Advancements in science and technology, particularly in ultrashort-pulse lasers and refrigeration, have highlighted the wave-like behavior of heat propagation. Consequently, the generalized theory of thermoelasticity, which addresses finite-speed heat conduction, has gained widespread attention. Research indicates that materials with memory and path-dependent characteristics exhibit abnormal diffusion and anomalous heat conduction. However, the traditional generalized theory of thermoelasticity relies on integer-order differential terms in the heat conduction equation. These terms are based on the definition of local limits and only consider the current state of a material point, failing to account for memory-dependent characteristics. In contrast, fractional calculus uses convolution integrals to define its concepts, analyzing differentiation and integration of any real order, as well as methods for solving differential equations containing derivatives of any real order. The integral terms in fractional calculus can describe memory-dependent processes of a system. This paper introduces the development of fractional-order generalized theory of thermoelasticity and fractional calculus, summarizing recent research in this area, including the effects of magneto-electric multi-field coupling, diffusion, and viscoelasticity on the response of fractional-order generalized thermoelastic problems, as well as fractional-order heat conduction in biological tissues. It also identifies limitations in current studies, such as the challenges of short time scales in experimental research and the lack of exploration into high-frequency and high-gradient electromagnetic fields on thermoelastic responses. By addressing these topics, the paper provides a comprehensive overview of the current state and emerging trends in fractional-order generalized thermoelastic problems, aiding researchers in advancing their investigations in this field.

The chip packaging structure is commonly considered to be composed of different material layers stacked together. Due to the inconsistent thermal expansion coefficients of materials, the structure is prone to thermal warping deformation when subjected to significant changes in ambient temperature. At present, thermal warping is a typical failure mode in the field of microelectronic packaging. With the development of ultra-thin packaging components, thermal warping will become more pronounced. However, excessive warping deformation can lead to problems such as chip cracking, interface delamination, and solder joint failure. First, this paper considers the actual size differences between bare chips and substrates, and establishes a heterogeneous stepped double-layer plate model. Second, a thermal warpage experiment platform was constructed using a VIC-3D non-contact full-field strain gauge based on 3D digital image correlation, an infrared thermal imager, and a high-temperature heating stage. Then, the thermal warping deformation of the double-layer plate structure was observed during the heating process, and an equivalent finite element model was established to verify the experimental results. Subsequently, the thermal warpage control of the stepped double-layer board was achieved by attaching a frame sub-structure to the edge of the bottom plate, with its effectiveness verified through both simulations and experiments. Finally, the effects of the geometric and material parameters of the frame sub-structure on the thermal warpage control of the stepped double-layer plate structure are also discussed in detail. It is found that the thermal warping deformation obtained through experimental methods is in good agreement with the simulation results. Moreover, the warping control method using the frame sub-structure can significantly reduce the thermal warping deformation of the heterogeneous stepped double-layer plate structure. The width of the frame structure is the primary factor, and increasing the width can reduce thermal warping deformation effectively. The coefficient of thermal expansion and thickness also have a significant impact on the thermal warping control. As the coefficient of thermal expansion and thickness increase, the thermal warping deformation decreases. The research findings of this paper can provide theoretical guidance for solving thermal warping issues in multi-material laminated structures in microelectronic packaging.

Piezoelectric quasi-crystal materials possess excellent piezoelectric and phonon-phason coupling effects, ensuring their promising applications in piezoelectric devices, such as sensors and transducers. The performance of piezoelectric devices is closely related to the vibration characteristics. Therefore, the free vibration characteristics of one-dimensional hexagonal piezoelectric quasi-crystal discs are investigated. First, the dynamic equations of one-dimensional hexagonal piezoelectric quasi-crystal discs are derived in the context of three-dimensional phonon-phason-electro-elastic multifield couplings. The traction-free and short-circuit boundary conditions at the upper and bottom surfaces are incorporated into the constitutive equations by introducing the rectangular window function. The double Legendre orthogonal polynomial method is employed to obtain the solutions. To improve the computational efficiency, the analytical expressions of numerical integrations are derived. The influence of the diameter-height ratio and phonon-phason coupling effect on the resonance frequency is then analyzed. Subsequently, based on the finite element method, a simulation program for the free vibration characteristics of one-dimensional hexagonal piezoelectric quasi-crystal discs is developed for the first time to verify the theoretical calculation results. The partial differential equation (PDE) module in the COMSOL software is utilized to conduct the simulation. It is found that, compared with the traditional double orthogonal polynomial method, the analytical double orthogonal polynomial method significantly improves the computational efficiency, with an improvement rate of up to 99%. Changing the diameter-to-height ratio significantly influences the normalized frequency of the phason modes, and the higher-order modes are more sensitive to the change of the diameter-to-height ratio. The normalized frequencies of phonon modes and phason modes increase with the diameter-to-height ratio (D/H). The increase of phonon-phason coupling coefficients leads to a decrease in the normalized frequencies of phonon modes and phason modes, and its influence on the phason modes is more significant. The obtained results lay a basis for designing and optimizing the piezoelectric quasi-crystal sensors and transducers with excellent performance.

This study investigates the fatigue behavior of electroactive polymer (EAP) membrane actuators under coupled electromechanical loading to enhance the reliability and durability of EAP-based devices in smart applications. The motivation of this study is to address fatigue failure in EAP membranes, which are increasingly used in soft robotics, artificial muscles, and adaptive structures, yet frequently experience premature failure under dynamic loading conditions. The research employs a viscoelasticity neo-Hookean model to simulate the mechanical behavior of EAP membrane actuators. Based on the principles of crack nucleation and configurational mechanics, the three principal configurational stresses of the model are calculated. A fatigue life factor is introduced to evaluate the fatigue state of the membrane at different positions. The investigation focuses on two key factors influencing fatigue behavior: the elastic polymer network ratio and pre-stretch level. The study systematically analyzes the fatigue increment of the membrane over time under both constant and half-sine cyclic loading conditions. Simulations demonstrate that appropriate pre-stretching significantly improves fatigue resistance of EAP membrane actuators under both constant and half-sine cyclic loading conditions, identifying an optimal pre-stretch level. Additionally, the study reveals that the elastic polymer network ratio plays a crucial role in determining fatigue behavior, with higher network ratios generally leading to improved fatigue performance. These findings inform the design and application of EAP-based devices. By providing insights into fatigue mechanisms and offering strategies to mitigate fatigue failure, this study contributes to the development of more reliable and durable soft actuators. The results can be applied to optimize EAP membrane performance in various smart systems including soft robotics, wearable devices, and adaptive structures.

Soft composites exhibit significant potential in advanced engineering applications but face critical computational challenges due to their inherent heterogeneity and geometric nonlinearity. Traditional meso-scale finite element analysis suffers from low efficiency, rendering macro-meso coupled multiscale analysis impractical for real-world engineering scenarios. To address this limitation, this study develops a clustering-based reduced-order homogenization method that synergistically integrates reduced-order homogenization techniques with clustering analysis, achieving remarkable computational efficiency while maintaining sufficient accuracy. First, we establish a two-scale analysis framework for soft composites on the basis of finite deformation theory. On the meso-scale, an energy density function is used to describe the constitutive behavior of the micro constituents. Then, we perform clustering analysis on the microscale representative volume element (RVE) to partition it into uniform subdomains called clusters. The clustering analysis groups regions with similar mechanical behavior and thereby reduces the system's complexity and related computational cost. After that, proper orthogonal decomposition (POD) is employed to generate reduced bases for approximating the mesoscopic deformation gradient fields. An efficient sampling strategy is used for both snapshot generation and model validation. A clustered version of reduced-order model (CROM) is established based on the principle of minimum energy. Numerical examples demonstrate that the developed CROM can maintain a high level of accuracy while achieving a computational acceleration of about 10⁴ compared to traditional finite element methods. A comparison to an existing clustering approach named self-consistent clustering analysis (SCA) is also given. Although the computational cost of the offline phase for the CROM is relatively high, the online analysis is rather fast. This significant improvement in efficiency makes the method highly suitable for problems that require frequent microscale RVE predictions, such as multiscale analysis or multiscale parameter identification. In conclusion, the developed CROM offers a promising and practical tool for engineers, which can be further applied in the design, optimization, and analysis of soft composites.

This study aims to explore the variation law of threaded joints' loosening under transverse vibration and examine the mechanical behavior during the loosening process. Using a single-bolted, single-lap joint structure, a preload degradation model for bolted connections was developed. Friction torque and shear models were established for both the bearing surface and thread surface. The friction-shear model for the bearing surface and the thread surface caused by the additional bending moment was also established. The impacts of vibration amplitude, thread pitch, and initial preload on the variation of bolt preload were analyzed, and the failure mechanism of bolt loosening was explored through case studies. A transverse vibration test bed was designed and fabricated, and the preload decline curves under different parameters were obtained, verifying the rationality of the theoretical model between loosening factors and the preload. The results indicate that when the loosening torque exceeds the combined friction torque of the bolt head's bearing surface and the thread surface, the bolt reaches the critical condition for loosening. The friction torque between the bolt head's bearing surface and the thread pair's surface decreases when the vibration amplitude increases. When the vibration amplitude reaches the critical value, the bolt loosening further accelerates. A higher initial preload makes loosening harder to reach and slows preload decay. Under identical conditions, larger vibration amplitude and thread pitch accelerate preload decline.

The coupled corrosion-fatigue failure of steel wires is a prevalent and critical failure mode in cable structures. However, protective sheaths prevent simultaneous corrosion and fatigue, complicating failure analysis. Traditional methods based on damage mechanics and fracture mechanics have been widely used to study fatigue fracture. However, damage mechanics approaches are often computationally complex and difficult to apply in engineering practice, while fracture mechanics methods typically require the assumption of pre-existing cracks, limiting their real-world applicability. To address these limitations, this study proposes a comprehensive theoretical framework for evaluating the corrosion-fatigue failure of high-strength steel wires. First, the fatigue damage state of steel wires is assessed using S-N curves under non-corrosive conditions, assuming the protective sheath remains intact. Once damage to the sheath occurs, a corrosion kinetics model is employed to simulate the growth of corrosion pits in steel wires. The transition from corrosion pits to cracks is then predicted by determining the critical fatigue cycles required for crack initiation. Subsequently, crack propagation is analyzed using fracture mechanics principles and Franc3D software, enabling the estimation of the fatigue life of corroded steel wires. To validate the theoretical predictions, an experimental study is conducted to investigate the coupled effects of fatigue and corrosion in high-strength steel wires, where fatigue loading is applied prior to corrosion exposure. Comparison of experimental results with theoretical calculations reveals minimal deviation, confirming the accuracy and effectiveness of the proposed theoretical approach. In summary, the failure analysis methodology developed in this study offers a computationally efficient and practically applicable approach for assessing the corrosion-fatigue behavior of steel wires in cable structures. The method exhibits strong agreement with experimental observations and provides a valuable reference for the design, operation, and maintenance of cable structures. Furthermore, the proposed framework can be extended to other high-strength steel components exposed to coupled fatigue and corrosion conditions, contributing to the reliability and durability assessment of engineering structures in harsh environments.

Hydrogels have received increasing attention for their diverse applications in flexible wearable devices, bionic actuators, and biomedicine. However, conventional hydrogels often exhibit poor mechanical properties. Inspired by muscle training, this paper proposes a new method that combines the ice template method with mechanical training to prepare anisotropic tough hydrogels, and analyzes the effects of different training times on their mechanical properties. In the preparation process, PVA was first dispersed in deionized water, heated, and stirred to form a homogeneous solution, which was then slowly dripped into a mold and frozen with liquid nitrogen from the bottom up to form a PVA hydrogel with a fibrous structure. This hydrogel was then immersed in a glycerol-water mixture and mechanically trained using a custom cyclic tensile tester. The mechanical properties of hydrogels prepared by different methods were tested. Results showed that the anisotropic hydrogels prepared by the ice template method displayed a distinct fiber structure, albeit with significant fiber orientation dispersion. Following mechanical training, the fiber orientation of the hydrogels became highly consistent and more compact. The mechanical properties of the hydrogels were significantly improved by the combination of the ice template method and the mechanical training method. In addition, an anisotropic hyperelastic constitutive model was proposed, taking into account variations in composition and fiber orientation. Comparison with experimental results verified that the model can effectively describe the mechanical behavior of the hydrogels. This study offers a new method for preparing anisotropic tough hydrogels and provides a theoretical basis for predicting and analyzing their mechanical responses.

The superior electrical and mechanical properties of flexible electronics enable the breaking of the limitations of traditional electronic devices, and promise wide applications in the fields of bionic electronics, energy monitoring, and medical monitoring. Transfer printing is the mainstream technology for the fabrication of flexible electronics, realizing the processes of picking up electronic devices from the donor substrate and printing them onto the receiver substrate. Transfer printing greatly enriches the fabrication methods of flexible electronics and promotes the development of related industries. However, even with encouraging advantages, current transfer printing processes still face some challenges that cannot be ignored. For example, the preparation process of the stamp is often complex and requires high-precision machining and fine control. In addition, most external excitations cause damage to electronic devices, hindering the further promotion and application of transfer printing technology. To tackle these technical challenges, this paper proposes a load-combination modulation-based transfer printing method. This scheme is proposed to control the loading sequences of rigid pillars on the stamp, modulate the displacement/stress distribution at the stamp/device interface, realize the interface adhesion control, and finally complete the transfer printing on different rigid/flexible substrates. This paper also considers the complex nonlinear relationship between the geometric parameters of the stamp and the energy release rate during the transfer printing process. The related theoretical models and finite element analysis provide valuable insights for the design of actual transfer printing stamps. Physical experiments further validate the effectiveness and reliability of the transfer printing method proposed in this paper. This method not only has high compatibility and adaptability with the morphology of electronic devices and receiver substrates, but also supports large-scale, multi-layer, and multi-time integration of micro-silicon wafers on flexible substrates. Experimental results demonstrate significant application potential and market prospects.

The drilling environment and drill string assembly in deep and ultra-deep wells are complex, leading to increased vibration loads that can cause fatigue and crack propagation in drill pipe joints, resulting in premature scrapping. This paper addresses these issues through several research steps. First, a dynamic calculation model for drill pipe joints is developed to analyze the axial force, torque, and bending moment on the joints beneath the well. Next, a finite element analysis model is constructed to assess whether the forces on the joints meet material strength requirements. Additionally, a crack propagation model is established to evaluate the remaining service life of the joints. The findings are as follows: The dynamic calculation model is validated against laboratory experiments. In the target environment, drill pipe joints are subjected to an axial force of 13.11 kN, a torque of 35 kN·m (including make-up torque), and a bending moment of 0.75 kN·m. The analysis of composite loads reveals maximum von Mises stresses of 551.2 MPa for internal thread joints and 323.2 MPa for external thread joints, both of which satisfy material strength requirements. Furthermore, cracks in the threads of drill pipe joints are primarily opening cracks, with depth significantly influencing crack propagation more than length. Under current operating conditions, a minimum crack propagation size of 3×2 mm corresponds to a remaining service life of 126,820 cycles.

To investigate how hydrogen atoms affect the fracture of metallic materials at the microscopic level, this paper develops a model of crack-dislocation interaction incorporating hydrogen infiltration at the crack tip across multiple grains, based on discrete dislocation theory. The model examines how hydrogen alters dislocation distribution on slip planes within grains, affects dislocation penetration through grain boundaries, and initiates wedge cracks at these boundaries. It applies to both body-centered cubic (BCC) and face-centered cubic (FCC) crystals. Through calculations, theimpact of varying hydrogen concentrations and infiltration ranges at the crack tip on dislocation distribution in front of the crack is analyzed. Results show that hydrogen at the crack tip promotes dislocation emission, increases the driving force for dislocation movement on slip planes, and facilitates dislocation penetration through grain boundaries. The relationship between wedge crack initiation at grain boundaries and hydrogen presence at the crack tip is explored. It is found that at large grain boundary angles, an increase in the hydrogen concentration and infiltration range at the crack tip makes it easier for wedge cracks to initiate at grain boundaries. Additionally, the model assesses how hydrogen infiltration at the crack tip influences shear stress in the dislocation-free zone in front of the main crack. It reveals that increased hydrogen concentration and infiltration range at the crack tip enlarge the dislocation-free zone in front of the crack, reducing the shielding effect of dislocations and facilitating crack propagation. This model effectively demonstratesthe influence of hydrogen atoms at crack tips on dislocations in crystals, providing a foundation for studying metal fracture in hydrogen environments.