Introduction to Aerospace Engineering

Transcription

1 Introduction to Aerospace Engineering Lecture slides Challenge the future 1

2 Temperature & environment Material properties & degradation Faculty of Aerospace Engineering Delft University of Technology Challenge the future

3 Learning objectives Student should be able to Describe effects of low or elevated temperature on typical aerospace material properties Explain the significance of temperature for aircraft & spacecraft Explain what environments may influence the properties Environmental aspects 2 19

4 Material properties Significance of temperatures Materials & structures are often operated at Low temperatures High temperatures High temperature ranges For a long time Environmental aspects 3 19

5 Material properties Effect of temperatures Material properties change with temperature (metals) Ultimate strength 700 Modulus of elasticity 600 Yield strength Elongation 500 Ultimate & yield strength [MPa] σult,rt σy,rt 2024-T hours 100 hours 1/2 hour Temperature [Celsius] Environmental aspects 4 19

6 Material properties Effect of temperatures Material properties change with temperature (polymers) Modulus of elasticity Elongation glass transition temperature E T g T m Environmental aspects 5 19

7 Material properties Effect of high temperatures Phenomena Creep Low yield strength (easier to deform plastically) Thermal stresses (inhomogeneous temperature distribution) High temperature applications Turbine blades Thermal protection systems Environmental aspects 6 19

8 Material properties Effect of high temperatures Thermal stress Coefficient of thermal expansion 1 dv α = V dt Environmental aspects 7 19

9 Material properties Effect of high temperatures Mechanical properties Fatigue properties Thermal stresses Environmental aspects 8 19

10 Material properties Effect of low temperatures Mechanical properties Resistance against plastic deformation Chemical reaction & diffusion rates Environmental aspects 9 19

11 Material properties Effect of low temperatures Fracture toughness Example: T2 and Liberty ships 16 January 1943, S.S. Schenectady, a T2 tanker, 24 hrs old Environmental aspects 10 19

12 Material properties Effect of low temperatures Fracture toughness Transition from ductile to brittle fracture Temperature ductility and notch sensitivity Environmental aspects 11 19

13 Environmental aspects Example environments Air/moisture/salt Space & re-entry Fuel Hydraulics Cleaning agents Environmental aspects 12 19

14 Environmental aspects Example environments Air/moisture/salt Sea Environmental aspects 13 19

15 Environmental aspects Example environments Space & re-entry Radiation/UV exposure Atomic Oxygen (O + ) Vacuum (degassing) Environmental aspects 14 19

16 Environmental aspects Example environments Fuel Integral fuel tank: structure sealed during manufacturing Environmental aspects 15 19

17 Environmental aspects Example environments De-icing Mechanical/thermal (scraping/heating) Liquid chemicals (salts/alcohols/glycols) Cleaning compounds Prescribed cleaning method Environmental aspects 16 19

18 Environmental aspects Example environmental effect: corrosion In time environment affects the material & structure Environmental aspects 17 19

19 Environmental aspects Example environmental effect: corrosion Example: Galvanic corrosion Bicycle in winter: road salt & mud galvanic corrosion between chromium plated brass spoke nipple and aluminium rim Environmental aspects 18 19

20 Summary Temperature & environment Material properties change with temperature Properties may change drastically Glass transition temperature for polymers/composites Ductile to brittle transition temperature for certain steel alloys Environment may affect properties in time Air/moisture/salt Space & re-entry Fuel Hydraulics Cleaning agents Environmental aspects 19 19