Synchronising development

John O’Connor, director of product & market strategy at Vistagy demonstrates how its software can close the loop between design and analysis in aerospace applications and reap the benefits of composite materials.
The mechanics of composite materials are well described by classical laminate theory, which combines the properties of individual composite layers to predict the behaviour of a laminated structure. Yet in many instances, despite the well known nature of these materials, analysing practical composite structures remains a challenge. These challenges derive in part from the complexity of the design definitions and lead to approximations and ambiguity in the analysis. This pushes design engineers to use increased margins in aerostructure design to account for uncertainty. Ultimately, this leads to designs that weigh and cost more, decreasing the competitiveness of composites as a material choice and making their implementation less straightforward. The typical serial product development processes associated with composite part development eliminate many chances to make the complex adjustments necessary to improve a design. This negatively affects design advantages that are specific to composites, such as tailoring material orientations. Serial processes also routinely inflate design allowances and safety factors, forgoing the benefits to be gained by the design of the material itself. The ideal scenario would be to exchange data quickly and easily between a composites design tool and the structural analysis tool in a way that captures the definition, or ‘DNA’, of the design accurately and completely. For example, in preliminary design there is usually very little detail of the geometry that will go into the design. It is here that the logical definition of the composite design is first created. If this cannot be transferred directly to the systems used by the design engineer, the potential for errors to occur in the ensuing manual translation is very high. Once detailed design begins, analysts need to provide updated laminate definitions for design engineers. This may be because of a change in specification to account for new load cases or simply because the analysis has been updated to a more accurate level. Being able to easily and accurately communicate this information to the design engineer, who now has begun to define the final design, is critical. Failure to communicate this information efficiently will result in lost work because the design will have to be totally rebuilt to incorporate the changes. This can make the difference between world class products and those that fail to meet specification. To help eliminate these problems in aerospace companies, FiberSIM provides the capability to define composite structures with enough fidelity that the specialised details of a design are captured. It communicates this definition without loss to and from a variety of structural and thermal analysis software packages (Fig 1). Optimising design Composite parts are not really parts. They are complex, inseparable assemblies of individual pieces of composite material. Because they are defined within the CAD geometric modelling systems as single parts their logical structure, which is mostly non-geometric, is poorly expressed. There are many obstacles to effective collaboration between designers and analysts due to different domain knowledge and special techniques, and the use of different vocabularies. Analysts think in terms of material properties, load cases, stress and strains. Designers work with ply coverage, non-structural details and design rules. However, there is a common set of data that the design engineer and the analyst share, which describes the intrinsic definition of the composite part: The structure of this data set and its contents form the DNA of a composite part. To enable the highest levels of efficiency between design and analysis, part-type specific approaches are necessary to capture the essential elements of a design. For example, the definitions of fuselage panels, frames, stringers, or other complex composite aerostructure components are fundamentally different in their basic structures such as lay-up of the composite layers, their orientation, expected manufacturing methods and material. FiberSIM accounts, for example, for the common elements between analysis and design definitions for such as certain ‘touch points’. Often, these touch points comprise ‘zones’, which are built from loft surfaces provided by the systems group and from material specifications and sizing data from the analysis group. Touch points are unlikely to change frequently or drastically and they represent information that can be used as the basis for shared concepts. In the current development process, the designer provides the analyst with a definition based on the initial laminate specifications. The analyst maps this data onto the initial finite element (FE) mesh of the part. The designer moves on to designing non-structural wing elements, laying out transitions, detailing the design of drop-off areas, and preparing fasteners and inserts. The analyst applies physical properties to the meshed geometry as well as loads and boundary conditions. Iterations that take place now involve concurrent data exchange between FiberSIM and CAE systems. Possibilities revealed Sharing this intelligent information between FiberSIM and CAE systems lets analysts directly apply composite design features, such as system lines and zone partitioning, to create and control a mesh for a composite skin. The interface also enables analysts to use lines of beams for stiffening elements, such as stringers or frames in a fuselage section. In addition, common access to native geometry exposes named attributes from CAD, which supports automated responses to design changes. Here, sharing composite DNA across disciplines allows users to seamlessly exchange and optimise designs. For example, when designing a fuselage panel, this approach assigns new specifications to zones. These definitions are shown in magenta and represent the footprints of the underlying substructure, which will drive the composite part definition. Increasing ply count or altering zone thickness triggers an automatic update that adds new ply drop-offs, while maintaining transition definitions, material choices, and detailed geometry. In parallel with the analysis, the design engineer creates design zones from the analysis zones to create the detailed ply definitions. The ability to connect this detailed analysis data to the final ply definitions makes the iterative and evolutionary process of design more tractable, and in the case of complex designs, even possible. The ability to automate the consolidation of analysis zones to design zones dramatically speeds the development process and assures accuracy as data is exchanged within the design team. This approach to concurrent engineering yields shorter leadtimes and a parallel workflow that supports more and faster iterations. The technique also cuts the risks, program costs and potential liabilities associated with using new materials and novel technologies. FiberSIM makes all this possible by developing a design definition that captures the part-type specific DNA of a composite structure and provides high fidelity between the CAD and CAE representations of the design. www.vistagy.com