Numerical modeling and validation of auxetic cell geometries for FDM infill pattern improvement

Abstract The vehicle construction sector is constantly engaged in the pursuit of lightweight structures to reduce the overall weight of vehicles. This objective aligns well with sustainability requirements, as reducing structural weight and excessive raw material usage simultaneously lowers fuel consumption. However, these lightweight panels sometimes experience a decline in mechanical properties or exhibit unpredictable failure mechanisms due to their large internal voids. To optimize material usage, 3D printing was explored, enabling the creation of highly customized infill patterns. The innovative aspect of this research lies in developing a cellular design by selecting an optimal infill configuration capable of withstanding the expected loads. Numerical modeling was employed to analyze how different cell specifications interact with the geometry of the structure and the applied loading conditions. As a result, an auxetic design was chosen for the cellular structures. This design was fabricated using fused deposition modeling (FDM) and tested under flexural and impact loading. A comparative analysis was then conducted with samples of equivalent infill density but featuring conventional infill patterns to assess performance differences. Even if the flexural tests show a decrease in resistance and stiffness of the auxetic structures than the traditional ones, the last under-impact load shows an increase in impact rigidity which is also influenced by the angle value. Furthermore, the specimens can preserve their impact absorption capacity failure mode even if load absorption and damage are completely different. A numerical model development was useful for understanding the different behaviors and it was able to reproduce the impact behavior with high precision.