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排序方式: 共有212条查询结果,搜索用时 15 毫秒
81.
High temperature vacuum assisted resin transfer molding of phenylethynyl terminated imide composites
Xiang Fu Chuck Zhang Richard Liang Ben Wang Jennifer C. Fielding 《Polymer Composites》2011,32(1):52-58
Vacuum Assisted Resin Transfer Molding (VARTM) has proven to be a cost effective process for manufacturing composite structures compared with prepreg/autoclave and traditional resin transfer molding (RTM) processes. However, VARTM has not been accomplished with high temperature resins (such as polyimides) until recently, primarily because no resins had low melt viscosity and long melt stability that are required by VARTM. With the recent invention of phenylethynyl terminated imides (PETIs), high temperature VARTM has been achieved. Two processing methods, in‐plane and through‐thickness resin flow, were proposed and tested. Both methods are capable of fabricating polyimide matrix composites; and the carbon fiber laminates yield good fiber‐resin interfacial bonding and comparable mechanical properties to those laminates fabricated using RTM. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers 相似文献
82.
Romuald Aufrre Jay Gowdy Christoph Mertz Chuck Thorpe Chieh-Chih Wang Teruko Yata 《Mechatronics》2003,13(10):1149-1161
The Navlab group at Carnegie Mellon University has a long history of development of automated vehicles and intelligent systems for driver assistance. The earlier work of the group concentrated on road following, cross-country driving, and obstacle detection. The new focus is on short-range sensing, to look all around the vehicle for safe driving. The current system uses video sensing, laser rangefinders, a novel light-stripe rangefinder, software to process each sensor individually, a map-based fusion system, and a probability based predictive model. The complete system has been demonstrated on the Navlab 11 vehicle for monitoring the environment of a vehicle driving through a cluttered urban environment, detecting and tracking fixed objects, moving objects, pedestrians, curbs, and roads. 相似文献
83.
Carbon nanotube (CNT) emitters on buckypaper were activated by laser treatment and their field emission properties were investigated. The pristine buckypapers and CNT emitters' height, diameter, and spacing were characterized through optical analysis. The emitter spacing directly impacted the emission results when the laser power and treatment times were fixed. The increasing emitter density increased the enhanced field emission current and luminance. However, a continuous and excessive increase of emitter density with spacing reduction generated the screening effect. As a result, the extended screening effect from the smaller spacing eventually crippled the field emission effectiveness. Luminance intensity and uniformity of field emission suggest that the highly effective buckypaper will have a density of 2500 emission spots cm(-2), which presents an effective field enhancement factor of 3721 and a moderated screening effect of 0.005. Proper laser treatment is an effective post-treatment process for optimizing field emission, luminance, and durability performance for buckypaper cold cathodes. 相似文献
84.
Jingjing Qiu Jing Li Chuck Zhang Richard Liang Shui‐Shun Lin Ben Wang Shawn Walsh 《Polymer Composites》2008,29(12):1310-1320
In the vacuum assisted resin transfer molding (VARTM) process, part‐to‐part variations such as the uncertainty in the permeability and race tracking phenomenon make it difficult to achieve consistent mold filling and ensure part quality of composites. Alcohol pre‐infusion was presented in this study as a novel real‐time monitoring and control approach for the flow process in the VARTM process, alcohol test fluid is infused before the actual resin infusion to locate the potential dry spots without using the large quantity of sensors. Then corresponding process control strategy is designed, such as opening the auxiliary gate at specific moment on those predicted dry spot locations to compensate flow defects. Moreover, alcohol can be easily removed by heat without changing the local permeability. The influence of alcohol pre‐infusion on the quality of VARTM composites were investigated in this study. The mechanical tests were conducted to verify that the alcohol pre‐infusion approach has no significant effect on composite properties because alcohol can be removed from fiber by heat and air flow. Specifically, DMA, TGA, and FTIR spectrum proved that negligible difference existed on the resin–fiber interface between the composites with or without alcohol pre‐infusion. Finally, the microscopy results revealed a similar failure path in a resin matrix. TMA results also demonstrated similar dimension stability. This alcohol pre‐infusion approach was effective when compared with computer simulation and could eliminate the occurrence of dry spots and voids without using sensors or data‐acquisition system. The control schemes were shown in a case study to be capable of compensating the flow defects and achieving desired fill patterns in the face of permeability uncertainty. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers 相似文献
85.
Myungsoo Kim Young-Bin Park Okenwa I. Okoli Chuck Zhang 《Composites Science and Technology》2009,69(3-4):335-342
Carbon fiber-reinforced epoxy composites modified with carbon nanotubes (CNTs) were fabricated and characterized. High-energy sonication was used to disperse CNTs in the resin, followed by infiltration of fiber preform with the resin/CNT mixture. The effects of sonication time on the mechanical properties of “multiscale” composites, which contain reinforcements at varying scales, were studied. A low CNT loading of 0.3 wt% in resin had little influence on tensile properties, while it improved the flexural modulus, strength, and percent strain to break by 11.6%, 18.0%, and 11.4%, respectively, as compared to the control carbon fiber/epoxy composite. While sonication is an effective method to disperse CNTs in a resin, duration, intensity, and temperature need to be controlled to prevent damages imposed on CNTs and premature resin curing. A combination of Halpin–Tsai equations and woven fiber micromechanics was used in hierarchy to predict the mechanical properties of multiscale composites, and the discrepancies between the predicted and experimental values are explained. 相似文献
86.
Companies adopting enterprise resource planning (ERP) systems have often focused primarily on implementation-related factors while neglecting those of post-implementation. As a result, the usefulness and operation of the ERP systems, once installed, are compromised. This research adopted a case study approach to demonstrate that ERP adoption efforts that fail to pay attention to post-implementation requirements (especially those relevant to maintenance and support (M&S)) from an early stage in the project lifecycle will face dire consequences. It points out that poor planning and management of M&S services can imperil the normal operations of an ERP system and the daily activities of a business. With the life span of ERP systems getting shorter, sound M&S practices can extend their life and create a stable system platform to support efficient and effective business operations. M&S issues deserve to be considered as integral elements among the critical success factors (CSF) of ERP adoption projects. In other words, ERP success requires a full lifecycle perspective to be taken by adopting companies. With lessons having been learned from the mistakes in the first project, the company in this case study revamped its ERP implementation second time out, with due consideration being given to M&S strategies and practices from project initiation onward in order to realize a stable, usable, and maintainable system. The case study explores and identifies the critical success factors (CSF) of ERP adoption, and shows that M&S must be included as a key element from the outset and throughout the system lifecycle. Our findings capture a great deal of experience for any ERP adopting companies to follow in order to avoid learning costly lessons both in implementation and subsequent M&S throughout the lifespan of the system. A set of propositions is also presented for academic researcher to consider in future ERP research endeavors. 相似文献
87.
88.
An in situ functionalization method was used to graft epoxide onto single-walled carbon nanotubes (SWNTs) and improve the integration of SWNTs into epoxy polymer. The characterization results of Raman, FT-IR and transmission electron microscopy (TEM) validated the successful functionalization with epoxide. These functionalized SWNTs were used to fabricate nanocomposites, resulting in uniform dispersion and strong interfacial bonding. The mechanical test demonstrated that, with only 1?wt% loading of functionalized SWNTs, the tensile strength of nanocomposites was improved by 40%, and Young's modulus by 60%.These results suggested that efficient load transfer has been achieved through epoxide-grafting. This investigation provided an efficient way to improve the interfacial bonding of multifunctional high-performance nanocomposites for lightweight structure material applications. 相似文献
89.
Mechanical and electrical properties of polycarbonate nanotube buckypaper composite sheets 总被引:1,自引:0,他引:1
Pham GT Park YB Wang S Liang Z Wang B Zhang C Funchess P Kramer L 《Nanotechnology》2008,19(32):325705
The thermogravimetric, mechanical, and electrical properties of composite sheets produced by infiltrating single-wall carbon nanotube films (also known as 'buckypapers') with polycarbonate solution were characterized. The composite sheets showed improved stiffness and toughness, while the electrical conductivity decreased, as compared to a neat buckypaper. In addition, polycarbonate/buckypaper composite sheets showed higher resistance to handling and processing damages. Experimental results suggest the viability of the infiltration process as a means to toughen buckypapers and to fabricate polymer/carbon nanotube composites having high nanotube concentration and controlled nanotube structure. 相似文献
90.
Software-Based Video/Audio Processing for Cellular Phones 总被引:1,自引:0,他引:1
Nowadays, most cellular phones are used beyond voice communication. Although the processing power of cellular phones is sufficient for most data applications, it is difficult to play video and audio contents in software because of their computational complexity and lack of basic tools for multimedia processing, so software-based multimedia processing on cellular phones is a challenging issue. Several transcoding methods are introduced to address this issue, but they are mainly of the DCT-domain conversion. Hence, they are only applicable to high-end cellular phones. To develop a solution for low-end and mid-tier cellular phones, we begin this paper by analyzing the complexity of existing video standards to see if it is possible to play them on cellular phones by software. Next, various coding profiles as combinations of subalgorithms are studied, and we select a profile that adapts its complexity to the processing power of cellular phones. Also, an efficient dithering algorithm called out-of-order dithering is developed. We implement the profile with out-of-order dithering in an actual cellular phone software environment and present the performance results. The performance results show that software based video/audio processing is indeed possible on low-end cellular phones. 相似文献