Mechanical properties and predictive analysis of multi-material polypropylene-glass fiber sandwich structures produced by material extrusion

Combining multiple filaments in material extrusion (MEX) to tailor mechanical properties is increasingly significant in science and applications. However, understanding the interaction between different materials, the influence on the mechanical properties and the predictability of such properties is still poor. Therefore, this study investigates the tensile and flexural behavior of 3D-printed sandwich-type composites made of polypropylene (PP) and glass fiber-filled polypropylene (PPGF). The materials exhibit different mechanical properties, with PP being more ductile and flexible and PPGF being more brittle and stiff. Various contents of PP and PPGF were used. Measured mechanical values were correlated with theoretical predictions. The tensile properties scaled linearly with the material composition, covering a range of moduli and strength values between 500-2910 MPa and 18-43 MPa, respectively. A rule of mixture could be applied, although PPGF layers tended to crack early. The ductile nature of PP allowed for bridging cracks, preventing premature failure. In flexural tests, the shell material dominated modulus, strength and failure mode. The samples with PPGF shells failed by cracking, while specimens with PP shells showed high deformation without clear failure. By varying contents and layer order, flexural moduli ranging from 680 to 3180 MPa and flexural strengths from 25 to 65 MPa were reached. Additionally, the study demonstrated that theoretical calculations and predictions of tensile and flexural moduli were highly accurate with an average deviation of 6.0% and 1.4%, respectively. This highlights the potential for tailoring mechanical properties based on the characteristics of PP and PPGF.Highlights High PP/PPGF interface adhesion ensures reproducible multi-material printing. Whole range of mechanical properties from ductile PP to stiff PPGF is reached. Order and amount of both materials determine failure behavior. Analytical prediction of modulus is very accurate.