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.
In order to seek a lattice structure with better mechanical properties, a reverse Kagome lattice unit cell model is proposed based on the point group theory, and it is contrastively analyzed with the ...kagome unit cell model in the mechanical properties. The stress and strain theory is used to determine the key parameter of the reverse Kagome unit cell, which is the range of the inclination angle ω on the constraint condition of realizing the compression performance, shearing property and reaching the relative density and bearing capacity of the reverse Kagome. Combined with the finite element analyze results, it can determine the value of ω of this model under the best mechanical performance. An experiment of the reverse Kagome lattice model is performed to verify the correctness of the theoretical analysis. The research shows that when the tilt angle ω is 52°, the reverse Kagome lattice structure has the best compression resistance, and when the tilt angle ω is 38°, the shear performance of this structure is
In order to explore the influence of different TPMS pore structures on the mechanical properties of the porous scaffold, TPMS expressed by implicit function was used as the basic pore unit to ...construct the micro-porous structure. TPMS porous scaffolds with different structural characteristics were constructed by defining the distance function, And AlSi10 Mg porous scaffolds were prepared by SLM. Finite element Method（FEM） analysis and mechanical test method were used to study the influence of different pore structure characteristics on mechanical performance of porous TPMS scaffolds and analyze the influence law of different distance function k values on porosity, elastic modulus, yield strength and failure of Primitive（P） and F-RD porous structure scaffolds. Finite element analysis and experimental results show that with the increase of distance function k, the elastic modulus and yield strength of the P unit porous scaffold presented an increasing trend, However, the elastic modulus and yield strength of th
In order to meet the condition of high precision,efficiency and speed of modern NC machine tools and to improve the static,dynamic performance as well as lightweight design of their basic ...components,the design of bed saddle which is the key components of ADGM numerical control machine tool was optimized based on topology optimization method. Firstly,according to variable density method,which makes bed saddle quality be objective function and allows stiffness as well as natural frequency to be constraint condition was established,then the best structure layout of bed saddle was acquired as a result of topology optimization.Finally,the integral design of the bed saddle was accomplished,with the basis of best structure layout of bed saddle and the requirements of the reasonable design. Compared with the original design,new design reduces 13% of bed saddle’s weight,and the maximal displacement decreases 6%. Also,the first order natural frequency increases 8%,while the second order natural frequency increases 7%,a
