Optimization of Laminated Composite Structures Using Sub-Laminate Based Optimization Concept

In composite design, individual plies or groups of plies are frequently defined on specific application areas. Consequently, one part of the application area may belong to a dierent zone than another part. Zones have unique lay-ups and related section data definitions. Modern finite element analysis (FEA) software provide tools for this so-called ply-based modeling where the pre-processing is handled very manufacturing oriented manner and where the input files for solvers are automatically converted to be internally solved with a zone-based approach. Typically, several plies are introduced in the same application areas. Parts of this area specific stack of plies can be considered as a sub-laminate for which the laminate lay-up optimization problem is defined. In this paper, dierent sub-laminate based lay-up formulation concepts are evaluated. Implementation and performance of the laminate lay-up optimization problem formulations together with numerical results are reported. he design optimization of laminated composite structures is challenging due to the complex mechanical behavior of the structures and the number of design variables involved. A composite laminate is typically formed from a number of fiber-reinforced layers having directional properties. Basically, for each layer of the laminate, design variables are the choice of material system, thickness of the layer, and orientation of the layer. In practice, laminate design is more constrained. The choice of material systems is almost limitless, but as a result of the conceptual design phase, only a few possible candidates are usually left. For solid laminates the use of multiple material systems is beneficial in several applications, though the use of a single material system is more common. Sandwich structures consist of two material systems in minimum. The thickness of reinforced layers is usually determined by the choice of material system and processing. However, in sandwich panels the thickness of the core material can be chosen quite freely. The choice of layer orientations is often constrained to 0,90,+45, and 45 deg. Other o-axis directions may substitute ±45 deg. To avoid undesirable anisotropy of the structure, various constraints are often set for the lay-up. For instance, symmetry with respect to the laminate midplane may be required and a balanced lay-up with an equal number of o-axis layers with minus and plus orientation is usually preferred. Due to manufacturing, some regularity may be desired in the laminate lay-up. This can be achieved, for instance,