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National Strategic Materials: Special Engineering Materials
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Effect and Mechanism of Low Temperature Curing on the Early Performance of Epoxy Resin Based Mortar
LYU Yan, BAI Erlei, WANG Zhihang, XIA Wei
Materials Reports
2024,38(5 ):23080222 -6. DOI:10.11896/cldb.23080222
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Epoxy resin based mortar is a new high-performance engineering material. In order to study the effect of low temperature curing conditions on the working performance and early mechanical properties of epoxy resin based mortar, a low-temperature environment was constructed using a low temperature test system. The compressive strength, flexural strength, flowability, setting time, and internal temperature were tested, and the microstructure and pore structure of epoxy resin based mortar were analyzed. The results show that the performance of epoxy resin based mortar is greatly affected by temperature. When the temperature is 0 ℃, the fluidity is only 112 mm, but it increases rapidly with increasing temperature. Low temperature curing weakens the internal thermal effect of mortar and delays the setting time. The early strength loss is also significant. At 0 ℃, the mortar is cured for 1 d to form strength, indicating that the low-temperature environment greatly delays the curing rate of the system. Microscopic analysis shows that low-temperature curing leads to loose internal structure, increases cracks and pores in the mortar, indicating incomplete curing reaction and thus reducing the performance of the mortar. When the curing temperature is 20 ℃, the internal structure is relatively dense and the macro structure also exhibits high strength.
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Dynamic Mechanical Properties of Modified Polypropylene Fiber-reinforced High-strength Coral Concrete Under Impact Load
CHENG Yuzhu, MA Linjian, WANG Lei, GENG Hansheng, GAO Kanghua, TAN Yizhong
Materials Reports
2024,38(5 ):23070191 -7. DOI:10.11896/cldb.23070191
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The impact compression test of modified polypropylene fiber-reinforced high-strength coral concrete was performed by using a 100 mm split Hopkinson pressure bar device, and the dynamic compression strength, deformation characteristics and energy dissipation of modified polypropylene fiber-reinforced high strength coral concrete samples with different fiber dosages were analyzed. The results show that the dynamic compressive strength, fracture state and toughness index of modified polypropylene fiber-reinforced high-strength coral concrete with different fiber dosages have obvious strain rate effect. With the increase of the fiber dosage, the damage degree of modified polypropylene fiber-reinforced high-strength coral concrete gradually decreases, and the peak strain, toughness index and energy dissipation gradually increase. In conclusion, mo-dified polypropylene fiber can effectively enhance toughness and reduce brittle failure characteristics of coral concrete.
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Preparation and Finite Element Analysis of Lightweight Aggregate Cement-based Multi-function Absorbing Materials
WU Zihao, SU Ronghua, MA Chao, XIE Shuai, JI Zhijiang, WANG Yingxiang, WANG Jing
Materials Reports
2024,38(5 ):23080253 -7. DOI:10.11896/cldb.23080253
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In order to analyze the effects of lightweight aggregate type and particle size on the properties of wave absorbing materials, five kinds of lightweight aggregate with particle sizes ranging from micron to millimeter were used to prepare lightweight cement-based absorbing materials, and their electromagnetic parameters and reflection loss (RL) were tested. 2D cross-section model was constructed by finite element analysis method to simulate the electromagnetic field distribution inside the wave absorbing materials. The mechanical properties and thermal conductivity of the wave absorbing materials were tested. The results show that the impedance matching performance of cement-based materials and the average RL are improved via increasing the content of lightweight aggregate and particle size, as well as broaden the effective absorption bandwidth, and the absorption peak is moved to high frequency. When the thickness is 20 mm, the optimal RL of the wave absorbing material is -29.1 dB at the low frequency of 1.2 GHz and -20.9 dB at the high frequency of 5.9 GHz, and the maximum effective absorbing bandwidth can reach 14.49 GHz. The finite element simulation results show that the electromagnetic wave transmission direction can be changed by adding lightweight aggregate, the electromagnetic wave loss path is increased, and a strong loss is produced between neighboring aggregates, then the loss occurs inside aggregate, which provides a theoretical basis for the selection of aggregate type, particle size and the design of lightweight absor-bing materials. The density, mechanical strength and thermal conductivity of wave absorbing materials are reduced via increasing the particle size of lightweight aggregate, the wave absorption efficiency and the heat preservation effect are better.
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Incorporation Technique and Preparation Process of Solid-Liquid Phase Change Material and Its Research Progress in Construction Field
CHENG Xinlei, MU Rui, SUN Tao, LIU Yuanxue, HU Zhide, JIANG Haoyang
Materials Reports
2024,38(5 ):23080048 -15. DOI:10.11896/cldb.23080048
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With the rapid development of human society, people have increasingly higher demands of construction indoor thermal comfort, but the continuous increase of building energy consumption in the process of building development is a prominent issue of building energy conservation. Phase change energy storage technology refers to the storage or release the heat through the thermal storage characteristics of phase change materials, and ultimately achieve the goal of temperature regulation. In recent years, the high heat storage density, isothermal phase change process, releasing or absorbing heat by latent heat makes phase change materials a unique advantage in the energy storage technology which in turn enjoys bright prospects in their application in construction field. With the continuous development of phase change material preparation, composite and encapsulation technology, more and more phase change materials are incorporated in building materials and components, which provides a new development model for thermal insulation and energy storage materials in the construction field. This paper starts with ela-borating on the traditional phase change materials and further reviews the heat transfer theory, incorporation technique, heat transfer and energy storage, and engineering applications of phase change materials commonly used in construction field, and looks forward to the problems, challenges, and future development direction of phase change materials research and application in this field.
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Ring Shear Characteristics Between Aeolian Sand-Loess Mixtures and Steel Interface
YAO Zhihua, ZHANG Jianhua, XIN Jianping, MU Rui
Materials Reports
2024,38(5 ):23070012 -8. DOI:10.11896/cldb.23070012
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The northern side of the Loess Plateau is bordered by many deserts, forming a widely distributed mixed distribution area of aeolian sand and loess. The aeolian sand-loess mixture (ASLM) presents different physical and mechanical characteristics under different proportion conditions, and the interfacial contact mechanical behavior of the ASLM foundation of ten occurs with other materials during field construction, and the relevant research is rarely mentioned at present. This work obtained the maximum dry density of the ASLM under different sand content conditions, prepared circular specimens of the ASLM with the same compaction degree and different sand content, and conducted ring shear tests on the interface between the ASLM and steel under different vertical pressures and shear velocities. The particle distribution properties and particle fragmentation characteristics of different sand content were observed using scanning electron microscopy, and the formation mechanism of resi-dual strength of ASLM with steel in ring shear condition was revealed. The test results show that the physical and mechanical characteristics of ASLM transition from loess to sandy soil with the increase of sand content. When the vertical pressure is less than 100 kPa, the probability of dilatancy of the mixture increases. There is a linear relationship between the interface residual strength and vertical pressure between the ASLM and the steel, which is consistent with the Mohr-Coulomb law. As the sand content increases, the crushing effect of aeolian sand particles increases, and the interfacial residual internal friction angle and the interfacial residual cohesion between the ASLM and steel decrease. An increase in shear rate shorten the contact time between the mixture and the steel interface, making it difficult to exert the contact and bite effects between the two, thereby reducing the residual strength of the interface between ASLM and steel. The research results predict the proportion of loess added to aeolian sand, which can provide useful reference for the treatment of aeolian sand foundation and also provide scientific reference for revealing the construction mechanics of ASLM.
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Retention Factor-based Stress-Strain Models of Austenitic Stainless-Steel Bolts at Elevated Temperatures
SUN Tao, WANG Hui, ZHANG Lei, LIU Xiaoying, ZHAO Honggang, JIANG Wei, CHENG Xinlei, HE Xiaoyong
Materials Reports
2024,38(5 ):23080049 -9. DOI:10.11896/cldb.23080049
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Stainless steel bolts are increasingly used in bolted semi-rigid connections due to their remarkable durability, ductility, and fire resistance. Stainless steel bolts, like their base material (stainless steel bars), exhibit smooth non-linear characteristics at both ambient and elevated temperatures, and they do not have a well-defined yield point in their stress-strain curves. This material behavior can be analytically represented by different material models, the most popular of which is based on the Ramberg-Osgood formulation or its extensions thereof. However, the available prediction formulas for the associated parameters in the material model of stainless steels are not necessarily applicable to austenitic and duplex stainless steel bolts subjected to work-hardening and cold-forging processes. Therefore, this paper proposes a nonlinear elevated tempe-rature constitutive model for stainless steel bolts based on their high-temperature reduction factors from previous studies. Supposing that five mechanical parameters (Young's modulus, proportional limit, yield strength, ultimate strength, and ultimate strain) are given at ambient temperature, and the reduction formulas derived for stainless steel bolts is used to obtain five mechanical parameters at a specified temperature and to evaluate the correlation of the tested stress-strain curve with the predicted one. This prediction methodology shows that the predicted curve is in clear agreement with the tested one, which is shown to be that the elevated temperature material model based on the reduction factor has consi-derable prediction accuracy. Thus, a stress-strain curve at a given temperature can be predicted based on five mechanical parameters at ambient temperature by combining the elevated temperature reduction equations for stainless steel bolts.
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Analysis of the Influence of Surface Core Debonding Defects on the Buckling Characteristics of Composite Cylindrical Shells
CHEN Yue, HUANG Jing, ZHU Zixu, LI Huadong
Materials Reports
2024,38(5 ):23070044 -6. DOI:10.11896/cldb.23070044
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Surface core debonding is a common damage type of composite sandwich structures. Considering the coupling effects of surface core interface damage evolution, layered buckling and layered extension, a method for predicting the ultimate bearing capacity of composite cylindrical shells under deep water static load was established. Based on the nonlinear ultimate load calculation method, the buckling characteristics of composite cylindrical shells with surface core disbonding defects were analyzed by prefabrication of initial defects, and the influence mechanism of typical surface core disbonding defects on the failure mode and bearing characteristics of composite cylindrical shells was revealed. The influence laws of different surface core disbonding types, disbonding sizes and disbonding positions were obtained. It is found that the failure mode of the structure evolves from global buckling to mixed buckling to local buckling with the increase of core disbonding length. The outer skin/core layer core stripping is more sensitive to the ultimate load bearing of the cylindrical shell with the core stripping of the annular through surface, and the inner skin/core layer interface stripping is more sensitive to the ultimate load bearing of the cylindrical shell with the core stripping of the longitudinal through surface. For multiple local circular core desticking, the more concentrated the longitudinal distribution and the more discrete the circumfe-rential distribution, the higher the structural ultimate load loss rate. The research results have a good guiding significance for the optimal design and reliability evaluation of cylindrical shells with surface core disbonding defects.
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Unconfined Compressive Strength Comparative Experimental Research of Sintered Snow with and Without Pressure
HUO Haifeng, YANG Yajing, SUN Tao, FAN Rong, CAI Jing, HU Biao
Materials Reports
2024,38(5 ):23060124 -6. DOI:10.11896/cldb.23060124
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Snow sintering is an important step in the construction of snow runways in high latitude cold regions around the world, which refers to the process of increasing strength of snow over time. In order to explore the strength change law of naturally deposited snow (sinter with pressure) and compacted snow layer (sinter without pressure), the sintered snow samples were studied by using self-developed pressurized equipment for unconfined compressive strength test. It was found that the unconfined compressive stress-strain curves presented both peak and no-peak strength forms, and the case with peak was more likely to occur under high pressure and long sintering time. The density of pressurized sintered snow samples grows with sintering time and shows the characteristics of fast and then slow, while the density of unpressurized sintering basically does not change. The strength and elastic modulus of pressurized sintered snow samples are greater than that of unpressurized sintering, and the growth rate of both are also greater than that of unpressurized. During the construction of snow runways, it is recommended to take 15 d as the design sintering time for compacted snow layers, and the unpressurized sintered snow strength slows down significantly after 15 d at sintering temperatures of around -10 ℃. The research results have excellent guidance for the determination of snow layer strength index and deformation index in the construction of snow runways.
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Research and Application Status of SiO
2
Nanoparticles in Lubrication Field
CHEN Jin, LI Mohan, RUAN Wenlin, SUN Tao, LIU Xiaoying
Materials Reports
2024,38(5 ):23080225 -9. DOI:10.11896/cldb.23080225
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In recent years, the maintenance or replacement of materials caused by friction loss has brought huge economic losses. In order to reduce the loss of materials as much as possible, the design and development of materials with self-lubricating function has become a research hotspot. Because of its small size and high surface activity, nanoparticles have exhibited excellent tribological properties, and have received extensive attention in tribology field. Among them, SiO
2
nanoparticles have excellent tribological properties due to their high hardness and sphericity. The application of SiO
2
nanoparticles in the field of self-lubrication can be divided into liquid lubrication and solid lubrication. The liquid field refers to that when SiO
2
nanoparticles are added to the liquid lubricant as an additive, the lubrication effect of the lubricant can be significantly enhanced. The solid field refers to the fact that the wear resistance of raw materials can be significantly enhanced when SiO
2
nanoparticles are compounded with other particles to make solid self-lubricating composites and further applied to paint/coating designs. Currently, most researchers mainly elaborate on one of the above two types of application fields, which makes readers lack a comprehensive understanding and thinking about the practical application of SiO
2
nanoparticles. Therefore, this review mainly introduces the lubrication mechanism and influencing factors of SiO
2
nanoparticles, and discusses the relevant research and application status of SiO
2
nanoparticles in the field of liquid lubrication and solid lubrication in detail, including the relevant surface treatment and modification means adopted in practical application. The role and great potential of SiO
2
nanoparticles in improving polymer matrix self-lubricating materials in solid self-lubricating composites were introduced. Finally, the application and development of SiO
2
nanoparticles in the field of self-lubrication are described and prospected.
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Cement-based Composite Materials for Infrared and Radar Wave Stealth
MA Chao, XIE Shuai, WANG Yongchao, JI Zhijiang, WU Zihao, WANG Jing
Materials Reports
2024,38(5 ):23080165 -9. DOI:10.11896/cldb.23080165
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Infrared and radar wave stealth primarily enhance the concealment of targets by reducing the signals of infrared radiation and radar echoes. A dual functional cement-based composite material that combines infrared and radar wave stealth was developed by encapsulating phase change materials (PCM) with carbon black (CB) as phase change units (PCU) and combining them withexpanded perlite-magnetic particle/cement composite materials. The electromagnetic wave (EMW) absorption and thermal properties of samples were tested and simulated. The experimental results indicate that CB has a minimal impact on the phase change temperature of PCMs, with only a 1.9% decrease in latent heat. After 500 cycles of heating and cooling, the PCMs retain approximately 78.3% of fusion latent heat, demonstrating good cycle stability. The PCU and expanded perlite can enhance the EMW absorbing performance of cement-based materials, with adjustable reflection loss ranging from -5 dB to -15 dB. The PCU reduces the external surface temperature of the sample by absorbing a significant amount of heat, thereby weakening infrared radiation. The addition of PCMs increases the thermal conductivity of cement-based composites. However, the high thermal storage density of PCU and low thermal conductivity of expanded perlite contribute to a more significant insulation effect in cement-based composites, resulting in a reduction of infrared radiation signal. The simulation results express that magnetic loss only occurs in the cement matrix, and the PCU affects the EMW absorbing performance of cement-based materials through resistance loss. The heat conduction is hindered at the PCU, causing the conduction heat flux to bend at the edge of the PCU. After the phase change is complete, the heat distribution tends to be uniform. Therefore, cement-based composite materials can achieve multi-band stealth in different complex environments, such as infrared and radar waves, by dissipating EMW and absorbing target heat, respectively, thereby reducing radar echo signals and infrared radiation.
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Research on the Application of a New Type of High Strength Steel Plate in Structures Resistance to Contact Explosion
FANG Xinyu, XU Gancheng, WEI Yingqi, LIU Yanquan, YUAN Weize, ZHOU Junpeng
Materials Reports
2024,38(5 ):23060206 -7. DOI:10.11896/cldb.23060206
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In order to study the enhancing effect of NFB700E1 high-strength steel plate on the anti-collapse performance of reinforced concrete structures, five sets of contact explosion tests on the composite structure were carried out(including a control group of Q345 ordinary steel plate), while an effective numerical simulation model was established based on the test results. Through lots of numerical simulation tests, the equivalent non-collapsing coefficient (ENC for short) of composite structures are calculated, by which the enhancement range of anti-collapsing steel plate is quantified. The results show that, in the anti-explosion tests, the equivalent diameter of blast pit, the depth of blast pit and the maximum deformation of anti-collapsing steel plate all grow up with the decrease of the thickness of reinforced concrete target plate. By comparing the depth of blast hole and the maximum deformation of steel plate in both simulation and tests, the finite element numerical simulation model was continuously iterative optimized. The ENC of compose structures and reinforced concrete were calculated. For the NFB700E1 steel plates of different thickness, the ENC were about 0.141(8 mm) and 0.159(6 mm), which were 70.3% and 66.5% higher than that of reinforced concrete (ENC=0.475), respectively. Compared to the Q345 ordinary steel plate (ENC=0.230), the increases were respectively 38.7% and 30.9%. The numerical simulation model established in this work can be extended to more working conditions and provide reference for the research of anti-collapse in other protection engineering.
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Enhancing the Wave Damping Performance of Structures Using Local Resonance Metaconcrete: a Review and Prospect
YAO Weilai, LIU Yuanxue, SUN Tao, ZHAO Honggang, MU Rui, LEI Yixin
Materials Reports
2024,38(5 ):23080236 -14. DOI:10.11896/cldb.23080236
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Metamaterials are man-made materials that are designed to have extraordinary physical properties not found in natural materials, not from the material components, but from specially designed artificial structures. Metamaterials originally originated in the field of electromagnetism. The materials are engineered to exhibit frequency forbidden bands (bandgaps), i.e., a spectral range within which electromagnetic wave transmissions are effectively suppressed. This ability to manipulate and handle electromagnetic waves facilitated the solution of various engineering problems and inspired its migration to other disciplines. Subsequently, acoustic metamaterials were proposed to similarly manipulate acoustic waves, enabling the silencing and insulation of sound. Similarly, mechanical metamaterials were also created, which utilizes bandgap properties to manipulate stress waves, achieving wave dissipation, filtering, and improving structural protection. Metaconcrete is a specific application of mechanical metamaterials in the field of civil engineering, which makes use of the local resonance behavior of artificial aggregates to generate a bandgap and realize the blocking of specific frequency stress waves. Metaconcrete from the wave manipulation point of view to achieve the protective performance, and the traditional protective materials through the strength, toughness to achieve the protective purpose are essentially different. To carry out research on metaconcrete to enhance the structural protective performance is of great significance. In this paper, the main research on metamaterial concrete has been systematically sorted out in the past ten years since it was proposed based on the perspective of engineering application. The practical verification of wave dissipation of metaconcrete, resonance aggregate bandgap characteristics and design guidelines, spatial distribution of resonance aggregate and admixture effect, energy transfer law under dynamic loading, and resonance aggregate modification are reviewed. The main conclusions of the current research are summarized, and the outlook of future research is put forward with close reference to the practical application of engineering.
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