Abstract For materials/structures of small scale, size effect needs to be considered. In this paper, we apply the Fourier–Bessel series (FBS) system of vector functions along with the dual-variable and position (DVP) method to the cracked layered elastic media. The nonlocal effect is considered based on the Eringen’s nonlocal elasticity theory. While the DVP matrix method is unconditionally stable for handling layered media as compared with the existing layer matrix methods, the FBS is mathematically elegant and computationally efficient as compared with the traditional integral method, based on either the Hankel transform or the Fourier transform. The computational saving is due to the fact that in terms of the FBS, the expansion coefficients, also called Love numbers, need to be calculated only once on the crack surface, independent of the number of the field points on this surface. The mixed boundary-value problem where a circular crack is located horizontally within the layered media is solved by using this newly proposed approach. Numerical examples are presented to demonstrate the effect of nonlocal parameters on the field distribution. The effect of material anisotropy and layering is also analyzed.

Abstract The oscillating wing plays a crucial role in aerodynamic performance and is often affected by dynamic stalls characterized by laminar bubble separation, large vortices and vortex separation. We used a 3D NACA 0012 oscillating wing to achieve realistic flow and improved aerodynamic performance. A 3D wing was simulated using the OpenFOAM CFD toolbox with a large eddy simulation (LES) turbulence model and plasma actuators to enhance aerodynamic performance. This study investigates the difference between the linear plasma actuator and the spanwise segmented plasma actuator at the leading edge of the airfoil compared to the case without plasma. The case without plasma is used as a baseline after a grid-independent test to understand the effect of plasma over an airfoil. A simulation without and with plasma strengths of 40 kN/m3, 7 kV and 1.2 kHz was carried out for linear and spanwise segmented plasma cases. As a result, the upstroke shows a better lift coefficient (Cl) for the oscillating wing with a linear plasma actuator, increasing by 10.34% compared to the case without plasma. Comparatively, a spanwise segmented plasma actuator, from an angle of attack (AoA) of 7–23° during the upstroke, achieved a Clmax improvement of 14.77% over a baseline case. The aerodynamic performance (Cl/Cd) was also improved from an AoA of −5° to 15°, with a maximum percentage of 21.44% compared to the baseline Clmax. Both plasma cases enhance the aerodynamic performance. Hence, the superior enhancement is found in spanwise segmented plasma actuators due to its ability to prevent large-scale separations.

Abstract This paper uses the viscous-spring artificial boundary method and variable-kinematic finite beam elements to solve wave propagation problems in infinite space. According to the artificial boundary technique, springs and dashpots with appropriate elastic and damping coefficients are applied at the external surfaces of the domain to ensure the absorption of the incident waves. The finite-element matrices and vectors corresponding to various 1-dimensional kinematic models are obtained with the Carrera Unified Formulation. In particular, using Lagrange-type expansions for approximating the primary variables over the finite beam element cross-section has enabled the artificial boundaries to be easily applied. Both outer- and inner-source problems have been considered to compare the methodology with analytical and numerical solutions available in the literature. Moreover, the current approach has been adopted to solve wave propagation problems of a configuration consisting of a semi-infinite space and a beam-like structure on its free surface and subjected to various loading conditions.

ABSTRACT In this work, ceramic particle and metal matrix interfacial delamination in transformation-induced plasticity steel composite reinforced with magnesium partially stabilized zirconia particles is investigated using a parametric modeling approach. The global behavior of the composite is modeled using elastic and Johnson-Cook plasticity models for the ceramic particles and the austenite matrix. Interfacial degradation is implemented through a cohesive zone model with a traction-separation law. Both perfect and damaged models are considered in the global stress-strain curve analysis. In the damaged model, the plastic region is characterized by softening and hardening stages, corresponding to unstable and stable crack propagation, respectively. To comprehensively identify the interfacial evolution, parameters such as normal contact strength, normal separation and stiffness degradation are evaluated along the particle/matrix interface. From a statistical perspective, the mechanical behavior of the system is analyzed through the kernel distribution plots for both the particles and the matrix. As the strain level increases, right- and left-skewed distributions are observed in the particles and matrix, respectively, particularly under high-strain conditions. Consequently, in the plastic hardening region, the median value exceeds the mean value, indicating that relying solely on the average stress value results in an underestimation during significant delamination.

Abstract In order to study the mechanical properties and microscopic damage of red sandstone by dry and wet cycling, this paper establishes a 3-dimensional uniaxial compression model of red sandstone by using PFC3D software. On this basis, microscopic cracks were introduced to analyze the influence of different cracks on the mesoscopic cracking of the model. The results show that the error between the simulation results and the test results is less than 10% for the model established by PFC3D software. Based on the discrete element model, displacement and velocity maps were obtained, and the values are larger at the contact with the load and smaller at the distance from the load. With the increase of the initial crack angle, the peak stress gradually increases, and with the decrease of the crack size, the peak stress gradually decreases, and the contact force also decreases.

ABSTRACT The benefits of wafer-level packaging include better thermal dissipation, lower latency and reduced space consumption. Accelerated thermal cycling test (ATCT) is a regulation that determines whether a product is ready for mass production, but it takes a long time and is costly to perform. The design-on-simulation approach can reduce the number of ATCT experiments and shorten the design cycle. However, the simulation method must be verified before it can be treated as an experiment; if the simulation consistently matches experiments at close range, it can also be treated as an experiment. In addition, the verified simulation method can be used to develop a machine learning (ML) database and obtain an artificial intelligence model for long-term reliability prediction. Due to its effectiveness in solving nonlinear problems with relatively short computation times, polynomial regression (PR) is used in this study as ML model. Results show combining PR with an unsupervised learning algorithm, K-means, can produce more accurate predictions.

Abstract An axisymmetric theoretical model is simplified to investigate sound absorption in the underwater anechoic coating with spherical cavities. An empirical equation is put forward to predict the frequency at the first absorption peak. The sound absorption mechanism of viscoelastic solid with cavity is clarified by the power analysis method. The quantitative analysis of viscoelastic power dissipation on sound energy provides a new idea for the structural topology optimization of anechoic coatings. These formulas are given to calculate the dissipation power of viscoelastic solid. The dependence of sound absorption performance of the anechoic coating upon radius and position of single or two spherical cavities of the unit cell is analyzed in detail. The study provides guidance for the design of anechoic coatings with cavities.

Abstract A mechanical metamaterial has been constructed using a network of interconnected isosceles triangles and right triangles by inspiration from the seesaw motion. The connections are defined as hinges with rotationally elastic restraints wherein each isosceles triangle is connected to three neighboring rotating units, while each right triangle is connected to four neighboring rotating units. The effective Poisson's ratio under on-axes loading were established using geometrical approach, while the on-axes Young's moduli were developed by matching the spring rotational energy at the hinges of the metamaterial during relative rotation of the rigid units with the strain energy of deformation of the homogenized continuum. Results reveal that by adjusting the geometrical parameters, the Poisson's ratio can range from positive to negative values. The results also show that both the Poisson's ratio and Young's moduli have a wide range of geometrical parameters for fine-tuning at low mechanical properties and well as a narrow range of geometrical parameters for coarse tuning at high mechanical properties. These observations suggest that the metamaterial has a wide range of applications from soft robotics to structural applications by adjustment of its geometrical parameters.

Abstract This work is focused on the strong deformation motion mechanism of multi-layer metallic materials under extreme pressure conditions accompanied by a strong impact effect between the projectile composed of multi-layer metallic materials and the steel barrel of the launcher itself. Here, this transient engraving process of the projectile with complicated stress–strain based on a new type of structure and propulsion pattern is firstly studied by proposing a new physical and mathematical model with a coupling of dynamical equations and two-stage combustion ballistic equations. Comparisons of engraving distance of computational results are done with experimental studies, and a reasonable match has been obtained in these comparisons. Further, the thickness effect of the metal jacket of the projectile on the engraving stress and deformation level is analyzed to obtain universal engraving resistance equations. The results have also shown that the projectile's whole transient deformation motion process in the launcher can be divided into three periods due to the initial slide impact effect under the first-stage propellant gas and the later propelling effect as the second-stage propellant is ignited. However, the engraving durations are all less than 0.7 ms with different levels of elastic-plastic deformations between multi-layer metallic materials for different conditions.

Abstract A method of solving plane-strain boundary value problems for a reduced version of the double slip and rotation model is developed. It is assumed that the intrinsic spin vanishes. Elastic strains are neglected. The Mohr–Coulomb yield criterion is adopted. An analogy between the solutions for this model and classical rigid plastic solutions of pressure-independent plasticity is revealed. The method is based on introducing auxiliary variables that satisfy the equation of telegraphy in regions where both families of characteristics are curved. Therefore, Riemann's method can conveniently be applied to solving boundary value problems. The method is employed for analyzing the processes of plane-strain drawing and extrusion through a wedge-shaped die. Friction is neglected. The solution is given in terms of ordinary integrals. The effect of the angle of internal friction on processes’ parameters is revealed. The solution reduces to available solutions of pressure-independent plasticity if the angle of internal friction vanishes.