Additive Manufacturing (AM) technologies offer unique methods for the fabrication of structural and functional components. Fused filament fabrication (FFF) process, also known as fused deposition modeling (FDM) is one of the vastly commercialized AM methods that has application in numerous industries. In this method, parts are fabricated directly from a 3D computer model with layer by layer deposition of a polymer-based filament. It offers shorter cycle times, customized designs, complex geometries, and multi-material printing capabilities. Of particular interest to this study is the ability of FFF method to print multi-materials, where dissimilar materials are fused to one another as adjacent layers or rasters. This can facilitate the fabrication of complex geometries with spatial gradient properties such as stiffness or strength. Multi-material printing becomes more challenging as the properties of the constituent materials differ more from one another. Some works have been reported in designing and printing multi-material parts using rigid and soft thermoplastic polymers, but little is known about their interfacial bond strength and its relationship to the process design and material combination.

This work reports the development of asymmetric double cantilever beam (ADCB) specimen and its use in the analysis and understanding of bond strength in 3D printed rigid/soft interfaces. Acrylonitrile butadiene styrene (ABS), polycarbonate (PC), polylactic acid (PLA) were chosen as the rigid polymers and combined with thermoplastic polyurethane (TPU) as the soft component. ADCB specimens were designed, printed, and loaded under mode I (opening) until fracture to obtain the load-displacement data. The maximum load was used as an indication of the interfacial bond strength. Two different cases of interfacial crack locations were designed to investigate the effect of print sequence and material combinations. In Case 1, TPU was printed on top of rigid material, while in Case-2, the rigid polymer was printed on TPU. The results showed that the print sequence has a significant effect, up to 100%, on the interfacial bond strength as well as on the failure mode. In ABS-TPU-ABS and PC-TPU-PC combinations, Case-2 specimens showed higher failure loads, whereas in PLA-TPU-PLA combination, Case-1 specimens were found to be stronger. Independent of these apparently contrary trends, it was found that the differences in print temperatures of the discrete materials govern the adhesion quality between them. Microscopy observations also showed that at a proper choice of material combination and print sequence, a cohesive failure at the interface is obtained, indicating that an excellent bonding between dissimilar materials at the interface. The method provides a valuable tool in identifying the adhesion quality of various dissimilar materials printed by FFF process and the results contribute to the material selection and process design in multi-material printing. The future work will be devoted to developing finite element models to calculate fracture energies.


Interfacial Bond Strength of Various Rigid/Soft Multi-Materials Printed via Fused Filament Fabrication Process

Division / Sponsors: 
Aerospace Division

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2020/volume/84027

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