Size Effect on the Strength and Deformation Behavior of Glassy Carbon Nanopillars
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.648
Size Effect on the Strength and Deformation Behavior of Glassy Carbon Nanopillars Almut Albiez1 and Ruth Schwaiger1 1 Institute for Applied Materials (IAM), Karlsruhe Institute of Technology (KIT), P.O. Box 3640, 76021 Karlsruhe, Germany
Corresponding author: Ruth Schwaiger, e-mail: [email protected]
ABSTRACT
Glassy carbon nanolattices can exhibit very high strength-to-weight ratios as a consequence of their small size and the material properties of the constituent material. Such nanolattices can be fabricated by pyrolysis of polymeric microlattices. To further elucidate the influence of the mechanical size effect of the constituent material, compression tests of glassy carbon nanopillars with varying sizes were performed. Depending on the specific initial polymer material and the nanopillar size, varying mechanical properties were observed. Small nanopillars exhibited elastic-plastic deformation before failure initiation. Moreover, for smaller nanopillars higher strength values were observed than for larger ones, which might be related to smaller defects and a lower defect concentration in the material.
INTRODUCTION Glassy carbon nanolattices can be derived from polymeric photoresists by a pyrolysis process in the absence of oxygen [1-4]. High strength and hardness [5] as well as Young’s modulus in the range of 15–40 GPa [1, 4-7] have been reported for glassy carbon, together with a low density (1.3–1.55 g/cm3) as a consequence of the porous structure [4-6]. The combination of these material properties makes glassy carbon an excellent candidate for high-strength low-weight microlattices. It has already been demonstrated that glassy carbon nanolattices exhibit outstanding strength-to-weight ratios and increasing strength with decreasing lattice size [1]. These increasing strength values might be related to both, structural size effects of the nanolattice as well as material size effects of the constituent material.
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In this paper, we report compression tests of differently sized glassy carbon nanopillars to analyze the material size effect on the mechanical properties of glassy carbon, which is in addition to structural size effects an important factor contributing to the extraordinary strength of nanolattices. The smaller pillars exhibit higher strength and ductility values, which are affected by the initial polymeric material. EXPERIMENTS Glassy carbon nanopillars with varying heights and diameters were fabricated. The fabrication process consists of two steps, i.e. 3D direct laser writing (3D-DLW; Photonic Professional, Nanoscribe GmbH) of polymeric micropillars on a silicon wafer with the proprietary resist IP-Dip (Nanoscribe GmbH), followed by a pyrolysis process of the polymeric microp
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