In order to confirm the early failure cause of a four-row cylindrical roller bearing at the backup roll position of a six-high cold sheet mill, its lubrication behavior under harsh operating conditions is investigated...In order to confirm the early failure cause of a four-row cylindrical roller bearing at the backup roll position of a six-high cold sheet mill, its lubrication behavior under harsh operating conditions is investigated. Through establishing and solving the Elastohydrodynamic Lubrication （EHL） model of the roller-inner raceway contact region, the minimum oil film thickness and the real lubrication performance are achieved. The results show the bearing failures come from the poor oil film thickness in the case of high temperature and low rotational speed, which leads to contact wear. So various approaches to improve bearing life via improving lubrication are compared. It has been proved decreasing surface roughness of both contact bodies is an effective way.展开更多
Thermal barrier coatings(TBCs)suffer from spalling failure resulting from the rapid growth of thermally grown oxides(TGO)on the metallic bond coat.In this study,to achieve the optimal lifetime of TBCs,a lifetime phase...Thermal barrier coatings(TBCs)suffer from spalling failure resulting from the rapid growth of thermally grown oxides(TGO)on the metallic bond coat.In this study,to achieve the optimal lifetime of TBCs,a lifetime phase diagram was constructed for the entire service of TBCs.Herein,both the thermal mismatch stress during thermal cycling and the TGO growth stress during thermal exposure were considered.First,thickening behavior of the Al_(2)O_(3) scale related to grain size was investigated.Second,transverse delamination failure due to the thermal mismatch stress was analyzed.Third,vertical cracking failure related to early scale growth was explored.Finally,a critical scale grain size of~2.5μm was identified for achieving the optimal lifetime of TBCs.It was experimentally proved that vertical cracking of the Al_(2)O_(3) scale occurred during early oxidation as the scale grain size was larger than~4μm after pre-oxidation.The proposed lifetime phase diagram and critical scale grain size effect serve as novel criteria for the design of next-generation durable TBCs.展开更多
基金This paper is supported by National Natural Science Fundation of China under Grant No.50405030.
文摘In order to confirm the early failure cause of a four-row cylindrical roller bearing at the backup roll position of a six-high cold sheet mill, its lubrication behavior under harsh operating conditions is investigated. Through establishing and solving the Elastohydrodynamic Lubrication （EHL） model of the roller-inner raceway contact region, the minimum oil film thickness and the real lubrication performance are achieved. The results show the bearing failures come from the poor oil film thickness in the case of high temperature and low rotational speed, which leads to contact wear. So various approaches to improve bearing life via improving lubrication are compared. It has been proved decreasing surface roughness of both contact bodies is an effective way.
基金the Postdoctoral Innovative Talent Support Program(No.BX2021238)the National Natural Science Foundation of China(No.51671159)。
文摘Thermal barrier coatings(TBCs)suffer from spalling failure resulting from the rapid growth of thermally grown oxides(TGO)on the metallic bond coat.In this study,to achieve the optimal lifetime of TBCs,a lifetime phase diagram was constructed for the entire service of TBCs.Herein,both the thermal mismatch stress during thermal cycling and the TGO growth stress during thermal exposure were considered.First,thickening behavior of the Al_(2)O_(3) scale related to grain size was investigated.Second,transverse delamination failure due to the thermal mismatch stress was analyzed.Third,vertical cracking failure related to early scale growth was explored.Finally,a critical scale grain size of~2.5μm was identified for achieving the optimal lifetime of TBCs.It was experimentally proved that vertical cracking of the Al_(2)O_(3) scale occurred during early oxidation as the scale grain size was larger than~4μm after pre-oxidation.The proposed lifetime phase diagram and critical scale grain size effect serve as novel criteria for the design of next-generation durable TBCs.
