STRENGTH MEASUREMENT OF CARBONACEOUS CHONDRITES AND MICROMETEORITES USING MICRO COMPRESSION TESTING MACHINE. A. Tsuchi

Abstract

Introduction: It is important to know the mechanical properties, such as strength, of extraterrestrial materials for understanding dust aggregation in the early solar system, shapes and surface morphology of small solar system bodies, and development of sampling devices for sample return missions from small bodies. Strengths of carbonaceous chondrites, which are from C-type or related asteroids, have not been known so far except for Murchison meteorite [1] due to lack of samples with sufficient sizes for conventional strength measurement (e.g., [2]). In this study, strengths of small pieces of fragile carbonaceous chondrites and micrometeorites were measured using a micro compression testing machine. Experimental: Five carbonaceous chondrites (CM: Murchison and Murray, CI: Ivuna and Orgueil, Tagish Lake (TL)) and seven micrometeorites collected from Antarctic ice or snow were used. For comparison, one L6 ordinary chondrite (La Criolla) and aggregates of spherical particles were also used. Most of the samples were crushed, and ~50-200 μm fragments were picked up. Spherical meteorite samples were also made by Bond method. Most samples were observed under an SEM before and after the compression experiments. 3-D structures were also obtained by microtomography for some samples. The compression test was made using Shimadzu MCT-W500 with 500 μmφ flat diamond indenter (load: 9.8-4903 mN, displacement: 0-100 μm). Tensile strength was obtained from a load-displacement curve [3]. Results and discussion: Tensile strengths of carbonaceous chondrites are scattered from ~0.3 to ~30 MPa. Any shape effects on the strength, such as by the difference between sphere and irregular shape and aspect ratios, were not observed. The averages show a tendency of CM>CI>TL in the strength. The strength of the L6 chondrite (~40 MPa) is larger than those of the carbonaceous chondrites. This is consistent with prospect that highly thermal-metamorphosed chondrites have large strengths. The strengths of the micrometeorites range from 4 to 40 MPa and are also larger than those of the carbonaceous chondrites in general. This is also consistent with that the present micrometeorite samples are more or less scoriaceous and heated during atmospheric entry. The present results show that the strengths can be measured for more primitive micrometeorites and probably smaller IDPs, especially of cometary origin. It is generally expected that the strength is dependent on the