2 1 1 A Aerospacematerialsinvestigation 264z18

Tyler Sallee

Activity 2.1.1 Aerospace Materials Investigation Introduction Within aerospace design, material selection has a large impact on overall design performance as well as production and maintenance costs. Aerospace designers and developers must always be aware of the impact that material selection has on design specifications ranging from propulsion requirements to environmental factors. In this activity you will investigate properties of materials in several categories. Within each category you will consider the suitability of the materials in aerospace applications.

Equipment   

Computer with Internet access Engineering notebook Pencil

Procedure 1. Open the PBS Forces Lab at the following link : http://www.pbs.org/wgbh/buildingbig/lab/forces.html 2. Click the Forces tab along the top. 3. Click Squeezing option. Click and drag the slider and observe the effect on the material. 4. Observe images by clicking See It In Real Life. 5. Repeat this exploration for each force and use what you learned to complete the following table.

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Forces

Squeezing

Engineering term (look above the block) Compression

Definition (in your own words)

Two examples of how this force can affect airplanes (your ideas)

Force that shrinks an object

Gravity squeezes it before takeoff The wheels are compressed before takeoff

Stretching

Tension

Force that enlarges an object

Drag creates tension Lift and gravity create tension

Bending

Bending

Force that makes a straight object curved

Drag bends the wings back Lift vs. gravity bend the wings

Sliding

Shear

Force that causes one part to Slide The engine want to shear off past another The cargo try to shear through the bottom

Twisting

Torsion

Force that bends an object two or more directions

The wind will bend it a different direction than gravity Lift will pull different from wind

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6. Now that you understand forces, let’s observe various materials used in aerospace applications. Click on the tab labeled Materials. Metals 7. Click on each material shown below and move the slider until the material cracks. Use the tick marks on the scale to assign a number to the force, cost and weight. Record this number on the following table. Move the slides completely to the maximum to see a message about the material. Complete the table below using what you learn. Type of Material

Strength in Strength in Cost Tension Compression (Stretching) (Squeezing) Aluminum 4 4 9

3

Pros: Light, no rust, strong Cons; Expensive

Wings, boats, cars, skyscrapers

Steel

9

Pros:strong Cons: rust, not temperature resistant

Cables, trusses, beams, columns

4

3.5

7

Weight

Pros and Cons

Applications

8. Based on your results, in which loading condition (tension or compression) are metals strongest? Compression 9. Even though steel is an exceptionally strong metal, why wouldn’t it be a good choice for use inside jet engines? It doesn’t preform well in high temperatures

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Polymers 10. Click on the material shown below and move the slider until the material cracks. Use the tick marks on the scale to assign a number to the force, cost and weight. Record this number on the following table. Move the slides completely to the maximum to see a message about the material. Complete the table below using what you learn. Type of Material

Strength in Tension (Stretching)

Plastic

4

Strength in Compressio n (Squeezing) 4

Cost

Weight

Pros and Cons

Applications

9

1.5

Pros: Flexible, lightweight, longlasting, stone Cons: expensive

Umbrellas, inflatable roofs

11. As noted in the investigation, plastics are strong and very light, both of which are desirable characteristics to engineers. However, watch carefully as you apply tension and compression to the plastic. Note how it behaves. Based on your observations, would plastic be a suitable alternative to aluminum for airplanes, or steel for buildings? Why or why not? No, it has a higher elasticity, it bends far more Ceramics 12. Click on the material shown below and move the slider until the material cracks. Use the tick marks on the scale to assign a number to the force, cost and weight. Record this number on the following table. Move the slides completely to the maximum to see a message about the material. Complete the table below using what you learn. Type of Material Brick

Strength in Tension (Stretching) 1.5

Strength in Cost Compression (Squeezing) 4 2.1

Weight

Pros and Cons

Applications

4

Pros: cheap, strong (compression Cons: Heavy, weak (tension)

Walls, domes

13. Based on your observations, in which method of loading (tension or compression) are ceramics strongest? In your opinion, why do you think ceramics behave this way? Compression, there is more air in the object to be pushed out, but it increases cracks made by tension © 2011 Project Lead The Way, Inc. AE Activity 2.1.1 Aerospace Materials Investigation – Page 4

14. Since ceramics can be so strong (and relatively inexpensive), why aren’t they used to make aircraft or other transportation machines? Why do we only seem them used in buildings or structures? They do not take tension well 15. Why wouldn’t brick be used to make the cables which hold up a suspension bridge? Cables rely on tension Composites 16. Click on each material shown below and move the slider until the material cracks. Use the tick marks on the scale to assign a number to the force, cost and weight. Record this number on the following table. Move the slides completely to the maximum to see a message about the material. Complete the table below using what you learn. Type of Material Wood

Strength in Tension (Stretching) 2.5

Reinforced 4 Concrete

Strength in Cost Weight Pros and Cons Compression (Squeezing) 3 2.1 1 Pros: Cheap light, moderately strong Cons: Rot, swells, burns

4

4.5

6

Pro’s: cheap, fireproof, weatherproof, molds, strong Cons: Can crack as it cools

Applications

Bridges, houses, roller coasters

Bridges, Dams, Domes, Beams, columns

17. Note the arrangement of the steel rods in the reinforced concrete and the fibers of the wood. Why were these materials strongest pulled along the rods and fibers? Because those are what hold them together 18. In your opinion, what would have happened if we would have pulled on the wood/reinforced concrete from the top and bottom instead of the sides? Why? They would break into segments based on where the rods, or fibers were 19. Click on the unreinforced concrete and perform a tension/compression test. How does adding the steel rods improve the strength of the concrete (and in which mode, tension or compression)? Explain. © 2011 Project Lead The Way, Inc. AE Activity 2.1.1 Aerospace Materials Investigation – Page 5

It gives something for the concrete to hold onto. 20. As noted in the investigation, wood and reinforced concrete are relatively strong and inexpensive. Why don’t we use these particular composite materials to construct aircraft or other transportation vehicles? Wood is not nearly as strong, and concrete cracks in forming. 21. The PBS Forces Lab is a resource designed to show qualitative comparisons between broad material categories. Engineers need accurate material properties to design safe and predictable products. These material properties were measured using stringent testing standards. These properties are published in sources for reference such as MatWeb http://www.matweb.com. Use this site or a similar site to find properties of the materials shown below. Material Steel

Density or Specific Gravity 8.05 g/cm3

Tensile Strength

Elongation at Break

(Yield)

(if available)

58,000–80,000 psi

19.44%

3

(AISI Type S14800 Stainless Steel condition A)

0.290824700707875lb/in

Aluminum

0.0975 lb/in³

>= 67000 psi

14%

0.0198 lb/in³

7,300

5%

0.0112 lb/in³

40

(6061-T8) Plastic (PVC, Extruded) Wood (American Sitka Spruce) 22. Based on the information from the table rank the material for selection for an aircraft material choice for best strength to weight ratio. Use density as a substitute for weight. Show calculations.

0.290824700707875lb/in3/80,000 psi=3.6*10^-6

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0.0975 lb/in³/67000 psi=1*10^-6 0.0198 lb/in³ /7,300=3*10^-6 0.0112 lb/in³ /40=2.8*10^-4

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Conclusion 1. What role does material selection have in aerospace design? If inadequate materials are chosen, the plane will not last long.

2. Why would an aerospace designer specify an inferior material compared to other materials if both materials meet the design specifications? Because the inferior material has a lower cost.

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