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How many INDEPENDENT elastic constants does a GENERAL ANISOTROPIC linear-elastic material have?
A{'text': '21 — symmetric 6×6 stiffness matrix gives 21 = 6·7/2 unique entries', 'label': 'B'}
B{'text': '9', 'label': 'A'}
C{'text': '36', 'label': 'D'}
D{'text': '27', 'label': 'C'}
Answer & Solution
Correct answer: A. {'text': '21 — symmetric 6×6 stiffness matrix gives 21 = 6·7/2 unique entries', 'label': 'B'}
Stiffness tensor C_ijkl has minor symmetries (from σ and ε symmetry) reducing 81 → 36 components. Major symmetry (from strain-energy existence) reduces 36 → 21 independent. The 6×6 contracted matrix has upper-triangle 6+5+4+3+2+1 = 21 entries.
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