  • Creates a lightweight yet strong structural framework
• Often made from composite materials like carbon-fiber reinforced composites
• Reduces weight while maintaining structural integrity by 30-50%
• Utilized for large-scale space components such as solar arrays and payload adapters
  • Has high mass efficiency and 3D additive manufacturing

Honeycomb Structure

• Minimizes material usage and reduces weight and material cost
• Geometry can vary, it can take the form of hollow cells between walls
• Has high strength-to-weight ratio, high stiffness-to-weight ratio, good shock absorption and good structural stability