Composites Structural Design

Designing functional, structural composites in an industrial environment is an extremely complicated task that uses various numerical tools, with several disciplines working together in an iterative manner. In this blog, the focus is on understanding the key steps in designing structural composites with examples of aerospace components; i.e. wing and fuselage.


Key Concepts

  • A focus on thin-walled structures made up of plies with continuous unidirectional fibers or woven fabrics, embedded in a polymer matrix

  • Structural composites design typically involves working with CAD, CAM and CAE iteratively

  • Structural composite components use a large number of parameters needed to describe their mechanical properties e.g. the dimension and the location of plies, their thickness, their orientation, and the definition of the stacking sequences

  • The use of optimization techniques becomes essential in the design and analysis phases, especially if the fiber-reinforced materials are to be tailored to the specific needs and the benefit of their anisotropy is to be maximized


The Structural Composite Design Process

General Layout of Composite Structures

A composite structure is made up of several plies of different orientations and shapes. The plies are stacked together in defined zones. In each zone, a laminate has a given stacking sequence. As shown in the figure below, the stiffeners and ribs of the wing naturally define the zones of constant stacking sequence.


A wing made of composite materials
Fig. A wing made of composite materials


The Design Phase: CAD and Link toward CAM

The design process uses these zones as a basis for the preliminary design of the composite part. This is called a zone-based design, in which the CAD software assigns a given number of laminates i.e. defined by the total number of plies and their orientations in each zone. At this stage, it is possible to estimate the deviation of fiber orientations, ply drops (i.e., the gradual thickness changes at the boundary of the laminates). A link toward CAM can be provided as shown in the figure below.

Illustration of the CAD and CAM capabilities for the design of a fuselage
Illustration of the CAD and CAM capabilities for the design of a fuselage


The Analysis Phase: CAE Tools

The structural analysis of complex composite parts is carried out with the finite elements method. Only for simple geometries and approximated boundary conditions are analytical solutions possible. During the CAE phase, the design provided by the designer in the previous step is validated and possibly modified by the analyst. Structural integrity is checked, and design improvements are provided, the ultimate goal being to provide a correct (optimal) stacking sequence in each region of the structure. A summary of the methods used for the optimal design of structural composites is shown in the figure below.

summary of the methods used for the optimal design of structural composites
Fig 2: Summary of the methods used for the optimal design of structural composites

Further detail on modeling will follow in our next blog!

Key take away

  • Industries heavily rely on a series of CAD, CAE, and CAM iterative processes to optimize the design.

  • The major design consideration at this stage is to identify the optimal stacking sequences

  • The block-by-block approach runs in a sequence and repeats to achieve an optimal solution.

Sources

Composite Design and Analysis Software

New FEA Tools Tackle Composite Challenges

Best Practice Guide: Design Tools for Fiber Reinforced Polymer Structures

Structural composite design: concepts and considerations