bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effects of stress cracking on the fracture toughness of polycarbonate
Authors: Petrie S. P. , Dibenedetto A. T. , Miltz J. 
Published: December 2004

AbstractThe growth of crazes from a sharp crack in extruded polycarbonate sheets immersed in ethanol was measured. Below a critical level of the stress intensity factor craze growth was controlled by solvent diffusion through the end of the notch and fracture was prevented by craze arrest. Above a critical level, growth was controlled by either end diffusion or a combination of end diffusion and diffusion through the faces of the extruded sheet, and in both cases the final result was brittle fracture. The effects of annealing and quenching was studied at various sheet thicknesses. In thin specimens annealing and/or quenching had a significant effect on crack growth rate, which was predictable in terms of the state of stress. As the specimen thickness increased, causing a transition from plane stress to plane strain conditions, the previous thermal history had a diminishing effect on craze growth rate. The effects of thermal history and thickness on the fracture toughness of polycarbonate was also investigated. It was found that thickness was the more important variable and that at a ½ in. thickness the effects of thermal history were statistically insignificant. The effect of ethanol exposure on fracture toughness was studied. It was found that exposure to solvent initially caused an increase inkICwith time to a maximum value, followed by a substantial decrease with time which eventually led to brittle fracture. This behavior was explained as a competition between plasticization of the crack tip and coalescence of crazes to form microcracks.
Penetration behavior of the system sphere‐cylinder
Authors: Hrouz J. , Vojta V. , Ilavský M. 
Published: December 2004

AbstractAn equation has been derived allowing calculation of the penetration modulus A for the indentation of a hard sphere having the radius R′ into a sample in the shape of a cylinder having the radius R in a direction transverse to cylinder axis. The correction function (determined by the elliptic integrals), ℋ︁/\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt 2 $\end{document} = ƒ(R′/R) needed in the calculation of A, has been tabulated. An approximative equation has also been suggested which adequately describes the dependence of m ℋ︁/\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt 2 $\end{document} on R′/R; in the range 0 < R′/R ≤ 1 it describes this dependence with an accuracy of 2.5 percent. While in the case of the penetration of a cylinder the geometry is fully defined and the derived equation is generally valid, in the case of indentation of a plane sheet the equation holds only if the thickness of the sheet is infinite. Experimental results for the penetration of a steel sphere with various R′ on samples of vulcanized silicone rubber in the shape of cylinders with different R gave an A independent of R′/R, which was in agreement with the shear modulus Gt = E/3 (E is Young's modulus) with an average deviation of 2.3 percent. Further, it has been found experimentally that in the case of penetration of a cylinder the equilibrium is attained more readily than in the case of indentation of a plane.
FDT: A technique for direct study of water attack at the silane‐filler interface
Authors: Rosen M. R. , Goddard E. D. 
Published: December 2004

AbstractA technique is presented for the direct study of water attack at the silane‐filler interface. This technique, Filler Desorption Test (FDT), involves observations of surface tension changes which occur when a silane‐treated filler is floated on a water surface. If all the silane has been appropriately cured to form one integral polymerized siloxane network, then the rate and degree of surface tension lowering are a sensitive measure of the adhering tendency of the polymerized silane film. Data are presented which suggest that, all other things being equal, the strength of the coupling agent (C.A.)‐filler bond under water attack can be assessed by observation of the ease with which thefirstsmall amount of polymerized silane leaves the filler and the relative degree of hydrophobicity of the resulting surface. FDT is a new tool for fundamental studies of the coupling agent‐filler interface and interphase. The method also allows rapid screening and evaluation of a wide range of chemical and physical modifications designed to improve C.A. response on various filler systems.
Evaluation for the curing characteristics of phenolic molding compounds by rockwell hardness test at an elevated temperature
Authors: Tonogai Saburo , Hasegawa Kiichi , Inada Masao 
Published: December 2004

AbstractRockwell hardness measurement at an elevated temperature has been proposed as an evaluation method for the curing characteristics of thermosetting molding compounds. This method is convenient and has a high accuracy over a wide range of curing, Using a cone indenter, the following advantages are brought about: a good correspondence with acetone extraction test, in showing the degree of cure of the internal part of a molding rather than that of the skin layer, and a higher sensitivity in measuring higher degrees of cure. On examining curing behavior of commercial phenolic molding compounds by this method, an inflection point was observed on a plot of the hardness vs log curing time. This critical point has been called “the minimum cure time”, beyond which the molding exhibits good physical properties.
The ductile‐brittle transition of low‐density polyethylene
Authors: Zewi I. G. , Rudik W. J. , Corneliussen R. D. , Lind E. V. 
Published: December 2004

AbstractThe impact behavior of a low‐density polyethylene was studied with an instrumented Charpy tester. A change from elastic or ductile response to brittle fracture was observed over a small temperature interval, usually within 1°C. This characteristic impact transition temperature (ITT) was highly sensitive to shallow, sharp notches. Whereas an unnotched test bar had a very low impact transition temperature of −94°C, a razor cut with a depth of only 5 percent of the total thickness raised it to −4°C. The impact transition temperature was effectively reduced by increasing the cooling rate during specimen preparation and by the addition of nonpolar liquids, On the other hand, impact properties were adversely affected by aging, annealing, and adding other thermoplastics.
Rheology of short glass fiber‐reinforced thermoplastics and its application to injection molding I. Fiber motion and viscosity measurement
Authors: Crowson R. J. , Folkes M. J. , Bright P. F. 
Published: December 2004

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 viscosity.
Influence of moisture content on curing behavior of two‐step phenolic molding compounds
Authors: Tonogai Saburo , Hasegawa Kiichi , Kondo Hitoshi 
Published: December 2004

AbstractUsing prepared and commercial two‐step phenolic molding compounds, the influence of moisture on their curing behavior was examined by the disk cure test and the solvent extraction method for the early and middle stages of the curing process, respectively. It was determined that moisture in the compounds could enhance the curing rate and the degree of cure as well as flowability. A possible mechanism explaining the acceleration of curing was proposed, suggesting that moisture might facilitate catalytically the decomposition of hexamine or hexamine‐novolac adduct into reactive low molecular weight materials, which could then easily react with a resin even in a state of fairly advanced cure due to their facile diffusion.
Rheology of rubber‐modified polymer melts
Authors: Münstedt H. 
Published: December 2004

AbstractThe influence of rubber particles on rheological properties of styrene‐acrylonitrile, and poly(vinyl chloride) was investigated. The temperature dependence of the viscosity functions was found to be independent of the kind of rubber and its concentration. The extrudate swell becomes smaller with increasing particle concentration, the entrance pressure loss remaining nearly unaffected. The strong viscosity increase at small shear rates is more pronounced the higher the concentration and the smaller the size of the particles. It can be interpreted by the assumption of a yield stress caused by the fillers. This yield stress is independent of temperature within the accuracy of the measurements and comes out distinctly higher in elongation than in shear. An analytical expression of the dependence of the viscosity on particle concentration cannot be given. It is demonstrated how sensitively an agglomeration of particles is reflected in elongation and recoverable strain. Based on the morphology shown by electron micrographs of acrylonitrile‐butadiene‐styrene and acrylonitrile‐styreneacrylic ester copolymers, two different models for the occurrence of a yield stress are discussed qualitatively.
Analysis of the packing stage in injection molding
Authors: Chung T.‐S. , Ryan M. E. 
Published: December 2004

AbstractAn unconditionally stable explicit finite difference numerical scheme is used to determine the pressure distribution during the packing stage of a rectangular mold cavity. Different initial conditions arising from both an isothermal and nonisothermal mold filling analysis are considered in relation to subsequent packing behavior. The packing stage is of short duration, may be assumed to be isothermal, and gives rise to a more uniform pressure distribution within the mold cavity.
Comparison of eccentric rotating disk and oscillatory measurements of dynamic moduli in polymer liquids
Authors: Vrentas C. M. , Rochefort W. E. , Smith G. G. , Graessley W. W. 
Published: December 2004

AbstractMeasurements to obtain the dynamic moduli G′(ω) and G″(ω) for several polymer liquids were made with the Rheometrics mechanical spectrometer using the eccentric rotating disk (ERD) and the forced oscillation methods. The ERD data were corrected for instrument compliance with the Macosko‐Davis formula. Oscillatory results were confirmed in several separate studies including testing of a Newtonian liquid and an elastic solid. Agreement between the two geometries on G′(ω) and G″(ω) was generally good (±5 percent) for |G*| less than 2 × 106 dyne/cm2. If no compliance correction was applied, departures occurred near a |G*| an order of magnitude lower, indicating strongly the need for applying a compliance correction to ERD data for most polymer systems. However, as |G*| approached 107 dyne/cm2 (where compliance corrections of 50 percent or greater occurred), the two geometries yielded results which differed by 20 percent or more. No single variable was found which correlated the departures for different liquids. Nevertheless, the departures were such that values obtained in the two geometries for the plateau modulus of polyethylene, G ≈ 2 × 107 dyne/cm2, agreed within about 10 percent.
Determination of capillary entrance pressure losses and first normal stress difference in polystyrene and high impact polystyrene melts
Authors: Peña Juan J. , Guzmán Gonzalo M. , Santamaria Anton 
Published: December 2004

AbstractIn industrial polymer processing, polymeric melts give rise to shear stresses above 105 dynes/cm2. For the determination of rheological properties and particularly melt elasticity, only the capillary type instrument is applicable to this range. In this paper, a comparative experimental study of the first normal stress difference, obtained from end pressure losses, entrance pressure losses and die swell is reported for polystyrene and high impact polystyrene. Good agreement between results from the three methods of measurement was obtained. The results are in accordance with literature data obtained using a capillary rheometer. It is seen that the values of first normal stress difference are greater in polystyrene than in high impact polystyrene.
Design and application of an instrumented falling weight impact tester
Authors: Wnuk A. J. , Ward T. C. , McGrath J. E. 
Published: December 2004

AbstractWithin the past decade, instrumented impact testers have become important tools for characterizing the response of polymers to short term loads. Unlike conventional test equipment which yield only the fracture energy, the instrumented devices are capable of providing detailed force vs time plots of the impact process. An instrumented falling weight impact tester is described which is equipped with an accelerometer which permits direct observation of the weight's deceleration as it strikes and pierces the test specimen. Integration of the resulting acceleration vs time curve provides the velocity change upon impact from which the fracture energy can he calculated. The impact tester is capable of accepting a wide range of specimen shapes and sizes and is especially useful where small amounts of material are at hand. To date, it has proved its utility in characterizing thin plastic sheets as well as fiber‐reinforced laminates.
Physical aging studies of styrene‐butadiene and carbonate‐siloxane block copolymers
Authors: Tant Martin R. , Wilkes Garth L. 
Published: December 2004

AbstractThe physical aging process in styrene‐butadiene and carbonate‐siloxane block copolymers has been studied by monitoring the time dependent changes in mechanical and thermal properties. Specifically, stress‐strain, stress relaxation and differential scanning calorimetry experiments were utilized. For the styrene‐butadiene systems, it was found that the rate of physical aging increases with decreasing glassy content between 50 and 100 percent glass. However, the rate must decrease to zero when the percent glass reaches zero. The occurrence of physical aging was also noted in the carbonatesiloxane block copolymer investigated. The data are discussed in light of the practical ramification of utilizing these block copolymers in material applications.
Dependence of mechanical properties in polyolefin blends on shear and thermal history
Authors: Schreiber H. P. , Kapuscinski M. 
Published: December 2004

AbstractVariously dispersed two‐component blends of linear polyethylene and a thermoplastic rubber were subjected to different thermal histories after compression molding and their properties were evaluated. It has been shown that ultimate properties of the blends are not defined by the composition, but vary greatly with degree of dispersion and thermal history. Stronger materials failing in a ductile manner were produced under shock cool conditions and in, finely‐dispersed blends. Brittle failures and weaker materials were favored by annealing procedures and in blends subjected to brief and/or lowshear dispersion procedures. Time and temperature dependent changes in properties of blends prepared under standard conditions have been observed and activation energies for the aging process calculated. Data interpretation was based on a hypothesis of domain morphology in the blends, and on the existence of “tie molecules” which help to determine the cohesive strength of domain boundaries.
The effect of molecular orientation on the mechanical properties of fiber‐filled amorphous polymers
Authors: Patel Prakash D. , Bogue Donald C. 
Published: December 2004

AbstractThe technology of using glass fibers to increase the modulus and the strength of polymeric systems is well‐developed. Much less widely exploited has been the enhancement of properties by orienting the molecules of the polymer itself. The purpose here was to look for a synergistic combination of these two strategies: using glass fiber‐filled polystyrene and introducing molecular orientation into the polystyrene matrix. For rheological reasons it is not possible to introduce large stretch ratios in the rubbery state and thus the amount of molecular orientation that can be frozen into the quenched glassy composite is small. Even so, however, the rubbery elongation (which we associate with subsequent molecular orientation) has a very significant effect on the final (room temperature) mechanical properties. Analysis of these properties was made in terms of various theoretical models (those of Brody and Ward, Smallwood‐Guth, and Russel and Acrivos for the Young's modulus; and that of Kelly and Tyson, as modified by Lees, for the tensile strength). These comparisons showed that the brittleness of unoriented polystyrene is such that the matrix does not effectively distribute the stress along the length of the fiber and thus the benefit of the length is not realized; whereas the higher ductility of oriented polystyrene allows such transfer and a consequent improvement of properties.
Curing of compression molded sheet molding compound
Authors: Lee Ly James 
Published: December 2004

AbstractA recently developed kinetic model has been applied here to describe the polyester‐styrene addition copolymerization. By assuming that the termination step is negligible and the reaction rate between inhibitor and initiator free radical is much, faster than any other reactions, the kinetic mechanism can be simplified to be expressed as a single equation. The parameters, rate constant of initiator decomposition and rate constant of propagation, are estimated from the induction time and the time to the peak exotherm of isothermal differential scanning calorimetry (DSC) curves. Temperature profiles inside plate sections of SMC parts during molding are predicted by a mathematical model in which addition polymerization is coupled with heat transfer. The predicted temperature profiles compare well with the experimental results. The model is also used to predict the cure time of different part thicknesses, mold temperature and initiator concentration. Glass fibers playa role as a heat sink as well as heat conductor during curing. Adding glass fibers to SMC not only lowered the maximum exotherm but also reduced the cure time.
Rheological characterization of unsaturated polyester resin sheet molding compound
Authors: Silva‐Nieto R. J. , Fisher B. C. , Birley A. W. 
Published: December 2004

AbstractThis paper presents a theoretical and experimental analysis of the rheological behavior of sheet molding compound (SMC). The work analyses the squeeze flow in a parallel plate plastometer of SMC discs which contain 25 percent of fiber glass by weight. This method of flow characterization gives a good insight into the basic rheological behavior of SMC for the compression molding process when producing flat parts. The theoretical analysis applies to thickened and matured SMC at room temperature. The analysis treats SMC as a viscoelastic material having an equation of state with viscous, elastic and yield elements. The time variation of compressive force when squeezing SMC discs between two parallel plates (one fixed and one mobile) has been derived from the equation of state. The values of the viscous, elastic and yield parameters were determined by using a least squares method of curve fitting to the experimental results. There are two aspects to the reported experimental work. One aspect is concerned with showing that the three element model for the equation of state provides a realistic mathematical basis for characterizing the rheological behavior of SMC at room temperature. The other shows how the parallel plate plastometer can be used to give data which characterize SMC flow behavior under conditions similar to those of the actual compression molding process.
The toughness of copolymers of polypropylene
Authors: Fernando P. L. , Williams J. G. 
Published: December 2004

AbstractA series of fracture mechanics tests of a set of random and impact copolymers of polypropylene, in which the ethylene content was varied, is described. The plane strain toughness is found to change from the homopolymer value, but thereafter to be independent of ethylene content. The yield stress of the impact copolymers decreases markedly with ethylene content, while that for random copolymers increases only slightly. This is reflected in toughness values in tension. A comparison with the behavior of other rubber‐modified materials is made and it is concluded that crazing is an important mechanism in polypropylene and is perhaps more rate and temperature sensitive than in acrylonitrile‐butadiene‐styrene (ABS).
Prediction of solubilities for volatile hydrocarbons in low‐density polyethylene using UNIFAC‐FV model
Authors: Iwai Yoshio , Anai Yoshiyuki , Arai Yasuhiko 
Published: December 2004

AbstractThe UNIFAC‐FV model has been applied to predict the weight‐fraction Henry's constant of n‐hexane, n‐octane, benzene, and toluene in low‐density polyethylene in the region 124 to 250°C. By adjusting the number of external degrees of freedom per hydrocarbon molecule, the weight‐fraction Henry's constant was correlated with good agreement by the model. Namely, the solubilities of hydrocarbons in the polymer can be obtained correctly from the model at low pressures, less than 2 atm. Although the model is very useful, its applicability is limited to the subcritical temperature range of a volatile hydrocarbon.
Plane strain fracture toughness testing of high density polyethylene
Authors: Chan M. K. V. , Williams J. G. 
Published: December 2004

AbstractThe concepts of linear elastic fracture mechanics (LEFM) are applied to three grades of high density polyethylene in an attempt to determine their fracture behavior in terms of a linear elastic fracture toughness,Kc. The effect of specimen size (thickness and width), crack length and the mode of loading onKchas been investigated in order to determine the plane strain fracture toughness,KIc, of these materials. The effect of temperature (between +23 and −180°C) on their fracture behavior has also been investigated and compared in terms of their plane strain fracture toughness values.
Kinetics of a sterically hindered amine‐cured epoxy resin system
Authors: Buckley Leonard , Roylance David 
Published: December 2004

AbstractFourier transform infrared spectroscopy (FT‐IR) and torsional braid analysis (TBA) were used to study the reaction of an epoxy resin system cured with a sterically hindered amine. Isothermal torsional braid analysis showed the apparent activation energy to be approximately 42 kJ/mol. The reaction kinetics were also considered from the unreacted freshly mixed condition and a partially reacted “B‐staged” condition using infrared spectroscopy, The B‐staged condition is unreactive and stable at room temperature due to the quenching of the primary amine reaction by the glassy structure and the steric hindrance of the secondary amine reaction. Apparent activation energies for these two conditions were found to be 49.4 kJ/mol and 49.0 kJ/mol respectively. The storage life at room temperature of the B‐staged resin system is predicted to be at least three months based on extrapolation of the experimental kinetic data.