Michael J. Van Tooren

Multi-Axis Multi-Material Fused Filament Fabrication with Continuous Fiber Reinforcement

Additive Manufacturing (AM) has become a well-recognized method of manufacturing and has steadily become more accessible as it allows designers to prototype ideas, products and structures unconceivable with subtractive manufacturing techniques for both consumer grade and industrial grade applications. Commonly used thermoplastics for 3D printing have properties that may not be sufficient to comply with the application’s certification requirements, or their performance is less than desirable for aerospace and other high performance applications. Additionally, additively manufactured parts have reduced mechanical properties in the build direction of the print, and are generally weaker than their equivalent injection-molded parts. Furthermore, Computer Aided Design and Manufacturing (CAD/CAM) tools have evolved together with the evolution of processes for subtractive and deformative based manufacturing methods, and ply-based additive composite manufacturing. For AM to gain more traction in industrial engineering environments, the process specific algorithms for AM need to be implemented in CAD/CAM software. There is therefore a need for reinforcement of both the material and the structures, and for proving the industrial capabilities of additive manufacturing, in particular fused filament fabrication, through a new set of processes that complement the existing design paradigm. A promising solution to the above mentioned problems of strength is using engineering thermoplastics and through the addition of continuous carbon fibers in the print. Unfortunately, engineering-thermoplastic impregnated continuous carbon fiber filaments for 3D printing do not exist due to the low demand and pure filament is currently only available for proprietary printers at steep prices. Additional strength increase

Optimization of variable stiffness composite plates with cut-outs subjected to compression, tension and shear using an adjoint formulation

This paper presents an improved and extended version of a framework for the design of variable stiffness fiber composite panels developed by the authors. The framework supports the design of panels subjected to multiple load cases, each case a combination of compression or tension and shear. The framework consists of a finite element (FE) solver, an optimizer, a novel approach to relate design variables to the stiffness matrix in the FE module, constraint evaluation modules for manufacturing and buckling constraints and a postprocessor that translates the theoretical optimal result from the optimizer into discrete tow paths for each ply including a cut and restart function. The formulation of the design variables using a manufacturing mesh separate from the FE mesh limits the number of design variables while preserving smoothness of the solution and allows easy specification of manufacturing constraints enforced by the envisioned fiber steering process, for example the minimum course radius to prevent tow buckling. The framework is intended for inclusion in an MDO based aircraft wing weight estimation tool in which it is combined with aerodynamic analysis and optimization. Results obtained with the framework show the structural benefit of using variable stiffness also in case of multiple load cases. The design variable formulation and the adjoint based sensitivity analysis lead to acceptable calculation time while preserving accuracy and smoothness of the solution. Separation of optimizer and tow path planner allows multiple practical interpretations of the theoretical optimization result. This preserves the influence of the manufacturing engineer on the practical panel lay-up and enables the user to control overlaps and gaps using cut-and-restart functionality.

Toward Wing Aerostructural Optimization Using Simultaneous Analysis and Design Strategy

The application and computational efficiency of wing aerostructural optimization us- ing simultaneous analysis and design (SAND) strategy is investigated. A coupled adjoint aerostructural analysis method based on quasi-three-dimensional aerodynamic analysis is used for this research. Two different optimization problems are tested. In the first case a wing aeroelastic optimization is performed using both nested analysis and design (NAND) and SAND strategies. In this optimization the wing box structure is optimized to achieve minimum wing weight. In the second optimization the wing structure as well as the outer aerodynamic shape are optimized to achieve minimum aircraft fuel weight. The results of both SAND and NAND optimizations have been compared based on accuracy and compu- tational cost