Structures midterm Flashcards
List four different grades/types of steel. For each, briefly describe the properties and typical aerospace applications.
Low-carbon steel (e.g., SAE 1010-1030): Safety wire, nuts.
Medium-carbon steel (e.g., SAE 1035): Rod ends, forgings.
High-carbon steel (e.g., SAE 1095): Springs, high-strength wires.
Stainless steel (e.g., 18-8 steel): Exhaust systems, fasteners.
Why must rivets of a 2017 aluminum alloy be refrigerated before they are used?
Slows aging, allowing more time for installation before hardening.
What makes aluminum desirable for aerospace structures?
High strength-to-weight ratio, corrosion resistance, lightweight.
What is the chief difference between heat-treatable and non-heat-treatable aluminum alloys? What alloy designations are typical of each case?
Heat-treatable alloys: Can be strengthened by heat treatment (e.g., 2000, 6000, and 7000 series).
Non-heat-treatable alloys: Strengthened by cold working (e.g., 1000, 3000, and 5000 series).
What are four common aluminum alloys used within the aerospace industry? What applications are they typically used for and why?
2024: Used in aircraft structures due to high strength and fatigue resistance.
7075: Used in high-stress applications like wing spars and fuselage frames due to its high strength.
6061: Used in general-purpose applications like fittings and brackets due to its weldability and corrosion resistance.
5083: Used in marine and cryogenic applications due to its excellent corrosion resistance.
How does titanium compare to aluminum and steel? What are some key advantages and disadvantages of using titanium?
Pros: Stronger than steel, corrosion-resistant, high-temp performance.
Cons: Expensive, harder to machine, heavier than aluminum.
What are the four steps of titanium production? Briefly describe each step.
Reduce ore to sponge.
Melt sponge to ingot.
Primary fabrication (bars, plates).
Secondary fabrication (finished shapes).
What is the most common alloy of titanium used in the aerospace industry? What are some of its applications?
Ti-6Al-4V (Grade 5), used in engines, landing gear.
What are the six steps of ceramic production? Briefly describe each step.
Milling: Raw materials are reduced to a smaller size.
Batching: Ingredients are weighed and prepared.
Mixing: Materials are mixed to form a homogeneous mixture.
Forming: The mixture is shaped into the desired form.
Drying: Water or binders are removed from the formed material.
Firing: The material is heated to high temperatures to achieve final properties.
What are the three different types of ceramics used in the aerospace industry? Briefly describe each type. What are the typical applications for each?
UHTCs: Rocket nozzles, heat shields.
Zirconia ceramics: Engine components.
Fiber ceramics: Jet engines, combustion chambers.
What are three applications of glass used in the aerospace industry?
Cockpit windows.
Optical components.
Thermal protection.
What are five common polymers used within the aerospace industry? What applications are they typically used for and why?
Polycarbonate (PC): Windows, cockpit instruments.
Polyetherimide (PEI): Cabin panels, connectors.
PEEK: Engine components.
PTFE: Seals, bearings.
Polyimide (PI): Electrical insulation.
What is the difference between thermosets and thermoplastics? What are some examples of each type?
Thermosets: Can’t be reshaped (e.g., epoxy).
Thermoplastics: Can be reshaped (e.g., polycarbonate).
Within the context of the aerospace industry, what is typically meant when referring to a “composite material”?
A mix of fibers and matrix for optimized strength, stiffness, and lightweight.
List six factors that can contribute to the breakdown of a composite material.
Fiber-matrix failure.
Fiber breakage.
Matrix cracking.
Delamination.
Environmental exposure.
Manufacturing defects.
What are four typical aircraft parts that are constructed out of composites?
Wing skins
Fuselage panels
Tail sections
Engine nacelles
What is the glass transition temperature (Tg)? What is its general relationship to the polymer matrix, and what properties can it affect?
Temperature where polymer changes from glassy to rubbery state, affecting stiffness and strength.
What makes water/moisture so dangerous to a composite material? List three possible effects of moisture uptake.
Reduces strength/stiffness.
Causes swelling/cracking.
Lowers Tg.
Each industry (aluminum, steel, titanium, polymers/composites) has its benefits and restrictions. What are the limitations or detriments for each of these four industries?
Aluminum: Lower strength, corrosion-prone.
Steel: Heavy, corrodes.
Titanium: Expensive, hard to machine.
Polymers/Composites: Degrade in moisture/UV, costly.
What are the key differences between aluminum alloy series 1000-8000?
1000 – Pure aluminum, excellent corrosion resistance, low strength (e.g., 1100).
2000 – Aluminum-copper, high strength, low corrosion resistance (e.g., 2024).
3000 – Aluminum-manganese, good corrosion resistance, moderate strength (e.g., 3003).
4000 – Aluminum-silicon, wear-resistant, used in engines and welding (e.g., 4032).
5000 – Aluminum-magnesium, corrosion-resistant, marine use (e.g., 5052).
6000 – Aluminum-magnesium-silicon, good weldability, structural use (e.g., 6061).
7000 – Aluminum-zinc, highest strength, aerospace use (e.g., 7075).
8000 – Miscellaneous alloys, used in foil and aerospace (e.g., 8011).
How is a material determined to be ductile vs brittle?
Ductile Materials:
Exhibit significant plastic deformation before fracture.
High percent elongation (>5%) and reduction in area (>10%).
Fracture surfaces are rough and jagged.
Stress-strain curve shows a yield point and large plastic region.
Brittle Materials:
Exhibit little to no plastic deformation before fracture.
Low percent elongation (<5%) and reduction in area (<5%).
Fracture surfaces are smooth and flat.
Stress-strain curve is linear up to fracture (no yield point).
What is a simple tensile test, and how is ductility measured?
A simple tensile test measures a material’s strength, ductility, and stiffness by applying a uniaxial tensile force until fracture.
Ductility is measured by:
Elongation
Reduction in Area
Stress-strain curves for mild steel show a distinct yield point, while aluminum alloys show a gradual transition from elastic to plastic deformation.
What are the main features of a stressed skin structure, and what are the functions of its components in a wing?
Stressed skin structure features:
Skin: Resists aerodynamic pressure and transmits loads.
Stringers: Provide longitudinal stiffening.
Ribs: Maintain shape and distribute loads.
Spars: Carry bending and shear loads.
Functions in a wing:
Skin: Supports aerodynamic forces.
Ribs: Maintain airfoil shape and distribute loads.
Spars: Carry primary bending and shear loads.
Stringers: Increase skin’s resistance to buckling.
