With the construction of infrastructure in cold areas and the economic development of cold areas, more and more engineering projects are carried out in cold areas. Ensuring the safety of major engineering projects in cold areas has become the primary problem facing engineering construction in cold areas. Frozen soil is the main bearing body of engineering in cold regions, and studying the impact dynamic mechanical properties of frozen soil has important practical significance for guiding engineering construction. Recently, Professor Zhu Zhiwu’s team from the School of Mechanics and Engineering of Southwest Jiaotong University has made new research progress in the impact dynamic mechanical properties of frozen soil. They proposed the equivalent relationship between the strain rate effect and temperature effect of frozen soil under impact loading, and revealed the mechanical mechanism of interdependence between the participants. Relevant research results were published in the flagship journal Journal of the Mechanics and Physics of Solids with the title A unified viscoplastic model and strain rate–temperature equivalence of frozen soil under impact loading.
Frozen soil, due to its internal soil, ice, water and other components, its impact dynamic mechanical properties are affected by factors such as strain rate, temperature, and ice-water phase transition. Under the impact loading condition, the impact deformation time is much shorter than the thermal diffusion time, resulting in adiabatic condition dominating. At this time, the heat generated by the severe plastic deformation is concentrated in a local area, causing ice-water phase transition, lubricating the crack surface, and accelerating the destruction of frozen soil. Adiabatic temperature rise is an important mechanism of impact deformation of frozen soil, and there are few reports on shock dynamic constitutive models that consider the impact of adiabatic temperature rise of frozen soil. At the same time, for the strain rate effect and temperature effect of frozen soil under the impact loading condition, the academic circles mostly report the corresponding variability effect and temperature effect separately, and there is still a lack of systematic research on the deep connection between them.
In order to find the equivalent relationship between the strain rate effect and temperature effect of frozen soil under impact loading, the impact dynamic constitutive model considering the influence of adiabatic temperature rise during impact loading was studied, and the researchers carried out corresponding experimental and theoretical studies. In the study of the impact compression experiment of frozen soil, based on the technology of dual wave shaper, a method of waveform shaping by customizing the shape and size of the wave shaper and using the structure response of the wave shaper is proposed. By analyzing the experimental data, according to the similar effect of strain rate and temperature on peak strength, based on the analysis of thermal activation theory, the research team proposed for the first time the rate-temperature equivalence of frozen soil. Increasing the temperature lowers the energy barrier of the thermal activation process, making the thermal activation process easier to occur. The interdependence between the temperature and strain rate of frozen soil conforms to the Arrhenius equation. In the framework of the unified viscoplastic theory, an inelastic multiplier considering the source of inelastic deformation of frozen soil is constructed. Further considering the characteristics of thermal damage during the impact loading process of frozen soil, a parameter evolution equation considering the influence of adiabatic temperature rise is established based on the damage theory. Finally, a unified viscoplastic damage constitutive model that can reasonably describe the impact deformation mechanism of frozen soil and driven by adiabatic temperature rise is established.
Compared with the existing literature, this article proposes a wave shaping method suitable for low-impedance material impact compression experiments. This method utilizes the structural response of the wave shaper, can effectively protect the low-strength rod system, and is an economical and efficient wave shaping method. At the same time, the rate-temperature equivalence of frozen soil proposed based on the thermal activation theory enriches the research content of frozen soil mechanics. The proposed constitutive model has fewer parameters and simple determination method, which can ideally describe the nonlinear characteristics of frozen soil stress-strain curve and reveal the impact deformation mechanism of frozen soil.
This research was supported by National Natural Science Foundation of China "Dynamic mechanical behavior and constitutive relationship of frozen soil under combined dynamic and static cyclic impact loading" (No.11672253), “Dynamic mechanical behavior and constitutive relationship of freeze-thaw cycle unsaturated frozen soil under impact loading " (No.11972028) and the Open Fund of the State Key Laboratory of Frozen Soil Engineering "Research on the Dynamic Mechanical Behavior and Service Performance Evolution Law of Frozen Soil of High-speed Railway in Cold Regions under Impact Loading" (No.SKLFSE201918). The School of Mechanics and Engineering of Southwest Jiaotong University is the first completion unit and the first communication unit of the results, and Professor Zhu Zhiwu is the corresponding author. The authors of the paper include PhD students Zhang Fulai (first author), Professor Zhu Zhiwu, researcher Ma Wei (State Key Laboratory of Frozen Soil Engineering, Northwest Research Institute, Chinese Academy of Sciences), and Associate Researcher Zhou Zhiwei (State Key Laboratory of Frozen Soil Engineering, Northwest Research Institute, Chinese Academy of Sciences) ), PhD student Fu Tiantian.
Paper link:
https://doi.org/10.1016/j.jmps.2021.104413
