Optimization 

of the Composite Structural Parts

· Optimal selection of the constituent materials, optimal fiber pattern (lay-up), optimal shape and dimensions

 of a composite component according to its required mech. & phys. properties, min. weight, costs, etc.

· Multi-angle lay-ups, hybrid lay-ups
· Respecting anisotropic material temperature and moisture expansions
· Respecting manufacturer's processing constraints, given by his special processing technique and equipment 

· Arbitrary reinforcing fibers: Glass, carbon (graphite), aramids,  ceramic, etc.

· Arbitrary matrices

Most manufacturers use the FEM (Finite Element Method) for design of the composite components / structures. Optimization procedure exploiting the FEM is complex, labour intensive, time consuming and expensive. 

Optimization procedure exploiting the analytical models of the component / structure from fibrous anisotropic material is much faster and cheaper. 

Examples of the optimized filament wound components: 

• C/EP composite spinnaker pole tube with local protective Ar/EP covers against impact (see examples), manufactured by the CompoTech Plus Ltd., determined and used for BT Global Challenge 2000 racing yachts), optimized for the lowest possible weight with equal or better properties in comparison with aluminum pole - achieved weight just of 42 % of that of aluminum extruded profile

• Hybrid composite sail battens (8 pcs = 1 set), optimized for the lowest possible weight (with assigned fixed values of flexural stifnesses and foreign impact resistance) - achieved set weight just of 39 % of that of the ordinary E-Gl/EP set

• C/EP composite post grinder - achieved fundamental frequency 2.7-times higher than of the current WC/Co post grinders

• Filament wound driving shafts - typically optimized for max.fundamental frequency & max.transmitted torque

• Filament wound pressure vessels (pressure cylinders) with metallic or plastic liner - typically optimized for the highest possible value of the quality index = filling pressure*volume/weight

• composite plates/sandwiches with/without stiffening ribs of various profiles - typically optimized for the lowest possible costs

• structural tubes with zero thermal expansion

• etc.

Optimization Procedure

Substantial part of the optimization process is performed by a special computer code, based upon:

• classical micromechanical models for building laminate plies

• classical lamination theory with expansions from temperature and moisture changes and with effect of prestraining tow force (for filament winding)

• multiaxial strength criteria 

• analytical models of component behavior and anisotropic material behavior at critical locations

The use of analytical models is necessary for assuring necessary computing speed. 

Selection of the parameters, being a subject of optimization, is optional. Since the desired optimized results cannot be calculated directly, a computer code examines randomly generated design versions by procedure containing: 

            Selecting number of plies (random)

            Selecting materials of the plies (by experience, by requirements, random)

            Monolayer properties (micromechanical models or experiments)

            Selecting fiber orientations in plies (random, special requirements)

            Manufacturing requirements and constraints

            Building a laminate => elastic properties of the laminate

            Selecting shape, characteristic dimensions and joints of the component (by experience or random)

            Building the component => weight, materials consumption, energy consumption, costs, mechanical properties

            Loading the component => component behavior under load

            Checking component behavior by the selected criteria

            Checking material behavior at critical locations by selected criteria

            Saving the solution alternative matching all requirements and criteria

A good solution alternative, which can be considered as close to actual optimum, shall be selected ex-post from the stored solution alternatives meeting all pre-set requirements. Usually many tens-thousand designs alternatives can be examined to select several good solutions. 

                Input specifications for each ply:    - constituent materials (filament, matrix) 

                                                                          - tow type (for filament winding)

                                                                          - tow spacing (for filament winding)

                                                                           - V_f (or number of tows for filament winding)

                                                                          - pre-straining tow force (for filament winding)

                                                                           - fiber orientation

                                                                          - ply thickness

                                                                           - ply unit weight

                                                                          - ply unit cost

                Results of optimization:     - Total number of plies

                                                            - Component shape and dimensions  

                                                            - Total weight  

                                                            - Total cost

                                                            - Curing temperature

                                                            - Stiffness (elastic properties)

                                                            - Expansions (thermal & moisture)

                                                            - Strength, resulting actual safety factors

                                                            - Component behavior under service conditions and environment

                                                            - Material behavior at critical locations

                                                            - Allowed service conditions 

                                                            etc.

The arbitrary combinations of strength, strain, strain energy, displacement, deflection, stiffness, buckling strength (elastic stability), thermal expansions, pre-straining tow force, fundamental frequency, weight, price, etc. may serve as the decisive criteria for optimization.

The optimization process is provided as a client service. It is applicable to all cases for which a classical lamination theory can be valid.

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