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This thesis covers the application and evaluation of new methods to describe laminate stiffness and strength. It has been shown that the trace of laminate stiffness is a rotation-invariant quantity and exactly describes the stiffness potential of a material. Together with an invariant strength criterion, the unit circle criterion, this makes the trace-based sizing approach for the design of composite structures possible. The use of so-called double-double [±Φ/ ±Ψ] sublaminates allows a continuous field of possible fiber angles and an efficient method for optimizing laminate properties. Using homogenized asymmetric stacking sequences makes the trace-based sizing approach possible and simplifies manufacturing rules. A metamodel for grid reinforced structure has been derived using artificial neural networks. The metamodel shows good predictive quality for the weight response of those grid/skin structures and provides a fast tool for a weight estimation of a fail-safe design. The unit circle criterion appers to be quite conservative for shallow fiber angles and non-conservative for steeper fiber. The traditional [0/ ± 45/90] laminate of an aerospace wing could be replaced by a [±Φ/ ±Ψ] sublaminate with significant reduction of the weight of over 10%. The commercial softwares Abaqus, Matlab and optiSLang are used. A laminate search algorithm for the best fiber angles shows good agreement with the nonlinear programming algorithms. Computational effort can be drastically reduced with the former. Thermomechanically induced warping or spring-in appear to be a challenge when using asymmetric stacking sequences. A hull of a race car has been optimized with the software OptiStruct. A weight of 2.86 kg for the composite is achieved while meeting several design constraints.