Fracture Resistance of Brittle Materials Under Local Loading by Scratching to Edge Chipping. Part. 1. Methodical Grounds
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FRACTURE RESISTANCE OF BRITTLE MATERIALS UNDER LOCAL LOADING BY SCRATCHING TO EDGE CHIPPING. PART. 1. METHODICAL GROUNDS OF RESEARCH V. V. Khvorostyanyi
UDC 539.42
Methodical aspects of experimental investigation of brittle materials under local edge loading by scratching the specimen surface with a Rockwell indenter to its edge chipping (S+EF method) are detailed. The edge damage parameter range (fracture distance) had its basis in the literature data on numerical simulation of the stress-strain state in the local indentation zone of the material surface to its edge chipping. Fractographic analysis of tested edges revealed their damage behavior under given loading conditions. The paths of fracture crack propagation to the formation of “shell-like” chip scars, which are asymmetric quasi-conical crack traces, are studied. Partially formed or strained chips having a somewhat distorted fracture surface as compared to the “ideal” geometry of the edge chip were also found. The asymmetry of chip scars was established to have no effect on the fracture resistance of the material. The validity of empirical investigation results was achieved with a minimum test scope, determined by statistical data processing. This test method of low material intensity can be effectively applied to different lines of research. Keywords: ceramics, experimental procedure of scratching to edge chipping, fractographic analysis, chip scar, fracture distance, fracture resistance. Introduction. Brittle nonmetallic materials like structural ceramics and glasses possess a complex of physical and chemical properties basic for the structure elements, used in different engineering fields for the products operating under tough service conditions. They find their application in the heavy-duty and functional machine and instrument components for aerospace, military, and medical engineering. These materials exhibit certain features in common, viz practically ideal elasticity, high hardness, as well as low resistance to crack nucleation and extension in comparison with metals. Stress concentration, e.g., under contact interaction with solids, can induce an unpredictable deterioration of the carrying capacity of brittle elements as a result of the surface damage with crack nucleation, which leads to complete or local fracture of products under certain conditions. The edge fracture of brittle products is a rather widespread phenomenon. In the majority of cases, it is of negative nature. Nevertheless, edge chipping is of practical value: it is used to produce chamfered edges, which results in lower local stress concentrations. But such edge smoothing is often inadmissible. For instance, edge chipping damages of cutting tools can lead to the loss of their functionality. It also refers to the fracture of dental and orthopedic implants, which influences directly the quality of human life. The edges of brittle materials are most sensitive to mechanical loads; in this connection, the improvement of their fracture resistance is of great scientific and practical int
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