摘要:

AbstractThe rheological and thermokinetic aspects of the cure of epoxy based composite laminates are analyzed by means of a computer program developed using the heat transfer and heat generating characteristics of a polymerizable system. In particular, the temperature and degree of cure influence on the resin viscosity have been first considered, then the temperature profiles, calculated according to an appropriate kinetic and heat transfer modeling, have been used to predict the corresponding viscosity profiles. Molecular and thermocalorimetric parameters are used for the prediction of the theoretical chemorheological behavior. Commercial epoxy systems commonly used in the preparation of carbon fiber laminates have been characterized by Differential Scanning Calorimetry (DSC) and dynamic viscosity measurements and the results are compared with the theoretically predicted values.

ISSN:0032-3888    

DOI:10.1002/pen.760291502

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe flow of two grades of polydimethysiloxane (Dow Corning type 200 grades 60 Pa's and 300 Pa's) was studied in a 60° wedge flow cell. The stress‐optical law was validated along the center‐line (extensional strains only) and at off centerline locations (extensional and shearing strains combined). Values for stressoptical coefficient were 8.01 × 10−11Pa−1and 9.61 × 10−11Pa−1respectively, the differences apparently being due to experimental error. Orientation angles along a fixed radius at 20° to the cell center‐line were almost constant. Center‐line orientation angles were zero, as expected. Orientation angles at a constant radius for various angular positions varied from zero at the centerline to 54° near the wall. A method for testing constitutional relations for stress is presented. The power law model and linear viscoelastic models are shown to be inadequate in describing orientation effects caused by rotation in the flow. The Goddard‐Miller model was shown to express this but accuracy was not very good, perhaps because of the si

ISSN:0032-3888    

DOI:10.1002/pen.760291503

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe use of frequency dependent impedance measurements in the Hz to MHz range for continuousin situmeasurements of the processing properties of unsaturated polyester resins both in a laboratory and manufacturing tool is presented. The frequency dependence of the complex impedance is used to separate and measure ionic and dipolar mobility. These two parameters are used as molecular probes to monitorin‐situthe reaction onset, point of maximum flow, gel, post gel buildup in modulus, and the final degree of hardnes

ISSN:0032-3888    

DOI:10.1002/pen.760291504

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThis paper describes the development of process control schemes for the free radical initiated (reactive) degradation of polypropylene in an extruder (reactive extrusion). The objective of the work was to control the amount of degradation in order to produce polypropylene with a specified molecular weight. The die pressure drop was used as a measure of the amount of degradation (the measured variable) and the initiator concentration was used to control the amount of degradation (the manipulated variable). The reactive degradation process was modeled empirically to determine the dynamic relationship between the input degradation initiator concentration and the output die pressure drop. Several control schemes were evaluated for controlling the die pressure drop (amount of degradation) with emphasis placed on schemes designed to overcome the non‐linear process gain and dead tim

ISSN:0032-3888    

DOI:10.1002/pen.760291505

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractUsing the Melt Transformation Coextrusion process it is possible to enhance the mechanical and thermal properties of polymeric extrudates directly from the melt and maintain continuous production rates. This adaption of melt transformation extrusion has significantly enhanced line speed compared to the precursor process. The required operating pressures in both processes are low enough to allow for the usage of commercial plasticating extruders as the polymer melt sources. Molecular orientation necessary to produce property enhancement is induced in the converging section of specially designed dies and retained by the core layer of the extrudate by imposing a steep temperature gradient in the land section of the die. Mechanical properties (i.e. tensile strength and modulus) and melting point elevation observed for the polypropylene core/polyethylene skin extrudates were functions of extrusion pressure. The highest values of these properties noted were: tensile modulus, 9.37 × 105psi; tensile strength, 2.10 × 104psi; and melting point elevation in excess of 10 K. The levels of property enhancement seem to be bound in their lower limit by a metastable liquid crystalline form. The upper theoretical limit of property enhancement should correspond to a fully extended chain morpholog

ISSN:0032-3888    

DOI:10.1002/pen.760291506

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractMelt Transformation Coextrusion for power law fluids was analyzed with particular attention being paid to the influence of the die's geometrical shape on flow patterns, and to skin layer effect on the velocity profile and shear stress at the interface between layers in a three‐layered system. Volumetric flow rate expressions were also generated for the aforementioned system, and stream and potential functions were derived for a free boundary converging film geometry. Newtonian as well as non‐Newtonian fluids were considered for this analysis in which the streamline shape changes their convergence downstream into the land section. Also, a finite element solution technique was utilized to reveal shear stress profiles that arise from the flow of high density polyethylene at 200°C in a converging fixed boundary geom

ISSN:0032-3888    

DOI:10.1002/pen.760291507

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractCo‐rotating twin screw extruders are widely used for various mixing and reactive extrusion tasks in polymer processing operations. In this study, the prevailing mixing mechanisms of various screw elements employed in co‐rotating twin screw extrusion process, including regular flighted, and reverse and forward kneading disc elements, were experimentally investigated. A direct goodness of mixing technique based on pigmented thermoplastic elastomers and computerized image analysis was used. The results were elucidated in conjunction with mixing indices suitable for image analysis and the continuous mixing process. Significant differences in the distributive mixing characteristics of various screw elements were revea

ISSN:0032-3888    

DOI:10.1002/pen.760291508

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractCompression molding is a widely used method of forming composite materials where long fibers are necessary for strength requirements. Compression molding involves putting the charge through a specific, material dependent temperature and pressure path to induce thermochemical cure. During cure, certain temperatures are required for a time. Spatial variation of the cavity temperature can lengthen time needed for curing and cause voids and residual stresses in the part. Towards the goal of uniform cavity surface temperature, an interactive graphics based computer aided system for compression mold heating design has been developed. The system employs a boundary element method treating long, thin cylindrical electric heating elements as singular line sources. It is coupled with a CONMIN algorithm, a nonlinear constrained minimization procedure to, optimize the heating system for uniform temperature over the cavity surface. Realistic constraints are featured to insure design feasibility. The problem is also decomposed in such a way to allow easy redesign and a sensitivity study. Through the optimization process, it was found that uniformities can be obtained which are far better than anything that could be achieved through common sense.

ISSN:0032-3888    

DOI:10.1002/pen.760291509

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA two‐phase model is presented for simulating the injection mold filling process including the effect of transient melt solidification, i.e., the phase change effect. The liquid region is governed by Hele‐Shaw flow for a non‐Newtonian fluid using a modified Cross model to describe viscosity under non‐isothermal conditions. Further, the energy equation of the solid phase is dominated by a transient condition. The interfacial energy balance equation is also proposed to predict the solidified layer thickness and temperature profile. Two well‐characterized semicrystalline materials, polypropylene and polyethylene, were used in the present work. Good agreement is obtained between the predicted results and experimental observations from this study and the previous literature concerning the thickness of solid layer, the shape of, advancing melt front, and the pressure traces. In particular, the predicted pressure based upon the two‐phase model is higher than that in terms of the single‐phase model by about 13 percent. Finally, the semicrystalline structure of the frozen skin layer and the central core were investigated with a scanning electron microscope to verify the tw

ISSN:0032-3888    

DOI:10.1002/pen.760291510

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA finite element technique has been developed for coupled reaction and heat transfer analysis in which mass diffusion is negligible. The temperature unknowns are located at nodal points, while the reaction variables (species concentrations, reaction rates) are at the Gauss points in each element. With a mechanistic kinetic model, the SMC (sheet molding compound) cure in 2‐D and 3‐D geometries was analyzed. The results for plate‐and‐rib configurations show the progression of cure and heat transfer and the influence of geometry on the progression. The analysis for a flat sheet of SMC in a mold with localized heating using bubblers indicates the thermal interaction between the mold and the curing SMC. Temperature and reaction profiles are given for ea

ISSN:0032-3888    

DOI:10.1002/pen.760291511

出版商:Society of Plastics Engineers    

年代:1989

数据来源: WILEY