Acta Mechanica Solida Sinica最新文献

The scattering of shear horizontal (SH) waves by a circular hole in an infinite piezomagnetic medium affected by magnetic field and compressive stress has been investigated theoretically in this study. The effective elastic, piezomagnetic, and magnetic permeability constants of the piezomagnetic material change with the external magnetic field and compressive stress. The governing differential equations for SH waves scattered by a circular hole are solved using the wave function expansion method. The effects of the magnetic field and compressive stress on mechanical displacement, dynamic stress, and magnetic potential of SH waves around a circular hole are discussed in detail. It has been found that the mechanical displacement around the circular hole increases with magnetic field and decreases with compressive stress. As the magnetic field increases, the maximum dynamic stress increases and structural resonance is strengthened. The findings presented in this study are beneficial for improving the performance of magnetoelastic acoustic wave devices.

A theoretical model is developed to investigate the sliding electrical contact behavior with the consideration of the electrical-thermal–mechanical coupling effect. The interfacial electrical resistance and electrical constriction resistance are both involved. The Joule heating due to electrical contact resistance and the frictional energy dissipation are considered in the model for the assessment of the temperature rise at the contact interface. A singular integral equation for sliding electrical contact considering both frictional and Joule heat is developed and solved to obtain the contact pressure, current density, and temperature rise. Furthermore, a discrete fast Fourier transform-based boundary element method is applied to obtain the numerical solution of sliding electrical contact. Good agreement is achieved between theoretical and numerical results. After the validation, the effects of potential drop and sliding velocity on sliding electrical contact behavior are investigated. The results indicate that the proposed theoretical model can provide an exact prediction of multi-physics sliding electrical contact behavior.

The human body displays various symptoms of altitude sickness due to hypoxia in environments with low pressure and oxygen levels. While existing studies are primarily focused on the adverse effects of hypoxia and oxygen supplementation strategies at high altitudes, there is a notable gap in understanding the fundamental mechanisms driving altitude hypoxia. In this context, we propose a sophisticated two-way fluid–structure interaction model that simulates respiratory processes with precisely structured and deformable upper airways. This model reveals that, under identical pressure differentials at the airway’s inlet and outlet, the inspiratory air volume remains largely consistent and is minimally affected by specific pressure changes. However, an increase in the pressure differential enhances gas inhalation efficiency. Furthermore, airway morphology emerges as a pivotal factor influencing oxygen intake. Distorted airway shapes create areas of high flow velocity, where low wall pressure hampers effective airway opening, thus diminishing gas inhalation. These results may shed light on the effects of low-pressure conditions and upper airway structure on respiratory dynamics at high altitudes and inform the development of effective oxygen supply strategies.

Twisted and coiled polymer actuator (TCPA) is a type of artificial muscle that can be driven by heating due to its structure. A key issue with TCPA performance is the low driven frequency due to slow heat transfer in heating and cooling cycles, especially during cooling. We developed a numerical model of coating heating and nitrogen gas cooling that can effectively improve the driven forces and frequencies of the TCPA. Results indicate that natural cooling and electric fan cooling modes used in many experiments cannot restore the TCPA to its initial configuration when driven frequencies are high. Nitrogen gas cooling, at high driven frequencies, can fully restore the TCPA to its initial configuration, which is crucial for maintaining artificial muscle flexibility. In addition, as driven frequency increases, the corresponding driven force decreases. Systematic parametric studies were carried out to provide inspirations for optimizing TCPA design. The integrative computational study presented here provides a fundamental mechanistic understanding of the driven response in TCPA and sheds light on the rational design of TCPA through changing cooling modes.

Given the significant potential of multi-directional functionally graded materials (MFGMs) for customizable performance, it is crucial to develop versatile material models to enhance design optimization in engineering applications. This paper introduces a material model for an MFGM plate described by trigonometric functions, equipped with four parameters to control diverse material distributions effectively. The bending and vibration analysis of MFGM rectangular and cutout plates is carried out utilizing isogeometric analysis, which is based on a novel third-order shear deformation theory (TSDT) to account for transverse shear deformation. The present TSDT, founded on rigorous kinematics of displacements, is demonstrated to surpass other preceding theories. It is derived from an elasticity formulation, rather than relying on the hypothesis of displacements. The effectiveness of the proposed method is verified by comparing its numerical results with those of other methods reported in the relevant literature. Numerical results indicate that the structure, boundary conditions, and gradient parameters of the MFGM plate significantly influence its deflection, stress, and vibration frequency. As the periodic parameter exceeds four, the model complexity increases, causing result fluctuations. Additionally, MFGM cutout plates, when clamped on all sides, display almost identical first four vibration frequencies.

This paper aims to seek expedited fatigue analysis methods using the infrared self-heating technique. The fatigue analysis of NiTi shape memory alloys is obtained through a hybrid approach: fatigue tests to failure yield relatively shorter fatigue lives, while determining the fatigue limit, normally involving extremely high cycles approaching 10⁷ cycles, is directly achieved via self-heating tests. This methodology significantly reduces testing cycles, costing only a fraction of the several-thousand-cycle tests typically required. The validity of this approach is successfully demonstrated through fatigue testing of 18Ni steel: the entire S–N curve is examined using the traditional fatigue test until a life of up to 10⁷ cycles, and the indicated fatigue limit agrees well with the one directly determined through the self-heating method. Subsequently, this developed approach is applied to the fatigue analysis of shape memory alloys under complex loading, enabling the concurrent estimation of the limits of phase transformation-dominated low-cycle fatigue and high-cycle fatigue in the elastic regime on a single specimen. The results obtained align well with other supporting evidence.

The tubular Miura-ori (TMO) structure has attracted much attention due to its excellent folding capability and rich application diversity. However, the existing theoretical research on origami structure is overly complex, and kinematic analysis rarely involves bending motion. In the present work, based on geometric kinematics, “equivalent deformation mechanism” is proposed to study the axial and bending motions of TMO under small in-plane deformations. Firstly, the geometric design is studied using the vector expression of creases. To simplify the kinematic analysis of axial motion, TMO deformation is equated to a change in angle. The proposed method is also applicable to bending motion, because both bending and axial motions can be described using similar deformation mechanisms. In addition, the accuracy of the proposed method is validated through numerical analysis, and the error between analytical and numerical solutions is sufficiently small for the folding angle (gamma in left[ {25^circ , 65^circ } right]). Finally, the numerical simulation is validated with mechanical experiments. Results show the effectiveness of the proposed method in describing the kinematic law of TMO structures in a simple way. This research sheds light on the kinematic analysis of other origami structures and establishes a theoretical framework for their applications in aerospace engineering, origami-based metamaterials, and robotics.

The first principal stress plays a key role in ductile fracture processes. Investigation of the distribution and evolution of the first principal stress at the crack tip is essential for exploring elastoplastic fracture behaviors. A semi-analytical model was developed in this study to determine the maximal first principal stress at the mode I crack tip with 3D constraints for materials following the Ramberg–Osgood law. The model, based on energy density equivalence and dimensional analysis, was validated through finite element analysis (FEA) of various materials and geometric dimensions of specimens with mode I cracks, under over 100 different types of working conditions. The dimensionless curves of maximal first principal stress versus load, as predicted by the model, agreed well with the FEA results, demonstrating the accuracy and applicability of the model. This research can provide a basis for future theoretical predictions of crack initiation and propagation.

In order to enhance the fatigue properties of metallic materials, a feasible rationale is to delay or prevent the interior and surface fatigue crack initiation. Based on this rationale, the study investigates the approach of improving the very high cycle fatigue properties of TC6 titanium alloys through near-β forging coupled with shot peening, conducted at 930 ℃ and ambient temperature, respectively. To unveil the associated mechanisms, microstructure, microhardness, residual stress, and fatigue properties are thoroughly analyzed after each process. Results indicate a considerable refinement in microstructure and significant mitigation of the initially existed strong texture post near-β forging and annealing, efficiently delaying crack initiation and propagation. As a result, the very high cycle fatigue property of TC6 achieves remarkable enhancement after forging. Compared to near-β forging, shot peening might not necessarily improve the very high cycle fatigue performance, particularly beyond 10⁶ cycles.