Fractal And Energy Consumption Characteristics Of Concrete Under Impact Loading

In order to systematically study the compression deformation and energy evolution characteristics of concrete under dynamic load,the Hopkinson bar test device was used to test the concrete specimens with an aggregate rate of 0,37%,42%,and 47%,respectively,at an impact velocity of 5,6and 7 m / s.Based on the fractal theory,the distribution characteristics of the broken pieces of the concrete specimen were studied,and the relationship between the fractal dimension of the fragment distribution and the dynamic mechanical parameters of the concrete was analyzed.From the perspective of energy,The energy dissipation law of concrete in the process of failure is analyzed,and the relationship between the absorbed energy of concrete specimens and the surface energy of fragments is established.The main work and conclusions are as follows:(1)Based on the original stress wave obtained from the experiment,the transmission and change law of the incident wave,reflected wave,and transmitted wave affected by the impact velocity and aggregate rate are analyzed.The deformation process of the concrete specimen and the stress-strain relationship curve obtained from the original stress wave are analyzed.The correlation between the peak stress,the peak strain,the impact velocity and the aggregate rate,and the failure mode of the specimen were analyzed in combination with the stress state of the specimen,the law of stress wave transmission,and the failure shape of the specimen.The results show that the peak values of incident and reflected waves increase with increasing impact velocity,and the peak values of transmitted wave decrease with increasing impact velocity.As the aggregate rate increases,the peak value of the transmitted stress wave increases at the same impact velocity.,The time span becomes longer;when the aggregate rate is the same,the peak stress and strain of the specimen increase with the increase of the impact velocity;at the same impact velocity,the increase of aggregate will increase the stress peak of the concrete specimen and reduce the peak strain.;Under the action of impact compression load,concrete specimens are mainly subject to tensile cracking。(2)The distribution characteristics of concrete fragments are described based on fractal theory.It is found that the distribution of concrete fragments has certain self-similar characteristics under dynamic impact compression,which is in line with the fractal law.The internal relationship between the fractal dimension of the fragment distribution and the impact velocity,strain rate,dynamic compressive strength,and aggregate ratio was systematically studied.According to the causal relationship between the crack path and the fragment distribution,the fractal dimension was specified.As the characteristic amount of the surface roughness of the fragments,the total surface area of the fragments after the concrete specimen is broken is calculated.The results show that the fractal dimension of the distribution of concrete fragments has a positive correlation with the impact velocity.When the aggregate rate is the same,the impact fractal dimension is large when the impact velocity is high.The number of fragments and the particle size are small after the specimen is destroyed.The degree of damage is high;when the impact velocity is low,the fractal dimension of the fragments is small,the number of fragments is small,the particle size is large,and the degree of damage is low;The fractal dimension of concrete fragments has a negative correlation with the aggregate ratio.At the same impact speed,the higher the concrete aggregate content,the smaller the fractal dimension of the fragments after the failure.The fractal dimension of concrete fragments has a high logarithmic relationship with the dynamic compressive strength.The dynamic compressive strength increases with the increase of the fractal dimension.(3)According to the evolution law of the incident energy,reflection energy,and transmission energy of the concrete specimen during the test,the energy consumption density is specified as the energy loss criterion when the specimen is destroyed.The energy density and absorbed energy,incident energy,strain rate,and fragmentation are studied.The relationship between block distribution fractal dimension,dynamic compressive strength,etc.Finally,the unit surface energy is calculated based on the split tensile test,and the surface energy of the fragment during compression failure is calculated.The surface energy is compared with the absorbed energy of the specimen and the surface energy,absorbed energy,and fractal dimension are established.Relational expression.The results show that the energy density increases with the increase of impact speed and strain rate,and decreases with the increase of aggregate rate;the transmission energy increases with the increase of aggregate rate,and the concrete test increases with the increase of aggregate rate.The increase of the transmitted energy of the piece is always greater than the decrease of the reflected energy;the dynamic compressive strength of the concrete increases with the increase in the energy fractal dimension of the concrete fragment distribution;the energy absorbed by the test piece is about 86.8% Surface energy.