Mechanical characterization of hybrid reinforced polypropylene composites with talc fillers and cellulose nanofibers
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Tatsuto YAMAMOTO (JAPAN), Luo CHAO (JAPAN), Yasutomo UETSUJI (JAPAN)Abstract :
The improvement in mechanical properties of thermoplastic polypropylene (PP) composites, which are widely used mainly in automobiles, by the addition of talc fillers and cellulose nanofibers (CNFs) was investigated experimentally and by multiscale numerical simulation. Multiscale simulation has been applied to glass, carbon fibers and carbon nanotubes in many cases, and the influence of fiber morphology on mechanical properties has been well discussed. On the other hand, the mechanical properties of PP/talc composites have remained confined to experimental approaches and classical composite laws, although industrial applications are flourishing. There is a strong need for multiscale simulation for hybrid reinforced PP composites in order to cope with the increase in design parameters and the complexity of the reinforcement mechanism due to the multi-filler technology.
In this study, first, hybrid reinforced PP composites were produced by injection molding and tensile loading experiments were carried out. The results showed that talc filler was effective in improving elastic properties and CNFs in improving elastic properties and maximum tensile stress. Nonlinear properties of hybrid reinforced PP composites were analyzed by two-step homogenization multiscale simulation. After confirming that the numerical simulation reproduced the experimental results well, a new parameter based on strain energy was introduced to quantify the effect of filler addition. The mechanical properties of PP composites could be linearly approximated by the introduced filler contribution ratio, and a simple design method based on this relationship was proposed. As a validation example, the elastic modulus and maximum tensile stress could be predicted within an error of 5% for unknown PP composites with different filler contents.
Second, hybrid reinforced PP composite filaments were produced by extrusion molding and 3D printed specimens were also produced through fused filament fabrication. Nonlinear properties were evaluated by tensile loading experiments and compared with the injection-molded specimens described above. The results showed that, compared to the injection-molded specimens, the maximum tensile stress was reduced by 10% to 20% even in the 3D printed specimens with 100% filling rate. Cross-sections of 3D printed specimens were observed under an optical microscope, and multiscale simulations based on microstructural models constructed from the binarised images were performed. Numerical results show that the property degradation in 3D printed specimens is due to three factors: voids due to incomplete filling, lack of reinforcement in the interfacial phase between molten filaments and degradation of interfacial phase properties. The effects of talc fillers and CNFs content on the mechanical properties of 3D printed specimens were elucidated in order to redesign the filler content to compensate for these reduced properties.
In this study, first, hybrid reinforced PP composites were produced by injection molding and tensile loading experiments were carried out. The results showed that talc filler was effective in improving elastic properties and CNFs in improving elastic properties and maximum tensile stress. Nonlinear properties of hybrid reinforced PP composites were analyzed by two-step homogenization multiscale simulation. After confirming that the numerical simulation reproduced the experimental results well, a new parameter based on strain energy was introduced to quantify the effect of filler addition. The mechanical properties of PP composites could be linearly approximated by the introduced filler contribution ratio, and a simple design method based on this relationship was proposed. As a validation example, the elastic modulus and maximum tensile stress could be predicted within an error of 5% for unknown PP composites with different filler contents.
Second, hybrid reinforced PP composite filaments were produced by extrusion molding and 3D printed specimens were also produced through fused filament fabrication. Nonlinear properties were evaluated by tensile loading experiments and compared with the injection-molded specimens described above. The results showed that, compared to the injection-molded specimens, the maximum tensile stress was reduced by 10% to 20% even in the 3D printed specimens with 100% filling rate. Cross-sections of 3D printed specimens were observed under an optical microscope, and multiscale simulations based on microstructural models constructed from the binarised images were performed. Numerical results show that the property degradation in 3D printed specimens is due to three factors: voids due to incomplete filling, lack of reinforcement in the interfacial phase between molten filaments and degradation of interfacial phase properties. The effects of talc fillers and CNFs content on the mechanical properties of 3D printed specimens were elucidated in order to redesign the filler content to compensate for these reduced properties.