Lunar In Situ Large-Scale Construction:Quantitative Evaluation of Regolith Solidification Techniques

Lunar habitat construction is crucial for successful lunar exploration missions.Due to the limitations of transportation conditions,extensive global research has been conducted on lunar in situ material processing techniques in recent years.The aim of this paper is to provide a comprehensive review,precise classification,and quantitative evaluation of these approaches,focusing specifically on four main approaches:reaction solidification(RS),sintering/melting(SM),bonding solidification(BS),and confinement formation(CF).Eight key indicators have been identified for the construction of low-cost and highperformance systems to assess the feasibility of these methods:in situ material ratio,curing temperature,curing time,implementation conditions,compressive strength,tensile strength,curing dimensions,and environmental adaptability.The scoring thresholds are determined by comparing the construction requirements with the actual capabilities.Among the evaluated methods,regolith bagging has emerged as a promising option due to its high in situ material ratio,low time requirement,lack of hightemperature requirements,and minimal shortcomings,with only the compressive strength falling below the neutral score.The compressive strength still maintains a value of 2–3 MPa.The proposed construction scheme utilizing regolith bags offers numerous advantages,including rapid and large-scale construction,ensured tensile strength,and reduced reliance on equipment and energy.In this study,guidelines for evaluating regolith solidification techniques are provided,and directions for improvement are offered.The proposed lunar habitat design based on regolith bags is a practical reference for future research.

Effects of retained dry material on the impact,overflow and landing dynamics

During long-term operation,the performance of obstacles would be changed due to the material accumulating upslope the obstacle.However,the effects of retained material on impact,overflow and landing dynamics of granular flow have not yet been elucidated.To address this gap,physical flume tests and discrete element simulations are conducted considering a range of normalized deposition height h0/H from 0 to 1,where h0 and H represent the deposition height and obstacle height,respectively.An analytical model is modified to evaluate the flow velocity and flow depth after interacting with the retained materials,which further serve to calculate the peak impact force on the obstacle.Notably,the computed impact forces successfully predict the experimental results when a≥25°.In addition,the results indicate that a higher h0/H leads to a lower dynamic impact force,a greater landing distance L,and a larger landing coefficient Cr,where Cr is the ratio of slope-parallel component of landing velocity to flow velocity just before landing.Compared to the existing overflow model,the measured landing distance L is underestimated by up to 30%,and therefore it is insufficient for obstacle design when there is retained material.Moreover,the recommended Cr in current design practice is found to be nonconservative for estimating the landing velocity of geophysical flow.This study provides insightful scientific basis for designing obstacles with deposition.

Coupled effects of particle overall regularity and sliding friction on the shear behavior of uniformly graded dense sands

Particle morphology has been regarded as an important factor affecting shear behaviors of sands,and covers three important aspects,i.e.global form(overall shape),local roundness(large-scale smoothness),and surface texture(roughness)in terms of different observation scales.Shape features of different aspects can be independent of each other but might have coupled effects on the bulk behavior of sands,which has been not explored thoroughly yet.This paper presents a systematic investigation of the coupled effects of the particle overall regularity(OR)and sliding friction on the shear behavior of dense sands using three-dimensional(3D)discrete element method(DEM).The representative volume elements consisting of ideal spheres and irregular clumps of different mass proportions are prepared to conduct drained triaxial compression simulations.A well-defined shape descriptor named OR is adopted to quantify particle shape differences of numerical samples at both form and roundness aspects,and the particle sliding friction coefficient varies from 0.001 to 1 to consider the surface roughness effect equivalently in DEM.The stress-strain relationships as well as peak and critical friction angles of these assemblies are examined systematically.Moreover,contact network and anisotropic fabric characteristics within different granular assemblies are analyzed to explore the microscopic origins of the multi-scale shape-dependent shear strength.This study helps to improve the current understanding with respect to the influence of the particle shape on the shear behavior of sands from different shape aspects.

基于嫦娥五号月球样品的月壤残余内摩擦角预测

随着人类探月工程的快速发展,月球基地建设以及月表资源开发利用有望更快实现,合理预测月壤工程力学性质对于未来深层次探月工程意义重大,我国嫦娥五号返回月球样品为研究月壤工程力学特性提供了直接的实测材料。然而,月球样品极其珍贵,难以满足传统土工试验测试.为了应对这一科学挑战,本研究从无损分析月球样品颗粒属性入手,使用高精度X-射线μCT扫描、三维白光干涉、原子力显微镜等无损测试手段,分析了不同类型月壤颗粒的三维多尺度形态、弹性力学和摩擦属性等指标.在此基础上,基于颗粒材料宏微观物理力学理论和数值模型尝试预测了嫦娥五号采样处月壤残余内摩擦角。本研究为基于月球样品信息跨尺度分析月壤工程力学性质提供了可行思路。

Complexities of the Turkey-Syria doublet earthquake sequence

WHAT,WHERE,AND WHEN In the early morning of February 6th,2023,an M7.8 earthquake occurred in southeastern T€urkiye near the northern border of Syria.The event initiated a complex sequence of aftershocks,including an M7.6 earthquake about 9 h later and 90 km to the north(Figures 1A and 1B).The earthquake sequence is also referred to as a strong doublet earthquake sequence.Aftershocks of the two strong earthquakes occurred along two separate branches of the East Anatolia Fault,with lengths of up to 300 km,and some aftershocks occurred in Syria(NEIC/USGS,2023).

State of the art review on the production and bond behaviour of reinforced geopolymer concrete

Geopolymer is produced through the polymerization of active aluminosilicate material with an alkaline activator,leading to the formation of a green,inorganic polymer binder.Geopolymer concrete(GPC)has become a promising low-carbon alternative to traditional Portland cement-based concrete(OPC).GPC-bonded reinforcing bars offer a promising alternative for concrete structures,boasting excellent geopolymer binder/reinforcement bonding and superior corrosion and high-temperature resistance compared to Portland cement.However,due to differences in the production process of GPC,there are distinct engineering property variations,including bonding characteristics.This literature review provides an examination of the manufacturing procedures of GPC,encompassing source materials,mix design,curing regimes,and other factors directly influencing concrete properties.Additionally,it delves into the bond mechanism,bond tests,and corresponding results that represent the bond characteristics.The main conclusions are that GPC generally has superior mechanical properties and bond performance compared to ordinary Portland cement concrete(OPC).However,proper standardization is needed for its production and performance tests to limit the contradictory results in the lab and on site.