Search

A high strain rate occurs when the strain rate exceeds 100 s−1. The mechanical behavior of materials at a high strain rate is different from that at middle and low strain rates. In order to study the dynamic compressive mechanical properties of ultra-high-performance steel-fiber-reinforced concrete (UHPSFRC) at high strain rates, an electro-hydraulic servo universal testing machine and a separate Hopkinson pressure bar (SHPB) with a diameter of 120 mm were used, respectively. A quasi-static compression test (strain rate 0.001 s−1) and impact compression test with a strain rate range of 90~200 s−1 were carried out to study the failure process, failure mode, and stress–strain curve characteristics of UHPSFRC at different strain rates and quantify the strain rate strengthening effect and fiber toughening effect. Based on the statistical damage theory and energy conversion principle, a dynamic damage constitutive model considering the effects of strain rate and fiber content was constructed. The results showed that the rate correlation of UHPSFRC and the fiber toughening properties showed a certain coupling competition mechanism. When the fiber content was less than 1.5%, with an increase in the steel fiber content, the crack initiation and propagation time of the specimen was extended, and the strain rate sensitivity gradually decreased. When the fiber content was 2%, the impact compressive strength of the specimen was optimal. Compared with UHPC, the dynamic increase factor (DIF) of UHPSFRC was significantly lower. The dynamic damage constitutive model established in this paper, considering the influence of strain rate and fiber content, has a good applicability and can describe the mechanical behavior of UHPSFRC at a high strain rate. [ABSTRACT FROM AUTHOR]

As the mileage of long tunnels and the number of underground engineering projects continue to increase, the issue of rock mass stability after fire and explosion becomes increasingly prominent. Therefore, studying high strain rates mechanical properties of rocks under different heat treatment methods is of great significance to the design of geological engineering. In this study, Caledonian granite of Sejila Mountain is selected as the research object. Impact compression tests are conducted after high-temperature natural cooling and real-time high-temperature treatment to analyze the mechanical properties and crushing energy consumption characteristics after exposure to 400 ℃. The results show that the temperature threshold of Sejila Mountain granite is 800 ℃. On average, the peak stress after natural cooling at 400 ℃, 500 ℃, 600 ℃, and 700 ℃ decreases by 6.96%, 8.77%, 16.11%, and 31.51% compared to room temperature. Under real-time high-temperature, the peak stress decreases by 8.36%, 14.65%, 27.83%, and 46.55% on average compared to room temperature. The specimen fragments under real-time high-temperature are more rounded than those after natural cooling, and the fractal dimension is larger. The specific energy absorption (SEA) has a sudden change critical temperature, which is 500 ℃ for real-time high-temperature and 600 ℃ for natural cooling. Highlights: The damage and deterioration laws of granite mechanical properties after natural-cooling and real-time hightemperature are compared through impact compression mechanical test. It is analyzed the mechanical properties and crushing energy consumption characteristics of Caledonian granite in Sejila Mountain at 400 ℃-800 ℃. The defects of fractal dimension calculation are discussed. [ABSTRACT FROM AUTHOR]

It has important guiding significance to study the influence of high temperature on physical and chemical properties and dynamic compression mechanical properties of rocks on the stability of rock mass engineering involving thermal behavior. The damage characteristics and dynamic mechanical characteristics of sandstone after different temperatures (20 °C, 200 °C, 400 °C, 600 °C, 800 °C, 1000 °C) are studied. The mineral composition, mineral content and pore structure of sandstone changed significantly after heat treatment. The content of clay minerals decreases and the content of quartz increases. And all the internal hematite is reduced at 400 °C. The content of macropores increases, and the pore size range decreases. The Split Hopkinson pressure bar is used to perform uniaxial impact compression tests on the heat-treated sandstone specimens with different average impact speeds (8.6 m/s, 14.6 m/s and 18.8 m/s). It is found that the impact speed would weaken the degrading effect of temperature on sandstone, and the temperature would increase the strengthening effect of strain rate. The change of the dynamic elastic modulus of sandstone under the coupling effect of temperature and loading includes the temperature weakening stage, the impact load enhancing stage and the temperature weakening stage. A damage dynamic constitutive model considering the combined effects of temperature initial damage and impact loading damage is established according to the study of the macroscopic and mesoscopic degradation characteristics of sandstone by temperature. The rationality of the model is verified. [ABSTRACT FROM AUTHOR]

To study the effect of freeze–thaw weathering damage deterioration on the strength of Huashan granite, this paper conducted a freeze–thaw (FT) cycle test on Huashan granite at − 20 to 20 °C and 0–100 cycles. Thus, the basic physical parameters change law of Huashan granite after freeze–thaw weathering are obtained. The SHPB (Split Hopkinson Pressure Bar) device was used to perform uniaxial and confining impact compression of granite, analyze the macro-mechanical test phenomena, and reveal the influence of freeze–thaw damage on rock strength. The results show that frost heave failure is the principal mechanism that causes the strength to decrease after freeze–thaw weathering. The static uniaxial compressive strength and maximum tensile strength of Huashan granite decreased by 38.4 and 21.5% after 100 FT cycles, respectively. The rate of reduction of peak stress does not necessarily grow with the increase of the number of cycles, and the average reduction rate in each phase ranges from 0.1 to 2.4%. It means that the damage accumulation of freeze–thaw weathering on rocks is not a uniformly increasing damage process. The radial restraint of confining pressure can effectively increase the peak stress of the material. When the strain rate is low, no failure occurs in the specimens due to the hoop restraint of confining pressure. [ABSTRACT FROM AUTHOR]

Because of large deformation and viscoelastic properties of rubber-like elastomers, it is very challenging to establish its rate-dependent constitutive relation. Based on the basic theory of thermodynamics, the energy dissipation rate of the materials is derived in this paper. Then, a viscoelastic constitutive relation suitable for describing the rate-dependent behavior of rubber-like elastomers is proposed based on the viscoelastic theory and energy dissipation rate. In order to explain the application of constitutive relation, the constitutive equation is simplified according to the deformation characteristics and boundary conditions of rubber-like elastomers under working conditions, and the simplified one- or two-dimensional constitutive forms are obtained. The existing classical data is fitted and analyzed through the simplified form of the model, and found that the new model has the ability to describe the stress-strain relationship of the materials under common deformation modes. Meanwhile, through comparative analysis found that the overall prediction accuracy of the new model is better than that of some commonly used models. Finally, the newly proposed constitutive relation is used to predict the nonlinear mechanical behavior of three kinds of rubber-like elastomers at different strain rates, and the validity and universality of the constitutive relation are verified through comparative analyses. Unlabelled Image • A viscoelastic model is proposed based on thermodynamic derivation. • The mechanical responses at several loading conditions are calculated by new model. • New model can describe stress-strain relation under one- or two-dimensional loading conditions. • The experimental results of three rubber-like elastomers at different strain rates are predicted. [ABSTRACT FROM AUTHOR]