High-strength, continuous and uniform filament winding patterns remain challenging to find for non-axisymmetric models under various loading conditions. In this study, various loading conditions are considered in the development of an algorithm for generating uniform winding patterns for axisymmetric and non-axisymmetric mandrel models with flexible rotation at the ends of the mandrel. First, the mandrel surface is divided into sections by uniform quadrilateral elements and the ideal winding angle at each boundary is calculated based on the stress field. Then, stability analysis is used to calculate suitable winding angles as close as possible to the ideal winding angle for each boundary. These suitable winding angles can be used to generate the uniform winding pattern maintaining non-slippage and non-bridging while realizing flexible rotation at both ends of the mandrel. Finally, uniform patterns for various mandrel models are generated based on their respective suitable winding angles. Stress analysis result demonstrates that the wound mandrel generated by the proposed method can have better carrying capacity.

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.

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 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.

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.