Study On Mechanical Behavior Of Subsurface Kinked Crack

In most cases,the fracture of the material is caused by the internal crack of the material and the propagation,and the fracture of the material is a very dangerous failure mode.Under the action of external force,the material will generate cracks and expand.During the expansion process,the cracks will gradually deviate from the original expansion direction due to the influence of the load and the microstructure of the material itself to form kinked cracks,which will cause the material to peel off,fail and fracture.The propagation of cracks will vary greatly due to different materials,such as the propagation direction and path.Regarding the problem of crack propagation,there are still many problems that are still unclear,such as kinked cracks formed by crack propagation,zigzag crack propagation,etc.,and the related mechanical mechanisms still need to be improved.In this paper,the problem of kinked crack propagation is carried out as follows Work:(1)For brittle materials,regardless of the plastic effect of the crack tip,the distributed dislocation method is used to solve the propagation problem of the embedded kinked crack on the subsurface under the combined action of tension and shear in a two-dimensional plane.The variation curves of stress intensity factor and expansion angle of straight crack end and kinked crack end are obtained,and the effects of different length ratios,load ratios and embedded depths on crack propagation are analyzed.The results show that the stress intensity factor at the crack tip decreases with the increase of the embedded depth of the crack,and increases with the length of the crack in the kinked section and the load on the crack;the crack tends to expand to the surface to form a surface crack;For the extension direction of the crack in the kinked section,it is little affected by the embedding depth,but it will gradually increase with the increase of the load and the length of the kinked section;and the extension direction of both ends of the crack is clockwise.(2)In the linear elastic range,the effect of microcracks on kinked cracks is solved by the distributed dislocation method.The stress field of the overall model and the stress field of micro-cracks under the action of tensile load are obtained.The stress intensity factor,propagation direction and equivalent stress intensity factor of the straight crack end and the kinked crack end were obtained respectively.enhancement and shielding effects.The results show that: under the influence of micro-cracks,the stress intensity factor of the kinked main crack tip decreases with the increase of the distance between the micro-crack and the kinked main crack tip;when the micro-crack is below the deflected main crack,the micro-crack It can promote the expansion of the kinked main crack tip,and vice versa;its expansion direction is clockwise;when the microcrack is in a horizontal position,the expansion direction and equivalent stress intensity factor of the crack kinked section reach extremum.(3)For ductile materials,under the premise of considering the bilinear elastic-plastic stress-strain relationship,the plastic behavior of the embedded kinked crack tip was studied by the distributed dislocation method.At the crack tip,there is a large stress concentration,so a large plastic deformation will occur there.A theoretical model of subsurface kinked cracks in a semi-infinite plane under tensile load is established.Firstly,the plastic deformation at the crack tip is replaced by continuously distributed dislocations,and the dislocation bands at both ends of the crack are introduced to replace the plastic deformation at the crack tip,and the dislocation band is regarded as a crack.The crack can clearly predict its opening displacement and the size of the plastic zone,and explore the plastic deformation at the crack tip by exploring factors such as different embedding depths and the size of the dislocation-free zone.The research results show that the opening displacement at the crack endpoint increases with the increase of the load;and decreases with the increase of the embedded depth;under the influence of the free surface,the opening displacement of the straight crack segment and the size of the plastic zone are the same.greater than the corresponding value of the kinked segment.