Applied Composite Materials最新文献

Understanding the magnetic induction intensity distribution of current-carrying carbon fiber composites is of great significance for structural health monitoring. Here we report analytical and numerical modeling on magnetic induction intensity of carbon fiber plain woven laminates. The influences of current magnitude and current injection modes on the magnetic induction distribution have been obtained from modeling and verified with the tests. We found there is a linear relationship between magnetic induction intensity and current in the low-current range, while the magnetic induction intensity exhibited significant anisotropy under different current injection modes. The magnetic induction intensity changes with the current injection directions and composite structures, i.e., the electric conductive networks. It is believed that the correlation between the microscopic structure and the magnetic induction intensity could be used for non-contact structure health monitoring.

This study explores the impact of hybridization on the mechanical behaviour of carbon and flax fibre-reinforced epoxy laminates exposed to fire, aiming to enhance sustainability in aerospace applications while addressing flammability challenges. Hybridization combines flax’s environmental benefits and ductility with carbon’s strength and thermal stability. Objectives include evaluating pyrolysis effects from brief kerosene flame exposure (60 s under 116 kW/m², ~ 1100 °C) on carbon/epoxy (C/E), flax/epoxy (F/E), and hybrid carbon/flax/epoxy (C/F/E) laminates, and assessing residual flexural properties. Laminates were fabricated via compression moulding with Araldite LY 156 epoxy, 240 g/m² flax fabric, and 189 g/m² carbon twill, in six lay-ups and material configurations: [0_8C], [45_8C], [0_8F], [45_8F], [0_4C0_4F] and [45_4C45_4F]. Results indicate hybridization multiplies axial stiffness by ~ 6, optimized by outer carbon plies, reducing porosity and enhancing flexural strength, though carbon fractures first due to flax’s higher elongation. Flame exposure caused mass loss of 8–15% (higher in hybrids and [45₈] layups), with greater matrix degradation, cracks, and delamination in flax-rich areas. Residual flexural strength decreased by 20–30% (e.g., hybrid [0_4C0_4F]: 250–300 MPa virgin to 200–250 MPa post-fire), but ductility increased (strain 3–4% to 5–6%), shifting failures from shear to brittle/delamination modes. Hybridization provides a balanced thermal barrier, preserving load-bearing capacity better than pure flax, suggesting potential for fire-resistant aeronautical composites.

Accurate prediction of residual stresses in filament-wound composites is vital for their long-term performance and reliability. Many existing studies simplify these predictions by treating the fiber volume fraction (V_f) as static, neglecting its evolution during manufacturing. In reality, however, multiple process parameters, such as consolidation pressure, continuously alter V_f throughout the process, making such static approximations physically inconsistent with actual manufacturing behavior. To address this limitation, this study develops a comprehensive multiphysics simulation framework that captures the consolidation-driven evolution of V_f, resin pressure, temperature, and degree of cure (DoC) in filament-wound composites. The framework integrates thermochemical, resin-flow, and mechanical fields via finite element subroutines. The effects of consolidation-driven V_f evolution on residual stress development are investigated. Results indicate that processing conditions significantly influence V_f, which affects the thermochemical response and, consequently, the resulting mechanical performance by reducing internal exothermic heat generation and peak curing temperatures. These reductions suppress the thermal and chemical shrinkage strains responsible for residual stress buildup. Consequently, the framework predicts significantly lower residual stresses than those obtained using static-V_f approximations. These insights highlight the importance of incorporating consolidation-driven V_f evolution within simulation frameworks for accurate residual stress prediction, offering a more physically realistic tool for process and structural optimization of filament-wound composites.

Micro-voids within the bead microstructure of additively manufactured short carbon fiber- reinforced polymer composites are known to compromise the material performance. Unfortunately, a comprehensive understanding of the formation mechanisms of micro-voids during polymer processing is currently lacking. The present study considers micro-void formation at fiber interfaces, particularly those occurring at the end of suspended fibers. Micro-computed tomography (µCT) image acquisition techniques are used to characterize microstructural features of a 13wt% carbon fiber reinforced acrylonitrile-butadiene-styrene (CF/ABS) composite bead manufactured via Large Area Additive Manufacturing (LAAM). The results reveal a significant collection of micro-voids at the tips of fibers approaching 80% of the total micro-void volume fraction. In addition, fiber tip micro-voids are relatively larger and less spherical than micro-voids isolated within the ABS matrix. Theoretical formulations of several known mechanisms for micro-void formation during LAAM material processing indicate that localized fluid pressure likely plays a pivotal role in micro-void formation. To better expose this mechanism, we simulate the hydrostatic flow-field pressure distribution surrounding a single rigid fiber suspended in simple shear flow using finite element analysis (FEA). Computed results demonstrate that the polymer matrix pressure decreases significantly at the fiber ends where significant micro-void formation is experimentally observed to occur. Our approach provides the fiber surface pressure distribution in simple shear flow that typifies nozzle regions with extreme flow conditions, enhancing our understanding of micro-void development mechanisms as the polymer melt flows through the nozzle.

The present study employs an electrothermal vacuum bag curing process utilising carbon nanotube (CNT) films for the purpose of repairing defects in carbon fibre reinforced polymer (CFRP) laminates. Due to its superior properties, CFRP has found extensive application in the aerospace industry and other sectors. However, conventional repair methods struggle to address internal defects, such as delamination, effectively. This study combined direct current Joule heating with vacuum bag curing, employing CNT films to repair CFRP laminates with three layup configurations: pure 0°, orthotropic layup, and their corresponding DD layups. After this, a comprehensive evaluation of the mechanical properties was conducted. The results demonstrated that at 10 V, the CNT film uniformly maintained a curing temperature of 126.5 °C. After rectifying, the specimens showed an enhancement in bending strength that surpassed the initial levels. The eight-layer patches exhibited optimal performance, shear strength and flexural modulus that approximated those observed in the pristine material. Initial strength reduction and deflection loss due to interfacial failure remained below 15%, outperforming traditional prepreg repairs that recover only 76% strength. Furthermore, the CNT film possesses in-situ monitoring capability, exhibiting significant electrical resistance increases during interfacial damage for early warning. Microscopic analysis revealed primary damage as interfacial and intra-patch delamination, yet the repaired region retained substantial load-bearing capacity. In summary, this technology combines efficient repair with real-time monitoring, thus offering a novel approach to enhancing the safety and reliability of composite structures.

Tailoring the meso-structural parameters of braided composites offers a proactive strategy to optimize their damage modes and energy dissipation mechanisms under low-velocity impact. This paper systematically investigates the effect of the fiber bundle aspect ratio, as a key mesostructural design parameter, on the impact performance of braided composites. In this study, three types of laminates with different aspect ratios were fabricated by varying the braiding mandrel radius and were tested under impact energies of 20 J, 30 J, and an energy level adjusted to eliminate the effect of thickness. The results show that the high-aspect-ratio specimen exhibited a higher peak load and was not perforated, whereas the low-aspect-ratio specimen underwent perforation failure, indicating a significant enhancement in its impact resistance. Damage mechanism analysis reveals that the fiber bundle aspect ratio directly determines the single-ply thickness and crimp angle of the yarns: the large crimp angle caused by a low aspect ratio induced severe interlaminar shear stress under impact, promoting early and extensive delamination as the dominant failure mode. Conversely, the lower crimp angle in the high-aspect-ratio specimen effectively suppressed delamination, compelling the system to dissipate energy through the higher energy-threshold mechanism of bottom-ply tensile fiber fracture. This fundamental shift in the damage mode, from delamination-dominated to fiber-fracture-dominated, was corroborated at both macro- and meso-scales using quasi-static indentation (QSI) tests and X-ray micro-computed tomography (µ-CT). This study confirms that actively controlling the dominant failure mode by tailoring the fiber bundle aspect ratio is an effective strategy for enhancing the impact damage tolerance of braided composites.

In recent years, fiber-reinforced thermoplastic composites (TPCs) have gained significant traction in the aerospace industry due to their excellent mechanical properties, recyclability, and ability to be rapidly joined through thermal fusion. Among various joining technologies, ultrasonic welding has emerged as one of the most promising techniques for aerospace-grade thermoplastic composites. However, conventional energy directors (EDs) in triangular or rectangular geometries, or the use of flat thermoplastic films as independent energy directors, often result in pronounced interfacial temperature non-uniformity. This uneven heat distribution can lead to localized thermal degradation and, consequently, compromised weld strength. To address this challenge, this study introduces an innovative woven mesh structure energy director for ultrasonic spot and continuous welding of carbon fiber reinforced polyetheretherketone (CF/PEEK) composites. Under the optimal welding time of 550 ms, the spot-welded joints achieved a lap shear strength of 40.3 MPa. On this basis, a maximum joint strength of 33.9 MPa was obtained for continuous ultrasonic welding at an optimal welding speed of 25 mm/s, with uniform joint quality observed throughout the weld seam.

Deployable space structures require low mass, high reliability, and precise actuation, particularly for long-duration satellite missions where failure cannot be tolerated. This paper presents a design and optimization framework for a composite slotted tube tape spring hinge used in solar panel deployment. A 12 K T700 carbon fiber fabric with epoxy matrix was selected as the base material, and samples were fabricated and tested for viscoelastic behavior through shear relaxation. Relaxation-derived material parameters were incorporated into a finite element model to simulate long-term stiffness decay. The hinge geometry was optimized to enhance deployment speed, reduce overshoot, and ensure reliable performance over extended stowage periods. Simulation results showed a deployment time of 0.52s and a load-bearing capacity exceeding 1 kg, even after 24 months of relaxation, meeting CubeSat requirements. The study demonstrates how time-dependent material modeling combined with geometry refinement can yield a lightweight, durable, and high-performance deployable mechanism for future satellite applications.

Porous bone implants have been extensively studied with gradient structures receiving increasing attention due to their superior compatibility with bone tissue. However, comparative studies between gradient and uniform structures remain relatively scarce. In this study, selective laser melting (SLM) technology was employed to fabricate a gradient composite Ti6Al4V humeral bone scaffold, utilizing regular hexahedron as its unit cells. According to the Ashby Gibson theoretical model, we designed the porosity of the layered gradient structure within the range of 22.02%~94.37% to achieve the regulation of the equivalent elastic modulus of the titanium alloy macroscopic structure within the range of 1.8119 ~ 14.1154 GPa, effectively eliminating the stress shielding effect between the alloy and the humerus. The maximum yield strength of the gradient porous alloy produced by laser sintering process reaches 419.22 MPa, exceeding the yield strength of the humerus ranging 100 ~ 190 MPa. In addition, the layered gradient porous structure designed in this article exhibits a more uniform stress distribution mechanism under shear stress, eliminating the failure hazard caused by stress concentration under biomechanical effects. Compared to non-gradient models, gradient structures are more effective in controlling the direction of force transmission. These findings provide valuable insights for further research into gradient structure models of other rod-shaped unit cells, highlighting the mechanical advantages and structural performance of gradient structures over uniform ones.

This paper explores a new, sustainable, and economical approach to increase the compatibility between natural fibers and geopolymeric matrices by using a calcium hydroxide Ca(OH)₂ solution. Untreated and treated sisal fibers have been used as reinforcement in geopolymers, replacing 2 wt% of the river sand aggregate. To assess the effect of treatment duration on the properties of the resulting geopolymer composites, sisal fibers have been specifically soaked in an aqueous solution (2 g/L) of calcium hydroxide for 24, 48, and 72 h. The tensile properties and the thermal resistance of sisal fibers were investigated, together with their chemical composition and morphological features. The workability of fresh geopolymer materials was indirectly evaluated in this study by determining the initial and final setting times via needle penetration testing. Binary optical photographs were processed with image analysis software to quantify the porosity content of geopolymers. Quasi-static flexural, compression, and Brazilian (indirect tensile) tests were conducted on all geopolymer composites and the neat geopolymeric matrix. Experimental results demonstrated that, although slightly reducing fiber tensile properties, the proposed alkaline treatment improved the mechanical response of the resulting composites due to enhanced fiber-matrix compatibility, particularly toughness and post-peak behavior, regardless of loading configuration. Notably, the most favorable outcomes were achieved by treating sisal fiber in calcium hydroxide solution for 24 h.