Study Of Fracturing Characteristics And Mechanism Of High-Pressure Water Jet Impacting Concrete

Concrete crushing technology is very important in maintenance and repair of concrete structure of road and bridge.Comparing with the shortcomings of high cost,large workload and poor repair quality caused by common mechanical and chemical methods of breaking concrete,the technology of high-pressure water jet breaking concrete has obvious advantages such as low pollution,precise construction,wide selection,low damage to original structure,high efficiency,non-contact cutting,etc.which plays an extremely important role in road and bridge maintenance,post disaster reconstruction,emergency rescue,emergency demolition and other projects.However,the process of breaking concrete by high-pressure water jet is very short(microsecond level),and involves the dynamic coupling problem of non-linear collision between fluid and solid.The mechanism of breaking concrete by high-pressure water jet is relatively complex.The mechanism of breaking concrete by high-pressure water jet is not clear.There are still some problems in the technology of high pressure water jet breaking concrete,such as high threshold pump pressure,high specific energy consumption,lack of local precise breaking or controllable crack causing technology,etc.In order to promote the development of high-pressure water jet concrete breaking technology,improve the level of concrete structure repair and accident emergency breaking,this paper focuses on the research of the crack propagation characteristics and mechanical mechanism of concrete under the impact of high-pressure water jet from the aspects of experimental research and numerical simulation,and has achieved the following main results:(1)The homogeneous transparent concrete is prepared by using epoxy resin and curing agent in proportion.High pressure water jet was used to vertical impact homogeneous transparent concrete monitoring equipment to record the impact crushing process.By observing the crack initiation,propagation,penetration and fracture morphology in the process of crushing homogeneous and transparent concrete by high pressure water jet.The results showed that the evolution process of high-pressure water jet erosion concrete fracture zone mainly includes three typical stages: expansion of water hammer compression zone,expansion of non compression zone and expansion after penetration.In the water hammer compression region,the eroded holes propagate to the free surface in the shape of "petals",and there are plastic yield strips near the eroded holes,and the radial cracks and circumferential cracks interweave and connect with each other around the holes;in the non compression region,the material removal evolves into a completely brittle fracture mode,and there are no obvious plastic yield areas and cracks near the eroded holes After penetration and penetration,the diameter of the eroded hole will continue to expand in a certain period of time,and there are discontinuous and hemispherical microcracks in the near area of the hole wall.When the propagation reaches about 2 times of the initial through hole diameter,the main eroded hole tends to be stable.(2)Mica and transparent concrete are used to make internal crack transparent concrete.High pressure water jet is used to impact internal crack transparent concrete monitoring equipment to record the impact breaking process.During the process of high pressure water jet impact breaking internal crack transparent concrete,the crack initiation,propagation,penetration and breaking of the secondary cracks in the area affected by the pre cracks and pre cracks are observed The shape shows that the existence of the prefabricated cracks has a guiding effect on the crack growth process,which significantly improves the efficiency of water jet impact fracture and damage degree,mainly reflected in increasing the number of secondary cracks,promoting the development of secondary cracks in all directions,improving the speed of water jet through the test piece,and the spatial arrangement of the prefabricated cracks has obvious correlation with the guiding effect;penetration The length of the through test piece is: vertical prefabricated crack test piece < oblique 45 ° prefabricated crack test piece < horizontal prefabricated crack test piece,prefabricated double crack test piece < prefabricated single crack test piece;in order of the number of cracks,oblique 45 ° prefabricated crack test > The results show that the horizontal prefabricated crack is more than the vertical prefabricated crack,and the prefabricated double crack is more than the prefabricated single crack;the prefabricated crack not in the impact center will produce the crack tip effect,and promote the secondary crack to expand towards a large angle with the prefabricated crack surface.(3)Based on the smooth particle hydrodynamics(SPH)method,a numerical model of internal cracks in homogeneous concrete impacted by high-pressure water jet was established.Through the analysis of stress nephogram and typical particle stress curve of cracks in different stages of concrete,combined with the monitoring test of high pressure water jet impacting concrete surface strain,the mechanical characteristics of high pressure water jet impacting concrete are studied.It indicates that at the initial stage of liquid-solid contact,water hammer pressure forms a strong compressive shear stress in the erosion pit,and both the solid-liquid contact surface and its adjacent area are shear fracture;in the expansion stage of water hammer compression zone,the cone-shaped crack mainly originates from concrete shear failure,the radial crack,axial crack and circumferential crack all originate from concrete tensile failure;the tip of the prefabricated crack first appears damage,except for the prefabricated crack tip near the erosion pit and the prefabricated single crack with an angle of 45 ° The results show that the crack tip is shear failure,and the other is tensile failure.The impact efficiency gains of the prefabricated crack arrangement on the high-pressure water jet are also different.The axial growth gains of the internal cracks of the specimen are vertical arrangement >oblique arrangement > transverse arrangement;the radial growth gains of the internal cracks of the specimen are Single crack transverse arrangement > single crack vertical arrangement > single crack oblique arrangement,double crack transverse arrangement >double crack oblique arrangement > double crack vertical arrangement;The strain test in the course of high-pressure water jet impacting concrete is carried out,the synchronous change process of crack initiation,propagation,penetration and surface strain of concrete under jet impact is displayed,and the phased evolution law of surface strain of highpressure water jet impacting concrete is revealed.