Xin Yan

Carbon nanotube (CNT) reinforced aluminum composites (CNT/Al composites) are renowned for their remarkably low density and high strength. However, the underlying physical mechanisms by which intergranular and intragranular CNTs reinforce the aluminum matrix remain barely explored, primarily due to challenges in direct experimental observation. In this study, using molecular dynamics simulations, we systematically investigate the mechanical behavior of CNT/Al composites, with emphasis on distinguishing the reinforcement roles of intragranular and intergranular CNTs, as well as their sensitivity to other effects, like CNT size. Our results demonstrate that the composite reinforced with intragranular CNT exhibited higher peak stress than the one reinforced with intergranular CNT, which can be attributed to the structurally weaker effect of overlapped grain boundary and embedded CNT in the intergranular model. Increasing CNT size modifies the peak stress through coupled size and volume-fraction effects but does not alter the distinct failure sequences of the intragranular and intergranular configurations. These findings clarify the physical origins of CNT strengthening in aluminum composites and provide guidance for optimizing the microstructure and processing, thereby supporting the development of predictive continuum models.

High-quality manufacturing of fiber-reinforced composites via Automated Fiber Placement (AFP) critically depends on layup-feasible path planning. Traditional projection-iteration methods on precise Computer-Aided Design (CAD) models employ a fixed step size, suffering from cumulative projection errors and limited control over geodesic curvature. To overcome these limitations, this paper presents an adaptive step-size projection-iteration method for generating geodesic paths. The method centers on developing a dynamic step-size control criterion derived from local differential geometry, which adjusts the iteration step length in real-time based on surface normal variation and an explicit upper bound on permissible geodesic curvature. The step size is reduced in high-curvature regions to bound projection errors and increased in flatter regions to improve efficiency. Subsequently, an iteratively adjusted geodesic offset strategy generates a complete set of coverage paths while maintaining a constant geodesic distance between adjacent courses to avoid gaps and overlaps. Numerical experiments on a bend plate and a turbofan fan blade validate the method's effectiveness. Sensitivity studies across four tow widths and four layup angles further confirm its robustness in maintaining spacing accuracy and curvature constraints under varying process settings. Results demonstrate that the proposed method achieves computational efficiency comparable to fixed-step methods while significantly enhancing geodesic curvature control and offset spacing uniformity, facilitating the transition from high-fidelity CAD design to high-quality composite manufacturing in AFP.

High-quality manufacturing of fiber-reinforced composites via Automated Fiber Placement (AFP) critically depends on layup-feasible path planning. Traditional projection-iteration methods on precise Computer-Aided Design (CAD) models, employ a fixed step size, suffering from cumulative projection errors and limited control over the geodesic curvature. To overcome these limitations, this paper presents an adaptive step-size projection-iteration method for generating geodesic paths. The method centers on developing a dynamic step-size control criterion derived from local differential geometry. This criterion continuously adjusts the iteration step length in real-time based on the local surface normal variation and an explicit upper bound for the permissible geodesic curvature. The step size is reduced in high-curvature regions to bound the projection error, and increased in flatter regions to improve computational efficiency, thereby maintaining geometric feasibility while optimizing the trade-off between path accuracy and computational cost. Subsequently, an iteratively adjusted geodesic offset strategy is applied on the high-precision baseline path to generate a complete set of coverage paths, maintaining a constant geodesic distance between adjacent courses to avoid gaps and overlaps. To validate the proposed method, numerical experiments are conducted on representative models, including a bend plate and a complex free-form surface. The results demonstrate that the proposed method achieves computational efficiency comparable to fixed-step centerline projection methods while significantly enhancing geodesic curvature control. It also maintains comparable performance in offset spacing uniformity, with outliers lying closer to the theoretical value, facilitating the transition from high-fidelity CAD design to high-quality composite manufacturing in AFP.

Carbon nanotube (CNT) reinforced aluminum composites (CNT/Al composites) are renowned for their remarkably low density and high strength. However, the underlying physical mechanisms by which intergranular and intragranular CNTs reinforce the aluminum matrix remain barely explored, primarily due to challenges in direct experimental observation. In this study, using molecular dynamics (MD) simulations, we systematically investigate the mechanical behavior of CNT/Al composites, with emphasis on distinguishing the reinforcement roles of intragranular and intergranular CNTs, as well as their sensitivity to other effects, like CNT size. Our results demonstrate that the composite reinforced with intragranular CNT exhibited higher peak stress than the one reinforced with intergranular CNT, which can be attributed to the structurally weaker effect of overlapped grain boundary (GB) and embedded CNT in the intergranular model. Additionally, the CNT size modulates the peak stress of the composite but not the loading bearing mechanism. These findings clarify the physical origins of CNT strengthening in aluminum composites and provide guidance for optimizing the microstructure and processing, thereby supporting the development of predictive continuum models.

Molecular-level liquid bridges at contact interfaces have a much more important impact on micro-/nanosystems and flexible wearable sensors. However, their dynamic behavior and mechanical properties are still vague due to the limitations of current characterization methods. Here, under the support of molecular dynamic simulations on smooth, pillared, and concave pillared plates, the heterogeneous anisotropic pressure distribution of layered liquids is found to be distinct from the isotropic pressure distribution in the macroscale liquid bridge. Oscillating interfacial contact forces appear in the period of layered liquid compression due to the oscillating system free energy, in which the peak forces greatly increase as the number of layers decreases. The layered liquids with impressively remarkable solid-like pressure-bearing capacity at the gigapascal level and exceptional fluidity along confined atomic layers can spontaneously strengthen adhesion vertically and facilitate pressure transport horizontally, respectively. The significance of layered liquids in contact systems can improve our understanding of liquid bridges at the molecular level, which is beneficial for interfacial mechanical regulation.

The combination of continuous fiber-reinforced thermoplastic composites (CFRTPCs) and the continuous fiber 3D printing (CF3DP) technique enables the rapid production of complex structural composites. In these 3D-printed composites, stress transfer primarily relies on the fiber-resin interface, making it a critical performance factor. The interfacial properties are significantly influenced by the temperatures applied during the loading and forming processes. While the effect of the loading temperature has been extensively researched, that of the forming temperature remains largely unexplored, especially from an atomistic perspective. Our research aims to employ molecular dynamics simulations to elucidate the effect of temperature on the interfacial properties of continuous carbon fiber-reinforced polyamide 6 (C/PA6) composites fabricated using the CF3DP technique, considering both loading and forming aspects. Through molecular dynamics simulations, we uncovered a positive correlation between the interfacial strength and forming temperature. Moreover, an increased forming temperature induced a notable shift in the failure mode of C/PA6 under uniaxial tensile loading. Furthermore, it was observed that increasing loading temperatures led to the deterioration of the mechanical properties of PA6, resulting in a gradual transition of the primary failure mode from adhesive failure to cohesive failure. This shift in the failure mode is closely associated with the glass transition of PA6.