By Craig Collier, President, Collier Research Corp.
Recognizing the industry growth of composites in commercial aerospace, defense and private space ventures, NASA has created the Advanced Composite Consortium (ACC) to promote material, design and manufacturing advances with the long-term goal of reducing development and certification times by 30 percent within these market sectors.
While advances are already beginning to take place in the discrete areas of materials, design and production, integrating and automating these elements is vital to achieving affordable outcomes, high product quality and durability, and quicker turnaround of programs. Securing American leadership here will further drive aerospace market growth and progress in composite-related technologies.
Rapid Design Tools and DFM
Collier Research Corporation joined the ACC in April 2016 as the only software company in a group composed of research institutes, aerospace OEMs and Tier Ones. Our role is to help with design efficiency and flight certification of composite structures. Specifically, we are leading two cooperative research teams (CRT) for the ACC: Rapid Tools and Design for Manufacturing (DFM).
Rapid tools are important because the bulk of aircraft design development and structural certification analysis revolves around them. These tools are the individual analysis programs for failure prediction such as bonded joint, compression after impact, residual strength, and small and large discrete source damage of composites. All these failure criteria plug into the HyperSizer Stress Framework, our software analysis hub for ensuring margin-of-safety, design efficiency, and manufacturability.
DFM, our second ACC focus, considers production technologies such as robotic Automated Fiber Placement (AFP) and Automated Tape Layup (ATL) and how to simulate their requirements and behavior. Manufacturability analysis for AFP also resides within the software’s stress framework. Shortening the design maturation process, which now can span years, will definitely impact aircraft production timelines. Addressing production and material behavior early in design, in a unified environment, will bring industry closer to, or even beyond, the 30 percent time-reduction target.
Software can optimize composite structures for weight, strength, and margin-of-safety simultaneously with automated fiber placement (AFP) best practices to support efficient manufacturing.
Integrating Early Analysis with Manufacturing Parameters
Every industry knows that early, upfront inclusion of performance and lifecycle requirements creates a better-engineered product that is more likely to be delivered on schedule. One challenge to accomplishing this ideal within aerospace is the scale and complexity reflected in wings, fuselages and overall airframe structures. Many disciplines have a hand in aerospace design, and they use a broad range of tools just on the analysis side: FEA, CFD, and other multiphysics domains, along with system-wide engineering and management methods.
Where there are areas requiring deep expertise, communications silos separating them often occur. These professional silos are like breaks in machine language, interrupting flow and introducing opportunities for manual interpretation and errors. This is why integration and automation of the digital approaches that capture knowledge and data are so important—particularly now that composites have proven their value for strength and lightweighting. Improved cost, speed and production repeatability for composite laminates are high on the “to-accomplish” list.
With these goals in mind, a shift in communications priorities is now starting to occur. In evaluating the manufacturability of composites, best-case design scenarios are moving from the production floor back to the analysis and validation desks. The stress community is able to shorten the design-to-manufacturing cycle by accounting for the shop floor’s preferred production methods and system capabilities (AFP and ATL) upfront in their analyses. Of course there has always been a give and take between upfront and downstream processes, but the burden of analysis is now shifting to proving out what works best for manufacturing, first—their machine performance, observed defects, and the “bleeding edge” that they can reach in creating certain composite geometries at certain speeds.
Incorporating Feedback from Manufacturing
High-performance computing is driving CAD/CAE systems, tool simulations and machine controls for automated- and robotic-layup equipment. Stock materials and custom material formulations are advancing in tandem. Optimized wings and fuselages are evolving quickly, through use of topology- and sizing-optimization software that shortens weeks or months of calculations to hours or days instead. This faster environment enables rivers of information to flow upstream, permitting customer-specific manufacturing approaches to inform early design-tool applications in CAD and CAE.
In this scenario, HyperSizer software serves as an analysis hub calculating strength using OEM and supplier data for tow placement, fiber direction, machine turning and steering-radii limits for ply layup—and by communicating with AFP software such as CGTech’s VCP or Ingersoll’s iCPS for evaluating laps and gaps, tolerances, and potential fiber wrinkling issues. As manufacturing successfully tests their speeds and limits, this real-world information (i.e. the “as manufactured” model) returns to design for correlation and simulation: What are the tradeoffs between tape width and steering radius—between experimental geometries and strength? How do these parameters combine with the material behavior of the resins and tape, the customer-specific pathway to innovation and final product?
With data from manufacturing feeding back to design analysis, time-tested case scenarios (templates) and fresh FEA results can now be brought into play to determine if new variations of the manufacturing design pass stress and weight requirements—and by what margin of safety. The design can then be further tweaked until the optimal balance has been struck between the ideal case in manufacturing and what is required for certification.
Thus the influence of manufacturing on design occurs from day one. As a result, the iterative cycle between design and manufacturing is shorter, and the data that is now captured in digital form is also more accurate.
Designing for Certification
Such accuracy is obviously of critical importance for flight certification. To achieve this, meshes are imported from the global finite element model (GFEM), into the software. Structural-component CAD data surfaces for fuselages, wings, etc. are meshed into shell, beam and solid elements in FEA software such as Nastran, Abaqus, ANSYS and OptiStruct—along with the accompanying loads. Weight-bearing items are then optimized for strength and positive margins of safety covering all potential failure modes.
Serving as a communication hub for composite design and manufacturing data derived from computer aided design/ finite element analysis (CAD/FEA) and AFP machines, HyperSizer software analyzes the data for flight certification.
Next, the software optimizes the entire structure for manufacturing “ply compatibility.” Essentially, not only is the lightest design determined at this stage, but the most practical layup as well. With early manufacturing data now acting to guide upfront stress analysis, we certainly have a quicker path to determining the most efficient layup sequence, which also sets the conditions for helping develop future programs for automated processes.
Extensive evaluation of ply compatibility, entailing analysis of ply drop-offs and ply adds and more, is just part of arriving at the most manufacturable configurations. Beyond the upfront collaboration with manufacturing taking place, multiple team members can analyze and review options in the HyperSizer database from their different workstations. This is part of the growing communications loop that cuts time off design stages that are still partially sequential. Insights and final results are automatically stored to document airworthiness certification.
Despite a long history in engineering of conducting hand-offs between silos of experts, the progress of contemporary digital engineering tools in interconnecting and bringing data and people together is fairly amazing. Efforts by former CAD vendors to become true science platforms for engineering are central to where we are today, from their significant investments in Model-Based Definition to multiphysics. Subsets within the engineering market—such as Collier Research Corp., CGTech, and others, which are working together to bridge AFP composite automation/simulation with design tools—are also dedicated to integrating important processes beyond where they may already overlap. Down in the root CAD files, where our analyses circle back to update FEA models, data interoperability suppliers are aiding the all-digital movement by ensuring clean transfers and data integrity between different modeling engines and disciplines. NASA’s ACC offers an important collaborative umbrella for this kind of innovation and success.
Accelerating the aerospace composites delivery timetable
Composite Rapid Tooling and Design-for-Manufacturing programs are operating more efficiently and collaboratively in supporting stakeholders in the industry. Furthermore, during their analysis-and-optimization design phases these programs are increasingly addressing advances in technologies such as automated fiber placement, along with changing parameters in layup and curing methods. Integrating these process approaches early and iteratively will help engineers improve quality and consistency in laminate fabrication, resulting in fewer defects, lower costs and—particularly in aerospace—helping streamline the path to certification and reach those 30-percent-faster goals sooner.