To address the problems of the difficult processing and internal microstructure disorder of porous bearing cages, Polyetheretherketone (PEEK) porous self-lubricating bearing cage material was ...prepared based on a fused deposition molding (FDM) process, and the porous samples were heat-treated on this basis, the research was carried out around the synergistic design of the material preparation, microstructure, and tribological properties. The results show that the pore size of the PEEK porous material prepared by the FDM process meets the requirements of the porous bearing cage; the samples with higher porosity also have higher oil content, and all the samples show high oil retention. Under dry friction conditions, the higher the porosity of the porous material, the larger the friction coefficient, and the friction coefficients of each sample after heat treatment show the same pattern; under starved lubrication conditions, the friction coefficient of the porous PEEK material decreased significantly compared to the compact PEEK material, showing a better self-lubrication effect, and the porous samples reached the best self-lubrication effect after heat treatment. The optimal process parameters were 60% mass fraction of NaCl, 40% mass fraction of PEEK, and the applied heat treatment process.
Carbon fiber warp yarns tend to hang due to the gravity in the multi-layer weaving process, which leads to chaotic shedding and impairs fabric quality. The hanging shape of carbon fiber warp yarns is ...mainly determined by the applied initial warp tension in the weaving process, and excessive warp tension increases the friction between the yarn and the heald frame, resulting in yarn wear. A yarn hanging model based on catenary theory was established to estimate the applied minimum initial warp tension that could ensure clear shedding in the multi-layer weaving process. The relationship between the warp hanging shape and various weaving process parameters (warp tension, yarn specifications and the size of shedding) was obtained. According to the weaving conditions, the applied initial yarn tension could be estimated using the model before manufacturing. Multi-layer yarn hanging experiments were conducted using different specification carbon fibers and yarn tension, and the theoretical predictions and experimental results were compared. The results showed that the yarn hanging model could well simulate the actual hanging characteristics of carbon fiber warp yarn under different tension. The research results provide a tool for estimating the applied initial warp tension in the multi-layer weaving process.
In the process of dynamic unbalance detection for precision cylindrical rollers, challenges such as difficulty in achieving effective driving and susceptibility to surface damage during driving ...significantly impact the accuracy of unbalance detection. This hinders the industry’s ability to achieve the non-destructive detection of cylindrical rollers. Therefore, this paper proposes a novel driving method to enable non-destructive driving of precision cylindrical rollers. The structural principles of the driving mechanism are presented, and a mechanical model for the cylindrical roller is established to analyze the force distribution. Subsequently, a mathematical model for the air film bearing the cylindrical roller is developed to study the variation characteristics of the air film’s load-bearing capacity. The optimal air film thickness is determined, and the rationality of the mathematical model is validated through simulation analysis. Finally, an experimental platform for non-destructive driving is constructed to further verify the effectiveness of the proposed method. This research provides a prerequisite for the non-destructive detection of dynamic unbalance in precision cylindrical rollers.
Abstract
The original configuration of 3D layer-to-layer angle-interlock (LLA) woven fibers cannot be maintained during matrix impregnation and is unstable when the composite is subjected to loading. ...The fibers in the yarn are susceptible to lateral sliding, resulting in deformation of the textile geometry. The initial modulus of the composite in the warp direction is smaller and can be inconsistent owing to the unstable geometry of the fabric. A stable 3D layer-to-layer angle-interlock (SLLA) fabric was devised by constructing a denser yarn arrangement, and the properties of this new structure were investigated in this study. The geometric parameters of this novel reinforcing structure were mathematically modeled, and the results were validated experimentally. The results showed that the SLLA structure was more stable than that of the LLA fabric. The experimentally determined structural parameters were in good agreement with the theoretically calculated values.
Braided tubular composites have been widely applied in various industries, such as aerospace, automobile, and sports, due to their light weight, high fatigue resistance, and good corrosion ...resistance. It is necessary to study the effect of the preform parameters on the thermodynamic behavior of braided tubular composites. A thermoelastic model of braided multi-layered tubes was developed to investigate the effect of changing the braiding angle on the thermal stress distribution. The thermal stress distributions of different structures were analyzed based on the model. The analysis results show that the layer-by-layer braiding angle critically affects the gradient of the axial thermal stress. The change rates of the braiding angle also significantly affect the gradient of the radial thermal stress. The theoretical results were verified by finite element analysis. These results are beneficial to the optimal design of braided composite tubes subjected to thermal load.
Abstract
Fiber-reinforced composites have been widely applied in aerospace, transportation and other industrial applications. An effective method shaping the complex performs is draping plain fabrics ...on the mandrel surface. However, it is a challenge to realize and predict accurately the deformation of fabric. To establish an accurate deformation mode, plain weave fabrics with low-twist yarn were classified into a stable structure that are not easy to deform and an unstable structures with large deformability based on microstructure characteristics. A variable microstructure unit-cell model has been established to analyze the variation of fabric geometry and performance during deformation. To analyze the draping behavior of fabric with large deformation, a four-node unit was used to mesh the fabric, and then each node on the fabric was mapped to the mandrel surface. The deformation of fabric after draping was simulated by the continuous change of the unit mesh. Analysis results showed that the thickness of preform decreases with the increase of the major-axis of the yarn cross-section, and the formability of fabric increases with the increase of fabric pitch. The accuracy and effectiveness of the geometric mapping method are verified by the fabric drape experiment.
To address the problems of the difficult processing and internal microstructure disorder of porous bearing cages, Polyetheretherketone (PEEK) porous self-lubricating bearing cage material was ...prepared based on a fused deposition molding (FDM) process, and the porous samples were heat-treated on this basis, the research was carried out around the synergistic design of the material preparation, microstructure, and tribological properties. The results show that the pore size of the PEEK porous material prepared by the FDM process meets the requirements of the porous bearing cage; the samples with higher porosity also have higher oil content, and all the samples show high oil retention. Under dry friction conditions, the higher the porosity of the porous material, the larger the friction coefficient, and the friction coefficients of each sample after heat treatment show the same pattern; under starved lubrication conditions, the friction coefficient of the porous PEEK material decreased significantly compared to the compact PEEK material, showing a better self-lubrication effect, and the porous samples reached the best self-lubrication effect after heat treatment. The optimal process parameters were 60% mass fraction of NaCl, 40% mass fraction of PEEK, and the applied heat treatment process.
In order to solve the design and regulation problems of graded porous scaffolds, the triply periodic minimal surface (TPMS) that based on implicit function was taken as the pore unit for constructing ...the porous scaffolds. And the TPMS structure was controlled by selecting different types of TPMS and defining the distance function. The transition of different structures of TPMS was performed by the weight fusion method. And the dual contouring (DC) algorithm and octree algorithm were used to divide the solid model of the defect bone into hexahedral elements to determine the target assembly spatial. Through the coordinate transformation of the isoparametric element method, the pore units were mapped into the hexahedral elements to construct porous structure. Finally, a Boolean operation was used to obtain a bone scaffold model with porous structure. The examples showed that the gradient model of various irregular pores could be constructed, and the pore size, porosity, and specific surface area of porous scaffolds could be controlled by adjusting the deformation, distribution, volume of the hexahedral elements, and the structure of the TPMS pore units, which provides a feasible method for the design and regulation of heterogeneous porous scaffolds.
To meet the self-lubricating performance requirements of aerospace bearing cages, poly-ether-ether-ketone (PEEK)-based self-lubricating bearing cage materials were prepared based on the Fused ...Deposition Molding (FDM) process. The mechanical and tribological properties under high temperature condition (200°C) of the porous self-lubricating materials were researched. The results of microstructure analysis of porous sample showed that under laboratory conditions, NaCl can exhibit excellent pore-forming effect and could be effectively removed. The mechanical test results showed that the mechanical properties of the samples showed a significant decrease with the increase in porosity, and were affected by the synergistic effect of pore creation. However, the mechanical properties of heat-treated samples can meet the performance requirements of the bearing cage. The results of the tribological performance tests under high temperature conditions showed that the wear process of the dense samples was more smoother. Further comparing with the tribological properties at room temperature, it was found that the wear resistance of PEEK samples decreased under high temperature conditions. The normalized results of the mechanical and tribological properties data show that the samples with 50 wt% of porogenic agent can express the most balanced and excellent overall performance.
