Enhancement of fatigue life of rail-end-bolt holes by slide diamond burnishing

Abstract

The fatigue failure around rail-end-bolt holes is particularly dangerous since it leads to derailment of trains and consequently to inevitable accidents. It is well-known that the fatigue life of structural holed components, subjected to cyclic load, can be increased by generating compressive hoop stresses around the holes. These beneficial residual compressive stresses significantly reduce the maximum values of the operating tensile stresses arising at the critical points of the components and thus impede the formation of first mode cracks. A new approach to enhancement of fatigue life of rail-end-bolt holes has been developed. The approach involves sequential drilling and reaming through a new combined tool and then slide diamond burnishing by a new device. The technology implementation was carried out on machine tool. The process of creating residual stresses has been studied both experimentally and numerically. The experimental study was conducted by means of a modified split ring method. A reliable finite element modeling approach to the slide diamond burnishing process was developed. On this basis, the process was optimized by means of a genetic algorithm. As a result, the optimal combination of the governing process parameters is established, which ensures both maximum depth of the compressive zone and maximum absolute values of the residual stresses.

Improvement in fatigue strength of 41Cr4 steel through slide diamond burnishing

“…The FE approach is used considerably less-only 10% of the published studies use an FE method (FEM). It should be noted that the FEM has been used more extensively to explore the processes involved in rolling contact, i.e., roller burnishing [4][5][6][7][8][9][10][11][12][13][14][15] and deep rolling [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] (including the special case of deep rolling-low plasticity burnishing [31][32][33][34][35][36][37]), than for SB study [38][39][40][41][42][43][44][45][46]. When it comes to SB, the case in which the deforming element is a diamond is most often simulated [38,[40][41][42]…”

“…The object of study was most often the residual stresses introduced [38][39][40][41][42][43][44][45], but roughness [39], displacements [39,46], strains [39,46] and temperature [44] made appearances as well. The materials studied were: Ti-6Al-4V [38], 37Cr4 steel [39,44], 41Cr4 steel [40], 2024-T3 Al alloy [41,43], R260 rail steel [42], 6061-T6 Al alloy [45] and 20X steel [46]. 2D plane strain [38,39,46] as well as 3D [40,41,[43][44][45] FE models were used.…”

“…2D plane strain [38,39,46] as well as 3D [40,41,[43][44][45] FE models were used. Both 2D and 3D FE models were used in [42], and the result obtained were compared with the experimental results for the residual stresses. The deforming element has been modeled as a deformable solid [38,44,45] or rigid body (analytically rigid) [39][40][41][42][43]46].…”

“…Both 2D and 3D FE models were used in [42], and the result obtained were compared with the experimental results for the residual stresses. The deforming element has been modeled as a deformable solid [38,44,45] or rigid body (analytically rigid) [39][40][41][42][43]46]. The modeled portion of the workpiece had an elastic-plastic behavior.…”

“…The modeled portion of the workpiece had an elastic-plastic behavior. The initial roughness (before SB) was taken into consideration in [39,40,42,44]. SB, as well as the rest of the burnishing methods, acts on the surface and subsurface layers of the workpiece to a relatively small depth (under 1 mm).…”