RESUMO
To maximize the driving range and minimize the associated energy needs and, thus, the number of batteries of electric vehicles, OEMs have adopted lightweight materials, such as long fiber-reinforced thermoplastics, and new processes, such as microcellular injection molding. These components must withstand specific loading conditions that occur during normal operation. Their mechanical response depends on the fiber and foam microstructures, which in turn are defined by the fabrication process. In this work, long fiber thermoplastic door panels were manufactured using the Ku-FizzTM microcellular injection molding process and were tested for their impact resistance, dynamic properties, and vibration response. Material constants were compared to the properties of unfoamed door panels. The changes in mechanical behavior were explained through the underlying differences in their respective microstructures. The specific storage modulus and specific elastic modulus of foamed components were within 10% of their unfoamed counterparts, while specific absorbed energy was 33% higher for the foamed panel by maintaining the panel's mass/weight.
RESUMO
The goal of this paper is to enable three-dimensional (3D) printed lightweight composite foams by blending hollow glass microballoons (GMBs) with high density polyethylene (HDPE). To that end, lightweight feedstock for printing syntactic foam composites is developed. The blend for this is prepared by varying the GMB content (20, 40, and 60 volume %) in HDPE for filament extrusion, which is subsequently used for 3D printing. The rheological properties and the melt flow index (MFI) of blends are investigated for identifying suitable printing parameters. It is observed that the storage and loss modulus, as well as complex viscosity, increase with increasing GMB content, whereas MFI decreases. Further, the coefficient of thermal expansion of HDPE and foam filaments decreases with increasing GMB content, thereby lowering the thermal stresses in prints, which promotes the reduction in warpage. The mechanical properties of filaments are determined by subjecting them to tensile tests, whereas 3D printed samples are tested under tensile and flexure tests. The tensile modulus of the filament increases with increasing GMB content (8-47%) as compared to HDPE and exhibit comparable filament strength. 3D printed foams show a higher specific tensile and flexural modulus as compared to neat HDPE, making them suitable candidate materials for weight-sensitive applications. HDPE having 60% by volume GMB exhibited the highest modulus and is 48.02% higher than the printed HDPE. Finally, the property map reveals a higher modulus and comparable strength against injection- and compression-molded foams. Printed foam registered 1.8 times higher modulus than the molded samples. Hence, 3D printed foams have the potential for replacing components processed through conventional manufacturing processes that have limitations on geometrically complex designs, lead time, and associated costs.
