TY - THES

T1 - Fracture investigation of refractories under combined mode I and mode II loading

AU - Zhou, Ru

N1 - embargoed until null

PY - 2017

Y1 - 2017

N2 - This research aims to investigate the fracture behavior of two refractory materials under combined mode I and mode II conditions by a special wedge splitting test arrangement according to Tschegg [1]. By the wedge splitting test, the nominal notch tensile strength and specific fracture energy were studied for two materials, a magnesia material and a magnesia spinel material. In comparison with the pure magnesia material, magnesia spinel material has a lower nominal notch tensile strength and higher specific fracture energy. The wedge angle has influences on the determination of mechanical properties of both materials: The specific fracture energy of the magnesia spinel material does not show monotonous tendency with increasing asymmetrical wedge, and their nominal notch tensile strengths decrease with respect to asymmetrical wedge angle. In contrast, the specific fracture energy of the pure magnesia material increases with increasing asymmetrical wedge angle. Their nominal notch tensile strengths increase with the asymmetrical wedge angle and reach a plateau in 15-22.5°. Moreover, the fracture parameters measured under the asymmetrical loading with the wedge angle 10° are slightly lower than those under the symmetrical loading with the wedge angle 10°. Based on DIC strain measurement, the initiation and the propagation of the cracks and the development of fracture process zone were analyzed. Compared to the pure magnesia material, the magnesia spinel material develops a higher amount of microcracks, causing a larger fracture process zone. The fracture process zone in the magnesia spinel material develops before reaching the maximum load, and during the crack propagation process, crack branching phenomenon can be observed. Besides, the asymmetrical loading condition gives rise to a narrow crack propagation zone. In the case of pure magnesia material, the fracture process zone develops after reaching the maximum load and no crack branching phenomenon takes place; only a main macro-crack can be observed. For both materials, higher asymmetrical wedge angles result in more instable macro-crack growth.

AB - This research aims to investigate the fracture behavior of two refractory materials under combined mode I and mode II conditions by a special wedge splitting test arrangement according to Tschegg [1]. By the wedge splitting test, the nominal notch tensile strength and specific fracture energy were studied for two materials, a magnesia material and a magnesia spinel material. In comparison with the pure magnesia material, magnesia spinel material has a lower nominal notch tensile strength and higher specific fracture energy. The wedge angle has influences on the determination of mechanical properties of both materials: The specific fracture energy of the magnesia spinel material does not show monotonous tendency with increasing asymmetrical wedge, and their nominal notch tensile strengths decrease with respect to asymmetrical wedge angle. In contrast, the specific fracture energy of the pure magnesia material increases with increasing asymmetrical wedge angle. Their nominal notch tensile strengths increase with the asymmetrical wedge angle and reach a plateau in 15-22.5°. Moreover, the fracture parameters measured under the asymmetrical loading with the wedge angle 10° are slightly lower than those under the symmetrical loading with the wedge angle 10°. Based on DIC strain measurement, the initiation and the propagation of the cracks and the development of fracture process zone were analyzed. Compared to the pure magnesia material, the magnesia spinel material develops a higher amount of microcracks, causing a larger fracture process zone. The fracture process zone in the magnesia spinel material develops before reaching the maximum load, and during the crack propagation process, crack branching phenomenon can be observed. Besides, the asymmetrical loading condition gives rise to a narrow crack propagation zone. In the case of pure magnesia material, the fracture process zone develops after reaching the maximum load and no crack branching phenomenon takes place; only a main macro-crack can be observed. For both materials, higher asymmetrical wedge angles result in more instable macro-crack growth.

KW - Keispalttest

KW - DIC

KW - die Rissausbreitung

KW - die Nennzugfestigkeit

KW - die spezifische Bruchenergie

KW - wedge splitting test

KW - DIC

KW - crack propagation

KW - nominal notch tensile strength

KW - specific fracture energy

M3 - Master's Thesis

ER -