Study On Crack Propagation Of CrtsⅢ Track Slab In Severe Cold Area Under Load And Freeze-thaw Deterioration

There are a large number of microcracks on the surface and inside of CRTSⅢ track slab.Under the action of load and freeze-thaw deterioration,the cracks of track slab in seasonal freezing area may further expand and affect the durability.Therefore,it is necessary to study the crack propagation of CRTSⅢ track slab under load and freeze-thaw deterioration.Based on the theory of fracture mechanics and the extended finite element method,the crack propagation of CRTSⅢ track slab is studied in this paper.The main conclusions are as follows:(1)Main factors affecting crack propagation of track slabIn the temperature load,the negative temperature gradient load is the main factor affecting the transverse crack and longitudinal crack propagation of track slab,and the positive temperature gradient load is the main factor affecting the vertical crack propagation of track slab.The train load will promote the propagation of transverse crack and vertical crack of track slab and inhibit the propagation of longitudinal crack.(2)Influence of temperature load on crack propagation and crack propagation lawTransverse crack,longitudinal crack and vertical crack propagation are mainly mode I cracks.Only under the action of overall temperature drop,the transverse crack and longitudinal crack of track slab will not expand directly.Under the action of negative temperature gradient,the maximum stress intensity factor of transverse crack with depth of 20 mm and length of 400 mm has the risk of cracking.Under the action of positive temperature gradient,if the capillary crack at the bottom of track slab expands,it will only occur at the part combined with self compacting concrete layer.(3)Change of stress intensity factor at crack tip in the whole process of train passingThe train load mainly affects the propagation of transverse crack and vertical crack of track slab.With the passing of the train,the stress intensity factor of the crack changes,the change trend of each tip of the crack is consistent.The running of the train does not always promote the crack propagation.One train passing will not directly lead to crack propagation.(4)Effect of freeze-thaw deterioration on crack propagationThe freeze-thaw deterioration can reduce the difference between the stress intensity factor at the crack tip and the fracture toughness,and promote the crack propagation to a certain extent,but the track slab crack will not propagate directly.(5)Fatigue crack propagationAfter 60 years of temperature load cycle,the crack of track slab will not expand directly.Under the action of train load,the propagation rate of transverse crack C end and vertical crack A end and B end increases with the increase of crack length.