In this study, we fabricated poly (methyl methacrylate) (PMMA) microcellular foams featuring tunable cellular structures and porosity, through adjusting the supercritical CO₂ foaming conditions. Experimental testing and finite element model (FEM) simulations were conducted to systematically elucidate the influence of the foaming parameters and structure on compressive properties of the foam. The correlation between the cellular structure and mechanical properties was acquired by separating the effects of the cell size and foam porosity. It was found that cell size reduction contributes to improved mechanical properties, which can be attributed to the dispersion of stress and decreasing stress concentration.

Investigating the constitutive relationship and the damage failure mechanism of solid propellants is of significance for improving the safety, storage period and use efficiency of solid rocket motors. This paper focuses on the complex mechanical response behavior of composite solid propellants under loads and introduces experimental research on quasi-static and dynamic mechanical properties. Limited by the accuracy of instruments and testing methods, the research progress of macroscopic constitutive models, mesoscopic mechanical models and microscopic molecular models is summarized from the perspective of numerical simulations based on model scale and modeling methods. This paper tracks the historical progress of key models and summarizes the main achievements and prospects in this field. The research in this paper has high scientific and theoretical significance and engineering application value. It can provide an important reference and guidance for the structural optimization and performance improvement of solid propellants and lay a solid foundation for the development of solid rocket motors.

Cellular media materials are used for automobiles, aircrafts, energy-efficient buildings, transportation, and other fields due to their light weight, designability, and good impact resistance. To devise a buffer structure reasonably and avoid resource and economic loss, it is necessary to completely comprehend the constitutive relationship of the buffer structure. This paper introduces the progress on research of the mechanical properties characterization, constitutive equations, and numerical simulation of porous structures. Currently, various methods can be used to construct cellular media mechanical models including simplified phenomenological constitutive models, homogenization algorithm models, single cell models, and multi-cell models. This paper reviews current key mechanical models for cellular media, attempting to track their evolution from their inception to their latest development. These models are categorized in terms of their mechanical modeling methods. This paper focuses on the importance of constitutive relationships and microstructure models in studying mechanical properties and optimizing structural design. The key issues concerning this topic and future directions for research are also discussed.

Particle shape governs the macro-mechanical behavior of high explosives. This study develops 3D computational geometry techniques to determine commonly used sphericity and roundness definitions of typical high explosive particles, including HMX (octahydro-1,3,5,7-tetranitro- 1,3,5,7-tetrazocine), RDX (1,3,5-Trinitroperhydro-1,3,5-triazine), and CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane). This technique can automatically determine principal dimensions, volume, surface area, minimum circumscribed sphere, maximum inscribed sphere, and the 3D convex hull of 3D particle geometries and determine commonly used 3D sphericity descriptors of high explosive particles. This technique can also automatically identify corners on the 3D particle surface, fit appropriate spheres to these corners, and compute Wadell’s roundness of high explosive particles. This study demonstrates that the qualities of 3D particle geometries affect the computational results of particle sphericity and roundness descriptors of high explosives. These descriptors display a hierarchy of resistance to the effects of low image quality. Therefore, the minimum requirements for ensuring reliable shape characterization of these parameters are established for high explosives. This study systematically compares 2D and 3D particle shape characterizations of around 15,000 particles from three high explosives (HMX, RDX, and CL-20). Results show that 2D sphericity and rounded definitions either underestimate the corresponding 3D definitions or vary within large ranges leading to uncertainties for inferring 3D particle characteristics from 2D images of high explosives.

Since invented in 2003, rock-filled concrete (RFC) has gained much attention and has been successfully applied in more and more civil and hydraulic projects in China. This study developed a numerical framework to simulate self-compacting concrete (SCC) flows in the voids among rocks of RFC, which couples the lattice Boltzmann method and discrete element method (DEM). The multiple-relaxation-time scheme is used to simulate self-compacting mortar (SCM) for better stability while the motion of coarse aggregates in SCC is simulated with DEM. The immersed moving boundary method is incorporated to deal with the interactions between coarse aggregates and SCM. After validation, the coupled framework is applied to study SCC flows in a single channel and in porous media with multi-channels. A passing factor PF was proposed and calculated to describe quantitatively the passing ability of SCC through a single channel. The study found that jamming of SCC occurs when the ratio Ar of the gap width to particle diameter is smaller than 2.0 and the jamming risk increases with solid particles fraction while the passing ability has a weak relation with the pressure gradient. Further, SCC flow is self-tuning in porous media with multi-channels and it is prone to go through larger or wider gaps. Exceeded existence of narrow gaps will significantly increase the jamming risk.

To improve the mechanical properties of calcareous sand, it is proposed that microbial induced calcium carbonate precipitation (MICP) technology be used. A series of solidification tests were conducted in natural seawater and freshwater environments. The standard stress path static triaxial apparatus was used to conduct shear tests on calcareous sand and solids under varying reinforcement conditions. The composite power-exponential (CPE) model is proposed to describe the stress–strain relationship curve of the solid, and the method for determining model parameters is presented. The experimental results showed that the strength of calcareous sand with solids increased with the increase in number of reinforcement times for both test environments. Owing to the high salinity of seawater, which inhibits the activity of urease in bacterial solutions, the reinforcement strength in the seawater environment was generally lower than that in the freshwater environment. The compactness had an evident effect on the strength of the added solids. With the increase in compactness, the strength of the sample also increased, but the rate of increase was reduced. The simulation results showed that the established constitutive model can accurately describe the stress–strain relationship of microbial-reinforced calcareous sand and verified the applicability of the model.