The integrated optimization of topology and fiber path in variable-stiffness composite laminates (VSCL) poses significant challenges due to the inherent strong non-convexity. To address these issues, this paper proposes a novel three-stage integrated optimization framework. In the first stage, lamination parameters are selected as the intermediate variables to overcome the local optima behaviors derived from directly optimizing fiber angles. The Kreisselmeier-Steinhauser (KS) function aggregation strategy is employed to efficiently handle the feasible domain constraints of the lamination parameters. The optimal lamination parameter distribution and topology shape are obtained simultaneously. The second stage aims to retrieve the fiber angles from the optimal lamination parameters. An inverse model based on least-squares error minimization is established, followed by the Improved Direct Simulated Annealing (IDSA) algorithm for parallel discrete fiber angle search. In the third stage, a continuous fiber angle correction model is established, with the discrete fiber angles obtained in the previous stage taken as the initial solution. The continuous fiber angle distribution matching the optimal topological configuration is obtained. Subsequently, a curved fiber path fitting method is introduced to transform the continuous fiber angles into manufacturable paths that are continuous, equally spaced, and free of intersecting. Numerical examples demonstrate that the proposed framework achieves high-performance design for VSCL, while ensuring good convergence and robust global optimization capability.
This study addresses machining challenges of T800-grade unidirectional CFRP laminates by optimizing the tool structure, the CVD diamond coating thickness, and the cutting parameters. An asymmetric four-tooth milling cutter with varying helix angles (5°–45°) and segmented edge lengths was proposed, and six tooth arrangements were evaluated by finite element simulation. The optimal sequence—alternating long/short left-handed segments with varied helix angles—achieved the best thermal-mechanical balance, with only 26.5% high-stress zones and a peak temperature of 277°C, whereas unbalanced designs caused stress concentration or overheating above 350°C. Cutting tests were then performed with the optimized tool under a full factorial design covering coating thicknesses of 5–20 μm, spindle speeds of 8000–12,000 rpm, and feed rates of 300–500 mm/min. Regarding the machining parameters, the 10–20 μm coatings maintained stable cutting forces over the spindle speed range, whereas the 5 μm coating exhibited a marked force escalation at high speeds due to thermal softening. In addition, the axial force of the 5 μm-coated tool decreased with increasing feed rate, which is attributed to a transition from fiber ploughing to direct shearing. Concerning the coating thickness, wear resistance was non-monotonic, peaking at 15 μm (2696 μm 2 worn area) and offering the best balance between protection and adhesion, while the 20 μm coating suffered from brittleness and chip adhesion that degraded the surface quality. Overall, the proposed tool combined with a 10–15 μm CVD diamond coating enables low-damage, high-quality milling of T800-grade CFRP laminates.
As a sealing technology for aero-engines, finger seals play a crucial role in improving engine thrust-to-weight ratio and reducing fuel consumption. Carbon fiber-reinforced carbon matrix (C/C) composites exhibit excellent self-lubricating and wear-resistant properties, which are well matched to the requirements and application environments of dynamic sealing technology, and can significantly extend the service life of finger seals. This study focused on the laser cutting process of C/C composite finger seals. A numerical simulation model of the laser cutting process was established using thermal-mechanical coupling simulation analysis. Through systematic simulation calculations, the influence patterns of laser processing power and feed speed on workpiece displacement and deformation were analyzed. Actual machining experiments were conducted using a continuous-fiber laser. All experiments adopted the identical laser system, where laser type, wavelength and beam quality remained constant throughout the tests. Combined with practical machining trials, core indicators including cut-surface morphology, multi-directional displacement-deformation, as well as stress-strain distributions were comprehensively investigated. The results show that processing power and feed speed are key parameters for controlling laser cutting quality. Reasonably reducing processing power can effectively suppress workpiece displacement and deformation, while increasing feed speed can narrow the thermal damage range in the cutting zone. The simulation results show good agreement with experimental measurements in terms of variation trends, verifying the rationality of the thermo-mechanical coupling model.
Tailored Antisymmetric Composite (TAC) laminates have recently emerged as a new laminate architecture capable of achieving near-orthotropic bending behavior while simultaneously eliminating the bending–twisting coupling terms D 16 and D 26 . Although these coupling terms are known to influence the mechanical response of anisotropic laminates, their effect on guided-wave propagation and Structural Health Monitoring (SHM) performance has not been isolated analytically. This work demonstrates that TAC laminates provide a fundamentally different wave-propagation behavior from conventional anisotropic laminates by suppressing the coupling-induced steering mechanism associated with non-zero D 16 and D 26 . A low-frequency guided-wave formulation is developed from laminated plate theory and explicit analytical expressions for the group-velocity direction are derived. The analysis reveals that the odd-order coupling terms D 16 and D 26 introduce propagation-direction asymmetries that distort energy transport and produce a deterministic coupling-induced source-localization bias in SHM systems. A stiffness-matched comparison is performed between a conventional quasi-isotropic laminate and a TAC laminate possessing closely matched principal bending stiffnesses. Two complementary angular metrics are used throughout. The coupling-induced steering component is isolated by comparing a laminate with an otherwise identical uncoupled reference in which only D 16 and D 26 are set to zero. Separately, the actual conventional–TAC propagation-direction difference compares the two physically realizable laminate architectures and therefore also contains the small residual effect of their non-identical orthotropic bending terms. For the baseline conventional laminate, the maximum coupling-induced component is approximately 4.10°, whereas the maximum absolute conventional–TAC difference is approximately 4.90°. An independent transient finite-element verification in Abaqus/Explicit using S4R composite shell elements assesses the latter physical laminate-pair difference at 40 kHz. The results establish that suppression of D 16 and D 26 not only simplifies the bending response of composite laminates but also reduces coupling-associated propagation asymmetry within the low-frequency flexural regime considered here. TAC laminates therefore provide a design pathway in which laminate architecture itself can improve wave-propagation fidelity while retaining tailored anisotropic stiffness characteristics. The finite-element results also delineate the limits of the Kirchhoff idealization and show that transverse-shear effects reduce the predicted steering amplitude without changing the principal angular trends.
In this study, a hybrid multilayer composite shielding material was developed, and the effects of material type, layer number, stacking sequence, and interfacial architecture on total shielding effectiveness (SET) were investigated. For this purpose, 20 preforms consisting of high-conductivity carbon woven fabrics (CF), polyester/viscose (PES/VIS) fabrics with Ag-coated PA conductive weft yarns, and dielectric Twaron (T) layers were fabricated using an epoxy matrix via the hand lay-up method. Among the samples, 4-layer structures (Samples 7 and 8) exhibited SE values of 46–79 dB, while 9-layer structures (Samples 19 and 20) showed stable performance of at least 53 dB across the X-band. Maximum SE values were obtained as 91.56 dB at 11.5 GHz and 91.03 dB at 9.02 GHz. Analyses revealed that 28–65% of incident electromagnetic energy was absorbed, 33–72% was reflected, and transmission was negligible. Positioning Twaron on the incident side resulted in a higher absorption coefficient, whereas a carbon-fronted configuration exhibited a higher reflection coefficient. Shielding performance is governed by a balance between reflection and absorption. The incident wave is partially reflected, while the remaining portion penetrates the structure and interacts with the conductive carbon layers and the Ag-grid PES/VIS layer. Dielectric and conduction-related losses, together with multiple internal reflections and interfacial interactions, may contribute to electromagnetic attenuation within the multilayer structure. Overall, composite thickness, material selection, stacking sequence, and structural design are important parameters influencing EMI shielding performance and the balance between absorption, reflection, and transmission.
