| WANG Yan-li,BIAN Xiao-fang,FU Bin,CAO Qiang.Surface Integrity and Fatigue Behaviour of Holes Treated by Finishing & Burnishing and Split Sleeve Cold Expansion[J],48(9):336-345 |
| Surface Integrity and Fatigue Behaviour of Holes Treated by Finishing & Burnishing and Split Sleeve Cold Expansion |
| Received:March 07, 2019 Revised:September 20, 2019 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2019.09.041 |
| KeyWord:finishing & burnishing split sleeve cold expansion fastener hole surface integrity fatigue behavior |
| Author | Institution |
| WANG Yan-li |
1.State Wuhu Machinery Factory, Wuhu , China; 2.Army Academy of Armored Forces, Beijing , China |
| BIAN Xiao-fang |
3.PLA 93501 Troops, Beijing , China |
| FU Bin |
1.State Wuhu Machinery Factory, Wuhu , China |
| CAO Qiang |
1.State Wuhu Machinery Factory, Wuhu , China |
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| Abstract: |
| The work aims to disclose the differences of fatigue performances and surface integrity of holes treated by split sleeve cold expansion and finishing & burnishing. The fatigue samples containing central hole manufactured with titanium TA15 were processed by three different methods such as traditional drilling & reaming, finishing & burnishing and split sleeve cold expansion. Then, the fatigue tests and the statistical analysis methods of fatigue data were compared by constant amplitude to assess the fatigue performances of holes prepared by different technologies. The surface integrity of holes prepared by different technologies was analyzed by the followed techniques and methods. For example, the morphology of hole end and wall was observed by integrated microscope, the surface roughness of hole wall was tested by stylus surface roughness profiler, the surface residual stress on hole end was determined by XRD, the microstructure of hole wall was observed by TEM and the micro hardness was determined by micro hardness tester. SEM was used to calibrate the average spacing between striations on fatigue fracture surfaces and the crack length. Digital telephoto microscopy was used to calibrate the relationship between the crack length on the surface of the hole end and the number of fatigue cycles, thus quantitatively analyzing the fatigue nucleation life and crack propagation rate of the hole structures prepared by different processes. Finishing & burnishing and split sleeve cold expansion increased the median fatigue life with value of 63% and 317%, respectively. Finishing & burnishing could reduce the surface roughness Ra to 0.52 μm, but produced a sharp material pile up at hole end. Split sleeve cold expansion could reduce the surface roughness Ra to 0.73 μm, while simultaneously introducing a~4 mm deep residual compressive stress zone with a peak value of -500 MPa and increasing the dislocation density of material close to hole wall, without materials piled up at hole end. The main strengthening mechanism of finishing & burnishing is to minimize the surface roughness to extend fatigue nucleation life. On a contrary, split sleeve cold expansion is to impart a high-value and large-depth residual compressive stress zone and simultaneously improve the material microstructure to extend both fatigue nucleation life and crack growth life. Therefore, split sleeve cold expansion is better than finishing & burnishing. Considering that laminated hole structure are often used in actual mechanical equipment, split sleeve cold expansion is clearly more conducive to guarding the interlayer gap installation requirement, because split sleeve cold expansion do not produce pileup on the interlayer. |
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