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Highlight • A DIC based measurement technique is proposed for 3D sloshing surface profile determination. • The technique was verified through tests on water in a rectangular container. • Effect of the depth of the liquid on the sloshing surface was studied. Abstract Liquid sloshing is one of the major issues for the storage and transportation of liquid such as fuel tanks. This topic has been investigated with numerical simulations or by experimental methods. However, simulations are based on many assumptions and the results sometimes cannot fully describe the actual movements of the liquid inside the tank. On the other hand, sloshing experiments are usually conducted with two-dimensional images taken from the side of a liquid tank. This renders only limited information because liquid sloshing is three-dimensional in nature in majority of the tank structures. Therefore, current research is aimed to develop an experimental method, which is empowered by the state-of-the-art digital image correlation (DIC) technique that is capable of measuring three-dimensional (3D) surface profile of a sloshing liquid. The 3D sloshing surface profile of the liquid in a container oscillating horizontally was investigated to demonstrate the technique. The results showed that the accuracy of the proposed DIC-based experimental method is within 3.0% and the repeatability can be controlled within 4.0% when compared with more established method. The effects of different liquid depth on the surface profile of sloshing liquid were then studied by using the proposed technique. [ABSTRACT FROM AUTHOR]

Generally, the residual stress of thin film coatings is calculated using Stoney's equation. However, variables in the manufacturing of the coated film, such as crystalline particle size and the unevenness of the thickness of the film, cause the radius of curvature of the beam to vary all over the beam. The cantilever beam curves not only in the axial direction but also in the transverse direction. Therefore, the residual stress in a film coating comprises not only axial residual stress but also transverse residual stress, and its distribution is also not uniform. Under such conditions, Stoney's equation must be modified. In this study, Si was used as a substrate in the production of cantilever beam specimens. Chromium thin films of various thicknesses were coated onto the Si substrates. The 3D digital image correlation technique was used to measure the out-of-plane displacement of the specimens at various positions. Then the modified Stoney's equation was used to obtain the axial and transverse residual stress at each measurement point to study the effect of variations in the thickness of the thin film on the magnitude and uniformity of the distribution of the residual stresses. Three thin film thicknesses 1, 2, and 3 μm were studied, and three specimens for each thickness were used. For each specimen, axial and transverse residual stresses were obtained at nine test points, and the equivalent residual stress was calculated. The results of this study reveal that as the difference between the thicknesses of the coating increased, average equivalent residual stress decreased and the distribution of stresses became more uniform. By comparing the corresponding results for the 1- and 3-μm-thick films revealed that the confidence levels in the average value and uniformity of the equivalent residual stress distribution, which increased with thickness, were 92.81% and 80.57%, respectively. [ABSTRACT FROM AUTHOR]

This study numerically investigated the effects of different bolt pre-loadings on the performance of the gas diffusion layer (GDL) in a bolted proton exchange membrane fuel cell (PEMFC). Firstly, a complete three-dimensional finite element model of a PEMFC bolted by 12 bolts with a reactive area of 5 cm by 5 cm was established using the commercial software SolidWorks. Then, a pre-loading of 1 MPa to 7 MPa on each bolt was applied, increasing in increments 1 MPa, and the corresponding deformation and stress fields of each component of the fuel cell were obtained using the commercial software ANSYS 15.0/Workbench. Finally, the effects of the bolt pre-loading variations on the performance of the GDL were discussed. The results showed that the compression ratio of the GDL increased linearly with the magnitude of bolt pre-loading, and improving the performance of the GDL. However, when the pre-loading on each bolt reached 7 MPa, the compression ratio exceeded 15%, degrading the efficiency of the PEMFC. Also, by comparing the relationships between bolt pre-loading and conductivity and porosity of GDL, in order to obtain the maximum performance of GDL, an optimum value of 4 MPa for bolt preloading was recommended. [ABSTRACT FROM AUTHOR]

Cu–Cu ultrasonic bonding is a highly promising technology for advanced interconnect technology for a 3D integrated circuit micro bump. The interface kinetic friction characteristic is also a key factor in determining the level of bonding for this technology. This study uses molecular dynamics simulation to determine the effects of different temperatures on the material kinetic friction characteristics of Cu substrates in single-crystal and polycrystalline structures. The Taguchi method is used to optimize the simulation, in order to confirm that the convergent kinetic friction coefficients are not affected by size effect. A comparison between the results obtained in the present study and those of previous studies shows good agreement between these two sets of results for kinetic friction coefficients. In order to thoroughly understand the effect of temperature on material characteristics, this study uses the central symmetry parameter to monitor defected atoms and to determine the kinetic friction characteristics at various temperatures. The results show that in single-crystal structures, because the generation of dislocations is not restricted to grain boundaries, the normal force does not change significantly but the tangential force decreases as the temperature increases. Therefore, the kinetic friction coefficient for single-crystal Cu decreases as temperature increases. Because the generation of dislocations in polycrystalline structures is restricted to grain boundaries between 293 K and 650 K, the tangential force and the normal force do not decrease significantly as the temperature increases. Consequently, the kinetic friction coefficient for polycrystalline Cu remains stable and is unaffected by any increase in temperature. Between 825 K and 1000 K, although the generation of dislocations in polycrystalline structures is still restricted to grain boundaries, high temperatures soften the material, which leads to a significant decrease in the tangential force and the normal force. Therefore, the kinetic friction coefficient of polycrystalline Cu does not decrease significantly. Finally, at temperatures of less than 850 K, the kinetic friction coefficient for single-crystal Cu is greater than that for polycrystalline Cu. At 850 K, the kinetic friction coefficient for single-crystal Cu is equal to that for polycrystalline Cu, but at 1000 K, the kinetic friction coefficient for single-crystal Cu is less than that for polycrystalline Cu. The results of the simulation show that lattice structures have a significant effect on the kinetic friction coefficient at different temperatures. [ABSTRACT FROM AUTHOR]

Thermal deformations of a microstructure diffuser plate in an LED backlight unit subjected to a long period of illumination were studied. Mechanical properties of the microstructure diffuser plate in the LED backlight unit were determined and verified. Rather than using data from the relevant literature, accurate finite element solutions were obtained by using a microtensile test and thermo-mechanical analyzer to calculate the Young's modulus, Poisson's ratio, and thermal expansion coefficient of the microstructure diffuser plate. The measured mechanical properties were used as input data in finite element simulations. Comparisons of the finite element analysis results with the experimental measurements made using strain gauge yielded differences of less than 3%. Thermal warpage phenomena of the microstructure diffuser plate at various temperatures are discussed. Thermal deformations are also compared between the conventional diffuser plate and the microstructure diffuser plate. [ABSTRACT FROM AUTHOR]

Abstract: Elastomeric materials are used as gaskets or seals in polymer electrolyte membrane (PEM) fuel cells and stacks. These gaskets/seals in PEM fuel cells are exposed to acidic, humid air, mechanical compressive pressure and cyclic temperature environment. Both the physical and chemical long-term stabilities of these gaskets/seals are therefore crucial to the overall performance of the fuel cell. Chemical degradation of five elastomeric gasket materials in a simulated and an aggressive accelerated fuel cell solution at 80°C up to 63 weeks was investigated in this work using dynamic mechanical analysis (DMA) which assesses the change of dynamic mechanical properties of the five materials samples as they aged. The storage, loss modulus, and tan δ of the materials were presented that can reveal the glass transition temperature and other properties. The five materials tested are copolymeric resin (CR), liquid silicone rubber (LSR), fluorosilicone rubber (FSR), ethylene propylene diene monomer rubber (EPDM), and fluoroelastomer copolymer (FKM). [Copyright &y& Elsevier]

Abstract: Polymer electrolyte membrane (PEM) fuel cell stack requires gaskets and seals in each cell to keep the hydrogen and air/oxygen within their respective regions. The stability of the gaskets/seals is critical to the operating life as well as the electrochemical performance of the fuel cell. Chemical degradation of five elastomeric gasket materials in a simulated and an aggressive accelerated fuel cell solution at PEM operating temperature for up to 63 weeks was investigated in this work. The five materials are copolymeric resin (CR), liquid silicone rubber (LSR), fluorosilicone rubber (FSR), ethylene propylene diene monomer rubber (EPDM), and fluoroelastomer copolymer (FKM). Using optical microscopy, topographical changes on the sample surface due to the acidic environment were revealed. Weight loss of the test samples was monitored. Atomic absorption spectrometer analysis was performed to study the silicon, calcium, and magnesium leachants from the materials into the soaking solution. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy was employed to study the surface chemistry of the materials before and after exposure to the simulated fuel cell environment over time. Among the five materials studied, CR and LSR in the accelerated solution are not as stable as the other three materials. FSR appears to be the most stable. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of a pressure safety valve (PSV) is to protect the life and safety of pressure vessels in a pressurized system. If a weakened PSV fails to function properly, a catastrophic event might occur if no other protective means are provided. By utilizing the as-received test data and statistical analysis of the aging conditions of PSVs in lubricant process units, a risk-based inspection (RBI) system was developed in this study. First of all, the characteristics of PSV were discussed from the practical viewpoint of engineering inspection and maintenance. The as-received test data, which shows obvious PSV damage, will be separated from the data used in the following statistical analysis. Then, the relationship between the aging conditions and the corresponding PSV parameters was analyzed by using the statistical technique—analysis of variance (ANOVA). Finally, a strategy for semi-quantitative RBI is proposed. Also, a definitive estimated inspection interval for every PSV is suggested. The outcome indicated most of the risks result from a few PSVs, for which the corresponding inspection intervals will be shorter than the 2 years in accordance with relative standards and local government regulations. [Copyright &y& Elsevier]

Abstract: The existence of defects in the corresponding interfaces can gradually degrade the interfacial adhesion when the flip chip package is exposed to the high temperature and humidity. This study used the fuzzy controller to stabilize both the moisture weight gain and adhesion strength together for the button shear test specimen. Parameters design, although based on the Taguchi method, can optimize the performance characteristic through the setting of process parameters and can reduce the sensitivity of the system performance to sources of variation. However, most published Taguchi applications to date have been concerned with the optimization of a single performance characteristic only. For example, it is only concerned a single performance characteristic with the optimization of the adhesion strength or the moisture gain weight individually. In this study, the control rules of the fuzzy controller were formed using the authors’ experience and knowledge of the IC packaging process. The control parameters to be tuned were the membership functions. Therefore, the controller’s performance depended on the membership functions. The fuzzy controller combined Taguchi parameter design, which makes the control performance insensitive to the operating condition changes and noise was used to determine the membership functions. [Copyright &y& Elsevier]

Abstract: The CTE and CHE mismatch between materials in a thin PBGA package is primarily attributed to the warpage which occurs when the package is being mounted on to a PCB, especially when the moisture content reaches a specified value. In this paper, the stability equations for the warpage in a PBGA package without the solder balls being subjected to hygro-thermal loading, by modeling it as an initially perfect/imperfect composite plate, have been developed. The analytical closed-form solutions are found and used to compute not only the critical moisture content but also the warpage occurring before the critical loads are reached. The buckling of the PBGA package, at the solder reflow peak temperature, occurs when the theoretical moisture content reaches 0.259–0.283wt.%. This theoretical critical moisture content accurately predicts the experimental critical moisture content (0.25–0.30wt.%) derived from our previous work. The results, from comparison between theoretical and experimental critical moisture content, indirectly indicate that the PBGA package has little imperfection. However, the large initial imperfect structure of the package does not easily reach the buckling stage because of moisture absorption. In addition to this, the structure of the PBGA package before buckling become stress-free at the moisture level of 0.077wt.% and at room temperature during moisture conditioning. [Copyright &y& Elsevier]

The coefficient of temperature expansion mismatch between materials in a thin plastic ball grid array package is primarily attributed to the warpage when mounting the package to a printed circuit board, especially when the moisture concentration reaches a specified value. The influence of variations in storage conditions on warpage was investigated in this paper. The effects of the reflow parameters on warpage were also examined. Taguchi’s method was implemented for experimental design and data analyses. A critical relative moisture absorption between 0.25% and 0.30% was found for a considerable warpage response. [Copyright &y& Elsevier]

Abstract: The pure squeeze thin film elastohydrodynamic lubrication (thin film EHL) motion of circular contacts with effects of surface forces taken into account is explored under constant load conditions. The difference between thin film EHL model and EHL model is apparent as the film thickness is thinner than 5nm. The oscillation phenomena in pressure and film thickness come mainly from the action of solvation forces. The effects of surface forces become significant as the film thickness becomes thinner. Moreover, the viscosity is oscillatory due to its dependency on the hydrodynamic pressure which is affected by surface forces. [Copyright &y& Elsevier]