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Concurrency is a critical part of successful product development. It enables engineering teams to work in different domains simultaneously while facilitating collaboration across disciplines, allowing multiple iterations and improved communication. This leads to reduced rework, shorter product development cycles, and more robust and higher quality manufactured products.
(Published on June 2008 – JEC Magazine #41)
JOHAN GRAPE DIRECTOR OF TECHNOLOGY, VISTAGY, INC.
Traditionally, composite part design has not lent itself to concurrent development due to both the lack of mechanisms enabling communication between engineering disciplines, and the high complexity of the designs. It has been virtually impossible to achieve effective collaboration across analysis, design and manufacturing because it is so difficult for people in one of these disciplines to develop any significant understanding of the constraints, requirements and concerns facing people in any of the other areas.
But the barriers that impede collaboration within the product design environment are starting to crumble. For instance, FiberSIM®, VISTAGY’s CAD-integrated composite engineering software, enables cross-disciplinary collaboration through the exchange of high-level composite design information that is highly relevant to the operators. These capabilities form the foundation of a much improved collaborative composite part development effort, allowing multiple iterations through the design stages, easy integration of changes, and opportunities to manage rapid, highly concurrent composite part development across analysis, design and manufacturing.
Limited ability to respond to external input
After the initial requirements of a composite product have been outlined and have gone through preliminary design, each discipline will tend to pursue the goals set out for their phase of the design. The ability to respond to changes or recommendations from outside is limited, largely due to time and resource constraints. In such an environment, there are very significant inefficiencies.
A recommended modification may have a significant beneficial impact on the product with a very low level of risk, but still fail to be implemented because of the work required to make the change. In particular, the benefits associated with refinement through optimization in the analysis phase are lost because time constraints require full transition to detailed design as early as possible.
Similarly, the designer is unable to determine the impact of his design rules on the structural properties, resulting in quality degradation, insecurity and inefficiency. In modern structure and zone-based designs, these problems have resulted in weight problems due to a combination of over-specification and additional design details in which overall weight and performance impacts could not be known.
At the heart of current efforts to improve collaboration between engineering disciplines is an attempt to expose CAD functionality and native geometry to the CAE system. There is significant evidence that the next productivity improvements are expected to arise from such cross-disciplinary tools. Historically, the intent, analysis, design rules, materials specification, etc., of composite parts have not been expressed natively in the CAD model, but instead communicated through drawings and supporting documents. This indicates that simple native geometry-related integration between CAD and CAE will not address the core problem, which is the communication of high-level information about the design between the disciplines.
If you think of the composite part as a set of zones and drop-off transitions, the analyst is primarily concerned with the former, and the designer the latter. Considering the difficulty of expressing and maintaining these relationships in geometry, it makes sense to develop a composite design environment that expresses the design in these abstract terms.
VISTAGY’s FiberSIM® has been developed with the input of the composites industry and its best practices, and new capabilities now allow much closer collaboration between the disciplines by communicating change at the metadata level. With a data model that encompasses a large section of the methodologies associated with composite parts, and assistive simulation technology, it is becoming possible to engage in a process in which design modifications and optimization can be pursued much further into the process, enabling concurrency in the development stages and reducing the total development time. The task of the analyst can be summarized as estimating performance and thereby “sizing” the part, while the designer applies design rules as he integrates the parts and components, and the manufacturing engineer streamlines the process and applies physical constraints. In order to illustrate how these disciplines can work together more effectively, consider the example of weight optimization. Just a single unneeded ply distributed over the total size of any of the modern jetliners in development could result in hundreds of kilograms of excess weight, reducing overall payload and performance. There is great incentive to find and eliminate such over-design, but traditionally this has been very difficult to do after the initial sizing, even when the problem became known, because design changes are so hard to make. The weight of a composite part is driven by the number of composite material layers in the part. The number of layers is a consequence of the thickness required to provide the required stiffness and strength, which is determined from a large number of load conditions representing stress states under various operating and extreme conditions. In order to minimize the number of layers, the orientation of each layer needs to be tailored to provide maximum strength and stiffness under all of the load cases. While complex curvature has an effect on the resultant fibre directions once manufactured, only a subset of composite parts are of such complex curvature that it has a significant impact on fibre orientations. This is particularly true for the large structural parts that make up the bulk of the weight of an airframe. In these situations, it is beneficial to eliminate geometry as a factor and focus on the overall optimization of thickness and bulk orientation in order to reduce weight. This is done by changing ply count and orientation within zones, and considering the implications on performance.
The analyst generates a set of specifications to complete the preliminary sizing and then provides them to the designer, who uses them to develop the initial design. Typically, this specification is a written document and a spreadsheet that the designer would use to develop the boundaries of plies and schematics of cross-sections.
However, with FiberSIM, this specification can be ingested directly into the design model in the form of a simple neutral file that is easily derived from a conventional shell-element property card, such as a PCOMP. Figure 1 shows a
thickness plot of an analysis model from which the zone input was created and Figure 2 shows the resulting designed part with the plies fully developed with automated substructure avoidance and dropoff rules imposed.
In the past, making changes after this initial design became more and more difficult due to the overhead of implementation. Now, the FiberSIM Advanced Composite Engineering Environment™ can integrate such changes with great ease. All changes to stacking and observance of design rules are part of the solution, and changes to the analysts input can then typically be integrated very rapidly.
Figure 3 shows a thickness plot of the part shown in figure 2, but here the zone definition has been altered by the analyst. The same neutral data is then regenerated and transferred to the designer, who imports the changes into FiberSIM, resulting in the modified ply definition shown in figure 4.
The designer can now also return the resulting zone definition to the analyst, who can run verifications in his environment to ensure that the zone definition matches what was intended. The designer can also use FiberSIM to provide an exact mapping of properties with fibre orientations to the analyst’s finite element mesh. Figure 5 shows a thickness plot of the part used as an example above, with all drop-offs and design rules applied. The analyst thus has an exact representation of the as-designed part at any stage in the development, making additional input and enhancements possible.
With FiberSIM, an organization can also apply the same principles and enjoy similar benefits in areas such as detailed design alternatives, manufacturing and maintenance.
Enhancing performance while compressing development times
The dramatic changes to composite design and manufacturing technology that have become available recently place new strains on the development process. At the same time, requirements for increased performance, economy and safety are creating new pressures for the engineering organizations that design the parts. Improving collaboration and concurrency between analysis, design and manufacturing during the composite part development process represents an important method of addressing many of these concerns while simultaneously improving efficiency.
By providing engineers from each discipline with the confidence that they can influence modifications to design rules that can be easily integrated into the current product, FiberSIM is making it possible for organizations to greatly improve part performance and compress development, turning the concept of concurrent development from theory into a tangible and beneficial practice.