摘要:

AbstractAs large components of fiber reinforced composite materials are being more frequently produced by Resin Transfer Molding (RTM), a computer simulation of the injection process can help the mold designer to accomplish three important tasks: (1) to ensure a complete filling of the mold through adequate positioning of the injection ports and of the air vents; (2) to verify the integrity of the mold during the filling process through knowledge of the pressure distribution; and (3) to optimize the production cycle using information about the filling time. The resin impregnation is usually modeled as a flow through a porous medium. It is governed by Darcy's law, which states that the flow rate is proportional to the pressure gradient. In our model, Darcy equation is solved at each time step inside the saturated part of the mold using nonconforming finite elements. This method was chosen because the approximated flow rates, contrary to conforming finite elements, satisfy locally the important physical condition of resin conservation across inter‐element boundaries. This permits simplification of the numerical procedure. It is no longer necessary to resort to a control volume approach to move the flow front forward. The resin pressure distribution and the resin front positions are obtained by the computer simulation and calculated results for selected mold geometries are compared with experimental observations. Molds with inserts, multiple injection ports, and the case of anisotropic preforms can be analyzed by the computer program. © 1993 by John Wiley&Sons, I

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120401

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractStudies on the melting in a single‐screw extruder have mainly concentrated on the Maddock melting mechanism. The dispersive melting mechanism, named by us, is of great practical utility. A six‐block physical model is first proposed for the dispersive melting mechanism in the present study. Then nonisothermal non‐Newtonian mathematical models for the dispersive and Maddock melting mechanisms are developed. It has been demonstrated that the dispersive melting model has a number of advantages over the Maddock melting model: the mechanical power consumption can be decreased; the polymer temperature profile is more uniform and its average temperature is lower. Furthermore, melting can be accelerated and hence the total melting length shortened. © 1993 by John Wiley&Son

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractResearch in understanding the mechanisms behind driving forces in the fully filled nonintermeshing twin screw extruder concentrated on experimental analysis of the relation between stagger, screw speed, and cross‐channel flow due to measured pressure differential in the nip region. A new measure of the pressure driving force was also sought out, to correlate new data to previous findings from visual studies. The first part of the study was to obtain the values for the dynamic pressure on both sides of the nip region. Further refinements to the equipment used in previous studies allowed closer placement of the transducers in the nip region. After the data were stored, analysis started by determining the δpvalues from the trace of the pressure differential. By plotting these values, we obtain a highly repeatable curve confirming that the greatest pressure flow occurs at small staggers. A simple 2‐D model for pressure flow in the nip region was used to estimate the effect of the cross‐channel pressure differential. Values for the cross‐channel pressure flow were calculated and compared with the drag flow and found to be significant. © 1993 by John Wiley&

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe Intelligent Processing of Materials (IMP) concept has been applied to the calendering process with the goal of improving shape quality and process efficiency. All four basic features of the IPM, including modeling, data processing, sensing, and controlling, are considered. In the process modeling, bending and thermal models are developed. With these models, the relationship between the process parameters and quality of the calendered sheets has been established. A material data bank has been established to couple with the process modeling and real‐time sensing data. In sensing, ultrasonic and temperature sensors have been implemented to measure critical quality and process parameters in situ. The sensing data have been used not only to verify the modeling prediction but also to establish information needed to diagnose the causes of the layflat problem. Based on the model prediction as well as sensing information, a better control system to alleviate layflatness problems has been developed. Finally, a control strategy for future improvement of the calendering system is proposed. © 1993 by John Wiley&Sons, I

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe present article summarizes the author's recent work on the computer‐based molecular modeling of polysilanes [‐SiR2‐]. First, conformational energies were calculated by molecular mechanics on model compounds for poly(dimethylsilane) (PDMS), poly(diethylsilane) (PDES), and poly(di‐n‐hexylsilane) (PDHS). Discrepancies in conformational preferences between calculated and experimental results are attributed to factors not accounted for in these calculations, such as electronic stabilization and packing forces. Second, molecular dynamics simulations carried out on a model compound for PDHS suggest the presence of an abrupt “gas phase” thermochromic transition, analogous to the abrupt thermochromic transitions observed for PDHS both in solution and in the solid state. Third, we develop a methodology for testing Schweizer's theory of polysilane thermochromism based on the existence of a unique polymer‐solvent conformation‐dependent stabilization energy present in conjugated chains. In his treatment of the polysilanes, Schweizer adopted reasonable estimated values for this stabilization energy termVD. Presented here is a derivation of an analytical expression forVDbased on a first‐principles approach. © 1993 by

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractThe polydispersity index (PI) of polypropylene (PP) obtained from plotting the crossover point of shear storage modulus (G′) and loss modulus (G″) was comparable to that using gel permeation chromatography (GPC). The precise PI determination was dependent upon the material properties of PP and rheological measurement technique. The effect of testing percent strain on PI was determined over a wide range of melt flow rate (MFR). The employed percent strain could affect PI of this percent strain was not independent of the frequency at the crossover frequency of the resin. To measure PI precisely, a 5% strain was recommended for MFR ≥ 30, while a 15% strain was suitable for MFR<30. © 1993 by John Wiley&Son

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractTo provide a computer assisted system in finding optimum conditions for injection molding operations, an Expert System based on Artificial Intelligence (AI) technique and knowledge or “know‐how” from many skilled injection molding operators has been developed. For the construction of this Expert System, we have originally applied a new method of “Multi‐dimensional Matrix” that represents the relationship between the parameters of each molding condition and expert's knowledge. In this article we describe an outline of the system and the process of converting expert knowledge into AI rules, and demonstrate some molded samples obtained using this Expert System. © 1993 by John Wil

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

摘要:

AbstractPLASSEX is a forward‐chaining rule‐based expert system for plastic selection written in CParaOPS5. This system prompts the user for desired properties, and lists all plastics suitable for a particular application. At present, PLASSEX has 393 plastics in the data base and considers up to 39 polymer properties in order to select the right plastic. More properties can be added to the system with some understanding of the code. This system also provides the user with a help facility. PLASSEX has a number of other features; for instance it gives the user an opportunity to modify any property in case the system fails to come up with a suitable plastic the first time. © 1993 by John Wiley&Sons,

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY

ISSN:0730-6679    

DOI:10.1002/adv.1993.060120410

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1993

数据来源: WILEY