Variable stiffness composite shafts (VSCS) exhibit significant application potential in highperformance rotor systems due to their tailorable spatial stiffness adjustment ability. Nonclassical features, such as the non-homogeneity in stiffness and damping, the Coriolis effect, and both centrifugal softening and stiffening effects, pose significant challenges for accurate modeling using classical one-dimensional theories. This study develops a quasi-3D semi-analytical model based on the Carrera unified formulation (CUF) and the modified Fourier spectral method (MFSM). Through higher-order sectional expansion functions, the model precisely captures sectional warping and in-plane distortions under high-speed rotation, while integrating the Kelvin-Voigt model to characterize anisotropic internal damping. To ensure versatility across diverse constraint scenarios, the penalty method is utilized to formulate unified variational governing equations by parameterizing generalized boundary conditions. The proposed model is validated against ANSYS simulations and classical literature, demonstrating high computational efficiency and fidelity for both constant and variable stiffness configurations. Parametric studies are then implemented to investigate the influences of fiber paths, rotational speeds, and dimensions on the 3D dynamic response and stability thresholds of VSCS.

Conventional truss lattices (e.g. Face-Centered Cubic unit cell with Z-struts (FCCZ) face inherent trade-offs between load capacity and energy absorption due to stress concentration and abrupt buckling. To address this, we designed an octagonal prism truss-like lightweight structure (TLS) with eightfold rotational symmetry using space group 8 mm operations. Through finite element analysis and experiments on AlSi10Mg specimens, we investigated the effect of Z-strut length (15-65 mm) on compressive performance under volume-normalized conditions. Increasing base polygon edges from 4 to 8 reduced nodal stress concentration by similar to 19.3% and mitigated buckling mismatch. An optimal Z-strut length range was identified, balancing axial capacity and stability. Compared to FCCZ, TLS exhibited significantly higher specific strength and energy absorption under both equal-diameter and equal-material conditions, with a 2.1% higher load capacity than ISO structures-offering a robust inverse design paradigm for lightweight lattice structures.

Nonuniform deformation of the preform in complex components can lead to variations in the mechanical properties of composite materials, thereby reducing their strength and stiffness and potentially inducing localized failure, especially under complex loading conditions. To investigate the effects of structural parameters on the bending formability of 3D angle-interlock woven preforms (3DAWPs), a variable microelement method was adopted. Based on the analysis of the deformation mechanism, a progressive-curvature bending model was established using the representative volume element (RVE). The geometric characteristics after deformation and the distribution of fiber volume fraction (FVF) within the preform were predicted. The results show that the warp inclination angle is positively correlated with the cross-sectional deformation coefficients of warp and weft yarns. The RVE length and fiber volume fraction are positively correlated with the weft deformation coefficient but show an opposite trend for the warp deformation coefficient. The fiber volume fraction increases from the outer layer to the inner layer, with a maximum difference of about 9% forming a clear hierarchical distribution. At forming angles of 45 degrees, 60 degrees, 90 degrees, and 120 degrees, the thickness difference between the outermost and innermost unit cells accounts for about 22%, 16%, 11%, and 7% of the initial thickness, respectively, and the deviation of the fitted thickness curves gradually decreases. Bending forming experiments were conducted on 3DAWPs, and the experimental results validated the theoretical analysis and the proposed model. This research provides theoretical support for enhancing the reliability and durability of composite materials in complex components.

Radial fiber gradient design offers significant potential for optimizing high-performance composite shafts under geometric constraints. This study develops a 3D analytical model based on Lekhnitskii's anisotropic elasticity theory and the Mori-Tanaka homogenization method to investigate the mechanical response of gradient fiber-reinforced composite shafts (GFRCSs) under combined bending and torsional loading. The results indicate that the functionally graded V-type (FGV) pattern maximizes the stiffness of GFRCSs compared to the uniform distribution, sustaining a persistent 14% bending stiffness gain even in thin-walled configurations. The strength advantage of the FGV design relative to the uniform benchmark exhibits significant sensitivity to the bending-to-torsion load ratio. Although the FGV pattern enhances localized material strength, the induced stress attraction effect may cause the rate of stress accumulation to outpace strength increments. This mechanism triggers failure boundaries prematurely under combined loading and leads to an inversion of strength benefits when the bending-to-torsion load ratio exceeds the critical threshold. The established critical load ratios and failure moment maps delineate the strength-advantaged regimes and load-bearing capacity of the gradient design, providing theoretical guidance and quantitative evidence for the preliminary design of high-performance gradient shafts.

The strength ratio of composite pressure vessels is a critical measure of their structural performance and reliability, both of which are highly dependent on the effective allocation of design parameters. In this study, a three-dimensional elasticity-based theoretical model is developed for composite cylinders subjected to uniform internal pressure. An improved Gaussian quantum-behaved particle swarm optimization-differential evolution (GQPSO-DE) algorithm is employed to simultaneously optimize the winding angle and ply thickness. By maximizing the strength ratio of the weakest ply, the overall structural strength and load-carrying capacity of the vessel are significantly improved. Two representative composite cylinders with different radial ratios are subsequently investigated, and the corresponding optimal combinations of winding angle and ply thickness are obtained. The results demonstrate that the proposed method is effective in enhancing the strength ratio of the weakest ply.

Tractor-trailers are commonly used to load large cargoes onto roll-on and roll-off (Ro-Ro) ships. To safely load cargoes to the target position on the deck, the path of tractor-trailer needs to be designed for avoiding collision with obstacles. During the loading process, tractor-trailer has to through the inclined ramp which connects the horizontal dock with deck, and the path must be designed in three-dimensional (3D) space. Based on the dynamic relationship between tractor and trailer, the collision free path generation for tractor-trailer on two-dimensional (2D) plane could be realized. However, the proposed methods cannot appropriate for analyzing the motion of tractor-trailer in 3D space. This research investigated a method to generate the safest loading path of tractor-trailer in 3D space. First, the loading scenario was divided into seven sections and all the possible tractor paths were generated based on the Bezier curves. Next, the conversion of tractor-trailer dynamic relationship between 2D plane and 3D space was realized by using geodesic theory, and the trailer paths were calculated according to tractor paths. Then, all paths are sorted based on transportation efficiency and safety during the transportation process. Finally, collision detection is carried out on the generated paths in sequence to determine the safest loading path for the tractor-trailer. Simulation and experimental results verified that the proposed method could be used to design the loading path of tractor-trailer in 3D space under multiple scenarios.

In this study, nonlinear Lamb wave-based higher harmonic detection is employed to assess the tensile-induced microdamage in patch-repaired carbon fiber-reinforced polymer (CFRP) structures. With respect to the external repair design optimization model based on proxy technology, the minimum nonlinear coefficients are obtained from the optimal patch design parameters, thereby improving the tensile performance of the repaired structure and capturing the repair effect of the patch. First, the nonlinear Lamb wave propagation behaviors of patch-repaired CFRP laminates are assessed under different tensile displacements, and the accuracy of the finite-element model strategy is confirmed by experimental results. Second, on the basis of the tensile displacement induced under the highest nonlinear response, the effects of the radius, thickness and rotation angle of the patch on the secondary and tertiary nonlinear coefficients of the composite glued repair structure and the tensile damage area of the matrix are discussed. After the effects of individual parameters on the patch repair structure are analyzed, the effect of multiple target parameters on the quadratic relative acoustic nonlinearity coefficient of the patch repair structure is investigated via a Latin hypercube experimental design and the Diffuse Approximation method, and the optimal solutions for the mesh parameters of the patch repair structure are successfully obtained, which provides a reference for the multiparameter optimization of patch repair structures in engineering cases.

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.

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 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.

Spot welding is widely used for the lightweight and rigid bonding of metal parts. To plan the spot welding, the welding engineer should check the posture of a welding gun to ensure that it does not collide with the welding objects and fixtures. Although commercial programs can check the posture range of a welding gun, it requires a long calculation time, infeasible for industrial applications with hundreds or thousands of welding points. This study proposed a method for automatically calculating the weldable posture range for given welding points. The proposed method detects the possible collision areas between the welding objects and the welding gun in advance by the octree method, drastically reducing the calculation time. It used the central processing unit (CPU) parallel processing to calculate the exact weldable posture to shorten the calculation time further. The proposed method uses the stereolithography (STL) model as input for versatility for welding objects and guns. It also developed several algorithms to overcome the limited information available with the format. As a result, the program could calculate the weldable posture range within 4 s per single welding point with a one-degree resolution. The proposed method is intended for spot welding but may be utilized for other welding applications.

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.

As a connecting component of tubes, the elbow is indispensable to pipe-fitting in composite products. Previous studies have addressed methods for generating winding paths based on parametric equations on the elbow. However, these methods are unsuitable for elbows whose surfaces are difficult to describe using mathematical expressions. In this study, a geometric method was proposed for generating winding patterns for various elbow types. With this method, the mandrel surface is first converted into uniform and high-quality quadrilateral elements; an algorithm is then provided for calculating the minimum winding angle for bridging-free. Next, an angle for non-bridging was defined as the design-winding angle to generate the uniform and slippage-free basic winding paths on the quadrilateral elements in non-geodesic directions. Finally, after a series of uniform points were calculated on the selected vertical edge according to the elbow type, the pattern paths were generated with the uniform points and basic paths. The proposed method is advantageously not limited to the elbow’s shape.