This paper discusses a successful experimental procedure to determine the hygroscopic swelling property of polymeric materials used in electronic packaging. Saturated moisture concentration and moisture diffusivity were determined by measuring the weight gain during moisture absorption. Hygromechanical properties, such as the coefficientof moisture expansion (CME), were determined through Thermo-Mechanical Analyzer (TMA) and Thermo-Gravimetric Analyzer (TGA) techniques. Fick's law of transient diffusion is solved by using finite element (FE) analysis to evaluate the overall moisture distributions. Both two-dimensional and three-dimensional models based on the FE software ANSYS were developed to predict the thermal-induced strain, hygroscopic swelling deformation, and residual thermohygro-mechanicalstress distributions. Reliability analysis at three JEDEC preconditioning standards 60°C60%RH, 85°C60%RH and 85°C85%RH was carried out. A series of comprehensive parametric studies were conducted in this research.

Thermoelastic temperature, displacement and stress in heat transfer during laser surface hardening are solved in both Lagrangian formulation and Eulerian formulation. In the Eulerian formulation, the heat flux is fixed in space and the work-piece is moved through a control volume. In the case of uniform velocity and uniform heat flux distribution, the Eulerian formulation leads to a steady-state problem, while the Lagrangian formulation remains transient. In the Eulerian formulation, the reduction to a steady-state problem increases the computational efficiency. Also, in this study, an analytical solution is developed for an uncoupled transient heat conduction equation in which a plane slab is heated by a laser beam. The thermal results of the numerical models are compared with the results of the analytical model. A comparison of the results shows that numerical solutions in the case of uncoupled problem are in good agreement with the analytical solution.

The temperature versus life (T-N) curves of both centrally notched and unnotched AS-4/PEEK (APC-2) composite laminates due to constant stress amplitude tension-tension (T-T) fatigue loading were investigated systematically. The cross-ply laminate possesses the higher mechanical properties than those of the quasi-isotropic laminate at elevated temperature, and also the mechanical properties of both lay-ups are degraded significantly as the temperature increasing. Combining both effects of notch and temperature at various normalized stresses it is found the cross-ply laminate possesses more resistance to cyclic loading than that of the quasi-isotropic laminate. Additionally, the predictive strain model is in a practical and simple form. Alternatively, the T-N curves, instead of conventionally S-N curves, at variously applied stresses are accomplished for preliminary designs and applications.

In this paper a wide range of temp. dependent kernel function ρ(Z) and the strain-rate function h(, T) in the Endochronic viscoplasticity were established first by using experimental steady hysteresis loops of Wei et. al., for Sn/3.9Ag/0.6Cu Solder at fixed 298K or 373K and strain rate at 10−3, 10−4 and 10−51/s; and then extended to predict the thermomechanical behavior of solder under constant low strain rate (10−51/s), from 0 to 1% max. strain fatigue loading with in-phase thermal cycling between 298K and 373K.

A novel approach in the theory to account for the microstructural changes enhanced by the stressassisted grain boundary diffusion mechanism during thermal cycling was proposed by using a partial relaxation function h1(T) of back stress (i.e. ρ0 in ρ(Z)).The theoretical results were in very well agreement with experimental data. These results and the out-phase results from the present theory were new and might be used as references to compare with results derived from other theories.

The use of artificial roughness or turbulence promoters on a surface is an effective technique to enhance the rate of heat transfer of the fluid flowing in a duct. In this study, a computer code has been developed to perform a numerical simulation for optimizing the shape of two-dimensional channel with periodic ribs mounted on the bottom wall to enhance turbulent heat transfer. The Reynolds-Averaged Navier-Stokes analysis is used as a numerical technique and the SST k-(ω) turbulent model with near-wall treatment as a turbulent model. The simulations were performed for two rib shapes, trapezoidal with decreasing height in the flow direction with and without grooves between the ribs. The results are validated by comparing with existing experimental data and semi-empirical correlations. The Reynolds number, pitch-to-rib high ratio and relative groove position are chosen as design variables. The effects of roughness parameters on Nusselt number and friction factor have been discussed and the conditions for the best performance have been determined and presented.

Knowledge of the control of the musculoskeletal system in patients with knee osteoarthritis (OA) during gait is helpful for the development of intervention programs in the management of these patients. The current study aimed to investigate the leg and joint stiffness, aswell as the associated joint kinematics and kinetics, in patients with bilateral medial knee OA during gait. Joint angles, moments and stiffness, as well as leg stiffness from fifteen patients with bilateral knee OA and fifteen normal controls during level walking, were obtained and their values at the beginning and end of single leg stance were compared using a t-test.

Patients with knee OA were found to modulate their leg and joint stiffness through acquired specific biomechanical strategies in order to maintain normal temporal-spatial patterns of gait. During weight acceptance, they increased their leg stiffness with increased knee stiffness but unalterd hip and ankle stiffness. During weight release, they modulated their hip and ankle kinetics with increased knee and ankle stiffness to improve the control stability of the limb with unaltered leg stiffness. It is suggested that muscle strengthening exercise intervention and/or rehabilitation for patients with knee OA should focus on activities that develop and/or maintain functions not only of the knee, but also of the overall lower extremity.

In the step-by-step solution of a linear elastic system, an appropriate time step can be selected based on analytical evaluation resultsHowever, there is no way to select an appropriate time step for accurate integration of a nonlinear system. In this study, numerical properties of the Newmark explicit method are analytically evaluated after introducing the instantaneous degree of nonlinearity. It is found that the upper stability limit is equal to 2 only for a linear elastic system. In general, it reduces for instantaneous stiffness hardening and it is enlarged for instantaneous stiffness softening. Furthermore, the absolute relative period error increases with the increase of instantaneous degree of nonlinearity for a given product of the natural frequency and the time step. The rough guidelines for accurate integration of a nonlinear system are also proposed in this paper based on the analytical evaluation results. Analytical evaluation results and the feasibility of the rough guidelines proposed for accurate integration of a nonlinear system are confirmed with numerical examples.

Analytical study is conducted in this paper to understand the characteristics of sound transmission through cylindrical shell with free layer damping (FLD) treatment. It is assumed an infinitely long circular cylindrical shell subjected to a plane wave with uniform airflow in the external fluid medium. The damping layer applied on the surface of the shell is represented by HN model with frequency-dependent specifications. An exact solution is obtained by solving the Markus equations of FLD shells and acoustic wave equations simultaneously. As the pressure and displacement terms are expressed in series form, an iterative procedure is founded to cut them with an appropriatenumber of modes. Transmission losses obtained from the solution are compared with “modal-impedance method” for an especial case of untreated shell. Eventually, the numerical results show the effects of stiffness, loss factor and thickness of damping material, and also incident wave angles on TL curves.

An experimental study for determining the thermal contact conductance between two periodically contacting surfaces is presented. The influence of the frequency of contact upon the thermal contact conductance is investigated. Also, the results show that the thermal contactconductance decreases as the frequency of contact increases. The experimental results obtained from present work are in agreement with the previous published data.

In this study, a small two-medium duct with blast-wave propagation is numerically investigated by a high-resolution Euler/Navier-Stokes solver. The solver has a feature of treatment of the Tait equations of state for two media. One of the two media is water which is envisaged as a blood. The second medium is another liquid, used to simulate body's clot or tissue. The duct wall has a mass diffusion effect in addition to viscous effects. Since two different media are considered, the reflection and transmission of an underwater blast wave passing through the interfaces of the two media with different sound impedances are inevitable. The different properties of liquids may cause numerical oscillation at interfaces for very weak blast waves for a high-resolution scheme such as a 5th-order WENO scheme. In order to overcome this difficulty of numerical fictitious oscillation, a third-order WENO scheme was used. It was found that computed pressures of the transmitted blast wave for four kinds of simulated tissues are in good agreements with those obtained by the acoustic principle. Moreover, for the case of a simulated clot, the pressure force and impulse acted on the clot surface are investigated for different intensities of blast waves.

This paper concentrates on the wall shear stress discussion of implanting bi-leaflet aortic valve and concludes a better valve design. To simulate the haemodynamic characteristics of the blood flow, ANSYS CFX10.0 software was utilized to analyze the three-dimensional Reynolds-averaged Navier-Stokes equations. With a quasi-steady analysis model, we predict values of the blood velocity and the wall shear stress both over the valve leaflets and the endothelial lining. Analysis results highlight that leaflet opening angle and valve geometry affect the shear stress distribution and vortex flow regime. An analysis of haemodynamic study for the St. Jude valve with various openingangles is presented first and the sewing ring geometry change is then recommended. It is found that the wall shear stress decreases significantly after modifying the sewing ring geometry. Maximum shear stress reduces 18.5% compared to that of the original St. Jude model at peak systole. This would ease possible damage of endothelial lining of the aorta.

Research on new techniques of perforated silencers has been well addressed. However, the research work on shape optimization for a volume-constrained silencer within a constrained machine room is rare. Therefore, the optimum design of mufflers becomes an essential issue. In this paper, to simplify the optimum process, a simplified mathematical model of the muffler is constructed with a neural network using a series of input design data (muffle dimensions) and output data (theoretical sound transmission loss) obtained by a theoretical mathematical model (TMM). To assess the optimal mufflers, the neural network model (NNM) is used as an objective function in conjunction with a genetic algorithm (GA). Moreover, the numerical cases of sound elimination with respect to pure tones (500, 1000, 2000Hz) are exemplified and discussed.

Before the GA operation can be carried out, the accuracy of the TMM is checked by Crocker's experimental data. In addition, both the TMM and NNM are compared. It is found that the TMM and the experimental data are in agreement. Moreover, the TMM and NNM confirm.

The results reveal that the maximum value of the sound transmission loss (STL) can be optimally obtained at the desired frequencies. Consequently, it is obvious that the optimum algorithm proposed in this study can provide an efficient way to develop optimal silencers.

The consistence between the Stokes wave theory and general wave theory is examined in this study. As well known, the nonlinear terms of Stokes wave are generated by the self-interaction of first-order wave. On the other side, using the general wave theory one can also obtain the nonlinear solutions according to the interaction of n waves with the same amplitude, frequency and phase. It is found that the inconsistence between these two wave trains arises due to the subharmonic effects included in general wave theory but not considered in the Stokes theory. In conclusion, these two theories are substantially different unless the Bernoulli constants are properly chosen for mathematical equivalence.