Research On Energy Evolution Law And Damage Characteristics Of Coral Concrete During Deformation And Failure

Accelerating the construction of islands and reefs in the south China sea is an important measure to safeguard national sovereignty and security,build a maritime power,and cope with the increasingly deteriorating china-us relations.In the south China sea,using coral gravel,coral sand mixed with seawater,cement and water-reducing agent to prepare coral concrete instead of ordinary concrete for island and reef construction can shorten the construction cycle and reduce the construction cost.Coral concrete is a kind of rock material.It is of great theoretical and practical value to systematically study its energy evolution and damage characteristics in the process of deformation and failure.This paper,by using the MTS experimental system and the hopkinson pressure bar test system on the coral concrete respectively uniaxial static compression(including different specimen size),three axis static compression(including different loading rate and confining pressure),dynamic impact(including different impact speed)and loops and unloading(including the upper limit of different stress level,the lower stress level and load frequency)experiment,discusses the coral concrete in the deformation and failure mechanism of the energy in the process of evolution,analyzes the stress state,stress path and loading rate and geometrical size on energy evolution,the influence on the development of the injury.The main conclusions are as follows:(1)the energy evolution mechanism and rule of coral concrete in the process of deformation and failure are expounded.Part of the energy input from the outside will be converted into elastic energy and stored in the coral concrete,while the other part will be converted into dissipation and cause damage to the coral concrete.When the energy storage limit is reached,the elastic energy will be released and cause damage.Before the peak intensity,more than 80% of the energy is converted into elastic energy,and after the peak,it is mainly converted into dissipated energy.(2)under uniaxial static compression,reducing the geometric size will not only improve the strength of the coral concrete,but also enhance its ability to absorb,store and dissipate energy.Under conventional triaxial compression in the static loading range,with the increase of confining pressure,the energy storage limit and dissipated energy of coral concrete will increase greatly.Meanwhile,the high confining pressure also limits the release of elastic energy during the destruction.The loading rate only affects the dissipated energy,that is,the dissipated energy and its proportion decrease with the increase of the strain rate.(3)under dynamic impact,the time-history evolution curves of incident energy,reflected energy,transmitted energy and dissipated energy all show the law of s-type three-stage growth.The incident energy,reflected energy and dissipated energy all increased linearly with the increase of the average strain rate,and the failure degree of the specimen was positively correlated with the dissipated energy.(4)under cyclic loading and unloading,increasing the upper stress,increasing the loading frequency and decreasing the lower stress will increase the energy absorbed,stored and dissipated in a single cycle.Based on the proportional relationship between dissipated energy and elastic energy,the damping ratio is defined.The damping ratio of coral concrete is between 3.7% and 6.0%,which is generally higher than that of ordinary concrete between 1%and 2%.The relationship between the damping ratio and the upper stress,the lower stress and the loading frequency is established.The relevant mechanism of the damping ratio was analyzed and the coral was considered The characteristics of porous,angular and easily broken aggregate will increase the consumption of vibration energy absorbed.At the same time,the air in the closed pores also ACTS as a flexible buffer,resulting in a much higher damping ratio of coral concrete than that of ordinary concrete.(5)the damage variables of coral concrete are defined by the proportion of dissipated energy,and the evolution curve of the damage variables is obtained.The effects of stress state,stress path,loading rate and geometric size on the damage development are analyzed.The damage evolution equation is established to provide a theoretical basis for the constitutive equation in the future.The larger the specimen volume,the faster the damage development,the smaller the aspect ratio,and the smaller the final damage.Confining pressure can inhibit the development of damage,and the greater the confining pressure is,the slower the development of damage will be.The higher the strain rate,the earlier the damage will occur and the faster the damage will develop.Under cyclic loading and unloading,increasing the upper stress,decreasing the lower stress and reducing the loading frequency will accelerate the development of damage variables.