For electronic packaging structure, there are many design parameters that will affect its reliability performance, using experimental way to obtain the reliability result will take a considerable amount of time. Therefore, how to shorten the design time becomes a critical issue for new electronic packaging structure development. This research will combine artificial intelligence (AI) and simulation technology to assess the long-term reliability of wafer level packaging (WLP). A simulation technology using finite element method (FEM) with appropriate mechanics theories has been validated by multiple experiments will replace the experiment to create reliability results for different WLP structures. After a big WLP structure-reliability database created, this study will apply artificial neural network (ANN) theory to analyze this database and obtains a regression model for structure-reliability relationship of WLP. Once the regression model is established and validated, the WLP geometry, such as pad size, die and buffer layer thickness, and solder volume, etc. can be simply entered, and then the WLP reliability results can be immediately obtained through the ANN regression model.

A novel micromechanical approach is proposed to calculate the effective thermal conductivities of fiber reinforced composite materials. The key advantage of the present formulation is its ability to yield closed form solutions for the effective thermal conductivity of composites in both longitudinal and transverse directions for three dimensional heat transfer problems. The obtained results are in good agreement with the experimental data reported in the literature. When compared with analytical and finite element solutions, the results are seen to be in better agreement with the hexagonal packed array compared to the square packed array which thus represents a more realistic model of the fiber distribution in the matrix medium.

In this study, the anti-loosening characteristics of a precision flank-locking locknut fabricated under various machining processes and tested in different dynamic environments were investigated. The control parameters considered include the tightening torque and thread pitch of the set screw, machining process on the end plane of locknut, and vibration amplitude and frequency of dynamic loading in service, etc. Their sensitivities on the axial force ratio and anti-loosening ratio of the locknut were evaluated using Taguchi method. It was found that the pretension of locknut, the tightening torque and the pitch of set screw, and the machining process of the nut's end plane were the significant control parameters for the anti-loosening performance of the locknut. Moreover, the results of experimental measurements were employed in the regression fit on the performance of the locknut. The regression model was able to predict the anti-loosening ratio with 4.42% average error comparing with the measurements. Furthermore, the optimized design of the locknut through the Taguchi method was able to increase the axial force ratio and anti-loosening ratio by 20.4% and 16.8%, respectively, comparing with standard locknut.

Origami, the ancient paper folding art has inspired the engineering equipment and design for decades. The basic concept of origami is very general, which leads to applications ranging from small scale to large scale. Recently, researchers are interested in being able to create self-folding structures. Such a structure enables kinematic manipulation by external forces or moments without folding and/or unfolding operations. This is a beneficial application for many fields including aerospace systems, robots, small devices and self-assembly systems. In this paper, the investigation and analyses of the previous literatures on the key driving force of the actuation structure, including the heat, light, electricity, gas and other actuation methods. The aims are to provide researchers and practitioners with the support to systematically understand the latest technologies in this important and evolving field, with inspiration and direction for follow-up.

An algorithm for the computation and analysis of the Cosserat spectrum for an axisymmetric elasticity boundary-value problem in a finite-length solid cylinder with boundary conditions in terms of stresses is proposed. By making use of the cross-wise superposition method, the spectral problem is reduced to systems of linear algebraic equations. A solution method for the mentioned systems is presented and the asymptotic behavior of the Cosserat eigenvalues is established. On this basis, the key features of the Cosserat spectrum for the mentioned problem are analyzed with special attention given to the effect of the cylinder aspect ratio.

The paper analyzes the issues relating to the applicability of innovative material systems for flexible composite armors. The authors made several samplings of aramid fibers (Kevlar 49) by replacing the epoxy resin base, which is often described in the literature, with the thermoplastic matrix - polyethylene (HDPE) and polypropylene (PP). The samples were fired with .38 Special Full Metal Jacketed (FMJ) ammunition produced by the S&B Company, and then the process of firing was modeled in the ABAQUS program. The advantages and disadvantages of the new material system including the possibility of its use in the construction of hybrid composite armors have been presented on the basis of the results of numerical analyses and ballistic tests.

With the consideration of the flexoelectric effect, the dispersion feature of plane waves propagating in infinite piezoelectric medium and the reflection amplitude ratio at a mechanically traction-free and dielectrically charge-free surface of semi-infinite piezoelectric half-space are studied in this paper. The flexoelectric effect is essentially the microstructure effect of heterogeneous piezoelectric medium. Besides, the strain gradient effect and the micro-inertial effect are also introduced to reflect the influences of the microstructure. Different from the classical piezoelectric medium, there are five kinds of coupled elastic waves in the microstructured piezoelectric medium. The influences of the flexoelectric effect, the strain gradient effect and the micro-inertial effect upon the dispersion feature of the coupled elastic waves and the reflection amplitude ratio are studied numerically. The numerical results are shown graphically and are validated by the energy conservation law. It is found that these microstructure effects have obvious influences upon the dispersion feature of the coupled elastic waves and therefore also affect the reflection energy partition at the mechanically free surface. Especially, the micro-inertial effect has fundamental influences on the dispersion properties of the coupled elastic waves.

In engineering applications, it is pretty often to have domain heat source involved inside. This article proposes an approach using the boundary element method to study thermal stresses in 3D anisotropic solids when internal domain heat source is involved. As has been well noticed, thermal effect will give rise to a volume integral, where its direct evaluation will need domain discretization. This shall definitely destroy the most distinctive notion of the boundary element method that only boundary discretization is required. The present work presents an analytical transformation of the volume integral in the boundary integral equation due to the presence of internal volume heat source. For simplicity, distribution of the heat source is modeled by a quadratic function. When needed, the formulations can be further extended to treat higher-ordered volume heat sources. Indeed, the present work has completely restored the boundary discretization feature of the boundary element method for treating 3D anisotropic thermoelasticity involving volume heat source.

This study provides a solution for the bass extension of a microspeaker system in a mobile device that involves using a resonant combination of a front chamber and a rectangular, long, pipe-shaped port. The efficient resonant coupling of the microspeaker system to the acoustic load in this structure enables a microspeaker with modest cone displacement to achieve a high sound pressure level (SPL) and bass extension below the resonance of the microspeaker in free air, and the total dimensions of the structure are minimized. A combination of electro-mechanic-acoustic and finite element methods was applied to determine the SPL and bass extension levels for mobile devices. Simulation results show acceptable agreement with experimental results. A suitable extended-range microspeaker system was applied in a 10 inch tablet. The audio frequency response could be extended from 630 to 300 Hz with the greatest loudness. As much as possible add low bound frequency extension to make the article more clear. Finally, five cases of parameter settings for the front chamber volume, rear chamber volume, rectangular pipe-shaped port, cross-sectional area, and opening area were studied. The results can be applied for optimizing a suitable extended-range microspeaker system.

Temperature resulting from the joule heating power and the turn-on and turn-off dissipation of high-power, high-frequency applications is the root cause of their thermal instability, electrical performance degradation, and even thermal-fatigue failure. Thus, the study presents thermal and electrical characterizations of the power MOSFET module packaged in SOT-227 under natural convection and forced convection through three-dimensional (3D) thermal-electric (TE) coupled field analysis. In addition, the influences of some key parameters like electric loads, ambient conditions, thermal management considerations (heat sink, heat spreader) and operation conditions (duty cycle and switching frequency) on the power loss and thermal performance of the power module are addressed. The study starts from a suitable estimation of the power losses, where the conduction losses are calculated using the temperature- and gate-voltage-dependent on-state resistance and drain current through the device, and the switching losses are predicted based on the ideal switching waveforms of the power MOSFETs applied. The effectiveness of the theoretical predictions in terms of device’s power losses and temperatures is demonstrated through comparison with the results of circuit simulation and thermal experiment.

A numerical study was undertaken to investigate the mechanical properties of metal-ceramic multilayer micro-pillars under compression. The model system contains alternating layers of aluminum (Al) and silicon carbide (SiC) above a thick silicon (Si) substrate. The finite element analyses show that the pillar deformed in a non-uniform manner under compression, especially when a tapered side wall was included in the model. The heterogeneous feature of the structure plays a significant role in influencing the apparent stress-strain response. The elastic property of the pillar compares favorably with the true composite modulus, but a large discrepancy was found in the plastic response. The difference in deformation behavior between homogeneous pillars and multilayer pillars, along with other geometric effects, were examined in detail.

A modified bi-layer beam model is proposed to study the fracture-dominated scratch process of the brittle material with surface modification layer considering residual stress. The nonlinear analytical solution of the energy release rate is derived considering the graded distribution of the elastic modulus and residual stress. Finite element analysis is also conducted. Both analytical and numerical results show that the graded distribution of the material properties and residual stress plays an important role in the fracture process. Based on the inverse analysis, the proposed model could provide a convenient way to determine the energy release rate of materials possessing a surface modification layer.

A mechanical beam resonator engineered at nanoscale for suppressing thermoelastic damping to obtain ultrahigh quality factor is reported. The resonator employs the torsion mode of a spring beam to excite the rotation oscillation of a nanoscale resonant beam. The ultralow thermoelastic damping in the resonator is obtained by employing torsion oscillation. Optimal study of thermoelastic damping is carried out by varying the dimensional parameters of the resonator. The resonator operating in the MHz regime with the quality factor over one million is obtainable by the proposed oscillation exciting method and appropriate design of dimensional parameters of the beams. In order to obtain such overall intrinsic quality factor, virtual supports are employed to eliminate attachment loss in the resonator.

The present article deals with the influence of the induced magnetic field on an unsteady two dimensional incompressible free convective chemically reacting slip flow of Jeffrey fluid between two parallel plates under the influence of the thermal radiation, Soret and Dufour. It is assumed that the flow is generated due to periodic suction/injection and the non-uniform temperature and concentrations are varying periodically with time at the plates. The governing partial differential equations are reduced into nonlinear ordinary differential equations by using similarity transformations and solved by shooting method along with Rung-Kutta 4th order scheme. The results are analyzed for various flows, heat and mass transfer characteristics with respect to various prominent parameters such as the ratio of relaxation to retardation times, Deborah number, magnetic Reynold’s number, Strommer’s number, radiation parameter, chemical reaction parameter, Soret and Dufour numbers in details through graphs and tables. It is observed that the temperature of the fluid is enhanced with Soret and Dufour whereas the concentration is decreased. Also the mass transfer rate of the fluid is enhanced with Strommer’s number, whereas the heat transfer rate decreases with increasing of the Jeffery fluid parameter. The present results have good agreement with published work for Newtonian case.

Numerical analysis was investigated for steady two-dimensional double diffusive mixed convection boundary layer flow over a semi-infinite vertical plate embedded non-Darcy porous medium filled with nanofluid, in presence of thermal dispersion and under convective boundary conditions. The Buongiorno nanofluid model is used, while the porous medium is described by the Darcy-Forchheimer extension. The governing partial differential equations are transformed into four coupled nonlinear ordinary differential equations using an appropriate similarity transformations and the resulting system of equations is then solved numerically by the finite-difference method. Numerical results are presented to illustrate how the physical parameters affect the flow field, temperature, concentration and solid volume fraction profiles. In addition, the variation of heat, mass and nanoparticle transfer rates at the plate are exhibited graphically for different values of pertinent parameters.

This paper reports an investigation on thermo-electro-mechanical vibration of graphene/piezoelectric graphene/piezoelectric/graphene sandwich nanobeams. Based on the nonlocal elasticity theory, Timoshenko beam theory and Hamilton's principles, the governing equations are developed and solved using generalized differential quadrature (GDQ) method. The effects of the nonlocal parameter, external electrical voltage, temperature change and axial force on vibration of graphene/piezoelectric/graphene sandwich nanobeams are examined. The performance and the accuracy of the presented model are highlighted through numerical examples with different boundary conditions. This study reports that the nonlocal parameter and thermo-electro-mechanical loadings have important effect on the natural frequencies and the deflection mode shapes of the graphene/piezoelectric/graphene sandwich nanobeam. The present work can serve as guideline for the design of a nanoscale graphene/piezoelectric/graphene beams based electromechanical resonator sensors.

The mechanical properties of thin-walled plate with close-packed film cooling holes are studied based on the equivalent solid material concept. The equivalent principals of the method of equivalent strain energy, homogenization theory and uniform static deformation are considered. A simplification method of square penetration pattern for pitch and diagonal direction loading is presented. The goodness of fit is calculated to determine the optimal method. The tensile deformation, bending deflection, rotation displacement and maximum Mises equivalent stress of simplification plate models are in good agreement with plate models with close-packed film cooling holes. For square penetration pattern for pitch direction loading, the equivalent errors of Mises equivalent stress are all less than 10% when the ligament efficiency is more than 0.6.

Experiments are presented on the deformation of free surface induced by water exit of axisymmetric bodies, particular at the moment before body detaching from water. A set of experimental apparatus is designed to provide driving force for the bodies. A high-speed camera is adopted to capture the motion and deformation of the free surface. Bodies of various shapes, including a stretched spheroid, a sphere, a circular cone and a combination of cylinder and circular cone, are lifted out of water with different velocities, by using a straight rod attached on the top of models. It is found that free-surface deformation is affected by the moving velocity a lot. Three wake flow or free-surface spike patterns are generated corresponding to different velocities. When the velocity is larger than a critical velocity, cavitation incepts and bubble is entrapped inside the water spike, which changes the flow pattern and shape of the spike. It is aimed to explore the spike phenomenon of free surface and explain the reasons behind it.

In this paper, the comparisons of thermomechanical fatigue behavior of C/SiC and SiC/SiC fiber-reinforced ceramic-matrix composites (CMCs) subjected to different phase angles of θ = 0, π/3, π/2 and π have been investigated. The relationships between the fatigue damage mechanisms, phase angle, fatigue hysteresis dissipated energy, fatigue hysteresis modulus and fatigue peak strain, fiber/matrix interface debonding and sliding have been established. The differences between C/SiC and SiC/SiC composites under thermomechanical fatigue loading with different phase angles have been analyzed. The damage accumulation of 2.5D C/SiC and 2D SiC/SiC composites under thermomechanical fatigue loading have been predicted. With increasing of the phase angle, the fatigue hysteresis dissipated energy, fatigue peak strain and interface debonded length decrease for the SiC/SiC composite; however, for the C/SiC composite, the fatigue hysteresis dissipated energy, fatigue peak strain and the interface debonded length increase at the same cycle number.

An approach is presented for solving membrane vibration problems using an integrated scheme consisting of the Craig-Bampton (CB) reduction technique and a 2D dynamic infinite element modeling (DIEM) method. In the proposed CB-DIEM scheme, the substructure domain is partitioned into multiple layers of geometrically-similar infinite elements (IEs) which use only the data of the boundary nodes. A convergence criterion based on the first invariant of the DIEM mass matrix is used to determine the optimal parameters of the CB-DIEM scheme, namely the proportionality ratio and number of layers in the DIEM partitioning process and the number of retained frequency modes in the CB reduction method. Furthermore, in implementing the CB method, the inversion of the global stiffness matrix is calculated using only the stiffness matrix of the first element layer. Having reduced the DIEM model, a coupled DIE-FE algorithm is employed to model the dynamic problems of the full structure, which removes the respective methods disadvantages while keeping their advantages. The validity and performance of the proposed CB-DIEM method are investigated by means of three illustrative problems.