An Invariant-Based Constitutive Model for Composite Laminates.

Area of Science:

• Materials Science and Engineering
• Solid Mechanics
• Computational Mechanics

Background:

• Composite laminates exhibit complex anisotropic behavior, necessitating simplified yet accurate modeling techniques.
• Existing models may lack efficiency or require numerous independent material constants for accurate representation.

Purpose of the Study:

• To introduce a novel stiffness-invariants-based constitutive model for symmetric, balanced composite laminates.
• To reduce the number of independent material constants using invariant theory and a Master Ply concept.
• To validate the model by comparing its predictions of critical buckling loads against Classical Laminate Theory (CLT).

Main Methods:

• Development of a constitutive model based on stiffness invariants, specifically the trace of the stiffness tensor.
• Implementation of a Master Ply concept to reconstruct laminate stiffness matrices.
• Comparison of predicted critical buckling loads with CLT results, noting assumptions like neglected minor bending-twisting couplings.

Main Results:

• The invariant-based model accurately captures dominant stiffness characteristics of composite laminates.
• Predictions of critical buckling loads show good agreement with CLT, with CLT exhibiting a consistent conservative bias.
• The proposed model may slightly overestimate stability margins due to inherent idealizations.

Conclusions:

• The stiffness-invariants-based model offers an efficient framework for analyzing composite laminates.
• The novel quasi-Poisson's ratio parameter is a key innovation in this simplified modeling approach.
• The framework is suitable for integration with finite element analysis and can be extended to more complex laminate structures.