PSI - Issue 56

Laszlo Racz et al. / Procedia Structural Integrity 56 (2024) 3–10 Author name / Structural Integrity Procedia 00 (2019) 000–000

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As expected, patterns like grid 0-90°, fast honeycomb and triangular 60° have a difference upon E-modulus when full cross-section is used of around 25%. In Fig. 5 are presented the comparative results in shape of bar graph of the tensile moduli for different infill patterns. The value of E modulus (denoted E_Fcs) represents the measured tensile modulus of the specimen utilizing the full cross-section (Fcs) of the sample and the other one is the E modulus (denoted E_Calc) based on corrected cross-sectional area. It can be concluded that utilizing the full cross-section of the 3D printed specimens, even for a 100% infill rate, will not deliver for the E-modulus and ultimate tensile strength a result within a reasonable error range especially for patterns like grid 0-90°, fast honeycomb and triangular 60°.

Fig. 5. Comparative results of the tensile moduli with and without adjusted cross-sectional area for different infill patterns.

4. Conclusion In this paper 3D printed tensile specimens with different infill patterns were analyzed to understand the effect of internal structure on the mechanical behavior. An original approach, based on the printer generated G-code, to create numerical models of the parts was presented, that assists finite element analysis and assessment of the air gap - material ratio problem. The tensile strain resulted from the simulation were compared to experimental result, which confirmed that the area of cross-section extracted from the geometric model is predicted with reliable accuracy. Establishing of the E moduli of different infill patterns implied adjustment of the experimentally determined strain stress curves with the numerical calculated cross-section of the specimens. The obtained E moduli for different infill patterns can be used for FE simulation where the microstructure no longer must be modeled because the E modulus also contains the correct airgap- material ratio. The findings presented in this paper allow the following overall conclusions to be drawn: • The proposed methodology on building a finite element model starting from the printer generated G code is a reliable method to evaluate the influence of inner structure given by the infill pattern upon mechanical behavior of the FDM printed parts. • Adjustments to represent the intra and inter layer necking are necessary for accurate results and must be done on real printed specimens. • Cross-sectional area of a tensile specimen extracted from the numerical mode is predicted with good accuracy and allows estimation of strain-stress curves and E-moduli closer to reality. • Patterns like grid ±45°, full honeycomb and wiggle have a higher material to airgap ratio and proved reasonable results in terms of tensile strength and E-modulus comparative with those obtained using full material assumptions, so it would be recommended to be used for parts undergoing mechanical loads. • Patterns like grid 0-90°, fast honeycomb and triangular 60° have difference in terms of ultimate tensile strength and E-modulus when full cross-section more than 20%, which cannot be neglected in case of parts under mechanical loading.