CST & LST in FEA
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Transcript of CST & LST in FEA
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1
Chapter 8 – Linear Strain Triangle(Overview)
• Compare formulation of CST and LST• Comparison of element performance
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Comparison of CST and LST Formulations
CST:• Three nodes per element• 6 DOF per element
LST:• 6 nodes per element• 12 DOF per element
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3
Displacement Interpolation
CST:
LST:
yaxaa
yaxaa
yxv
yxu
654
321
),(
),(
21211
210987
265
24321
),(
),(
yaxyaxayaxaa
yaxyaxayaxaa
yxv
yxu
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4
Strains within each element
),(),,(~ yxvyxuy
orx
Recall:
CST:
LST:
~ constant => Constant Strain Triangle (CST)
~ at most linear in x & y => Linear Strain Triangle (LST)
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5
Element Stiffness Matrix
CST:
LST:
Since Bij terms depend on x & y, numerical integration is required (Chap. 10)
BDBtAk T6x6 6x3 3x3 3x6
12x12 12x3 3x3 3x12
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6
CST vs. LST – Performance Comparison
Consider the following plane stress analysis of a cantilever beam
“4 x 16” mesh
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7
CST vs. LST – Performance Comparison(cont.)
Test Cases:
Mesh Element Case
4x16 CST A-1
4X16 LST B-2
8x32 CST A-2
2x8 LST B-1
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8
CST vs. LST – Performance Comparison(cont.)