Studies on the temperature dependence of microstructure evolution for four models，namely single crystal and polycrystalline FeCoNiCrMn high-entropy alloys as well as single crystal and polycrystalline Ni，help elucidate the microscopic mechanisms of plastic deformation. Based on the nanoindentation method，this work focuses on comparative analysis of the effects of temperature variation from an extremely low temperature (1 K) to an extremely high temperature (1300 K) on the plastic deformation microstructure evolution，atomic displacement magnitude，shear deformation，total dislocation length，and von Mises stress distribution of single crystal and polycrystalline FeCoNiCrMn high-entropy alloys，together with single crystal and polycrystalline Ni. The results show that when the temperature rises from 1 K to 1300 K，the maximum load decreases by 37.69%，29.10%，55.06%，and 15.64% for single crystal FeCoNiCrMn high-entropy alloy，single crystal Ni，polycrystalline FeCoNiCrMn high-entropy alloy，and polycrystalline Ni，respectively. Defects exist at grain boundaries in polycrystalline FeCoNiCrMn high-entropy alloy and polycrystalline Ni；high stress concentration at grain boundaries induces dislocation nucleation and proliferation at grain boundary edges. The plastic deformation microstructure evolution of the four models under nanoindentation loading is dominated by the synergistic effect of stacking faults，twins，amorphous phases，and phase transformation：plastic deformation of single crystal FeCoNiCrMn high-entropy alloy generates bulge-like structures that restrain dislocation slip and propagation；prominent dislocation slip is observed in plastically deformed single-crystal Ni. Compared with polycrystalline Ni，polycrystalline FeCoNiCrMn high-entropy alloy forms thicker amorphous layers and exhibits shorter total dislocation length during plastic deformation，and this trend is weakly affected by temperature change from cryogenic to high temperature. Grain boundary migration and expansion occur in both polycrystalline FeCoNiCrMn high-entropy alloy and polycrystalline Ni during plastic deformation，which facilitates the formation of finer nanocrystalline structures. These findings provide important theoretical references for developing high-entropy alloy systems with outstanding strength-toughness synergy.
Ceramic cores are critical components for forming complex cooling channels in the investment casting of hollow aero-engine blades，and their dimensional accuracy directly determines the structural quality of the internal cavities and the casting yield of the blades. Due to its high resolution，high efficiency，and mold-free processing capability，vat photopolymerization additive manufacturing has shown great promise for the fabrication of complex ceramic cores. However，issues such as the stair-step effect，shrinkage-induced cracking，phase-transformation-induced fracture，and high-temperature creep still arise during printing，debinding and sintering，and casting service，thereby severely compromising the dimensional accuracy of the cores. Focusing on the entire lifecycle of ceramic cores，from raw materials to fabrication and service，this paper reviews the key factors affecting the dimensional accuracy of ceramic cores fabricated by vat photopolymerization additive manufacturing at different stages，together with the underlying mechanisms. Particular attention is given to the effects of slurry composition，printing parameters，sintering behavior，and high-temperature service conditions on dimensional stability. Finally，future development trends in this field are discussed，with emphasis on the design of high-performance slurries，the coordinated optimization of printing and sintering，as well as the establishment of dimensional accuracy evaluation methods and standard systems for engineering applications.
Fiber-bundle-missing defects of four severity levels (no missing bundle，1/3 bundle missing，2/3 bundle missing，and an entire bundle missing) are precisely introduced into 2.5D braided SiC fiber preforms by deliberate defect engineering，and the corresponding SiCf/SiC composites are fabricated via a combined chemical vapor infiltration (CVI) and polymer infiltration and pyrolysis (PIP) process. The effects of fiber bundle missing defects on the flexural properties and failure mechanisms of the composites are investigated using XRD，SEM，and CT characterization together with three-point bending tests. The results show that the as-fabricated SiCf/SiC composites possess a well-bonded BN interphase and a dense matrix microstructure. The severity of fiber bundle missing exhibits a significant negative correlation with the flexural performance of the material. The defect-free specimens exhibit the highest and most stable flexural properties，with an average flexural strength of 349.2 MPa and a coefficient of variation of 1.98%. As the severity of bundle missing increases，the flexural strength decreases progressively，reaching a minimum of 246.6 MPa for the specimens with an entire bundle missing. Specifically，the failure mode evolves from a stochastic，fiber-dominated failure in the defect-free condition，through an uncertainty-driven failure induced by local fiber absence，to a deterministic，defect-dominated failure when an entire bundle is missing. Microstructural analysis reveals that fiber bundle missing not only directly reduces the load-bearing cross-section，but also degrades the load-carrying capacity of the material by inducing local stress concentration and altering the crack propagation path.
This article addresses the poor bonding strength of continuous carbon fiber-reinforced thermoplastic polyaryletherketone resin (CF/PAEK) composites, which makes the mechanical test results of tabbed specimens easily affected. It investigates the effects of resistance-welded reinforcement tabs on the performance test results of 0u00B0 tensile and 0u00B0 compression specimens. Through analysis of the temperature distribution during the welding process and multiple sets of experimental results, it shows that the heat conduction of unidirectional specimens significantly affects the welding strength of the tabs near the working section of resistance-welded specimens, resulting in lower test results for 0u00B0 compression specimens but not for 0u00B0 tensile specimens or single-lap shear specimens. Adding an insulation layer to prevent edge heat dissipation improves the test results for 0u00B0 compression specimens. However, the two rapid temperature changes caused by resistance welding reduce the crystallinity of the specimens within the tabs without affecting the working section. This often leads to damage at the interface between the working section and the tab, so the compressive strength test results remain lower than those of adhesively bonded specimens.
The increasing demand for lightweight structures with high damage tolerance in aerospace, protective systems, and transportation has driven the development of advanced composite laminated plates. The negative Poissonu2019s ratio effect, commonly referred to as the auxetic effect, offers a promising avenue for functional design. Unlike conventional auxetic materials that rely on geometric deformation of microstructural unit cells, composite laminated plates can achieve equivalent in-plane or out-of-plane negative Poissonu2019s ratio effects through material anisotropy, layup configuration, reinforcement distribution, and interlaminar coupling. This paper reviews recent advances in the design, fabrication, and mechanical response of auxetic composite laminated plates. Predictive design methods are first summarized, including classical laminate theory, three-dimensional elastic constant models, multiscale finite element homogenization, lamination parameters, polar representation, and intelligent optimization algorithms. Experimental fabrication techniques and full-field strain measurement methods are then discussed. The coupling mechanisms between the auxetic effect and key mechanical responses are subsequently analyzed. In dynamic behavior, the auxetic effect alters the stiffness characteristics of laminated structures and couples with shear deformation and geometric nonlinearity. In buckling and thermal buckling behavior, its stabilizing influence is strongly dependent on boundary conditions, loading configurations, and the interplay between transverse deformation and in-plane forces. In impact response, the out-of-plane negative Poissonu2019s ratio is more closely associated with local contact stiffness and indentation resistance, whereas the in-plane negative Poissonu2019s ratio primarily affects stress redistribution and damage propagation. The review demonstrates that the mechanical advantages of auxetic composite laminated plates are not dominated solely by the Poissonu2019s ratio; they are governed by the synergistic effects of layup design, stiffness coupling, reinforcement distribution, boundary conditions, and loading modes. Future research should emphasize multi-objective layup optimization, decoupling auxetic effects from stiffness parameters, and extending current design methodologies to complex engineering plate and shell structures. This review serves as a valuable reference for the design and application of high-performance multifunctional composite laminated plates.
