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2026 Vol. 47, No. 3
Published: 2026-06-28
281
Thermo-mechanical Coupling Behaviors of Liquid Crystal Elastomer-Shape Memory Polymer Composite Structures
Liquid crystal elastomers (LCEs) exhibit rapid response, reversible deformation, and large actuation, making them promising for applications in soft robotics. However, their low modulus limits their ability to provide stable stiffness. In contrast, shape memory polymers (SMPs) can undergo significant changes in modulus with temperature variations and exhibit shape fixity ability. However, they lack reversible shape-changing capabilities. Therefore, combining LCEs and SMPs into a composite structure is considered as a promising design strategy to simultaneously achieve reversible actuation and shape locking. This paper verifies the feasibility of the proposed approach through numerical simulations. First, a thermo-mechanical-order coupling constitutive model for LCEs is established to describe the shape changes caused by the nematic-isotropic phase transition during temperature changes. A viscoelastic constitutive model based on the glass transition mechanism is further developed to capture the shape memory effect in amorphous polymers. The constitutive models are then implemented into finite element software. The study further investigates the influence of the nematic-isotropic phase transition region and the glass transition region on reversible deformation and shape locking, demonstrating the potential of LCE-SMP bilayer composite structures for realizing complex actuation behaviors.
2026 Vol. 47 (3): 281-290 [
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291
Thermo-Mechanical Coupling Based on Embedded Isogeometric Analysis
Accurate geometry and stable computation are essential for heat conduction and thermo-mechanical analysis of complex three-dimensional structures. Traditional finite element methods often require laborious mesh generation for CAD models, which compromises both efficiency and accuracy. While classical Isogeometric analysis (IGA) offers advantages, it still struggles with the parameterization of complex boundary representation (B-Rep) models. In this paper, we develop an embedded domain IGA method for thermo-mechanical coupling problems. We present a unified solution framework for steady-state heat conduction and thermal stress analysis. The method utilizes NURBS as background basis functions and incorporates a virtual domain with an element classification strategy. This strategy effectively identifies the relationship between the background grid and the physical domain. To ensure accurate geometric representation, we employ adaptive Gaussian integration based on a recursive octree sub-cell scheme. This approach allows the method to capture the precise boundary of the B-Rep model without the need for boundary-fitted meshes. Based on this framework, the discrete forms of the steady-state heat conduction equation and thermal stress are derived. The coupling between temperature and displacement fields is considered in a consistent manner to handle thermal expansion effects and temperature-dependent responses. The proposed method can accurately capture temperature distribution and thermal stress in complex structures. Several numerical examples are presented to verify the performance of the proposed method. The results show that the method can achieve stable, accurate, and robust solutions. It avoids mesh generation and geometric reconstruction, significantly reducing the pre-processing time for complex CAD models. Compared with traditional methods, it shows good numerical accuracy and optimal convergence behavior. In addition, it has strong adaptability to complex geometries. The proposed method provides an effective and flexible approach for thermo-mechanical coupling analysis of complex engineering structures. It has significant potential applications in practical engineering analysis and design involving complex CAD models.
2026 Vol. 47 (3): 291-305 [
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306
Numerical Simulation of the Dynamic Mechanical Behavior of Precipitation-Strengthened CoCrNi-Based Medium-Entropy Alloys
Precipitation-strengthened medium- and high-entropy alloys demonstrate significant potential for dynamic-loading applications, making it imperative to quantitatively elucidate their strengthening mechanisms and micro-scale deformation processes from a multi-scale perspective. This work employs a combined approach of split Hopkinson pressure bar (SHPB) dynamic compression experiments and crystal plasticity finite element (CPFE) simulations to systematically investigate the mechanical behavior and underlying microscopic mechanisms of a CoCrNiSi0.3C0.048 medium-entropy alloy over a strain rate range of 103 to 10? s?1. To elucidate the role of tertiary precipitates on dynamic mechanical response, we developed a crystal plasticity constitutive model that incorporates both the evolution of GND density and the effects of multi-scale precipitates. Results indicate that the model accurately captures the experimental stress-strain response. Hard precipitates are identified as the key agent responsible for heterogeneity in the microscopic stress field and local strain gradients, thereby promoting early-stage rapid accumulation of GNDs and markedly improving SSD storage efficiency. These two effects collectively account for the majority of the work hardening. High strain rates also amplify the strain gradient effect and dislocation multiplication through the suppression of dynamic recovery and the aggravation of dislocation pile-ups, thereby increasing the strength and hardening rate. Deformation incompatibility due to interfacial mismatches in stress, strain, and GND density was then quantitatively assessed at the grain scale.
2026 Vol. 47 (3): 306-320 [
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321
Crystal plasticity study of residual stress with martensitic transformation volumetric strain in laser welding
Martensitic transformation can significantly reduce the macroscopic residual stress in welds. Existing studies have generally attributed this effect to transformation-induced volumetric expansion. However, residual stress origin and evolution due to martensitic transformation at the grain scale remain unclear. To address this issue, this study investigates the effect of martensitic transformation on residual stress for P91 steel during laser welding by combining microscale transformation volumetric strain with EBSD-based microstructure reconstruction and crystal plasticity finite element simulation. The results show that the proposed model can effectively capture the microscale evolution characteristics of residual stress in the weld zone. The transformation volumetric strain is introduced as eigenstrain via the deformation gradient. At the macroscopic scale, it compensates for cooling shrinkage deformation. At the microscopic scale, transformation mismatch among grains induces local stress accumulation and release. This leads to a strongly heterogeneous residual stress field. Dislocation density analysis reveals a threshold effect of cooling rate on transformation volumetric strain. The effect is significant below 10 °C/s but insignificant above this value. This work clarifies the mechanism of martensitic transformation-induced micro-stress at the grain scale and reveals the role of cooling rate in regulating phase transformation behavior. These findings provide a theoretical basis for understanding residual stress formation in the weld zone of P91 steel.
2026 Vol. 47 (3): 321-333 [
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334
Phase Field Model of Graded Materials with Residual Stress Under Thermomechanical Load
This study develops a phase-field fracture model to investigate the cracking behavior of a novel YTaO4/8YSZ functionally graded thermal barrier coating (TBC) under extreme thermomechanical loading. The performance of such coatings is often limited by fracture driven by thermal mismatch and residual stresses, yet predictive models capturing the coupled effects of temperature-dependent properties and intrinsic stress states are lacking. To address this, we propose a coupled thermomechanical framework with three key innovations. First, a temperature-dependent damage criterion, based on a mechanical-thermal energy density equivalence principle, is introduced to modify the critical energy release rate and other material parameters. Second, the Voigt homogenization scheme is employed to model the continuous gradation of material properties. Third, the eigenstrain method is integrated to incorporate the initial residual stress field from fabrication. The model is implemented numerically on the COMSOL Multiphysics platform. Its validity is first established by accurately simulating crack propagation patterns in alumina plates during water quenching. The model is then applied to analyze thermal shock-induced fracture in the YTaO4/8YSZ graded structure. The simulation results reveal that the temperature-dependent criterion significantly improves the prediction accuracy of crack initiation time and propagation paths compared to models using constant parameters. Furthermore, the initial residual compressive stress plays a beneficial dual role by effectively delaying crack nucleation and subsequently inhibiting crack growth into the coating. The coupling of damage-dependent thermal conductivity is also shown to influence local heat flux and crack branching behavior. This work provides a reliable and advanced numerical tool for probing the complex fracture mechanisms in graded TBCs, offering valuable insights for optimizing their design to enhance durability in high-temperature applications such as gas turbines and aero-engines.
2026 Vol. 47 (3): 334-349 [
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350
Discussion on the Dynamic Characteristics of Iced Contact wire
Focusing on the unclear dynamic response mechanism of ice-covered contact wires under impact load in shock-based de-icing technology, this study takes a single-span ice-covered contact wire as the research object. By combining theoretical derivation with finite element simulation, a dynamic model of the ice-covered contact wire is established. Through the introduction of a dimensionless parameter ξ, a mechanical state criterion ranging from flexible cable to elastic beam is developed, clarifying that the ice-covered contact wire operates in a cable-dominated state under typical parameters. The research indicates that transverse wave propagation exhibits significant dispersion characteristics, with its wave speed dependent on axial tension and equivalent bending stiffness, increasing with higher frequencies; whereas longitudinal wave speed is governed by both the stiffness ratio γ and the mass ratio δ, with increasing ice thickness leading to a decrease in wave speed. This study systematically reveals the wave propagation mechanism in ice-covered contact wires, providing a theoretical basis for the parameter design and engineering application of shock-based de-icing technology.
2026 Vol. 47 (3): 350-362 [
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363
Closed-Form Solutions to the Anti-plane Problem of Double-Period Cracks in One-Dimensional Hexagonal Piezoelectric Quasicrystals
This paper investigates the anti-plane problem of double-periodic cracks of unequal sizes in a one-dimensional hexagonal piezoelectric quasicrystal material under combined anti-plane mechanical loading and in-plane electrical loading. By employing the elliptic function theory and the conformal mapping techniques, a closed-form analytical solution to the problem is derived. Based on this solution, exact expressions are obtained for the field intensity factors of stress and electric displacement at the crack tips, as well as for the effective electro-elastic moduli of the cracked material. Numerical calculations are conducted to reveal the mechanical-electrical coupling effects induced by multi-crack interactions, particularly the shielding and amplification effects of smaller cracks on the main crack. Furthermore, the degradation of the effective electro-elastic moduli due to micro-crack arrays is quantified. The obtained solution encompasses various typical crack configurations as special cases, such as rectangular arrays with equal crack lengths, rhombic arrays, and staggered row-column cracks, thereby providing a theoretical basis for fracture analysis of one-dimensional hexagonal piezoelectric quasicrystal materials.
2026 Vol. 47 (3): 363-378 [
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379
Fracture Toughness Evaluation of Gas Turbine Blade Material Using Mini-SEB Specimens
Gas turbine blades operate under severe conditions including high temperature, complex stresses, oxidation, corrosion, and cyclic loading. Local crack initiation and growth can therefore degrade structural integrity and service reliability. However, standard fracture toughness specimens are difficult to prepare from blade materials because blades are thin-walled, geometrically complex, and limited in sampling volume. Different blade regions may also exhibit distinct microstructures and local mechanical responses. A miniature-specimen-based approach is thus needed for local fracture toughness evaluation. In this study, an RA-series nickel-based superalloy blade was investigated. Specimens were extracted from the blade airfoil and blade root. Metallographic observations were first conducted to characterize regional microstructural features. Small rectangular tensile specimens were then tested at room temperature and 900 °C to evaluate local tensile behavior without a macroscopic crack. Mini-SEB specimens were machined from the same regions to assess fracture behavior under cracked conditions. Fatigue pre-cracking was introduced under constant ΔK control. Fracture toughness tests were performed under displacement control, and the J–Δa curves and the conditional initiation toughness JQ0.2BL were determined using the normalization procedure recommended in GB/T 21143-2014. Fracture surfaces were further examined by macroscopic observation and scanning electron microscopy. The results show clear regional dependence of both tensile properties and fracture resistance. At room temperature, the blade root exhibits a higher yield strength, whereas the blade airfoil shows a higher ultimate tensile strength and larger fracture strain. At 900 °C, this trend reverses, and the blade root becomes superior in both strength and ductility. For both regions, the J–Δa curves at 900 °C lie above those at room temperature, indicating improved crack-growth resistance at elevated temperature. The average JQ0.2BL of the blade airfoil increases from 70.65 to 103.78 MPa·mm, while that of the blade root increases from 36.78 to 145.53 MPa·mm. All specimens show ductile fracture characteristics. These results demonstrate that Mini-SEB testing can provide reliable local fracture toughness parameters for gas turbine blades under restricted sampling conditions and support local structural integrity assessment at representative service temperatures.
2026 Vol. 47 (3): 379-391 [
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Analysis of nonlinear influence of clearance at the connection between nose landing gear and airframe on landing gear shimmy
To reveal the influence law of the clearance at the connection between nose landing gear and airframe on shimmy stability, a six-degree-of-freedom shimmy dynamic model with such clearance was established. The clearance was converted into strut rotation angle via geometric mapping, and the nonlinear stiffness torque equation was smoothed. The influence of the clearance on shimmy stability was analyzed based on bifurcation theory. The results show that considering airframe local stiffness significantly affects the shimmy region; the torsional shimmy region expands as equivalent stiffness decreases, while the lateral shimmy region shows an opposite trend with equivalent stiffness variation; with increasing clearance, the torsional shimmy region shrinks and the lateral one expands; at a fixed taxiing speed, 0.1-0.2mm clearance can effectively suppress shimmy amplitude.
2026 Vol. 47 (3): 416-430 [
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