JEC COMPOSITES MAGAZINE - Issue #41 - June 2008 - 37

Development 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. Fig. 2: Complete ply definition automatically generated by FiberSIM from analyst's laminate specification 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 Fig. 3: Thickness plot of modified zone definition the changes into generated with MSC.Software’s SimXpert 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 Fig. 4: Updated FiberSIM ply definition automatically definition matches generated from analyst's changed laminate specification 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 Fig. 1:Thickness plot of composite zone definition generated with MSC.Software’s SimXpert No41 June 2008 / JEC Composites Magazine 37

JEC COMPOSITES MAGAZINE - Issue #41 - June 2008

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #41 - June 2008