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排序方式: 共有148条查询结果,搜索用时 15 毫秒
91.
Lei Nie Maik Mueller Michael Osterman Michael Pecht 《Journal of Electronic Materials》2010,39(8):1218-1232
In this study, ball grid array (BGA) packages with Sn-3.0Ag-0.5Cu (SAC305) solder balls were reballed with Sn-37Pb solder
balls. Three different reballing methods were used. The non-reballed lead-free BGAs were assembled with SAC305 and Sn-37Pb
solder pastes to form the lead-free and mixed assemblies. The reballed Sn-Pb BGAs were assembled with Sn-37Pb solder paste
to form the reballed Sn-Pb assemblies. All assemblies were subjected to a temperature cycling test with a temperature range
of −55°C to 125°C. For the same component type, the reballed BGA assemblies showed similar temperature cycling reliability
regardless of the reballing methods. However, the temperature cycling reliability of the reballed assemblies was worse than
that of the mixed and the lead-free assemblies. The mean cycles-to-failure of the mixed assemblies was larger than or equal
to that of the lead-free assemblies. Failure analysis revealed that the failure site in reballed Sn-Pb assemblies was located
in the bulk solder at the component side regardless of the component type and the reballing method, indicating that the reballing
method did not influence the crack propagation in reballed assemblies. The mixed assemblies had the same failure site as the
lead-free assemblies, i.e., in the bulk solder at the component side. The microstructure differences between the tin-lead,
lead-free, and mixed assemblies are also discussed in detail. 相似文献
92.
Partial cure of thermosets is a promising approach to enhance manufacturing possibilities of reinforced and unreinforced polymers. If partial cure is taken into consideration as a genuine process parameter, novel manufacturing technologies can be developed by exploiting the specific properties of incomplete polymer networks. A main concern in this context is to control the kinetic reaction avoiding inhomogeneous or instable degrees of cure. Based on a combination of numerical simulations and experiments, a methodology is presented that enables a systematic assessment of the reproducibility and stability of partial cure. Special attention is paid to the interaction of thermal boundary conditions and the cure kinetic of thick samples as well as the storability of partially cured resin under different conditions. Guidelines for cure cycle selection, mold design, and storage are derived. The possibility to use complex multistep cure schedules and extended storage periods is demonstrated for an unmodified noninhibited epoxy resin. © 2019 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals Inc. J. Appl. Polym. Sci. 2020 , 137, 48342. 相似文献
93.
Georg A. Buchner Maik Rudolph Jochen Norwig Volker Marker Christoph Gürtler Reinhard Schomäcker 《化学,工程师,技术》2020,92(3):199-208
A novel CO2 utilization technology allows for the inclusion of CO2 as carbonate units and double bond moieties to give additional functionality in polyether polyols. This study examines the chain-elongation kinetics of these diols with diisocyanates to polyurethane rubbers by means of thermal analysis. A reaction order of 1 indicates a strong influence of the chains' mobility on the reaction rate. Spectrometry and comparison with non-double-bond polyols reveal that the effect cannot be attributed to a substantial occurrence of side reactions but is rather due to the intertwining of lengthy chains. 相似文献
94.
The combination of an alkaline water electrolyzer (AWE) with a battery system powered by photovoltaics (PV) for the production of green hydrogen is investigated. A model describes the power distribution between these three subsystems (AWE, battery and PV). Variation of AWE and battery power and capacity is carried out for two locations, to identify the most appropriate setup, where the highest energy usage and operating time can be reached. The battery helps to reduce the power level of the AWE. However, an estimation of the costs indicates that further optimization is necessary. 相似文献
95.
We demonstrate terahertz (THz) imaging with a quasi-time-domain spectrometer. This type of THz system is inexpensive, compact, and relatively easy to set up. Beating the simultaneously emitted equidistant modes of a compact diode laser allows for analysis of samples at multiple frequencies with a single measurement. Thus, this technique merges the potential of terahertz time-domain spectrometers with the simplicity of continuous wave lasers. Multiple imaging applications and stability issues are discussed. 相似文献
96.
Eleonora Cataldi Martina Raschig Dr. Marcus Gutmann Patrick T. Geppert Matthias Ruopp Marvin Schock Hubert Gerwe Dr. Rüdiger Bertermann Prof. Dr. Dr. Lorenz Meinel Prof. Dr. Maik Finze Prof. Dr. Agnieszka Nowak-Król Prof. Dr. Michael Decker Prof. Dr. Tessa Lühmann 《Chembiochem : a European journal of chemical biology》2023,24(5):e202200570
The incorporation of photoswitches into the molecular structure of peptides and proteins enables their dynamic photocontrol in complex biological systems. Here, a perfluorinated azobenzene derivative triggered by amber light was site-specifically conjugated to cysteines in a helical peptide by perfluoroarylation chemistry. In response to the photoisomerization (trans→cis) of the conjugated azobenzene with amber light, the secondary structure of the peptide was modulated from a disorganized into an amphiphilic helical structure. 相似文献
97.
Jiaming Zhang Fuxiang Zhang Maik Lang Fengyuan Lu Jie Lian Rodney C. Ewing 《Acta Materialia》2013,61(11):4191-4199
The response of a material to a high radiation field is important when selecting materials for nuclear applications, such as structural materials, nuclear waste forms and inert matrix fuels. In the present study, the radiation response of orthorhombic, rare-earth titanates, Ln2TiO5 (Ln = La, Nd, Sm, Gd, Dy and Y), was investigated by 1 MeV Kr2+ ion bombardment at temperatures ranging from 50 to 1073 K. In situ transmission electron microscopy revealed that the radiation tolerance and irradiation-induced structural transitions vary largely with composition. Y2TiO5 exhibits the lowest critical amorphization temperature (Tc = 623 K), above which crystals cannot be amorphized, which is consistent with its use in the form of nanoclusters in radiation-resistant oxide-dispersion-strengthened steels. The disordered fluorite structure type of Ln2TiO5, with smaller Ln cations, formed as an intermediate phase prior to becoming fully amorphous. The fluorite structure type of Ln2TiO5, containing more vacancies as compared with that of Ln2Ti2O7, may exhibit enhanced ionic conductivity, which highlights an effective way of using ion beams to modify the properties of materials. 相似文献
98.
Mathias Herrmann Akhilesh Kumar Swarnakar Maik Thiele Omer Van der Biest Iakovos Sigalas 《Journal of the European Ceramic Society》2011,31(13):2387-2392
B6O is a potential superhard material with a hardness of 45 GPa measured on single crystals. Recently it was found that different oxides can be utilized as an effective sintering additive which allows densification under low pressures. In this work the effect of addition of Y2O3/Al2O3 on high temperature properties was investigated using impulse excitation technique (IET), hardness measurements and dilatometric measurements. The IET technique reveals the softening of the residual B2O3 in the materials without additives at 450 °C; in the materials with Y2O3/Al2O3 the softening is observed at only about 800 °C. This data agrees with the values found for different borate glasses.The materials showed no pronounced reduction of hardness at these temperatures. This is additional evidence, supporting previous observations that the material consists of pure grain boundaries between B6O grains. Hardness values (HV5) of up to 17 GPa at 1000 °C were observed. 相似文献
99.
Falk Howar Malte Isberner Maik Merten Bernhard Steffen Dirk Beyer Corina S. Păsăreanu 《International Journal on Software Tools for Technology Transfer (STTT)》2014,16(5):457-464
The goal of the RERS challenge is to evaluate the effectiveness of various verification and validation approaches on reactive systems, a class of systems that is highly relevant for industrial critical applications. The RERS challenge brings together researchers from different areas of software verification and validation, including static analysis, model checking, theorem proving, symbolic execution, and testing. The challenge provides a forum for experimental comparison of different techniques on specifically designed verification tasks. These benchmarks are automatically synthesized to exhibit chosen properties, and then enhanced to include dedicated dimensions of difficulty, such as conceptual complexity of the properties (e.g., reachability, safety, liveness), size of the reactive systems (a few hundred lines to millions of lines), and complexity of language features (arrays and pointer arithmetic). The STTT special section on RERS describes the results of the evaluations and the different analysis techniques that were used in the RERS challenges 2012 and 2013. 相似文献
100.
Xiaochuan Sun Luiz F. Kawashita Tino Wollmann Sebastian Spitzer Albert Langkamp Maik Gude 《Production Engineering》2018,12(2):215-228
Braiding is an attractive manufacturing method for tubular elements such as hollow shafts and struts. One of the main challenges however is the integration of suitably performing end-fittings. Recent advances in additive layer manufacture have enabled the fabrication of end-fittings which can be ‘co-impregnated’ or ‘co-cured’ with the fibre preform in a single step, i.e. without the need for secondary adhesive bonding. This requires the introduction of protrusions onto the surface of the end-fitting to promote mechanical interlocking with the fibres. However, the lack of accurate modelling tools for the simulation of this manufacturing process means that much empiricism is currently used in the design of such structures. A novel numerical framework is presented here for the full-scale simulation of the braiding process over structured end-fittings. Nonlinear finite element analysis is applied at the meso-scale, with strands of beam elements representing individual yarns and meshed surfaces modelling the mandrel and tooling. Penalty-based contact formulations are then used to simulate all inter-yarn and yarn-metal interactions, enabling detailed predictions of fibre paths around surface protrusions. In order to verify and validate this numerical framework, a series of full-scale braiding experiments was conducted using additively-manufactured thermoplastic mandrels. Final braid patterns as well as the occurrence of braid imperfections were investigated and compared to model predictions. It is shown that the proposed modelling strategy reproduces well the trends observed experimentally in terms of final braid quality. A parametric study was then conducted on the effects of initial end-fitting alignment with respect to oncoming yarns, suggesting that better control over this parameter could reduce considerably the occurrence of braid imperfections. 相似文献