The component yarns and fabrics effected the formability and stability of preforms, and finally determined the performance of corresponding composites. In this research, four typical fabric structures of carbon fiber resin composites (CFRC) were introduced to conduct the comparative investigation. The stability of component yarns in natural state and in fabrics have been discussed at mesoscopic scale, and the main methods to improve the structural stability of preforms were proposed. Composites with and without stable-structural fibers and fabrics were manufactured by the modified curing process, and the yarn cross-sections in specimens were analyzed. The tensile and bending performance of these composite specimens was comparatively conducted to discuss the influence of stable preforms on the elastic properties. The fracture mode and mechanism of specimens were illustrated in meso-scale. The results depicted that yarns and fabrics with stable-structural cross-section could ensure a high fiber volume fraction, reducing the curvature of load-bearing yarns, and effectively reduce the yarn curvature along bearing direction. The high interfacial bonding strength of composites with stable geometrical fabrics exhibited the excellent in-plane mechanical properties, and presented the obvious brittle fracture characteristics when the fibers fully exert their load-bearing capacity.

Three-dimensional woven composites (3DWCs) have received widespread attention due to their advantages, such as integral near-net molding of complex components and high damage tolerance. However, 3DWCs exhibit significant variations in mechanical behavior under various influencing factors, which poses challenges in selecting appropriate application scenarios. In recent years, there has been rapid development in the performance analysis and modeling strategies for 3DWCs, leading to substantial results. This paper provides a comprehensive overview of the mechanical properties and damage mechanisms of 3DWCs under various influencing factors, aiming to facilitate the selection of 3DWCs for different engineering applications and to complement the existing database of mechanical properties.

The geometry of yarns effect the structural stability of 3D woven preform, which influence the mechanical properties of carbon fiber/epoxy composites. To investigate the effect of stable-structural preform on the elastic properties of 3D woven composites, the factors that caused the unstable structure of preform were discussed, and comparative study was conducted. The geometric models of yarn cross-section and preform were established to discuss the stability. The results showed that increasing the opening angle of warp yarns and the elongation of yarn outer contour can improve the stability of preform. The tensile and bending tests of 3DLAC and 3DBAC with stable and unstable structural preform were conducted. The results showed that the tensile and flexural elastic moduli were inversely proportional to the curvature of load-bearing yarns, and the elastic modulus of composites with stable-structural preform can increase by 9%–13%. The redistribution of internal stress in composites was macroscopically manifested as stable changes in experimental process. 3D woven composites with stable-structural preform showed the regular fracture cross-section, and fiber fracture and interface adhesion effect were the main failure mode in tensile tests, and fiber fracture on the compression surface and matrix cracking were the main failure modes in bending tests.

The minimum zone fitting and error evaluation for the arc-modified convex contour of a bearing roller have important applications for consistency detection and quantificational research of the elastohydrodynamic lubrication of a bearing roller. Based on the definition of the shape error and the geometric characteristics of the arc corrected roller convexity line of the bearing, a new fitting and error evaluation method for the total convexity contour of a bearing roller is presented. First, the reference cutoff points of the arc segment and straight line are determined based on the curvature difference of each measurement point. Then, the measuring points on both sides of the two reference cutoff points are selected as auxiliary cutoff points for arc fitting. The fitting error is obtained based on the minimum area method. Finally, a series of tangent equations are obtained based on the tangent principle between a line and two arcs, and the straightness error is determined by calculating the distances between the measuring points and the tangents. The example results show that an arc-modified convex contour can be fitted, and its global error can be evaluated effectively and precisely using the presented method. This study also provides a new idea for the minimum zone fitting of multi-segment curves along a plane.

Obtaining a uniform and continuous winding pattern for non-axisymmetric mandrel using current filament winding techniques is still a challenge. In this study, an algorithm was developed to generate winding pattern for axisymmetric and non-axisymmetric mandrels. Firstly, the mandrel surface is divided into uniform quadrilaterals, and the centerline of the mandrel is extracted according to the vertices of the quadrilaterals. Then, based on the centerline, the mandrel is divided into multiple intervals. Combined with the stability analysis of the winding path on the triangular facets, a series of non-slippage winding paths are generated within the intervals. Finally, the non-slippage winding paths are adaptively adjusted, and a uniform winding pattern is generated for the mandrel through iteration. The simulation results demonstrate that the generated paths pass through uniform points on the same cross-section, ensuring the uniformity of the winding pattern. The winding paths realize free rotation at the ends of the mandrel, ensuring the continuity of the winding pattern. And the proposed method can be applied to various types of non-axisymmetric mandrels, overcoming the limitation of previous methods which can only generate winding patterns when the mandrel surface is represented by mathematical equations.

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.

Interfacial bonding strength between the substrate and its coating is one of the important indexes affecting the service life of parts. To reduce the manufacturing cost, a mathematical model can be established to quantitatively describe the microscopic surface roughness and its anti-corrosion coating adhesion strength. Anti-corrosion life could be improved by controlling the surface roughness of the substrate. In this study, a model of interfacial bond strength and roughness, which was calibrated using the substrate surface and closely related to the cell spacing and length of the support, was established. Under the same condition as the coating, component materials and the coating thickness, results were obtained that the coating strength changed along with the substrate roughness. When roughness changed between 37.1 μm and 48.4 μm, the bonding strength showed a decreasing trend. The larger the value of the roughness, the more conducive it was to the bonding between the arc spraying layer and the substrate. The adhesion between the coating and substrate was not always increased with the higher roughness on the same surface. It should be evaluated based on the surface roughness and its evaluation parameters, and there was an optimal roughness evaluation and selection range. The experimental results were consistent with the theoretical predictions.

Truss-like lightweight materials (TLLMs) with superior mechanical performance and excellent energy absorption capability are extensively used in aerospace and automobile industries. The performance of TLLM was closely related to its meso-structure, but the lack of innovation and variety in the geometric configuration of TLLM’s meso-structure limits the reinforcement effect and strength enhancement. Hence, it is important to thoroughly study the theoretical design method for TLLM’s meso-structure. Inspired by the symmetric feature of TLLM’s meso-structures, the symmetric groups were applied to describe, classify and design TLLM’s meso-structures. First of all, it was found that the representative volume unit (RVU) of TLLM corresponded to point groups that contained the symmetry of TLLM’s meso-structure. Space groups, which consist of point groups and space lattices, could be used to describe the geometric configuration of TLLM’s meso-structures. Then, TLLM’s meso-structures were classified according to different types of point groups. Finally, a description and design method for TLLM’s meso-structure based on the symmetric group theory was proposed. In addition, a novel TLLM’s meso-structure was deduced through the symmetric operations of space group, which could verify the feasibility of the method. Therefore, the present study provides a basis for the design of high-performance TLLMs.

Truss-like lightweight materials (TLMs) have been widely used in aeronautics and astronautics, because of excellent mechanical property and superior energy absorption capability. The design of TLMs’ meso-structures was a critical task to improve its performance. Hence, a structure design method based on the symmetric groups was proposed for TLMs, and a novel hexagonal prism TLM’s meso-structure was deduced by the symmetric and translational operations of the space group P 6 mm . To investigate the performance of the novel TLM, the mechanical analysis model was established. The predictive equations of compression performance was proposed based on Euler–Bernoulli beam theory. The stress distribution of the novel TLM’s meso-structure under compression load was discussed by the finite element analysis method, and its compression and energy absorption properties were investigated. The simulation results were in agreement with the predictive results. In addition, the common FCC and BCC TLMs were discussed using the symmetry group analysis method, and their compression properties were predicted. The results showed that the proposed novel TLM in this study had better compression property than BCC and FCC TLMs at the same relative density.

Three-dimensional bidirectional angle-interlock woven (3DBAW) composites exhibit the orthogonal high modulus, which has the potential to be used in load-bearing components. 3DBAW preforms prepared using the certain and uncertain cross-sectional yarns exhibit various structural characteristics, and the mechanical properties of composites show the high variation. To investigate the effect of fabric structural stability on the elastic properties of 3DBAW composites and broaden its application, contrast analysis of quasi-static tensile properties of composite specimens was proposed, and the failure mechanism was analysed. The results showed that the high tensile initial elastic modulus of 3DBAW composites was attributed to the low curvature of load-bearing yarns. For composites with stable fabrics, the tensile process was smooth and steady owing to the uniform fiber spacing, and the tensile elastic modulus and strength show the smaller coefficient of variation. The tensile crack surfaces of composites with stable structural fabrics were regular, and making the full use of the load-bearing yarns. 3DBAW preforms with stable structure can effectively reduce the fluctuation of changes at the initial stage of loading, and the translaminar fracture and adhesive matrix failure are the main failure modes without the obvious interlaminar fracture. The results provided the support for the application of 3DBAW composite in load-bearing components.

The adhesion of wear-resistant diamond coating deposited on titanium was weakened by the porous titanium carbide interlayer, which was formed before film growth. In order to enhance substrate-coating adherence, a new pretreatment method was presented: Ti substrates were carbonized by hot filament chemical vapor deposition system, and then the carbonized substrates were ultrasonically vibrated using diamond micro-powder suspension. Diamond coatings were deposited by hot filament chemical vapor deposition as well. The effect of carbonization time on adhesion was investigated. The carbonized substrates and the interface between diamond coatings and substrates were characterized. The results showed that as the carbonization time increases, porous structures and cracks appear and increase on the surface of the substrate. The carbonized substrates possess high surface energy and thus the nucleation is promoted. After deposition, a dense and thin titanium carbide was observed. Ultrasonic after carbonization pretreatment can significantly enhance the adhesion of Ti-based diamond coatings by promoting nucleation and suppressing the formation of porous titanium carbide.

The unstable meso-structure of preform affects the mechanical properties of 3D angle-interlock woven composites, which restricts the application in load-bearing component. To enhance the elastic properties of composites, the modified curing processes were proposed to improve the structural stability of preform. Two typical methods of the modified curing processes were described in this research, and three typical composite samples were manufactured. The influence of different curing processes on meso-structural characteristic and mechanical properties of composites was investigated. Then, the quasi-static tensile and three-point bending tests were carried out, and the load–deflection curves and stress–strain curves were obtained. The failure modes and damage mechanisms of three typical composite samples were analyzed. The results showed that the modified curing process improved the structural consistency of preform, and the straightness of load-bearing yarns increased. The elastic modulus of samples was increased by about 20

Carbon fiber/epoxy woven composites with stable structural reinforcements exhibit a better static mechanical property than composites with unstable reinforcements. The stable structural reinforcements show a limited deformation during the curing process. To investigate the influence of reinforcements on the tension-tension fatigue properties of composites, three typical composite samples were manufactured and experiment research was developed. The results show that the composites with stable structural reinforcements prove excellent fatigue behavior, and the initial elastic modulus can be enhanced. The curvature of load-bearing yarns affected the loading capacity, and the low curvature improve the structural integrity. The unstable structural reinforcements lead to the "fatigue strengthening" after a limited number of cycles, owing to the straightening of load-bearing yarns. Reducing the curvature of yarns can effectively decrease the occurrence of initial cracks by altering the structural characteristics of reinforcements, which strengthens the bonding to improve fatigue resistance.

Multilayer cBN/NCD (cubic boron nitride and nano-crystalline diamond) composite coating with modulation periods of 1 mu m, 1.5 mu m and 3 mu m were deposited by anode layer linear ion source assisted radio frequency magnetron sputtering (ALLIS-RFMS) and microwave plasma chemical vapor deposition(MPCVD) on cemented tungsten tools (YG6) and Si substrates. The microstructures, mechanical and tribological properties of the multilayer composite coating were systematically characterized and investigated. In this work, with a decrease of modulation periods, the surface roughness of cBN/NCD multilayer composite coatings exhibited an increasing trend, but the mechanical properties were improved significantly. When the modulation period decreases to 1 mu m, the residual stress of the composite coating can be reduced to -0.61 GPa, fracture toughness increased to 4.81 MPa center dot m(1/2). Friction and wear tests demonstrated that the wear resistance of the multilayer cBN/NCD composite coating was related to the residual stress and fracture toughness, the friction coefficient keep a stable values about 0.12-0.15, the wear rate decreased significantly with decreasing modulation period, and the lowest wear rate was about 3.69 x 10(-6) mm(3)/(N center dot m) when the modulation period is 1 mu m. The work suggests that decreasing the modulation period is an effective way to improve the mechanical and tribological properties of multilayer cBN/NCD composite coating.

As a kind of sliding bearing, the gas bearing is widely used in high-speed rotating machinery. It realizes energy cleaning in the field of high-speed rotating machinery. In order to solve the problem of reducing the service life of gas bearings due to friction during startup and shutdown, we use micromachining technology to process groove textures with different groove widths on the surface of 0Cr17Ni7Al, a common material for gas bearings. A ball–disc friction contrast test is conducted under dry friction conditions with and without texture. The experiment shows that the lowest average friction coefficient of 0.8 mm texture is σ = 0.745. When the friction radius is 22.5 mm, the wear rate of 1.0 mm texture is the lowest at ω = 3.118 × 10−4mm3/N·mm. However, the maximum friction coefficient reached is σ = 0.898. Under the nanometer scale, the contact between friction pairs is fully analyzed. The influence mechanism of different groove widths, friction impacts and climbing heights on the friction and wear properties of the micromechanical groove texture on the surface of 0Cr17Ni7Al stainless steel is studied at the nano-fractal scale. The effects of different width grooves on the surface texture and tribological properties of the micromachine are studied.

Abstract Truss-like lightweight materials (TLMs) are a type of porous materials which have been widely used in aeronautics and astronautics because of excellent mechanical property and superior energy absorption capability, and these properties could be influenced by its meso-structure. Therefore, the meso-structure design is a critical task to develop high-performance TLMs. A novel meso-structure of TLM was deduced based on the symmetric operations of the space group P6mm. The mechanical model of the novel TLM was established to theoretically investigate its compression property, and it was found that the relative density and compression property of the novel TLM could be increased with the diameter-to-length ratio (d/l) and inclination angle (α) of strut. The equivalent elastic modulus, yield load and yield stress of the novel TLM could be predicted by theoretical analysis and verified by finite element analysis. The simulation results showed that the novel TLMs with varied relative densities have different loading capacity but the same failure mode. The compression and energy absorption properties of the novel TLM could be improved by increasing the structural relative density. In addition, this study indicated the novel TLM has better compression and energy absorption properties at the same relative density compared with other TLMs such as BCC and FCC, and its equivalent elastic modulus at the same relative density increased by 324.3% and 15.5%, respectively.

Yarn pre-tension is an important technological parameter in the weaving process and significantly affects the geometry and properties of woven composites. 3D bi-directional angle-interlock (3DBA) fabrics have the same yarn crimp in the warp and weft directions, which requires a special matching relationship between the warp and weft yarn tensions applied in the weaving process. This study focused on obtaining the pre-tension matching relationship that applied between the warp and weft yarns in the weaving of 3DBA fabrics. A quasi-static mechanical model of yarn interactions in the weaving of 3DBA fabrics was developed based on the 2D woven fabric yarn interaction model. The weaving process of 3DBA fabrics could be divided into two interweaves as one cycle. In a given interweaving of a single group of yarns, the pre-tension applied to the warp yarns tends to increase irregularly with the position of the interweaving point and varies linearly with the weft pre-tension. The weft crimps distribution of 3DBA fabrics was compared when yarns were applied to the different proportions of pre-tension in the weaving process. The experiment result shows that the sample with the best uniform distribution of yarn geometry is the one to which the yarn pre-tension calculated by the model is applied in the weaving process. The result provides theoretical support for warp and weft pre-tension applied in the 3DBA fabrics weaving process.

3D woven fiber/epoxy composites as structural components have attracted great attention in the industrial and civil fields due to high resistance to debonding or delamination. Structural components are often subjected to the conditions of cyclic loading, which detrimentally affect the service-life and damage tolerance. In this research, the fatigue properties of 3D woven fiber/epoxy structural composites were discussed, where 3D woven fabrics were embedded in epoxy matrix to enhance their mechanical properties. 3D woven fabrics were classified by the geometrical structures of repeat vertical and inclined units. Based on the testing method, the fatigue properties of corresponding composites have been reviewed. The influence of the internal and external parameters on the fatigue properties were investigated by using various observation methods, and the failure modes were also analyzed. The theorical prediction models were reviewed according to testing method, and future trends and challenges were discussed. The critical review can provide valuable ideas and guidance for future fatigue studies in 3D woven composites.

The application of carbon fiber/epoxy composites places more requirements on the selection of fabrics to meet the needs of structural components. Due to the large design space for reinforced fabric patterns, the relationship between the reinforcements and properties is essential to further understand. Four typical fabrics were manufactured in this research, named non-interlaced bidirectional fabrics, plain weave laminated fabrics, angle-interlock fabrics and bidirectional angle-interlock fabrics. The structural features of fabrics were analyzed by using representative geometric unit, and the symmetry properties were discussed based on group theory. Vacuum assistant resin transfer molding was adopted to obtain the corresponding resin matrix composite specimens. Quasi-static tensile and bending tests were conducted on these specimens. The stress-strain curves of specimens were illustrated, and the failure characterizations were also analyzed in mesoscopic scale. The results showed that the high crimp of yarns reduced the stability of composites. Both the tensile and flexural properties were affected by the curvature of yarns. The research results provided a theoretical basis for the selection of fabric structure and the application of carbon fiber/epoxy composites.

The application of three-dimensional angle-interlock woven composites (3DAC) as structure components in aerospace field creates tremendous demands for mechanical properties. A new kind of 3DAC with bidirectional fabric structure was proposed in this paper. The tensile properties of 3DAC and 3D bidirectional angle-interlock composites (3DBAC) were conducted by quasi-static tensile tests. According to three-point bending method, the flexural properties of 3DAC and 3DBAC were experimentally tested. The load–displacement curves of specimens showed that 3DBAC presented the better stability due to the higher noncrimp rate. The stress–strain curves indicated that the tensile modulus of elasticity in 3DBAC was larger than 3DAC, and the flexural modulus of 3DBAC gained an advantage over 3DAC. Based on the mesostructure of fabrics, the failure characterizations of specimens were analyzed. Results showed that the yarns in 3DBAC bear the maximum load, and the tensile fracture was regular. Through the analysis of crack morphologies, it is found that 3DBAC exhibits better flexural properties. The results supply the theoretical support for the manufacturing of structural components in the field of lightweight design.