Strength Degradation in Ceramics by Sphere Indentation. Si3N4 Sphere Indentation of Si3N4 Specimen-Case of Elastic Condition.

浩司, 大串; 恭二, 本間; 昌弘, 市川; 永年, 岡部; 徹, 高松; 隆, 松村; 豊, 阿部

doi:10.1299/kikaia.63.392

Cited by 2 publications

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“…For example, Takamatsu et al 19 reported that the diameters of ring cracks occurring on the plate surface were about 1.1 times that of the contact circle. This figure of 1.1 is fairly typical of what other researchers have found 20, 21 . The material investigated by Takamatsu et al was HIP‐silicon nitride (TSN‐03), which is the same as the material used in our experiments.…”

Section: Discussionsupporting

confidence: 82%

“…This figure of 1.1 is fairly typical of what other researchers have found. 20,21 The material investigated by Takamatsu et al was HIP-silicon nitride (TSN-03), which is the same as the material used in our experiments. The diameters of the semi-circular cracks observed in our experiments are larger than those of the ring cracks.…”

Section: Evaluation Of the Ring Crack Modelmentioning

confidence: 99%

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Flaking failure originating from a single surface crack in silicon nitride under rolling contact fatigue

Kida

Saito²,

Kitamura

2005

Fatigue Fract Eng Mat Struct

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A B S T R A C T Flaking failure caused by surface cracks of silicon nitride ceramic bearings has been investigated from the viewpoint of the ring crack model. However, the relation between surface and subsurface cracks under rolling contact fatigue is not fully understood. In this investigation subsurface cracks branching from an initial surface crack were observed in detail, and the process of flaking failure was investigated. The specimens were observed prior to the separation of the surface layers and it was found that the initial surface cracks grew vertically to the surfaces and did not curve as predicted by the ring crack model. Subsurface cracks branched from the single surface cracks and grew in a direction parallel to the surface. They grew in both the same and the opposite directions to the ball movement, with small upward and downward branches. These subsurface cracks grew prior to the semi-circular surface cracks. From these observations it was concluded that the flaking failures are not caused directly by the surface cracks, but by the subsurface cracks that branch from them.Keywords flaking failure; ring crack; silicon nitride ceramic bearing; subsurface crack branching; surface crack. N O M E N C L A T U R E2a = surface crack length c = half width of contact area O = centre of contact circle O = centre of initial surface crack X, Y, Z = coordinate system for contact circle X , Y , Z = coordinate system for initial surface crack σ = normal stress = film thickness parameter τ = shear stress I N T R O D U C T I O NCeramic bearings have been extensively investigated because they are lighter and harder than steel bearings. The performance of all-silicon nitride bearings and hybrid ceramic/steel bearings has been compared with steel bearings and has been shown to be superior in respects of speed 1 and life. 2,3 However, ceramics have lower fracture toughness and are more sensitive to surface cracks than steels. Therefore, the relation between surface cracks and the failure of ceramic bearings has been extensively inves-tigated. Up to the present time these investigations have been done in terms of the 'ring crack model'. [4][5][6][7][8][9][10][11] In the studies based on the ring crack model, the process of flaking failures of 'pre-cracked balls' is explained as follows. 5-9,11 A ring crack occurs on the surface of the specimen under rolling contact fatigue (RCF), and then multiple ring cracks occur around the first ring crack. These cracks grow from the specimen surface. After these cracks grow inside the specimen, a network of subsurface cracks is formed between them. This subsurface crack network then expands to a failure. The surface cracks are also formed under static pressure, and they have the same appearance as the surface cracks c

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Section: Discussionsupporting

confidence: 82%

Section: Evaluation Of the Ring Crack Modelmentioning

confidence: 99%