What are the key principles of composite laminate layup design?

Layup design determines composite properties through ply orientation. Principles: Balance - Equal number of +theta and -theta plies to prevent coupling; Symmetry - Symmetric about midplane to prevent warping (cure distortion); 10% rule - Minimum 10% of plies in each principal direction (0, 45, -45, 90); and Ply grouping - Limit adjacent plies of same orientation (typically max 4) to reduce delamination. Orientation effects: 0-degree plies - Longitudinal strength and stiffness; 90-degree plies - Transverse strength, prevent Poisson effects; and +/-45 degree plies - Shear strength and stiffness. Common laminates: Quasi-isotropic [0/45/-45/90]s - Equal properties in all in-plane directions; Orthotropic - Tailored directional properties; Angle-ply - Primarily shear loads. Design tools: Classical Lamination Theory (CLT) for stiffness, Finite element analysis for complex geometry. Stacking sequence affects interlaminar stresses, impact resistance.