TY - THES

T1 - Experimental and Numerical Investigation of Mechanical Metamaterials Produced by Selective Laser Sintering

AU - Huber, Philipp

N1 - no embargo

PY - 2023

Y1 - 2023

N2 - Mechanical metamaterials captivate through the possibility to achieve mechanical properties which are not commonly found in nature. Variable stiffness mechanical metamaterials are a group of metamaterials which allows the designer to create structures with uniquely tuned stiffness behavior in all three spatial directions by changing the geometric parameters of its unit cell. This study investigates the effect of tensile and three-point-bending based material modeling for finite element simulations of variable stiffness mechanical metamaterial structures. Furthermore, elastic-plastic material models were used to increase the simulation quality. Based on specimens produced by Selective Laser Sintering, different materials were investigated in this study: Polyamide 12, Polypropylene and TIGITAL® 3D-Set TPP. Dynamic mechanical analysis, Charpy impact tests, tensile and three-point-bending tests were performed with standard specimens. The variable stiffness structures were investigated by means of compression tests. Based on the tensile test and three-point-bending test data, a yield stress ¿ plastic strain approach and Johnson-Cook strain hardening model was set up respectively. Additionally, the standard tests were performed based on horizontal and vertical printed specimens. The tunability of the compressive modulus of the variable stiffness structure was evaluated using three different structures with different geometric parameters. The temperature dependence was determined by testing the materials and structures at -30 °C, 0 °C and 23 °C. The possibility of changing the compressive modulus by changing the geometric parameters of the metamaterial structures was shown by the investigation. Beyond that the simulation quality was significantly improved by using elastic-plastic when compared to pure linear elastic material models. Furthermore, it is shown that three-point-bending based material models based on test data of vertical printed specimens led to the best results.

AB - Mechanical metamaterials captivate through the possibility to achieve mechanical properties which are not commonly found in nature. Variable stiffness mechanical metamaterials are a group of metamaterials which allows the designer to create structures with uniquely tuned stiffness behavior in all three spatial directions by changing the geometric parameters of its unit cell. This study investigates the effect of tensile and three-point-bending based material modeling for finite element simulations of variable stiffness mechanical metamaterial structures. Furthermore, elastic-plastic material models were used to increase the simulation quality. Based on specimens produced by Selective Laser Sintering, different materials were investigated in this study: Polyamide 12, Polypropylene and TIGITAL® 3D-Set TPP. Dynamic mechanical analysis, Charpy impact tests, tensile and three-point-bending tests were performed with standard specimens. The variable stiffness structures were investigated by means of compression tests. Based on the tensile test and three-point-bending test data, a yield stress ¿ plastic strain approach and Johnson-Cook strain hardening model was set up respectively. Additionally, the standard tests were performed based on horizontal and vertical printed specimens. The tunability of the compressive modulus of the variable stiffness structure was evaluated using three different structures with different geometric parameters. The temperature dependence was determined by testing the materials and structures at -30 °C, 0 °C and 23 °C. The possibility of changing the compressive modulus by changing the geometric parameters of the metamaterial structures was shown by the investigation. Beyond that the simulation quality was significantly improved by using elastic-plastic when compared to pure linear elastic material models. Furthermore, it is shown that three-point-bending based material models based on test data of vertical printed specimens led to the best results.

KW - Mechanische Metamaterialien

KW - Variable Steifigkeit

KW - Selektives Laser Sintern

KW - Elastisch-plastische Materialmodelle

KW - Finite Elemente Analyse

KW - Mechanische Prüfung

KW - Mechanical Metamaterials

KW - Variable Stiffness Structure

KW - Selective Laser Sintering

KW - Elastic-plastic material modeling

KW - Finite Element Analysis

KW - Mechanical testing

U2 - 10.34901/mul.pub.2023.221

DO - 10.34901/mul.pub.2023.221

M3 - Master's Thesis

ER -