[S-CG54] 地球惑星科学におけるレオロジーと破壊・摩擦の物理

[SCG54-P10] オリビンの硬さと破壊靱性におけるサイズ効果

*小泉 早苗¹、鈴木 達²、平賀 岳彦¹ (1.東京大学地震研究所、2.国立研究開発法人物質・材料研究機構)

キーワード：オリビン、硬さ、破壊靱性、圧入サイズ効果、粒径効果

We conducted Vickers indentation tests on Fe-free (Mg₂SiO₄) and Fe-bearing (Mg_1.8Fe_0.2SiO₄) olivine. Their single crystals and highly-dense polycrystalline materials with various average grain sizes (d) from 170 to 890 nm were tested. The largest Vickers microhardness (H_v) of 18 GPa at the lowest load of 0.1 N, which corresponds an indentation depth (h) of 0.6 μm was measured from the polycrystalline material with the finest grain size. The H_v decreases with increasing d and h, both of which are represented by H_v ∝l^-x where l corresponds to both sizes with a common x value of ~0.09. The relationship no longer holds at of > 4 μm and of > 1 μm where H_v take constant values of ~9.5 and ~8 GPa for Fe-free and Fe-bearing olivine, respectively. Fracture toughness (K_IC) measured from indentation diagonal size and length of cracks radiated outward from the indentation corners is ~0.8 MPa・m^1/2 for the polycrystalline materials, whose value does not change with the applied load, and olivine chemistry and grain size. The single crystals exhibit lower and orientation dependent toughness from 0.4 to 0.7 MPa・m^1/2.