Study On Damage Of Limestone Under Impact Load

The Hopkinson pressure bar experimental system is mainly used as the experimental method,and the limestone is used as the research object.The conventional impact experiments at different strain rates and the cyclic impact experiments at the same amplitude are carried out.Through impact experiments,the dynamic mechanical characteristics and energy consumption of rocks under different loading conditions are studied,and the damage evolution law of rocks is analyzed.Then GDEM-Block Dyna numerical simulation software was used to simulate the rock with different initial damage conditions,and the rock damage failure law and crack propagation law under different loading conditions under different initial damage levels were obtained.The main content and conclusions of the full text are as follows:1)The processing and preparation of rock specimens and the determination of the basic mechanical parameters of rock specimens are completed,and the changes of rock strength and energy are analyzed.It is obtained that the compressive strength of the rock increases with the increase of the strain rate;the absorption energy per unit volume of the rock has a linear relationship with the strain rate.2)According to the cyclic impact test,under the same external conditions,as the number of impacts increases,the initial elastic modulus of the rock is the same,and the deformation modulus gradually decreases.As the number of cycles increases,the peak stress of the rock gradually decreases.The smaller,the maximum strain of the rock gradually increases.3)For intact rock,the left and right sides crack first,and then cracks begin to occur inside the specimen until the rock breaks.With the increase of loading speed,the shorter the crack initiation time and the faster the propagation speed,the shorter the time for rock failure,the greater the degree of fragmentation,the shorter the time for the stress to reach the peak,and the greater the peak stress.4)For damaged rocks,the rock fractures all crack at the crack tip.With the increase of the angle between the crack and the horizontal in the rock,the time for the rock to break down first decreases and then increases.With the increase of impact velocity,the crack initiation time of the cracks in the rock gradually decreases,and the crack initiation stress increases.Figure 53;Table 4;Reference 58...