CFR-PEEK11The abbreviation “CFR” in this manuscript stands for Carbon Fibre Reinforced PEEK (referring to the composite material) rather than Carbon Fibre Reinforcement PEEK (focusing on the reinforcement phase within the polymer). is a composite material that combines a poly-ether-ether-ketone (PEEK) matrix with short carbon fibres reinforcement (CFR). PEEK is a semi-crystalline thermoplastic polymer valued for its high mechanical and chemical resistance, as well as its ability to withstand elevated temperatures, with a melting point of 343 °C. The addition of carbon fibre reinforcement improves the mechanical properties of PEEK, and PEEK reinforced with 30% carbon fibre exhibits greater hardness and a higher elastic modulus than pure PEEK, with values comparable to those of cortical bone. In this context, CFR-PEEK is regarded as a promising material for biomedical applications as it helps avoid some of the drawbacks associated with metallic alloys, such as rejection or allergic reactions caused by metals in the body, as well as stress shielding that can lead to bone degradation. However, despite the growing adoption of additively manufactured PEEK-based implants, the fatigue resistance of additively manufactured CFR-PEEK remains insufficiently understood, particularly in the high-cycle fatigue regime, for which no studies were found in the literature. Accordingly, the research novelty lies in establishing the relationship between additive manufacturing parameters previously investigated and shown to yield satisfactory results, the fatigue performance of CFR-PEEK in both low- and high-cycle regimes, and its thermal, chemical, physical and mechanical properties through quasi-static and constant amplitude fatigue tests with an integrated differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) characterisation.
Dielectric relaxation is a ubiquitous physical phenomenon that renders dielectric permittivity complex, with its real and imaginary components strongly dependent on frequency and temperature. In piezoelectric composite structures, this relaxation affects coupled electromechanical wave response, yet its role in Rayleigh wave dispersion and attenuation remains insufficiently understood. Here, frequency and temperature-dependent permittivity described by Debye and Cole-Cole relations is incorporated into the electromechanical wave equations of a piezoelectric composite structure. The resulting complex dispersion relations are solved using an optimized Multidimensional Moduli Ratio Convergence (MMRC) method, with refinements introduced to identify complex roots corresponding to physically admissible modes in dissipative systems. This formulation enables reliable characterization of Rayleigh wave propagation, attenuation, and mode shapes over broad frequency and temperature ranges. The results reveal three key effects of dielectric relaxation: it extends the admissible phase velocity range beyond classical lossless bounds, reorganizes complex dispersion branches through mode disconnection and reconnection, and produces substantial phase velocity drift while largely preserving mode shape profiles. These findings demonstrate that dielectric relaxation is not merely a material loss effect, but an active electromechanical mechanism governing non-Hermitian Rayleigh wave dispersion, with implications for tunable wave propagation, attenuation control, and modal stability.
In recent years, extreme operating environments such as those encountered by spacecraft have placed greater demands on the coordinated development of lightweight structures, efficient thermal management, and high impact resistance. Re-entrant auxetic structure (REAs) can effectively control anisotropic thermal conduction by adjusting structural parameters, but its mechanical load-bearing capacity is insufficient. To improve its performance, a novel re-entrant auxetic mixed with body centered cubic structure (RBs) was developed by hybridizing the body centered cubic structure (BCCs) with REAs, combining high in-plane thermal conductivity with high out-of-plane load-bearing capacity. Mechanical property tests indicate that, compared to REAs, the effective absorbed energy and energy absorption efficiency values of RBs are 380.4 J and 0.432, respectively, representing increases of 65.68 % and 68.75 %; the maximum impact stress is 42.67 MPa, representing a decrease of 39.02 %; and the plateau stress is 21.98 MPa, representing an increase of 29.60 %. Thermal testing revealed that the anisotropic thermal conductivity coefficients of RBs and REAs were 3.25 and 3.34, respectively. The results indicate that RBs maintain a level of anisotropic thermal conductivity comparable to that of REAs. Furthermore, high-power laser ablation experiments demonstrated, compared to traditional BCCs sandwich panel, the maximum temperature on the back surface of RBs sandwich panel was reduced by 13.2 %. In summary, this study provides new insights and effective approaches for designing lightweight, multifunctional lattice structures that achieve synergistic enhancement of mechanical and thermal performance.Keyworks: lattice structure; anisotropic thermal conduction; load-bearing capacity; laser ablation.
Thermoplastic polyurethane (TPU)-coated woven fabrics exhibit anisotropy and tensile–shear coupling associated with evolving yarn geometry under off-axis loading. Conventional macroscopic models often represent these changes implicitly, whereas detailed mesoscopic models require substantial computational effort. This study develops a low-order natural-grid constitutive framework to predict the geometry-dependent in-plane response. Its central contribution is the unified treatment of the inter-yarn angle α and cell orientation angle β as distinct kinematic variables updated from the deformation gradient. The angle α and yarn stretches jointly determine the local network geometry and equivalent stiffness, while β governs the local-to-global stiffness transformation. Multi-orientation tensile tests over 50–300 N evaluate predictions at global, regional, and central-cell scales. Mean absolute relative errors in global displacement are 4.33 %, 5.30 %, 6.00 %, 4.34 %, and 9.27 % for the 0°, 15°, 30°, 45°, and 90° specimens, respectively; regional and central-cell mean errors range from 5.25 % to 5.59 %. The framework provides a compact, physically interpretable representation of the measured in-plane response within the investigated loading range.
Unsymmetric composite laminates exhibit bistability arising from post-curing thermal residual stresses, enabling large-amplitude shape transitions between stable configurations without continuous energy input. Prior studies have predominantly examined actuation under single-point loading, while multi-point loading interactions on snap-through transitions are underexplored. Understanding these interactions is crucial for optimizing actuation in reliable deployment applications. In this study, the snap-through response of unsymmetric [0°/ 90°] bistable composite laminates is experimentally and numerically investigated under various multi-point loading configurations. Initially, three symmetric loading cases are examined to elucidate how load placement governs the actuation requirement, curvature evolution, and strain energy variation. Subsequently, asymmetric multi-point loading with a fixed dead load is examined to reveal how preload modifies the stability landscape and gives rise to distinct snap-through behaviors depending on the secondary actuation location. Full-field deformation and curvature evolution during the transition are measured experimentally using stereoscopic 3D-DIC, while finite element simulations are employed to capture corresponding strain energy variation. The numerically predicted actuation requirement and curvature evolution are validated for some cases against experiments. These findings highlight the critical role of multi-point loading interactions in governing snap-through behavior and provide design insights for bistable laminates in adaptive structures.
