Topology optimization (TO) is increasingly used as a design tool for additively manufactured (AM) components. However, designing for AM has some inherent challenges that need to be addressed. Among these challenges is accounting for complex mechanical properties arising from the combination of the AM process itself and the AM materials such as common extrusion-based AM polymers. The extrusion process introduces orthotropy in these materials that has a significant impact on TO. The degree to which orthotropy is imparted in printed materials is even greater in polymer matrix composites, such as carbon fiber reinforced epoxy. The local material properties when printing with these materials are highly dependent on the local material orientation, which is determined by material deposition path. Determining the optimal local material orientation is thus crucial to designing for AM with TO. One method of optimizing local material orientation of orthotropic materials for mechanical stiffness is aligning the “strong” material axis with the maximum in-plane principal stress direction. This principle can be applied in TO protocols during the finite element analysis (FEA) process for minimum compliance problems. Application of this principle by updating local material orientation in an iterative manner concurrently with the update of density (representing material distribution in density-based TO methods) causes a coupling of orientation and topology that leads to more optimal designs.

The present research focuses on evaluating the Solid Orthotropic Material Properties (SOMP) method of TO in conjunction with the principal stress method of local material orientation optimization for the design of AM components. These approaches have been implemented in a TO framework and used to design an MBB beam for minimum compliance. A numerical study was done to consider the effects of several optimization and process parameters on the resulting optimal topology and orientation field. Some of the parameters that were examined in this numerical study include volume fraction, filter radius, mesh size, degree of material orthotropy and relative shear strength. Select topologies and orientation fields were used to generate printed experimental specimens, which were printed via Direct-Ink Writing (DIW) using carbon-fiber reinforced epoxy and hollow glass microsphere-reinforced epoxy. Designs were determined both with and without the use of the principal stress orientation method. Material properties that were used in the optimization tool for the TO calculations were determined via mechanical testing (flexure and shear) of material coupons. The printed beams were tested in 3-point bending, approximating the MBB beam boundary conditions used in the numerical calculations. Experimental results are used to validate the numerical design studies. In particular, they are used to quantify the increase in performance provided by consideration of local orientation in topology optimization for AM. 


A Numerical and Experimental Study of Simultaneous Topology/orientation Optimization via Somp and Principal Stress Directions

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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