Chapter 20 Materials Selection Problem 211

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Chapter 20 Materials SelectionProblem 211

• M. Scott Kimbrell
• 3-28-07

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The Problem
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The problem with The Problem.

• Yield strength cannot be greater than tensile
  strength!
• For plain carbon steel 1020, sYS 350 MPa, sYS
  420 MPa.

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Mechanical Design

• Functions
• Support tensile load without breaking/plastically
  deforming.
• Constraints
• L and F are fixed.
• d ?L is bounded.
• Dont break s
• Dont plastically deform s
• r is a free variable.

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• Objectives
• Minimize mass, m
• Equations correspond to constraints and
  objective

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Determine performance indices.
Example calculation
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Rankings by the PIs

• Ranking PId
• Brass
• Ranking PIs
• Steel

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PId Graph ? vs. E
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PId Graph ? vs. E
X
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PId Graph ? vs. E
X
X
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PId Graph ? vs. E
X
X
X
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PId Graph ? vs. E
Brass X
X
X
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PIs Graph ? vs. sYS
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PIs Graph ? vs. sYS
X
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PIs Graph ? vs. sYS
X
X
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PIs Graph ? vs. sYS
Brass X
X
X
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• Ranking by PId with table values
• Brass
• Ranking by PIs with table values
• Steel
• Ranking by PId ? vs. E graph
• Brass
• Ranking by PIs ? vs. sys graph
• Brass

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Conclusions

• Final rank
• Brass
• Aluminum and Titanium both are good picks for the
  aircraft application.
• Dont just plug blindly into PI equations!
• Here the simple 1-D method works, but in a
  situation with bending or torsional
  considerations, a more sophisticated model is
  required.

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More Relevance to Materials

• Aluminum is used extensively in aircraft
  construction due to its high strength-to-weight
  ratio (Wikipedia)
• The titanium 6AL-4V alloy accounts for almost
  50 of all alloys used in aircraft applications
  (Wikipedia).