Abstract
This paper is focused on exploring the dynamic mechanical properties and damage process of siltstone. For this purpose, different stress wave wavelengths (0.5 m∼2.0 m) and different strain rates (25 s−1∼120 s−1) were applied to siltstone specimens in the SHPB dynamic impact test. The experimental results show that the dynamic compressive strength of siltstone is linearly positively correlated with the strain rate, and the dynamic increase factor is linearly positively correlated with the natural logarithm of strain rate; the peak strain is linearly positively correlated with the strain rate, and the increase in wavelength causes the peak strain to increase. Through multiple impact tests, it is concluded that the cumulative damage to siltstone increases with the number of impacts. The cumulative damage curve exhibits an initial rapid rise, followed by a stable development, followed by another rapid rise. With increasing wavelength of the stress wave, the stable development of the curve gradually decreases, the cumulative damage to the siltstone is intensified, and the number of repeated impacts is reduced. Meanwhile, a model for damage evolution is established based on the inverse of the Gompertz function, and the physical meanings of the model parameters are determined. The model can reflect the influence of both stress wave parameters and impact times. Verification of the model demonstrates the rationality of the model and the correctness of the physical meaning of the parameters. The model could be applied in future studies of damage to sedimentary rocks.
Highlights
In many engineering constructions, such as tunnels, water conservancy, mining, and others, blasting is an efficient, economical, and reliable method, which involves the dynamics of rock under impact load. e mechanical properties of rock materials under impact loads are different from those under static loads; this is due to the transient response characteristics of the rock caused by the transient characteristics of the impact load
It was found that the dynamic increase factor was 1.0∼1.4, and the dynamic strength and strain rate were in a power function relationship. e failure mode is converted from tensile failure to splitting comminuted damage
A comprehensive analysis of Figures 2 and 3 shows that when the stress wave amplitude exceeds the static compressive strength of siltstone (76.13 MPa in this paper), the change of wavelength does not cause the change of dynamic strength; the decisive factor affecting the dynamic strength is the change of strain rate. e specific performance is as follows: the greater the impact velocity, the larger the amplitude and the greater the strain rate, resulting in an increase in dynamic strength. e Dynamic increase factor (DIF) is linearly positively correlated with the natural logarithm of the strain rate and can be expressed by using formula (2), and the correlation coefficient R is 0.89: DIF − 5.984 + 1.565 ln ε_, 60 < ε_ < 160. (2)
Summary
In many engineering constructions, such as tunnels, water conservancy, mining, and others, blasting is an efficient, economical, and reliable method, which involves the dynamics of rock under impact load. e mechanical properties of rock materials under impact loads are different from those under static loads; this is due to the transient response characteristics of the rock caused by the transient characteristics of the impact load. Based on the results of the brittle rock dynamic load test, Gao and Liu [23] introduced the relationship between energy dissipation rate and acoustic attenuation coefficient and established the dynamic damage evolution equation of rock. Many scholars have carried out more dynamic properties of rock from the aspects of constitutive [26, 27], loading mode [28], energy dissipation [28,29,30,31], and fracture [32, 33], they did not consider the effect of different stress wavelengths on dynamic mechanical properties, especially the sensitivity of damage evolution to stress wavelength. E mechanical properties and damage evolution of siltstone under different stress wave wavelengths and amplitudes are studied, and the corresponding damage model is established The impact test of siltstone under different combinations of impact rod length and impact velocity is carried out by using the Split Hopkinson Pressure Bar device. e mechanical properties and damage evolution of siltstone under different stress wave wavelengths and amplitudes are studied, and the corresponding damage model is established
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