摘要:

AbstractViscosity was measured as a function of time for the polymerization of a reaction injection molding (RIM) type urethane system: 4,4′‐diphenyl methane diisocyanate (MDI) with a polyester triol and dibutyl tin dilaurate catalyst. Viscosity was found to be independent of shear rate. Isothermal viscosity rise was related to extent of reaction and toMw, by branching theory. Isothermal results at several temperatures were able to predict viscosity rise under adiabatic conditions. The gel point test commonly used to evaluate RIM systems is shown to be essentially an adiabatic t

ISSN:0032-3888    

DOI:10.1002/pen.760201402

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractA study has been made of the fiber orientation in short glass fiber‐filled thermoplastics resulting from convergent, divergent and shear flows. Convergent flow results in high fiber alignment along the flow direction, whereas diverging flow causes the fibers to align at 90° to the major flow direction. Shear flow produces a decrease in alignment parallel to the flow direction and the effect is pronounced at low flow rates. Non‐linear Bagley plots have been observed, under some conditions, during rheological measurements. The data are consistent with a pressure dependent visco

ISSN:0032-3888    

DOI:10.1002/pen.760201403

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe effect of fiber concentration, fiber length, and temperature on the shear viscosity and die swell of several short glass fiber‐filled thermoplastics has been determined. In addition, a study of the injection molding behavior of these materials has been performed. At low shear rates, viscosity increases appreciably with both fiber length and fiber concentration, but at high shear rates the effect is much less pronounced. A qualitative explanation is proposed for these effects in terms of the fiber orientation studies reported in Part I of this paper (1). The die swell is an important parameter in determining the method of mold filling of these materials, and depends strongly on fiber lengt

ISSN:0032-3888    

DOI:10.1002/pen.760201404

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractRecent studies of the dynamic mechanical behavior of ultra high modulus polyethylene? are discussed in the context of our present understanding of the structure of these materials. In particular, the Takayanagi model is shown to achieve a new status in the light of direct measurements of crystal continuity from wide angle X‐ray diffraction data. It is further shown that the Takayanagi model in one formulation is compatible with the Cox model for a short fiber reinforced composite. The fiber composite model offers a simple physical understanding of the fall in modulus due to the α‐relaxation in terms of shear lag. This reduces the effectiveness of the continuous crystal fraction postulated in the Takayanagi model. The γ‐relaxation is considered to be associated primarily with an amorphous relaxation, consistent with the conclusions of previous workers for materials of lower dra

ISSN:0032-3888    

DOI:10.1002/pen.760201405

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractShear and elongational flow measurements on polystyrene melts reinforced with small particles were carried out. The influences of loading level, particle size and surface treatment on shear viscosity, principal normal stress difference, and elongational viscosity were discussed. These systems exhibited yield values for both shear and elongational flow. Experimental values for the ratio of the tensile to the shear yield stress give satisfactory agreement with the predictions of the von Mises yield criterion. The yield value appears to increase with decreasing particle size and may be varied with surface treatment. The principal normal stress difference at fixed shear stress decreases with volume loading of particulates. The results are interpreted in terms of a system forming a gel due to interparticle forces, which is disrupted by a critical distortional strain energy.

ISSN:0032-3888    

DOI:10.1002/pen.760201406

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe techniques of density, birefringence, and wide X‐ray diffraction were employed to characterize the microstructure of injection molded polyethylene parts. Generally, maximum crystallinity (density) occurs at the center of the molding, while the minimum crystallinity occurs near the surface. Higher densities are observed near the gate. Raising the injection temperature tends to cause a marginal increase in the crystallinity throughout the molding. Birefringence measurements suggest that the maximum orientation occurs near the surface and that the relative orientation distribution is independent of the injection temperature. X‐ray diffraction indicates that the crystallographica‐axis tends to orient in the flow direction while thebandcaxes vary symmetrically about that direction. Increasing the injection temperature createsc‐axis orientation near the surface, while towards the core regiona‐axis orientation is observed. Generally, near the surface it is the amorphous phase that makes the major contribution to the total orientation as measured by birefringence. Increasing the injection temperature tends to decrease the amorphous phase orientation near the surface. The crystalline phase contribution to the total orientation increases as distance from the surface increases, regardless of injection te

ISSN:0032-3888    

DOI:10.1002/pen.760201407

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe isothermal flow of a Newtonian liquid in a co‐rotating twin screw extruder having screw elements with three tips has been analyzed when the effect of the intermeshing zone on flow can be neglected. It was found that values for four dimensionless parameters must be specified in order to obtain a unique relationship between the dimensionless axial pressure gradient and the dimensionless volumetric flow rate. These parameters included the number of screw tips, the helix angle, the ratio of the clearance to the screw radius, and the ratio of the distance between screw centers‐to the screw radius Values for the dimensionless throughput and pressure gradient were computed for a range of helix angles at fixed values for all other dimensionless parameters. Shape factors were also computed and it was found that the shape‐factor for pressure How is substantially less than that for drag flow. Asymptotic values for both these factors at large values of the channel width (large helix angles) were found to be less than

ISSN:0032-3888    

DOI:10.1002/pen.760201408

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe stress vs strain and strain recovery characteristics of a series of low density polyethylenes of various molecular size and molecular size distributions have been studied in the melt state. The results show that the high molecular size portion of the molecular size distribution dominates the stress vs strain behavior. The high molecular size component causes a large increase in the stress overshoot and steady state stress. The high molecular size component also has a strong influence on the magnitude of recoverable strain, The strain recovery characteristics are dependent on the amount of strain applied. For large strains (above the yield point) the strain recovers slowly to a large extent (Type I). For applied strains below the yield point the strain recovery is rapid and finished in a short period of time (Type II).

ISSN:0032-3888    

DOI:10.1002/pen.760201409

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

摘要:

AbstractThe load carrying capacity of adhesive joints is analyzed by applying the principle of fracture mechanics in which failure is assumed to initiate from sites of initial imperfections such as bubbles, cracks or unbonded portions of the interface. The cohesive and adhesive modes of failure are investigated for a butt joint under angle loading. Based on the prediction of the strain energy density criterion, the lowest failure stress for the adhesive joint occurred when the load is applied at an angle with respect to the crack plane. This is in contrast to the homogeneous material solution where the lowest failure stress corresponds to normal loading. Numerical examples are provided for a joint made of DER 332‐TEPA epoxy with aluminum as the adherends. Discussed in detail are the dependencies of the strength of the joint with reference to the material properties of the constituents, geometries of the components, and direction of loadin

ISSN:0032-3888    

DOI:10.1002/pen.760201410

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760201411

出版商:Society of Plastics Engineers, Inc.    

年代:1980

数据来源: WILEY