Research On Three-dimensional Morphology Of Rail Cracks Based On Geometric Model Reconstruction Technology

With the continuous increase of heavy-load transportation demand,train axle load,running speed and driving density,the impact between wheel and rail intensifies,and the problem of rail damage becomes more and more serious,among which rail cracks are the most common one.Heavy-duty railway rail stripping off blocks and rail breaks have a lot to do with the expansion path of fatigue cracks,especially in heavy-duty small radius curve lines,the harm of rail fatigue cracks is more obvious,on the one hand,it brings harm to driving safety,on the other hand,it greatly shortens the service life of the rail,causing greater economic losses.Therefore,it is also of practical significance to study and grasp the development law of rail fatigue crack evolution under the transportation conditions of heavy-load lines,and provide certain references for railway related maintenance departments.Aiming at the rail cracks,wear,profile changes and other related damage of the small-radius curve of heavy-haul railway,this paper uses on-site measurement and sampling,laboratory metallographic analysis,geometric model reconstruction and other technical means,based on the principle of image recognition,extracts and analyzes the cracks of all metallographic analysis diagrams,obtains the crack propagation length,depth and angle characteristics on the two-dimensional section,and then reconstructs the morphology of the surface cracks of the track head in three-dimensional space.Based on the reconstructed three-dimensional cracks,a new mathematical and physical model is proposed and compared with the field sampling analysis map.The main conclusions reached are as follows:(1)After the crack germinates,the expansion path in the three-dimensional space should be a three-dimensional surface path,and the true morphology of the crack should be part of the hemispherical surface.When cracks cross,there is a high probability that the rail will peel off the block.(2)For rails with a small range of length,the wheel-rail contact state longitudinally along the rail surface can be regarded as similar.Therefore,when multiple main cracks are arranged longitudinally and parallel along the surface of the rail,the three-dimensional crack morphology of the rail head within a small length is approximately consistent.(3)The two-dimensional cross-sectional crack growth path of the rail is not a straight line expansion in the strict sense,but is approximated to the secondary parabolic propagation,the crack initiation point is roughly located at the parabolic vertex position,and the two-dimensional main crack has not changed greatly during its expansion process under the total weight of eight passes.(4)The length of the crack on the surface of the rail head,the length and depth inside the rail head expand along the hemispherical surface with the total weight,and the rate of expansion in all directions is close.(5)This conclusion is helpful to predict the crack expansion characteristics in three-dimensional space from the rail surface crack morphology observed on site,including the expansion angle,length and depth,and can also be used to accurately model the crack location and three-dimensional characteristics when studying rail crack propagation.