| Concrete is one of the most basic commonly used materials in construction projects.It is a cement of cement,aggregates,water,and additives.Because of its own different characteristics and mixed condensing of various materials,the concrete has complex and balanced internal holes and micro cracks.For a long time,scholars have been focusing on the research of concrete materials in terms of macroscopic mechanical properties,including the cubic compressive strength test,splitting test,static modulus test and shear strength test of concrete,the various damages that the components are subjected to by external forces are directly related to the internal damage(micro-holes,micro-cracks,etc.)when the force is deformed.However,research in this area is relatively lagging.Therefore,it is very necessary to study the effect of micro-fracture on the impact mechanical properties and failure of concrete treated by high-temperature and high bullet impact load conditions.The research specimen of this article is a commercial concrete specimen,which is marked with the C35 strength grade.The research methods are experimental research and energy law research: n the experimental study,after the concrete test pieces were made according to the different requirements of the test design,the dynamic mechanical properties of the uniaxial impact compression were tested using the split Hopkinson pressure bar,and study its mechanical properties and crushing conditions,based on which the analysis of the specimen fracture degree and block distribution;In the energy method,the crushing energy of the specimen in the SHPB uniaxial impact test is calculated to characterize the relationship between the broken state of the specimen and the energy absorption and dissipation,thereby revealing the relationship between the meso fracture characteristics of the concrete material and the impact mechanical properties.The conclusions are as follows:(1)Under different temperature conditions,the dynamic resistance to pressure of the specimen at lower temperature,the temperature has little effect on the dynamic mechanical properties of the specimen;but when the temperature exceeds the threshold temperature(400 °C),the initial temperature of the specimen Damage has increased.The bullet velocity has a certain strengthening effect on the impact mechanical properties of concrete specimens.Under the conditions of different temperature gradients,the weakening effect of rapid temperature rising specimens on concrete specimens is obviously stronger than that of slow temperature increasing specimens.The cooling method weakens the specimen.(2)According to the test data obtained from the screening test,the fractal dimension of the test specimen obviously has its upper and lower limits,and its numerical value is distributed between 2.0-2.6.Under different conditions,the fractal dimension of the crushing concrete specimens increases with the increase of the temperature and the velocity of the bullets;Under different heating gradients and water cooling conditions,the fractal dimension of the rapid temperature increase specimen and the slow temperature increase specimen both increase with the increase of temperature.Under the condition of slow temperature rise,the fractal dimension of the naturally cooled test piece is slightly higher than that of the water-cooled test piece,indicating that the natural cooling test piece crushing degree is larger than the water cooling test piece under the same conditions,but from the overall trend analysis,Both cooling modes show an upward trend with increasing temperature.(3)Under different temperature conditions,when the particle size is small(less than 2.5mm),the mass ratio of the broken test piece has a clear corresponding relationship with the temperature change,while the broken sample has a medium particle size(2.5mm-10mm)and a large The mass ratio of the particle size(16mm-25mm)continuously decreases as the temperature increases;There is a strong correlation between the mass ratio of the broken test piece and the bullet velocity of the test piece.When comparing different cooling methods,when the particle size of the broken pieces is smaller(less than 5mm),the mass ratio of the natural cooling crushing test piece is greater than that of the water-cooled crushing test piece under the same conditions,while the large particle size fragments(16mm-25mm)The mass ratio of the water-cooled crushing test piece under the same conditions is greater than that of the natural cooling test piece,Explain that the broken condition of naturally cooled specimens is more serious.(4)The crushing energy curve of a concrete specimen is divided into two parts,namely the ascending section and the stationary section.Under the same bullet velocity condition,with the increase of temperature,the absorption energy of the crushing energy of the specimen decreases,and the crushing threshold value also decreases.The incident energy and the crushing energy of the specimen increase with the increase of the bullet velocity,and the peak stress of the corresponding specimen increases obviously.The crushing energy consumption of the slow heating test piece is greater than the crushing energy consumption of the fast heating temperature test piece;under the same temperature and bullet velocity,the crushing energy consumption of the water cooling test piece is higher than that of the natural cooling test piece.(5)Based on the calculation data of the specific crush energy consumption of the SHPB test,a linear relationship was established and the following conclusions can be drawn: The first-order linear function of specific energy-peak stress,specific energy consumption-fractal dimension is ideal.The peak stress and fractal dimension all increase with the increase of specific energy consumption,which proves that there is a stronger rate correlation than energy-peak stress and specific energy-fractal dimension.But its ultimate performance is determined by the nonlinear competition and coupling mechanism of the strengthening and weakening of various factors. |
PDF Full Text Request