Ceramic matrix composites are ideal for thermo-structural components, where they often encounter complex multiaxial stress states. This study investigated damage evolution in plain-woven SiC/SiC tubes under combined tension-torsion loading using acoustic emission, three-dimensional digital image correlation, and fractography. Results demonstrated that the mechanical behavior was significantly influenced by the stress state. AE analysis revealed this was due to competitive and synergistic tensile-shear interactions, which intensify damage accumulation and drive a transition in the dominant energy dissipation mechanism. To quantify this damage evolution and identify the governing stress type, an AE-based damage initiation criterion and a failure progression envelope model were developed. Fractography further indicated that while the fracture path is governed by the governing stress type, a transition in governing stress type can occur during loading, specifically when tensile and shear stresses co-dominate. This shift directed fracture along the direction of maximum shear stress, consistent with observed fracture angles.

Perovskite solar cells (PSCs) experience mechanical damage and failure (i.e. degradation and fracture) induced by temperature changes under thermal cycling. However, few studies have been able to simultaneously suppress interface delamination and delay chemical degradation to ensure the mechanical integrity of perovskite film under thermal shock, making it challenging to improve the thermal cycling stability of PSCs. We report a universal interlocking strategy via the modification of polymethyl(hydro)/polymethylvinylsilazane (PHVS), which achieves interfacial interlocking through the condensation reactions with substrates, hydrogen bonding with the perovskite film, and a self-crosslinking reaction. The interlocked interface significantly enhances the interfacial adhesion toughness and releases the residual stress of the perovskite film, thereby suppressing the interface delamination and delaying the chemical degradation under thermal cycling. The PHVS-modified PSCs exhibit a certified efficiency of 26.82%. The encapsulated PSCs retain 96% of their original efficiency after 200 cycles of thermal cycling testing, and the perovskite modules maintain 95% of their original efficiency after 1000 h, day and night, outdoor testing. This work highlights the significance of enhancing the mechanical integrity of perovskite films under thermal cycling and provides a promising approach for achieving thermal cycling-stable PSCs with high efficiency.

Wrinkle defects frequently arise during automated fiber placement of thermoplastic composites due to inadequate process design, with prepreg buckling instability as a defining feature. In this paper, a defect prediction framework integrating multiple deformation mechanisms was constructed to simulate wrinkle formation during automated fiber placement. A hypoelastic constitutive model was developed to capture the mechanical response of unidirectional thermoplastic prepreg. The formation mechanisms of wrinkles under varying temperatures and steering radii were investigated, and the predictive capability of the model was validated experimentally. Wrinkle defects were attributed to mechanical instabilities driven by the interplay of deformation mechanisms, evolving through a dynamic process of shear compensation followed by buckling instability. Experimental and simulation results demonstrated that, as the temperature increased, in-plane shear deformation became the dominant mechanism, dissipating part of the compressive strain energy and thereby mitigating axial buckling. Wrinkle formation was fundamentally driven by axial compression induced by placement trajectory curvature. With reduced steering radii, bending progressively became the prevailing mechanism, while interlaminar bonding was insufficient to restrict fiber motion or accommodate it through shear. The localized accumulation of compressive strain energy subsequently triggered prepreg buckling, resulting in the formation of wrinkle defects.

Multiaxial loading experiments and damage characterization of carbon fiber reinforced polymer (CFRP) composites are of significant importance for their operation under complex service conditions. In this paper, the mechanical properties, damage evolution, and failure mechanisms of plain-woven CFRP tubes under combined tension-torsion loads are quantitatively investigated by integrating three-dimensional digital image correlation and acoustic emission (AE) techniques. The results indicate that the distributions of strain fields within the woven structure of the composite tube exhibit distinct differences under different load conditions. Shear loading influences the average axial tensile strain, while tension loading significantly enhances the shear strength and shear modulus of the tube. Improved schemes for failure criteria are proposed that are based on the shear strengthening effect of the tension-shear stress plane, and the AE signal characteristics were analyzed to categorize the damage types based on peak frequencies. As the normalized cumulative acoustic energy can serve as a damage factor for the quantification of both damage evolution and damage envelope flow, it assisted in further establishing a stress state-dependent damage assessment model. A combined analysis of the multiscale fracture characteristics of the CFRP tubes demonstrates that various types of damage exhibit distinct initiation and propagation mechanisms under different dominant stress types, and the damage patterns for the same damage type also vary across different locations within the woven structure. These variations ultimately influence the direction of crack propagation.

Cu-Al sliding electrical contacts are widely used in electromagnetic launch, high-speed electrified railways, and aerospace devices, but their service life is limited by the coupled development of adhesive Al transfer and arc erosion. Here, we report a scalable architectural strategy to decouple these degradation pathways via a coldsprayed CuW/graphene nanoplatelet (GNPs) composite coating. This design synergizes a rigid W load-bearing skeleton with GNPs-enabled interfacial regulation, stabilizing the complex current-carrying sliding interface under direct-current loads up to 15 A. The composite coating exhibits superior electro-tribological stability, reducing the coefficient of friction to 0.15 and restricting adhesive Al fractional coverage to merely 7.9%. Microstructural analyses reveal a fundamental shift in the erosion mechanism. The CuW/GNPs coating promotes the in-situ formation of a carbon-enriched tribo-film that suppresses Al adhesive transfer and reduces the spatial development of arc-prone Al-rich regions. Moreover, the exposed GNPs-rich features are spatially associated with localized and finer arc-eroded products, suggesting that GNPs participate in the local arc-response process. Consequently, the arc-erosion morphology changes from extensive melting to mild and localized surface remelting, thereby weakening the adhesive material transfer and arc erosion. This work establishes a manufacturable composite-coating design framework for durable, high-current sliding electrical contacts.

Stretchable electronics are typically of a structure of a stiff film on a compliant substrate and have various applications in engineering. The substrate usually displays time-dependent material behaviour due to its viscoelasticity, which can significantly affect the deformation pattern of the film/substrate structure. In this paper, the evolution of wrinkles on a film on viscoelastic-layer-elastic-substrate structure of finite thickness is investigated. In order to derive the equilibrium equation of this tri-layer structure, the normal and shear stresses between the film and the viscoelastic middle layer, and between the middle viscoelastic layer and the elastic substrate are obtained at first. Using Laplace transform, the analytical expression of the deformation of this structure is also obtained. Through numerical simulations, the influence of the viscoelasticity on the evolution of wrinkles in this structure is analysed. The proposed formation can well predict the wrinkling regimes, and the evolutionary paths for the kinetic single-layer and bi-layer wrinkling patterns are provided. In addition, the wrinkling pattern of this tri-layer structure would evolve from the kinetic bi-layer wrinkling to the single-layer wrinkling over time, and the viscoelasticity serves to increase this evolution time. The theoretical results reported in this paper provide a useful theoretical basis for the design of tri-layer type stretchable electronics.

The isolator, a critical component in RBCC engines, bridges the intake and combustion processes and plays a pivotal role in ensuring efficient performance across a wide speed range. However, designing variable cross-section curved isolators with optimal aerodynamic performance remains a significant challenge. This study investigates an efficient design-optimization methodology for such isolators. A convex optimization framework, incorporating sensitivity analysis of geometric parameters, is proposed and validated with multiple initial points. The aerodynamic performance of the isolator is evaluated across a wide speed range. The results demonstrate that: (1) A methodology for regulating the streamwise cross-sectional area distribution is established, enabling direct design of variable cross-section curved isolators; (2) A tailored optimization method, developed based on sensitivity analysis, reduces the number of iteration steps by nearly 87%, significantly improving design efficiency; (3) Compared to the baseline isolator, the optimized isolator achieves a remarkable reduction in total pressure loss by over 45% at the design point, while significantly enhancing total pressure recovery across the climb-type wide speed range trajectory. These findings not only provide valuable insights for the contour design of isolators in RBCC engines but also offer a robust framework for optimizing complex aerodynamic components in hypersonic propulsion systems.

Continuous alumina fiber‐reinforced alumina composite (Al 2 O 3f /Al 2 O 3 ) is an ideal material for developing high‐performance aero‐engine hot section components. In the present work, the air oxidation and steam corrosion behaviors of Al 2 O 3f /Al 2 O 3 at 1000°C–1200°C were investigated. X‐ray diffractometer, scanning electron microscope, and transmission electron microscope were applied to analysis the composition, fracture morphology and microstructure of the Al 2 O 3f /Al 2 O 3 . The degradation in the properties of the component was analyzed by nanoindentation. The results show that the strength of Al 2 O 3f /Al 2 O 3 decreases significantly after steam corrosion. The higher temperature leads to a greater degradation in the strength of Al 2 O 3f /Al 2 O 3 after steam corrosion. The damages of the composites are closely related to fiber strength and interfacial bonding strength. Fiber grain coarsening causes the reduction of the fiber strength, while strong interfacial bonding leads to the failure of the fiber toughening mechanisms.

The mechanical properties of polymer matrix composites often decrease due to hygrothermal environment. The hygrothermal aging tests and the compression tests are carried out before and after aging on the T700/BP9916 composites plate with open-hole， and the open-hole compression（OHC） strength is obtained. The residual stress distribution in the specimen after hygrothermal aging is simulated by ABAQUS software. Based on the hygrothermal expansion behavior and linear relationship between mechanical properties and the moisture absorption， OHC tests before and after hygrothermal aging are simulated. The results show that the moisture absorption of the T700/BP9916 composites have typical Fick diffusion behavior， and the maximum load of the OHC after hygrothermal aging decreases by approximately 5.2%. The internal stress caused by hygrothermal aging is very small and have no impact on the strength. The relative mass increment-time curve of moisture absorption obtained from the FEM simulation is in good agreement with the experimental. The relative error of maximum load of OHC test between the simulated and the experimental value is only 0.88% with non-hygrothermal aging， and the relative error is 6.21% during the hygrothermal environment. The increase in error is due to the fact that only the linear relationship between hygrothermal effect and the linear decline of material properties is considered in the simulation calculation.

Continuous alumina fiber-reinforced alumina composite (Al2O3f/Al2O3) is an ideal material for developing high-performance aero-engine hot section components. In the present work, the air oxidation and steam corrosion behaviors of Al2O3f/Al2O3 at 1000 degrees C-1200 degrees C were investigated. X-ray diffractometer, scanning electron microscope, and transmission electron microscope were applied to analysis the composition, fracture morphology and microstructure of the Al2O3f/Al2O3. The degradation in the properties of the component was analyzed by nanoindentation. The results show that the strength of Al2O3f/Al2O3 decreases significantly after steam corrosion. The higher temperature leads to a greater degradation in the strength of Al2O3f/Al2O3 after steam corrosion. The damages of the composites are closely related to fiber strength and interfacial bonding strength. Fiber grain coarsening causes the reduction of the fiber strength, while strong interfacial bonding leads to the failure of the fiber toughening mechanisms.

Ceramic particles in particle-reinforced metal matrix composites (PRMMCs) often cause significant stress concentration and load transfer behaviors under loading. In this study, various finite element models were developed to investigate the effects of particle shape, orientation, and content on stress concentration and load transfer behaviors, as well as their evolution mechanisms during loading. The simulation results revealed that particle shape and orientation significantly influence load transfer behavior between the matrix and particles. Additionally, the evolution patterns of stress concentration factors for particles and the matrix were found to be opposite to each other. Moreover, load transfer behaviors changed notably at different loading stages, with approximately 78

The recent advances of solid mechanics of polymer networks are that they can be well-modelled by a physically-based size-dependent constitutive relation via a simplified strain gradient elasticity theory. However, boundary value problems of plate models composed of polymer networks have not been reported, which limit wide applications of the models in the engineering science. In this paper, we systematically established a variationally consistent boundary value problems Mindlin plate models for polymer networks leading to the framework of a simplified strain gradient elasticity. This study considers the strain energy produced by the strain gradient in the thickness direction and proposes a well-posed boundary value problem for a Mindlin plate with arbitrary boundaries, discussing possible boundary conditions, especially higher-order nonconventional ones. The senses of stress resultants and double stresses acting on the face of a volume element are firstly explained. Surprisingly, it is found that unexpected corner condition related normal derivatives of shear force, bending moment, and twisting moment exists for plates with irregular boundaries-contradicting conventional mechanics notions of plates. For illustrative purpose, static bending analyses of a simply supported rectangular plate subjected to a uniformly distributed loading and a concentrated loading are provided. The effective Young's modulus predicted by this approach agrees well with reported result in the open literature. This work may be helpful in developing efficient numerical methods and offers new insights into the existence corner condition in Mindlin plates within the context of a simplified strain gradient elasticity theory.

To investigate the control effect and flow mechanism of the L-shaped endwall groove on corner separation in the real compressor stage, a single stage axial flow compressor is selected as the research object and the L-shaped grooves are introduced on the stator casing side. First, the experimental measurement is conducted on the optimal L-shaped groove obtained through a full factorial experimental design, and the results demonstrate that the optimal groove has a great control over the endwall flow. Moreover, the peak efficiency is improved by 0.9% and the stall margin is increased by 4.46%. Then, the flow field visualization of numerical results and analysis of variance method are employed to analyze the control mechanism and parameter control law of the L-shaped groove. It is found that the L-shaped groove can guide the skewed inlet endwall boundary layer towards the streamwise direction due to its confinement effect, thereby delaying the onset of corner separation and reducing the size of ring vortex. As a result, the aerodynamic performance of the compressor is enhanced. Furthermore, the groove depth and groove width play a significant role in controlling endwall flow among the three L-shaped groove design parameters. The larger groove depth and smaller groove width enhance the capability of the streamwise groove to constrain the endwall boundary layer, leading to a greater reduction in endwall loss.

Continuous fiber-reinforced ceramic matrix composites are widely used for high temperature components like aerospace engines due to their superior performance at elevated temperature. However, these materials are susceptible to damage from foreign object debris during service, which has become a significant concern. To investigate the impact damage characteristics of 2D-SiC/SiC composites, this study utilized a light gas gun to subject specimens prepared using chemical vapor infiltration (CVI) technology to ballistic impact. The impact processes were recorded with a high-speed camera, while the surface and internal structures of foreign object damage (FOD) were examined by optical microscopy and computed tomography (CT). This investigation revealed that conical cracks, interlaminar delamination, fiber fracture, and matrix collapse were the primary manifestations of high-speed impact damage. Damage characterization indicated that backside damage and edge delamination damage were caused by reflected tensile waves. As the impact velocity increased, the combined action of the projectile and tensile waves resulted in specimen penetration and weakening of edge delamination damage. Quasi-static tensile tests on high-speed impact specimens elucidated the relationship between residual mechanical properties and impact velocity, as well as projectile diameter. The results showed that residual tensile strength was a crucial parameter indicative of the severity of impact damage. Additionally, digital image correlation (DIC) was employed to determine strain distribution during tensile processes. By integrating residual tensile strength after impact with different projectile diameters and impact velocities, the study further explored the effect of varied parameters on impact damage. The research findings highlighted that projectile diameter as the primary factor influencing the extent of high-speed impact damage.

A conventional axial turbine drived by a pulse detonation combustor heavily challenges the turbine cooling and hot gas sealing. In order to fully understand the physical behavior of ingress and egress effect with the pulse inlet mainstream, a study is carried out to investigate the unsteady flow field and sealing efficiency inside the cavity using the method of unsteady, 3-D CFD simulation. The pulse detonation inflow boundary condition simplified using simple exponential decay formulas are applied to the inlet of mainstream passage. The results reveal that the magnitude of sealing gas pressure does affect the pressure and sealing efficiency distribution inside cavity. The sealing efficiency inside the cavity goes through three sub-stages, respectively, "the decline stage", "the plateau stage", and "the recovery stage". when the sealing gas pressure increases, the sealing efficiency of these three sub-stages will increase, and the duration of " the plateau stage " and "the recovery stage" will decrease. As a result, the ability of turbine cavity that resist the ingress of pulse detonation inflow can be augmented with the sealing gas pressure increases.

Carbon/Carbon (C/C) composites exhibit excellent mechanical properties at high temperatures, making them widely used in aerospace, such as the leading edges of spaceplane wings and the nose cones of hypersonic aircraft. However, damage caused by rain erosion to C/C composites affects their mechanical properties and poses significant challenges during operational service periods. A jet impingement test platform was employed to conduct single and multiple water-jet erosion tests on three-dimensional orthogonal C/C composite materials and to investigate the residual mechanical properties of the specimens after jet impact. The damage was characterized using optical microscopy, scanning electron microscopy, and X-ray computed tomography. The results showed that the damage types of the C/C composite materials under water-jet impingement included fiber bundle fracturing, delamination, and debonding. The extent of erosion damage was positively correlated with the jet velocity and diameter. The changes in the multi-jet damage indicated a cumulative expansion process, and z-directional fiber bundles exhibited superior resistance to jet impact damage propagation. The results of the three-point bending tests showed that the greater the initial impact damage, the lower the residual mechanical properties of the materials, and the residual strength of the specimen suddenly decreased when damage occurred at the back of the specimen.

The mechanical behaviors of hybrid metal-composite joints with different protrusion densities were investigated by combining numerical and experimental methods. High-fidelity finite element models that considered the failure modes of all components were developed, and specimens based on metal additive manufacturing technology were tested under quasi-static tensile load to verify the numerical calculations. The results showed that the load capacity and the dominant fracture mode of joints were significantly affected by the metal protrusion density. The failure mechanisms of joints under different protrusion conditions exhibited a clear difference, which proved the possibility of an optimal and functional joint design.

Ceramic matrix composites (CMCs) have been widely used in aerospace thermal-structures due to their excellent high-temperature performance. It is essential to understand the damage evolution of CMCs. However, in previous research work, the effect of thermal stress induced damage during CMCs fabrication on tensile response was often ignored. A damage evolution model that considers axial and radial thermal stresses to predict tensile response of unidirectional ceramic matrix composites was proposed in this study. The average relative errors between the current prediction and experimental data in the literature were calculated as 1.64 % and 1.91 %, validating this approach. Meantime, the damage evolution laws of interface debonding and the critical stress of matrix cracking in the Budiansky-Hutchinson-Evans (BHE) model were corrected to satisfy the discontinuous interfacial shear stress. According to the experimental data, the current model predicted critical stresses of matrix cracking better than the BHE model, with error rate reductions of 6.52 % and 15.38 %.