THE FAILURE OF METEORITES IN IMPACT TESTS: THE EFFECT OF STRUCTURE AND TEMPERATURE

There are few data about mechanical properties and behavior of meteoroids under shock load, yet these properties are crucial to understanding how to deal with asteroidal and cometary threat. In addition meteoroids were loaded dynamically during mutual impact action, interaction with atmosphere and earth surface. However, previously the majority of strength data were obtained from compressive tests while only few experimental results in this field were related to tensile tests. In this work we present the numerical results on impact strength and crack propagation resistance of both different meteoritic materials and ice.

Dynamic tests were performed using instrumented Tinius Olsen IT542 impact test machine at 300–77 K. Samples were prepared from monocrystalline and polycrystalline fragments of octahedrite Sikhote-Alin IIAB, impact-reheated meteorite Dronino (Iron-ung), ataxite Chinga IVB, chondrite Tsarev L5 and ice. SEM JEOL JSM-66490LV and TESCAN VEGA were used for fracture surface analysis of studied fragments. The SEM pictures were quantitatively processed using image analysis system SIAMS 700.

The highest values of impact strength (2210 kJ/m² and 2070 kJ/m²) and maximum of crack propagation energy were obtained for Chinga and Dronino iron meteorites which had submicroscopical (α+α₂+γ) and duplex (α+α₂) structures, respectively. Decrease of the test temperature down to 77 K led to decrease of impact strength values down to 47 kJ/m² for Dronino and 1170 kJ/m² for Chinga meteorites. Monocrystalline Sikhote-Alin meteorite samples demonstrated brittle transcrystalline fracture surface mode while polycrystalline Sikhote-Alin samples were characterized by intercrystalline fracture mechanism. In this case fracture energy was less than that for Tsarev L5 chondrite. The performed study clears up that the process of meteoritic materials failure is strongly affected by their chemical composition, type of microstructure and test temperature. It may be a result of different values of impact strength, impact testing parameters (ratio of crack initiation, propagation and total fracture energy) along the side with fracture mechanism transfer from ductile to brittle transcrystalline mode. This work was supported in part by the RFBR grant No 10-05-96047-r-ural-à.