The development process for any component consists of design, analysis and manufacturing phases, which are sometimes undertaken by separate groups within large organizations. However, for composites, these functions are inextricably linked and must be undertaken simultaneously if the component is to be manufactured economically. Thus, the principles of concurrent engineering must be followed particularly closely for composites development.

In general, the development process incorporates three phases:

Conceptual Development - here, the development team generates a number of conceptual solutions based on their interpretation of the requirements and knowledge of composite materials and processes.

Outline Development - thereafter, surface geometry is defined, a preliminary layup determined and analysis undertaken. Based on the interpretation of analysis results, the outline design may be modified through several iterations before an acceptable solution is reached.

Detailed Development - detailed drawings of the structure and required tooling are prepared together with plans for production.

The outline development process is the most critical phase in refining a design solution. Composite components and structures can be an order of magnitude more complex than items made of homogeneous materials. It is, therefore, essential to automate many repetitive tasks using computer-based tools. Depending on the application, these tools should have one or more of the features defined below.

It is important to integrate all tools for composites engineering within a single environment to allow simultaneous development of a product (see Figure 2‑1).

Furthermore, all design and manufacturing information should be readily transferable to and from a CAD system so that the intent of an optimized design can be realized.

The fundamental requirement is that the CAE tools treat the composite structure in a manner which reflects the real-world structure. In particular, many conventional CAE tools store and manipulate data on the basis of laminate materials as shown in Figure 2‑2. This representation means that the model becomes extremely complicated as soon as the layers making up the structure overlap. In contrast, all CAE tools should store the data describing the structure in terms of its constituent layers. This ensures that the construction is always representative of the manufacturing method, making the model easy to understand. Furthermore, changes are easily effected by adding and removing layers.

Any optimization during the development process is likely to involve the interpretation of results for various analyses. These results should be interpreted on the basis of layers, in the same way that the component is manufactured.

Furthermore, it should be possible to visualize results in the reference system of the material making up a layer, even where this reference system changes constantly over a surface.

The cost of composites materials are generally high. A CAE tool should allow the designer to interrogate the materials usage and approximate cost at any point in the development cycle.

Sufficient visualization tools should be provided to ensure that the form of the structure is easily checked and communicated. Such tools would include the ability to interrogate the extent and orientation of layers, generate core samples at various points, generate cross sections along arbitrary lines, and generate a layer sequence table.

Any CAE tool should produce fool-proof manufacturing guides, so that the design and analyses components are actually manufactured. For structures manufactured from sheet materials, this could take the form of a “ply-book” which has a page for every layer. This should present the cutout shape, views of the three-dimensional moulded shape and other essential information.

Typically, layers will be placed on a male or female mould surface. If the mould tool is closed. The software should calculate the exact thickness of the laminate stack which has been defined. This should include the effect of thickening which can occur as woven material is sheared to conform to a surface. Thereafter, a second mould surface should be defined which is offset from the original surface by the correct amount.

It should also be possible to define a secondary mould surface, and automatically define the cutout shapes of individual plies required to fill the entire mould.

Because composite materials are generally anisotropic, and have more variability in their properties than homogeneous materials, it is important to store and manipulate materials data in a consistent manner throughout the design process. In particular, the same data should be used for all subsequent analyses, so that any change is reflected throughout the entire cycle.

The state of composite materials can also be highly dependent on temperature, moisture content, and even the degree of shear which might be induced in a manufacturing process. This means that all data should be stored as a function of state, and the correct information retrieved for any analysis.

Because of the wide variety of states possible, material property data will only be available for a few states. It is, therefore, necessary to interpolate material property data for intermediate states in a
rational and repeatable manner. For example, if the properties of fabric are known when the warp and fill fibers are 90 and 60 degrees apart, the software should also calculate equivalent properties for 75
degrees separation.

A large proportion of composite structures are manufactured by placing essentially two-dimensional sheets of fabric onto three-dimensional surfaces. If the surface has curvature, then the shape of the sheet cannot be inferred directly from a projection of the surface onto a plane. Therefore, the draping simulation software must produce the cutout shape of the layer before it is applied to the surface.

If the surface is doubly-curved at any point, it is non-developable. In this case, the sheet material must shear in its plane to allow it to conform to the surface. The software must illustrate the degree of shearing in the sheet, and update the material property references to account for the changed material state. The shearing also means that the orientation of the material changes dramatically over a curved surface. The correct orientations must therefore be passed through transparently to all relevant analysis codes.

Sheet material can be extremely expensive. Therefore, so-called nesting software should be used to minimize the material required by aligning and placing the cutouts in an optimum way.

Any composite part must be thoroughly analyzed to ensure that it will withstand service loads. Many composite components are relatively thin so that through‑thickness stresses are low. This means that shell elements can be used to model the structure adequately. However, to model through-thickness stresses, solid elements must be used. For some problems, such as investigating through‑thickness stresses at edges, many high-order elements will be required through the thickness of the laminate to model stresses at all reasonably.

A major concern with composite materials are their resistance to damage, as the degradation of the material is very complex and not well understood. It is, therefore, important that the structural analysis codes provide for modelling the initiation, growth and effects of defects.

Resin flow should be analyzed for processes such as RTM to ensure that pockets of air are not trapped in the moulding, causing defects. In addition, resin flow has a dominant effect on cycle time, with its ongoing effect on manufacturing cost.

The curing of a composite component should be analyzed to determine the cycle time of the process. Also, it is essential to determine the extent of springback in the cured component.

Mould tool analysis is required to estimate deflections in the tool where small tolerances are required. The thermal behavior of the mould can also have a significant effect on the cutting of a composite component.

The Patran environment provides a rich core environment for the development of composite structures. Existing links are readily used to import geometry from leading CAD systems including CATDirect, CADDS 5, Unigraphics, Pro/ENGINEER and Euclid 3. Meshing and other general pre and postprocessing functions are available within Patran itself. Finally, the preference system enables the seamless use of a variety of analysis systems which would be useful for composites development.

MSC.Mvision allows the user to store and handle complex materials data such as that required for composites development.

The MSC.Laminate Modeler adds dedicated layer-based modeling and results processing functionality to Patran. This support greatly improves the ability of the user to define and modify representative composite structures, and then analyze their behavior using analysis packages supported by preferences.

The module also includes a drape simulation facility which can handle non‑developable surfaces. This allows the user to understand the deformation required of a sheet of fabric to cover a surface, predicts realistic material orientations over individual elements, and produces cutout shapes for use by CAM systems.

This general-purpose finite element analysis solver includes QUAD4/8 and TRI3/6 laminates shell elements which account for bending and extension deformation of a shell. The linear strain elements also model the transverse shear flexibility of the laminate.

HEX8/20 and WEDGE6/15 elements are available to model the flexibility of a laminate in all directions.

All composite elements provide the facility for inputting nonlinear material properties.

This specialized finite element analysis solver is used for detailed analysis of laminates with complex fibre geometry or unusual material behavior. It utilizes a family of elements with tri-cubic interpolation functions, with up to HEX64 topology. These allow the calculation of high stress gradients, such as occur at free edges or in components which suffer severe thermal stress during processing.