Compaction Stage Research Articles

Investigation of the bedding effect on coal rock under Brazilian splitting tests

This contribution focuses on understanding the bedding effect of coal rocks under the Brazilian splitting test. First, multiple Brazilian splitting tests were performed on coal rocks with various bedding angles to systematically investigate the influence of stratification. Subsequently, numerical models with stratified structures were constructed, and a continuous–discontinuous numerical analysis method based on the cohesive zone model (CZM) was employed to conduct the corresponding numerical investigations. Results indicate that the load–displacement curves of coal rock specimens with different bedding angles can be classified into four stages: initial compaction stage, elastic deformation stage, crack rapid coalescence stage, and final destruction stage. With increase in the bedding angle, the failure patterns of coal rock specimens can be categorized into three groups: 1) stretching damage along bedding planes; 2) mixed tension and shear failure along the bedding planes and the coal matrix; and 3) stretching failure passing through the coal matrix. Furthermore, the tensile strength and cumulative acoustic emission (AE) energy–displacement relations are significantly influenced by the bedding angle. The numerical model can effectively predict the mechanical responses and fracture behavior of coal rock specimens, providing empirical parameters for the simulation of similar rock engineering.

Model for fracture conductivity considering particle size redistribution caused by proppant crushing

Clarifying the dynamic evolution and control mechanisms of fracture conductivity is crucial for optimizing hydraulic fracturing design. Previous studies on fracture conductivity mechanisms in deep shale reservoirs have been insufficient, particularly when considering proppant crushing, rendering existing models inapplicable. Therefore, in this study, the coupled effects of particle size redistribution caused by proppant crushing were considered. A particle crushing model based on fractal theory was introduced. It was combined with the Kozeny–Carman equation, and equations were derived for the evolution of the equivalent diameter of the proppant pile gradation curve and permeability, establishing a new model for predicting the fracture conductivity considering the particle size redistribution caused by proppant crushing. Furthermore, it provides an optimized chart of conductivity that matches the supply conductivity of the reservoir. The results of the study reveal that the fracture conductivity decreases owing to proppant rearrangement, compaction, and crushing, with a more significant decline in the initial compression stage, where the rate of conductivity reduction is 2.5 times that of the compaction stage. Proppant crushing shifts the gradation curve leftward, reducing the equivalent particle diameter and, consequently, the fracture conductivity. By adjusting the crushing ratio, apparent Young's modulus, looseness factor, and proportion of large-particle components of the proppant, the fracture conductivity can be controlled. This provides a theoretical basis for the development of proppant properties and fracturing optimization in deep shale reservoirs.

In situ observation of the multistep process of cold sintering

AbstractA compact cold sintering stage was constructed to densify ceramic samples in capillary tubes for the purpose of conducting in situ experiments designed to elucidate fundamental cold sintering mechanisms. The stage was used to successfully densify samples composed of ZnO/CH₃COOH mixtures under a range of pressures (25–175 MPa) over a modest temperature range (room to 150°C) in capillary tubes (0.75 mm inner diameter). The progression of the cold sintering process of ZnO was monitored by both piston displacement and a camera. These measurements allowed the strain rate and fluid extraction during densification to be recorded. The results of these measurements are compared to existing models of cold sintering and pressure solution creep, and direct correlations are observed between abrupt changes to the densification rate during constant heating rate experiments and the observation of solvent extraction from the powder compact.

Study on the influence of aggregate on rheological properties of recycled aggregate asphalt mixture using microstructural quantification

Recycled aggregate (RA) is generated through the crushing process of Construction and Demolition Waste (CDW). Although there has been extensive research on the mechanical properties of recycled aggregate asphalt mixture (RAAM), the impact of recycled aggregate (RA) on its rheological characteristics remains underexplored. This paper aims to assess the rheological properties of recycled aggregate asphalt mixture (RAAM) during the processes of mixing and compaction. Firstly, different percentages of recycled aggregate (RA) were utilized in the design of the recycled aggregate asphalt mixture (RAAM), and rheological behaviors of RAAM during the mixing and compaction stage were characterized by mixing torque and compaction energy, respectively. Then, high-precision three-dimensional models of RA were reconstructed utilizing CT images, and four indices were established to quantitatively assess the macro shape and micro-morphology of RA particles, utilizing the spatial model data for precise measurements. Finally, a correlation was found between rheological properties of RAAM and RA morphology through a comprehensive analysis of laboratory test results and spatial model indicators. Results show that aggregate particles’ microstructural morphology significantly influences asphalt mixture’s rheological behavior during mixing and compaction. Additionally, the 3D spherical degree and Needle-flake index performed more significant correlations with mixing and compaction than the 3D angular index and 3D texture index. As opposed to natural aggregate, RA exhibits more intricate morphological characteristics stemming from its porous cement mortar composition. Increasing the RA content causes more energy consumption and increases the thickness of asphalt mortar film during the compaction process. In general, methods established in this study offer an efficient mean of quantifying the morphological characteristics of aggregate particles, thereby enabling the assessment of the impact of RA on the rheological properties of asphalt mixtures.

Effect of Brick Aggregate Content on Performance of Recycled Construction-Solid-Waste Aggregate.

In road engineering, road construction requires a large amount of natural aggregate; its substitution with recycled construction-solid-waste aggregate not only saves resources but also reduces the burden on the environment. The main components of construction solid waste are concrete blocks and brick slag; the breakability of the latter can affect the performance of mixed recycled aggregate, which hinders the use of construction solid waste in road engineering applications. To analyze the applicability of recycled construction-solid-waste aggregate containing brick slag aggregate in the subgrade layer, the effect of brick aggregate content on the CBR (California bearing ratio) and crushing value of mixed recycled aggregates was evaluated based on laboratory tests, and the field compaction quality of the recycled aggregates was analyzed. The results show that the 9.5-19 mm mixed recycled aggregate samples were crushed to a higher degree during the compaction process. A brick aggregate content less than 40% had little effect on the performance of mixed recycled construction-solid-waste aggregate. It is recommended to use a 22 t road roller for five passes (two weak vibrations + two strong vibrations + one weak vibration) at a speed of 3 km/h in the main compaction stage of the subgrade filling.

Study on triaxial compression performance and damage characteristics of fiber-reinforced ecological matrix cementing gangue gypsum fill material.

Polypropylene fiber was equally mixed into alkali-activated slag fly ash geopolymer in order to ensure the filling effect of mine goaf and improve the stability of cemented gangue paste filling material with ecological matrix. Triaxial compression tests were then conducted under various conditions. The mechanical properties and damage characteristics of composite paste filling materials are studied, and the damage evolution model of paste filling materials under triaxial compression is established, based on the deviatoric stress-strain curve generated by the progressive failure behavior of samples. Internal physical and chemical mechanisms of the evolution of structure and characteristics are elucidated and comprehended via the use of SEM-EDS and XRD micro-techniques. The results show that the fiber can effectively improve the ultimate strength and the corresponding effective stress strength index of the sample within the scope of the experimental study. The best strengthening effect is achieved when the amount of NaOH is 3% of the mass of the solid material, the amount of fiber is 5‰ of the mass of the solid material, and the length of the fiber is about 12 mm. The action mode of the fiber in the sample is mainly divided into single-grip anchoring and three-dimensional mesh traction. As the crack initiates and develops, connection occurs in the matrix, where the fiber has an obvious interference and retardation effect on the crack propagation, thereby transforming the brittle failure into a ductile failure and consequently improving the fracture properties of the ecological cementitious coal gangue matrix. The theoretical damage evolution model of a segmented filling body is constructed by taking the initial compaction stage end point as the critical point, and the curve of the damage evolution model of the specimen under different conditions is obtained. The theoretical model is verified by the results from the triaxial compression test. We concluded that the experimental curve is in good agreement with the theoretical curve. Therefore, the established theoretical model has a certain reference value for the analysis and evaluation of the mechanical properties of paste filling materials. The research results can improve the utilization rate of solid waste resources.

Angle between DNA linker and nucleosome core particle regulates array compaction revealed by individual-particle cryo-electron tomography

The conformational dynamics of nucleosome arrays generate a diverse spectrum of microscopic states, posing challenges to their structural determination. Leveraging cryogenic electron tomography (cryo-ET), we determine the three-dimensional (3D) structures of individual mononucleosomes and arrays comprising di-, tri-, and tetranucleosomes. By slowing the rate of condensation through a reduction in ionic strength, we probe the intra-array structural transitions that precede inter-array interactions and liquid droplet formation. Under these conditions, the arrays exhibite irregular zig-zag conformations with loose packing. Increasing the ionic strength promoted intra-array compaction, yet we do not observe the previously reported regular 30-nanometer fibers. Interestingly, the presence of H1 do not induce array compaction; instead, one-third of the arrays display nucleosomes invaded by foreign DNA, suggesting an alternative role for H1 in chromatin network construction. We also find that the crucial parameter determining the structure adopted by chromatin arrays is the angle between the entry and exit of the DNA and the corresponding tangents to the nucleosomal disc. Our results provide insights into the initial stages of intra-array compaction, a critical precursor to condensation in the regulation of chromatin organization.

Deterioration micro-mechanism of graded aggregates with different gradations under vibratory compaction using X-CT testing

This study aims to explore the compaction deterioration micro-mechanism of high-speed railway graded aggregate (HRGA) fillers and further improve the compaction quality of HRGA fillers, contributing to improving subgrade service performance. Firstly, based on the vibratory compaction experiments, the compaction deterioration macro-characteristics of HRGA fillers with different gradations were revealed from the mechanical properties (i.e., dynamic stiffness Kd and subgrade reaction modulus K20). Secondly, X-ray Computed Tomography (X-CT) testing was conducted based on the multiple typical compaction stages selected from the Kd curve. The internal microstructure (i.e., particles and voids) characteristics within HRGA fillers with different gradations were measured by high-precision image processing approaches. Finally, the evolution characteristics of Kd, K20, and microstructure were used to reveal the compaction deterioration micro-mechanism of HRGA fillers with different gradations, and further explore the relationship between filler gradation and compaction deterioration. The results indicated that compaction deterioration characteristics of HRGA fillers with different gradations could be characterized by the inflection points of Kd and K20 curves. Besides, during compaction deterioration, particle abrasion crushing and the increase in surface edges and corners of the void reduced the stability of the skeleton structure within HRGA fillers with different gradations, resulting in a gradual decrease of Kd and K20. Furthermore, the relationship between Kd, K20, and microstructure with gradation could be quantitatively characterized by quadratic functions. Hence, based on X-CT measurement, it was feasible to reveal the compaction deterioration mechanism of HRGA fillers from macro- and micro-perspectives. This study contributes to establishing a theoretical framework for revealing the compaction deterioration of high-speed railway subgrade fillers and improving the quality of vibratory compaction for on-site subgrade construction.

Compressive properties and energy absorption of selective laser melting formed Ti-6Al-4V porous radial gradient scaffold

Uniform porous structures are widely considered as the biological implant materials, but they are difficult to meet the needs of complex bone transplantation. The radial gradient porous structure can match the mechanical properties of different levels of natural femur by adjusting the internal and external porosity. Based on Gyroid unit cells, a parameterized model was employed to create a biomimetic bone structure. Uniform porous structure with an average porosity of 50% and radial gradient porous structure were prepared by selective laser melting (SLM).The mechanical properties, deformation behavior and energy absorption properties of uniform and radially graded porous structures were studied by compression test and finite element method (FE).The results show that the compression test curves of all porous structure exhibit elastic stage, platform stage and densification stage. In the platform stage, uniform porous structures are prone to early shear failure and poor energy absorption performance, whereas radially gradient porous structures exhibit higher elastic modulus and yield strength. When the strain is 0.3, uniform porous structures and porous structures with an inner porosity of 80% mainly exhibit 45° flexural-shear failures, while radially gradient porous structures with inner porosity of 62.5% and 70% experience V-shaped shear failures. Porous structures with an inner porosity of 70% have good energy absorption (107.99 MJ/m3), maximum energy absorption efficiency (46.94%), elastic modulus (5.2 GPa), and yield strength (296.02 MPa), matching the demands of cortical bone.

Study on Permeability Evolution Law of Rock Mass under Mining Stress

In order to study the stress–strain–permeability coefficient relationship of overlying strata in a fractured zone after coal mining, taking the Changcun coal mine in the Changzhi basin as an example, the permeability evolution law of coarse sandstone, fine sandstone, siltstone and mudstone during a stress–strain process was analyzed through a triaxial compression permeability test. The generalized model of the rock mass permeability evolution process under mining stress was summarized, and then a coupling model of the stress–water pressure–permeability coefficient of fractured rock was established based on the continuum model of rock mass. The results showed that the maximum permeability coefficient of different coal overburden types was quite different, and the peak strength of the rock mass preceded the maximum permeability coefficient during the rock mass failure process; the permeability coefficient first decreased and then increased, reaching its maximum value after the peak stress, which occurred during the strain-softening stage; the generalized model of rock mass permeability included the compaction stage, elasticity stage, stable fracture stage, unstable fracture stage, macroscopic failure stage and residual strength stage.

Study on rock energy evolution and constitutive model under water–rock interaction

To explore the degradation in rock mechanical properties due to water–rock interactions and formulate a nonlinear damage constitutive model for the entire stress–strain curve of rocks, experiments involving saturated, dry-wet cycling, and uniaxial compression tests were conducted on granite and siltstone. Based on energy theory, the energy evolution of the rock throughout the testing process was scrutinized. The range of the compaction stage was identified through the analysis of the dissipation energy change curve. A nonlinear damage constitutive model for rocks subjected to water-rock interactions was then devised, drawing on concepts from statistical damage mechanics. The findings indicated a progressive reduction in uniaxial compressive strength and elastic modulus due to water–rock interactions, while the Poisson’s ratio was observed to increase. The energy density curve under these conditions delineated four distinct phases: compaction energy dissipation, linear energy accumulation, pre-peak gradient increase, and post-peak sudden change. The introduction of the unit elastic strain energy density metric underscored the deteriorating effects from an energy standpoint. A nonlinear damage constitutive model, incorporating the compaction stage based on a coupled damage variable, was formulated. The predictions of this model closely matched the empirical data, thereby affirming its validity. This model provides an enhanced depiction of rock deformation and failure mechanisms under the influence of water–rock interactions.

Macro-meso properties and damage constitutive model of sandstone under chemical and freeze-thaw environments

The coupled effect of chemical corrosion and freeze-thaw cycle degrades the physical and mechanical properties of rock, affecting the safety and durability of underground rock mass engineering. This study investigated the deterioration laws of sandstone under pH = 1 and 3 chemical and freeze-thaw cycle action for different time considering macro and meso scales. The stress-strain curve of sandstone under uniaxial compression can be divided into compaction, elastic deformation, yield, and post-peak stages. The compaction of sandstone after chemical and freeze-thaw cycle action became apparent, elastic stage was relatively shortened, elastic modulus and peak strength decreased, and peak strain increased. The density and homogeneity of sandstone declined as per the CT scan and image processing technologies. The deterioration was prominent with longer action time and smaller pH value of the solution. After 120 days of pH = 1 and 3 chemical and freeze-thaw cycle action, the peak stress of samples decreased by 22.10% and 15.16%, the elastic modulus declined by 89.57% and 85.09%, the peak strain increased by 96% and 62%, and the damage variables reached 3.27% and 1.83%. The damage constitutive model of sandstone was established using statistical damage theories. The theoretical stress-strain curves were consistent with experimental ones. The insights of this research have implications for the theoretical foundation of safety assessments and disaster prevention in practical engineering scenarios under chemical and freeze-thaw environments.

The Practice of Adoption in the Sasak Community and Its Implications for Marriage Law in Indonesia

Adopting a child is a tradition that has long been practiced by Arab society and continues to this day. The practice of adopting children when Islam came was then perfected by the Prophet Muhammad PBUH, so that it has a basis in Islamic law. This study explores adoption practices in contemporary Sasak society and their implications for reformulating Islamic Marriage Law. This research uses a normative juridical approach analyzed with the theory of maqāṣid al-sharī'ah. The data analyzed are laws, legal regulations and decisions of religious courts on the island of Lombok, West Nusa Tenggara regarding child adoption cases and norms regarding child protection as normative legal material. These data sources are collected through documentation techniques and analysed using data compaction, display, and conclusion-drawing stages, employing analogical and teleological legal interpretation approaches. The study identifies three classifications of adopted children based on marital status and the presence of biological parents: legitimate children, illegitimate children, and children with unclear status. The research upholds the Islamic legal principle that adoption does not sever the child's lineage from their biological parents, even if their existence is unknown, and does not establish a lineage between the adopted child and their adoptive parents. The study has three implications for Islamic marriage law in Indonesia: including adoption provisions in the Marriage Law, eliminating the article that allows polygamy as a solution for childless couples, and adding requirements for marriages involving "unclear children" as authentic evidence to prove no blood relation between the prospective bride and groom, thus preventing invalid marriages.

Study on time–frequency features of induced charge signals during the damage and failure process of coal medium

Monitoring and preventing coal-rock dynamic disasters are vital for safe mining. To investigate the time–frequency features of induced charge signals with coal damage and failure of roadways, the generation mechanism of free charge in loaded coal is analyzed and the induced charge monitoring test is conducted. According to the stress-induced charge-time curves, the time-domain features of charge signals at each loading stage are obtained. The wavelet threshold denoising approach and generalized Morse wavelet transform method are applied to denoise the raw signals and study the frequency-domain features. Further, the quantitative relationship between the de-noised induced charge signals and the degree of coal damage is established. The results show that the event number, amplitude and fluctuation degree of available induced charge signals are all at a low level in the compaction and elastic stages of the coal, which are mainly generated by the piezoelectric effect and predominantly represent discreteness. When entering the plastic and failure stages, the available signals are primarily produced by the crack propagation and triboelectric effects, with a significant increase in the event number, amplitude, and fluctuation degree. Then the induced charge signals gradually transit from discrete to continuous. Generally, the dominant frequency of the available induced charge signals during the coal damage process is concentrated at 0 ~ 11 Hz. The available induced charge is positively correlated with the degree of coal damage, which can perform the damage degree of coal mass, providing a new approach to evaluate the stability of roadway surrounding rocks.

Survival and Development of in Vivo Produced Boran and Boran* Holstein Cross Embryos

One of biotechnology technique that is frequently used to enhance the number of animals with superior genetic ability and high productivity is embryo transfer. Embryos can be obtained in vivo or in vitro, and they can be frozen and then thawed before being delivered to the recipient animals. Conception rates are influenced by a number of variables, including the quality and developmental stage of the embryo, the location of the embryo's deposit in the uterus, the degree of difficulty of the transfer, whether to use a fresh or frozen embryo, the operator's experience, the corpus luteum's quality, whether to use a heifer or a cow, and the time of year the transfer occurs. The fertility of domestic animals is severely impacted by early embryonic death. For this reason, this study was carried out to gather data on early embryonic development that is normal, the amount and timing of embryonic mortality, potential endogenous and exogenous causes of embryonic loss, and to develop strategies to lower embryonic mortality. A total of 40 embryos (20 fresh and 20 frozen, 26 quality grade 1 and 14 quality grade 2, 29 compact Morula stage and 11 early Blastocyst stage) were transferred to 40 recipient cows (22 Boran and 18 H-B cross) with different body condition score. Return to heat was used as method of pregnancy diagnosis and all recipients were followed around day 14 post embryo transfer and 14 animals were shown heat sign, the rest 26 animals were suspected for pregnancy (65%). Using ultrasound, a pregnancy diagnosis was made on day 45, and 20 recipient animals were found to be 50% positive for PD. On day 60, PD positive animals were re-examined with ultrasound and only 10 were confirmed as PD positive (25%). The PD negative on day 45 and day 60 were suspected to be early embryonic mortality. Other pregnancy loss occurred in this study was abortion nearly after five month of pregnancy. It is not doubtful that, the technique of embryo transfer is utilized to increase the reproductive rates of important female animals. However, it needs proper management for both donor and recipient animals. Therefore, for the successful application of the technology optimum level of feeding both quantity and quality, health management and conducive environment should be fulfilled for all animals.

Experimental study on mechanical properties and microscopic mechanisms of layered sandstone after high temperature water cooling

During underground resource extraction and deep underground engineering development, the engineering rock body frequently encounters elevated temperatures and water cooling, leading to alterations in the mechanical properties of the rock. These changes will have an impact on the safety and stability of the project. This study aimed to investigate the changes in mechanical properties of rocks following treatment with high temperatures and water cooling. The experiment involved subjecting layered sandstone samples to heating and water cooling, followed by conducting uniaxial compression tests using a high-temperature furnace and a WA-1000 universal testing machine. The effects of temperature and inclination angles on the uniaxial mechanical properties of layered sandstone were then analyzed. Furthermore, the utilization of the scanning electron microscope and various other microscopic testing devices allowed for the examination of the micro-mechanism behind rock damage and rupture subsequent to undergoing heating and water-cooling treatment. The findings from the experiment suggest that: 1) the relationship between the changes in sandstones’ mechanical properties and temperature and bedding inclinations can be attributed to the uneven deformation of minerals caused by heating and water-cooling treatment, leading to the distribution of microcracks within the rock. 2) The stress-strain curve of the specimen can be divided as four-stages. With the increase of bedding inclination, the compaction stage of the specimen is more prominent. 3) As the bedding inclination increases, the specimens exhibit a pattern of initially decreasing and then increasing in terms of peak strength and strain. With the increase of temperature, the peak axial strain gradually increases, while it first increases and then decreases with the increasing dip angles.

Research on the Coupled Dynamic Response of Vibratory Roller-Unsaturated Subgrade under Different Compaction and Moisture Content States

The dynamic response between the vibratory roller and subgrade under vibratory compaction is essential to improve the compaction quality and optimize the construction technology. Considering the nonlinear hysteresis characteristics of the subgrade in vibratory compaction, a two-degree-of-freedom viscoelastic-plastic, vibratory roller-unsaturated subgrade coupling model, is established to evaluate the effect of compaction stage and moisture content on the vibratory roller-unsaturated subgrade coupling dynamic response. The dynamic resilient modulus semi-empirical model is established based on the dynamic resilient modulus experiment by considering the matrix suction of the unsaturated subgrade and it is the basis of the vibratory roller-unsaturated subgrade coupling model to consider the moisture content influence of compaction. In addition, a plasticity index was proposed to divide the selection of coupling models to consider the influence of compaction stages. The results show that the semi-empirical model takes into account the effect of moisture content by soil–water characteristic curve and it performs well in responding to the experiment results and other experimental data in the published literature. Based on this, the vibratory roller-unsaturated subgrade coupling dynamic response varied for different compaction stages and the moisture content of the unsaturated subgrade. The compaction quality gradually improved as the increase of compaction passes and the decrease of the moisture content. However, the compaction quality of the unsaturated subgrade is weakened by over compaction and excessive moisture content and should balance the compaction operation and quality assurance of the unsaturated subgrade. The results of the research will indicate the compaction mechanism of unsaturated subgrade and provide a theoretical basis for the development of intelligent compaction technology.

Parametric design and performance evaluation of gyroid triply periodic minimal surface preparation by LCD photopolymerization

In this paper, the Gyroid triply periodic minimal surface is prepared by liquid crystal display photopolymerization technology, and 10 models of the periodic parameter T in [1/5, 2] are designed. Using the method of finite element method and experimental verification, when T = 1/3, there are fewer stress concentration areas on the Gyroid surface, the number of grids is moderate, the compression crush rate is the smallest, and the porosity error is reasonable. Through the microscopic morphology, it is found that the surface, after printing, forms gear shape and resin residue so that the actual volume is larger than the theoretical volume, and the porosity is minor. Keeping periodic parameter T = 1/3 and porosity of 50%, four kinds of Gyroid surface structures were designed by changing the parameter surface offset, wall thickness, offset thickness, and gradient arrangement. The effects of different loading directions on its mechanical properties, deformation behavior, and energy absorption were discussed through compression experiments. The results show that the vertical load is applied to form a fault zone from the upper left angle to the lower right angle of 45°, and the parallel load is applied to create a fault zone from the upper right angle to the lower left grade of 45°. When the load is used in the vertical direction, the energy absorption and energy efficiency of the surface offset Gyroid surface are the largest. When the load is applied in the parallel order, the energy absorption curves of the four structures change similarly, and the deformation amplitude of the wall thickness Gyroid surface during the compression process is relatively stable. The energy efficiency of gradient arrangement Gyroid surface increases fastest in the compaction stage.

Role of mixed entropy in sintering of manganite-based perovskite oxides: Faster densification with delayed grain growth

High entropy perovskite oxides (HEPOs) have garnered significant attention due to their superior performance compared to conventional perovskite oxides. However, there is a limited understanding of the sintering behavior of HEPOs. This study aims to obtain a mechanistic understanding of how the sintering of the manganite-based perovskite oxides varies with the mixed entropy. Based on systematic sintering experiments, detailed microstructural characterization, and molecular dynamics simulations, we found that the densification process of manganite-based perovskite oxides with increasing mixed entropies follows a similar pattern to conventional perovskite oxides. The mixed entropy significantly influences the final and middle stages of densification but has negligible effects in the initial stage. More importantly, the densification becomes easier and faster with the increased mixed entropy, while the grain growth is delayed to the higher relative density and the corresponding activation energy for grain growth is also significantly enhanced. Consequently, this creates a more ideal situation for achieving denser materials with smaller grain sizes during sintering, shedding light on rational optimization of the sintering and resulting properties of high entropy perovskite oxide.

Hot Powder Bed Compaction: A Rapid Fabrication Approach for Thermoplastic Composite Components

Traditionally thermoplastic composite prepreg fabrication methods often rely on molds or costly tooling, limiting the agility and efficiency of the fabrication process. A compelling need for a high-performance thermoplastic composite prepreg fabrication approach that eliminates the dependence on molds, simplifies the fabrication process and accelerates prototyping, enabling rapid iterations in product development. The proposed hot powder bed compaction (HPBC) technique eliminates the need for specialized molds and still provides fully consolidated components. The HPBC process involved a three-step sequence comprising powder densification, heating, and consolidation stages. These stages help effectively control time–temperature-pressure parameters to achieve good fusion between the prepreg sheets. This paper showcased the HPBC process on a hinge bracket made from glass fiber-reinforced nylon prepreg sheets to illustrate its performance. Experimental mechanical characterization was carried out on treated HPBC coupons and compared with the molding process. Notably, the experimental flexural test results indicated a flexural modulus of 13.79 GPa and flexural strength of 295 MPa for HPBC-treated specimens, placing them in a comparable range with molded components. Microscopy analysis revealed the complete fusion interface of the prepreg sheets, and DSC analysis shows increases in crystalline fraction from 31.5 % to 44.1 % in PA6. Hence, the HPBC process presents a versatile and effective approach for fabricating high-performance, complex-shaped, void-free, components using thermoplastic composite prepreg.