| This article focuses on issues such as explosion wave field propagation,explosion stress wave and crack interaction,and crack and defect interaction.This paper mainly uses dynamic photoelasticity method,digital image correlation(DIC)method,explosive DGS method and dynamic caustics method to study the propagation of explosive wave field and its interaction with cracks.The following innovative research work has been carried out from the study of the propagation characteristics of explosive stress waves,the effects of explosive stress waves and stationary cracks,the effects of explosive stress waves and moving cracks,and the interaction of cracks and defects:First,a dynamic photoelasticity-digital image correlation comprehensive experimental system was established,and the function of collecting multiple sets of information in a single symmetric test piece was achieved.The propagation characteristics of the stress wave at the center point of the specimen and the explosion at the free boundary are studied.The front end of the explosion wave is a biaxial compressive stress state,and the tail of the P wave is a biaxial tensile stress state.The photoelastic fringe data and the strain data calculated by the digital image correlation method are compared and analyzed.The principal stress analysis is performed on a specific point,and the stress characteristics of the Mach cone wave at the free surface are obtained.An explosive load DGS experimental system was established to characterize the distribution of stress gradients of explosive stress waves in the propagation direction.Secondly,the dynamic photoelastic experiment method is used to study the wave propagation form and the change of the stress field at the crack tip during the action of the blast stress wave and the static crack in different quadrants.It is obtained that when the source point of the explosion wave is in the second quadrant and the fourth quadrant,the ?+? composite type equal streaks are generated at the crack tip,and the mode ? stress intensity factor K? of the crack tip is greater than zero.A real-virtual image system of explosion load caustics was established,and the change of crack tip field during the process of explosion stress wave and horizontal and vertical cracks was analyzed.It is obtained that when the compressive phase of the explosive wave P wave interacts with the vertical crack,the mode ? stress intensity factor K?<0,the mode ? stress intensity factor K?>0,and the mode ? stress intensity factor at the tip crack tip on the prefabricated crack.K?<0,type ? stress intensity factor K?<0.When secondary cracks occur in vertical prefabricated cracks,K?>0,K?<0 at the lower end of the crack,and the secondary crack initiates and propagates counterclockwise,and K?>0,K?>0 at the upper end of the crack,and the secondary crack initiates and propagates clockwise.When the moving crack penetrates the prefabricated static crack,the sudden release of energy at the crack tip will generate an unloading wave and propagate it around the penetrating point.The unloading wave plays an important role in the generation of the secondary crack of the stationary crack.Then,using dynamic photoelastic experiment method and dynamic caustics experiment method,the effects of normal and oblique incidence explosion stress waves on the characteristics of moving crack propagation were studied.The variation process of the crack stripe equiangular stripes during crack-wave interaction is analyzed.The difference of the deflection direction of the crack under the action of explosive stress waves in different directions is given.It is obtained that the normal incident blast stress wave does not change the moving crack propagation direction,and the oblique incident explosive stress wave will cause the crack deflection.The interaction between blast waves and opposite propagating cracks is quantitatively analyzed experimentally in this study.The evolution of isochromatic fringe patterns around a crack tip is clearly captured,which indicates that the classical K-dominance fracture theory is not valid during crack-wave interactions.With the incidence of the dilatational wave on the opposing propagating crack,not only the dynamic stress intensity factors Kd ? and Kd ? decreased but also the compressive nonsingular stresses ?ox and ?oy increased dramatically around the crack tip,which increase the crack extension resistance,strongly suppress the propagation of the crack and led to a drop in the crack velocity.In addition,the shear wave has a positive effect on crack fracturing,which decreases the crack extension resistance,and promotes crack propagation rapidly.When the direction of propagation of the blast stress wave was the same as the direction of moving crack propagation,the moving crack was deflected away from the blast wave source.When the blast stress wave propagation direction was opposite to the crack propagation direction,the crack was deflected toward the blast wave source.During the interaction of obliquely incident blast stress wave with moving crack,the P wave caused the deflection of the crack.The P wave tail and the S wave interacted with the kinked crack to increase the mode ? stress intensity factor K? and crack propagation velocity.Finally,the effects of the relative positions and interactions of cracks and defects on the propagation and deflection of cracks were studied using dynamic caustics and dynamic photoelasticity experiments.Crack interaction makes the crack initiation stress intensity factor K?d,the time required for crack initiation decrease.In the initial stage of crack propagation,the shear stress component of single-offset crack tip stress field is positive and the stress intensity factor K?d is greater than zero,the shear stress component at the crack tip in the same position with unilateral offset parallel double crack is negative and K?d is less than zero.The single-offset crack is deflected to the inside after the crack initiation,the crack at the same positon of the unilateral offset parallel double crack is deflected to the outside.Under the impact load,the relative offset position of the hole and the prefabricated crack affects the crack initiation direction and the crack and void penetration.In the case of prefabricated crack offsetting,at the time of crack initiation,K?d<0 and the direction of the fracture points to the empty hole;the hole has an attractive effect on the running crack,crack propagation path is parabolic,crack and hole coalesce,the crack will initial again at the top of the hole.Under the condition of hole offsetting,K?d>0 and crack initiation direction away from the hole;the role of hole on the propagating crack is attractive firstly,then repulsive and attractive finally,crack propagation path is S-type,crack and hole are not through.When the running crack and the empty hole penetrate,crack arrest will delay the destruction of the specimen on a time scale.But after the second crack initiation at the upper boundary of the hole,crack propagation velocity and dynamic stress intensity factor are increased accordingly,which will exacerbate the destruction of the specimen.During the action of explosive motion cracks in the opposite direction,the cracks are mutually repulsive and then attract each other.When the moving cracks are not staggered,due to the influence of the crack tip stress field between adjacent cracks,the mode ? stress stress intensity factor K?>0 at the crack tip.Both cracks will deflect along the forward direction and the two cracks will repel and the vertical spacing of the cracks is increased.After intersecting moving cracks,the mode ? stress stress intensity factor K?<0 at the crack tip,both cracks will deflect along the counter pointer and the two cracks will show mutual attraction,and the vertical distance of the cracks will continue to decrease. |
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