Acta Mechanica Solida Sinica最新文献

Flexoelectricity is present in nonuniformly deformed dielectric materials and has size-dependent properties, making it useful for microelectromechanical systems. Flexoelectricity is small compared to piezoelectricity; therefore, producing a large-scale flexoelectric effect is of great interest. In this paper, we explore a way to enhance the flexoelectric effect by utilizing the snap-through instability and a stiffness gradient present along the length of a curved dielectric plate. To analyze the effect of stiffness profiles on the plate, we employ numerical parameter continuation. Our analysis reveals a nonlinear relationship between the effective electromechanical coupling coefficient and the gradient of Young’s modulus. Moreover, we demonstrate that the quadratic profile is more advantageous than the linear profile. For a dielectric plate with a quadratic profile and a modulus gradient of − 0.9, the effective coefficient can reach as high as 15.74 pC/N, which is over three times the conventional coupling coefficient of piezoelectric material. This paper contributes to our understanding of the amplification of flexoelectric effects by harnessing snapping surfaces and stiffness gradient design.

This research explores the dynamic behaviour of horn-shaped single-walled carbon nanotubes (HS-SWCNTs) conveying viscous nanofluid with pulsating the influence of a longitudinal magnetic field. The analysis utilizes Euler–Bernoulli beam model, considering the variable cross section, and incorporating Eringen’s nonlocal theory to formulate the governing partial differential equation of motion. The instability domain of HS-SWCNTs is estimated using Galerkin’s approach. Numerical analysis is performed using the Haar wavelet method. The critical buckling load obtained in this study is compared with previous research to validate the proposed model. The results highlight the effectiveness of the proposed model in assessing the vibrational characteristics of a complex multi-physics system involving HS-SWCNTs. Dispersion graphs and tables are presented to visualize the numerical findings pertaining to various system parameters, including the nonlocal parameter, magnetic flux, Knudsen number, and viscous factor.

The multi-layer cylindrical helicoidal fiber structure (MCHFS) exists widely in biological materials such as bone and wood at the microscale. MCHFSs typically function as reinforcing elements to enhance the toughness of materials. In this study, we establish a shear lag-based pullout model of the cylindrical helicoidal fiber (CHF) for investigating interlayer stress transfer and debonding behaviors, with implications regarding the underlying toughening mechanism of MCHFS. Based on the shear lag assumptions, analytical solutions for the stress and displacement fields of the MCHFS during the pullout are derived by considering the CHF as a cylindrically monoclinic material and verified through the 3D finite element simulation. It is found that the helical winding of CHF results in both axial and hoop interlayer shear stresses. Both the helical winding angle and the elastic moduli of the fiber and matrix have significant influences on interlayer stress transfer. This work reveals a new interlayer stress transfer mechanism in the MCHFS existing widely in biological materials.

Scale effects play critical roles in the mechanical responses of microstructures. An isogeometric analysis was developed here to investigate the mechanical responses of an axially functionally graded microbeam. The Euler–Bernoulli beam model was utilized, and size effects in the structure were modeled with a stress-driven two-phase local/nonlocal integral constitution. The governing equation of microstructures was given in an equivalent differential form with two additional constitutive boundary conditions. The framework was verified and utilized to analyze the microbeam’s static and dynamic mechanical responses. The present work showed great potential for modeling various types of functionally graded microstructures.

In engineering applications, the notch effect and size effect significantly influence the evaluation of fatigue performance in components, necessitating special attention in life prediction. This study proposes a new probabilistic model, based on the theory of critical distance (TCD), to predict fatigue life, with the aim of quantitatively assessing the impact of notch effect and size effect. The stress distribution on the critical plane is first characterized using a sixth-order multinomial function, and the relative stress gradient function is utilized to calculate the value of the critical distance. Furthermore, the effect of the ratio of shear strain to normal strain on fatigue life under multiaxial loading is considered. Additionally, the integration of the Weibull distribution into the TCD is employed for conducting probabilistic modeling of fatigue life. Finally, fatigue experiments are conducted on notched specimens of Q355D steel, demonstrating that the life prediction results under 50% survival probability are superior to the traditional TCD method.

Micromechanics investigations of composites with fiber-shaped reinforcement are extensively applied in the engineering design and theoretical analysis of thermal composites in the aerospace engineering and high-tech industry. In this paper, a critical review of various classical micromechanics approaches is provided based on the classification framework and the development of micromechanics tools. Several numerical micromechanics tools have been developed to overcome limitations through exactly/approximately solving the internal governing equations of microstructures. The connections and limitations of those models are also investigated and discussed, based on which three recently developed numerical or semi-analytical models are explained, including finite-element micromechanics, finite-volume direct averaging micromechanics, and locally exact homogenization theory, as well as machine learning tools. Since it is almost inevitable to mention the interfacial effects on thermal behavior of fibrous composites, we review the new mathematical relations that interrupt the original continuity conditions due to the existence of interphase/interface within unit cells. Generally speaking, the interphase/interface is demonstrated to play a significant role in influencing the effective coefficients and localized thermal fields. The present work also briefly reviews the application of micromechanics tools in emerging engineered woven composites, natural fibrous composites, and ablative thermal protection composites. It is demonstrated that sophisticated micromechanics tools are always demanded for investigating the effective and localized responses of thermal fibrous composites.

By incorporating two different fracture mechanisms and salient unilateral effects in rock materials, we propose a thermomechanical phase-field model to capture thermally induced fracture and shear heating in the process of rock failure. The heat conduction equation is derived, from which the plastic dissipation is treated as a heat source. We then ascertain the effect of the non-associated plastic flow on frictional dissipation and show how it improves the predictive capability of the proposed model. Taking advantage of the multiscale analysis, we propose a phase-field-dependent thermal conductivity with considering the unilateral effect of fracture. After proposing a robust algorithm for solving involved three-field coupling and damage-plasticity coupling problems, we present three numerical examples to illustrate the abilities of our proposed model in capturing various thermo-mechanically coupled behaviors.

In the tapping-mode atomic force microscope (TM-AFM), the probe tip continuously taps the sample surface, which may cause plastic deformation of the sample and result in energy dissipation. The energy dissipation of the probe is closely related to the scanned phase image. To quantify the energy dissipation due to plastic indentations of the sample, this study utilized a combination of molecular dynamics (MD) simulations and experiments on single-crystal copper samples, including multiple nano-indentation tests. The energy dissipation of the probe due to the plastic deformation of the sample was calculated by integrating the hysteresis curve of the indentation depth versus the force applied to the indenter. The simulation results are in good agreement with the experimental ones. Both sets of results have demonstrated that the plastic energy dissipation decreases as the number of indentations increases, and eventually the energy of the probe tends to stabilize. This equilibrium energy dissipation is associated with other dissipation mechanisms. Furthermore, it was observed that, after hundreds of taps, the dissipated energy of plastic deformation could be ignored, implying that the scanned image may not reflect the plasticity information of the sample after multiple taps of the probe on the sample surface for scanning.

The classical adhesive contact models belong to isothermal adhesion theories, where the effect of temperature on adhesion was neglected. However, a number of experimental results indicated that the adhesion behaviors can be significantly affected by temperature. In this paper, the two-dimensional non-slipping anisothermal adhesion behaviors between two orthotropic elastic cylinders are investigated within the framework of the Johnson–Kendall–Roberts theory. The stated problem is reduced to the coupled singular integral equations by virtue of the Fourier integral transform, which are solved analytically with the analytical function theory. The closed-form solutions for the stress fields in the presence of thermoelastic effect are obtained. The stable equilibrium state of contact system is determined by virtue of the Griffith energy balance. The effect of temperature difference on adhesion behaviors between orthotropic solids is discussed. It is found that the difference between the oscillatory and non-oscillatory solutions increases with increasing the degree of anisotropy of orthotropic materials. The oscillatory solution cannot be well approximated by the non-oscillatory solution for the orthotropic materials with relatively high anisotropy.

Tough elastomers and gels have garnered broad research interest due to their wide-ranging potential applications. However, during the loading and unloading cycles, a clear stress softening behavior can be observed in many material systems, which is also named as the Mullins effect. In this work, we aim to provide a complete review of the Mullins effect in soft yet tough materials, specifically focusing on nanocomposite gels, double-network hydrogels, and multi-network elastomers. We first revisit the experimental observations for these soft materials. We then discuss the recent developments of constitutive models, emphasizing novel developments in the damage mechanisms or network representations. Some phenomenological models will also be briefly introduced. Particular attention is then placed on the anisotropic and multiaxial modeling aspects. It is demonstrated that most of the existing models fail to accurately predict the multiaxial data, posing a significant challenge for developing future anisotropic models tailored for tough gels and elastomers.