BS in Materials Engineering
Materials Engineering Department
Polymer matrix composites’ high strength to weight ratio has made them an ideal material choice for use in lightweight transportation vehicles. Aptera Motors, a company based out of Oceanside, CA, is currently developing a next-generation high efficiency passenger vehicle called the Aptera 2e. The 2e’s body is composed of a sandwich core composite containing laminates of E-glass fibers embedded within an epoxy matrix sandwiched between a polyester hexagonal core. This project looked to validate a secondary fabric supplier for use in Aptera’s composite and characterize the core shear properties of two alternate core materials for future iterations of Aptera’s vehicle. Validation of the secondary fabric supplier was achieved by experimentally determining and comparing the tensile strength and modulus, in-plane shear strength, and short-beam strength of laminates containing Aptera’s current fabric (Vectorply) and alternate fabric (Saertex). All mechanical testing followed appropriate ASTM standards (D3039, D3518, D2344). Using a two sample t-test, the mechanical properties of the laminates were determined to be statistically different. Laminates that contained Saertex fabrics had a greater mean tensile strength and modulus than laminates with Vectorply fabrics (95% CI: 7-29 MPa and 0.3-1.5 GPa, respectively). The mean short beam strength of laminates containing Saertex fabrics was also statistically greater than those containing Vectorply fabrics (95% CI: 4.6-7.3 MPa). Fracture surfaces of the two fibers were examined with a scanning electron microscope to qualitatively compare the adhesion at the fiber-matrix interface. Fibers within Saertex fabrics appeared to have greater adhesion at the fiber-matrix interface compared to Vectorply. Characterization of the alternate core materials was accomplished by measuring the core shear strength and flexural modulus of the composite in three-point bending following ASTM C373. The mechanical properties of the two alternate cores (TF2, LRC3) were compared to Aptera’s current core material (XF6). The TF2 core exhibited a greater mean core shear strength than XF6 (95% CI: 0.77-0.96 MPa), while LRC3 was less then XF6 (95% CI: 0.25-0.45 MPa). There was no statistical difference between the flexural modulus of the XF6 and TF2 cores, whereas LRC3’s flexural modulus was statistically less than XF6 (95% CI: 0.35-0.87 GPa). The difference in core shear properties was attributed to the varying amount of resin uptake of the various cores during the fabrication process.