tailieunhanh - Substrate and Coating Erosion_5

Tham khảo tài liệu 'substrate and coating erosion_5', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Material Removal Models 203 Fig. Finnie s 1958 micro-cutting model particle target surface Equation has the structure of when the material s flow stress is replaced by the hardness of the eroded material. The parameter KF is the ratio of vertical to horizontal force and ỶF L Jt Fig. . Later Finnie and McFadden 1978 improved the model leading to a particle velocity exponent of about . Bitter 1963 developed a more general model. He divided the entire material removal process into two modes which he called the cutting wear that happened at low-impact angles and deformation wear that occurred at high-impact angles. By considering the energies involved in the erosion process he derived two formulas for both material removal modes. For the cutting wear mode the following relationship was derived V _ mP- v2 cos2 ọ - C2 vp sinọ - vel 2 C2 _ f YM YP PM VM VP For the deformation wear mode the following relationship was derived mp vp sin ọ - vel 2 VMdef _ --------z ------------ 2 Cdef 204 5 Substrate and Coating Erosion The parameter UEL is a threshold impact velocity which must be exceeded to introduce the material removal process. For certain conditions is equal to . Neilson and Gilchrist 1968b later simplified this model. Hutchings 1979b introduced an alternative discussion of the micro-cutting processes during particle-induced erosion. Based on high-speed photographs and SEM observations he defined two modes of material removal due to micro-cutting namely cutting-deformation and ploughing-deformation . The ploughingdeformation mode dominates the material removal by spherical particles whereas cutting-deformation is significant for sharp-edged angular particles. Hutchings 1979b made a further subdivision of the cutting-deformation mode into type I cutting-deformation and type II cutting-deformation depending on the direction of the particle rotation. For forward rotating particles type I is dominant and for backward rotation type .