Effect Of Initial Structure Research Articles

Effects of initial structure on the deformation behavior of PP hollow fiber in continuous drawing

AbstractThe effects of the microcrystalline structure of undrawn fibers on the rheological behavior in the process of the polypropylene (PP) hollow fiber formation system were studied by a simple model describing the continuous drawing process. The predicted and observed drawing behaviors were explained in view of a simple approach based on the concept of strain‐rate sensitivity and strain‐hardening parameters. Various parametric studies showing the interactive nature of the strain‐rate sensitivity and strain‐hardening parameters on the drawing behavior were also numerically performed. Strain‐rate sensitivity affects mainly the intensity of the neck, and strain hardening has more effects on the position of the inflection point in continuous drawing. Details of the necking mechanism in the drawing process were studied by observing the deformation behavior of the specimens with different initial microcrystalline structures. The distinctive initial structure of undrawn PP hollow fibers can be formed by controlling the quenching condition in melt spinning. It was shown that the water‐quenched PP fiber exhibited an unstable smectic form, whereas the stable monoclinic phase was observed for the fiber prepared without quenching by forced convection. The experimental results of the drawing behavior indicated that the strain‐rate sensitivity of the fiber with a smectic form was larger than that with the monoclinic form. It was also shown that the hollowness was affected by the quenching condition in melt spinning and the deformation behavior in the drawing process. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2170–2182, 2001

Polymerizability of Cycloalkenes in “Living” Ring-Opening Metathesis Polymerization Initiated by Schrock Complexes, 2. Effect of Initiator Structure

The kinetics of ring-opening metathesis polymerization of norbornene were investigated in cyclohexane using several Schrock complexes as initiators. Three different Schrock complexes were used: Mo(CHC(CH 3 ) 2 Ph)(NAr)(O-t-Bu) 2 (NAr = Ph (iPr)2 ) (I). Mo(CHC(CH 3 ) 2 Ph)(NAr)(OC(CF 3 ) 2 CH 3 ) 2 (NAr = Ph (iPr)2 ) (II) and W(CH-tBu)(NAr)(O-t-Bu) 2 (NAr = Ph (iPr)2 ) (III). The presence of alkoxy-fluorinated ligands on II and on the corresponding propagating species enhances the polymerizability of norbornene and modifies the kinetic scheme compared to that of polymerizations initiated by the tert-butoxy complex. The greater electropositive character of II compared to that of I results in a majority of metalla-alkylidenic growing species being complexed to monomer, therefore, the coordination of the monomer is not the rate-determining step for the process. In contrast, the major part of growing species, which are derived from the tert-butoxy complex are in a non-coordinated state and, thus, the ability of the initiator to complex the monomer is decisive. In addition, this study allows to quantify the stronger reactivity of W-based complexes compared to that of Mo-based ones. These results were all corroborated by prior theoretical studies using ab initio calculations.

Effect of Initial Structure On Grain Refinement to Submicron Size in Al-Mg-Li Alloy Processed by Severe Plastic Deformation

Effect of Initial Structure On Grain Refinement to Submicron Size in Al-Mg-Li Alloy Processed by Severe Plastic Deformation

Effect of initial structure on recrystallization of the α matrix in an (α+γ) microduplex stainless steel

The high temperature annealing behavior at 1,273K after 80% cold-rolling of the {alpha} matrix in ({alpha} + {gamma}) microduplex structures in a Fe-26Cr-7Ni alloy has been studied with particular attention to the effects of the size of initial structure and the initial orientation of {alpha}. The main results obtained are as follows: (1) No recrystallization of the {alpha} matrix takes place when the initial structure before rolling is fine; the {gamma} particle size is smaller than 9 {micro}m and the {alpha} subgrain size is not larger than 10 {micro}m. This result deduces the conclusion that the {alpha} matrix in ({alpha} + {gamma}) microduplex structures is very hard to recrystallize. (2) Recrystallization occurs in the {alpha} matrix with the {l_brace}111{r_brace} initial orientation when the initial structure is coarse; the {gamma} particle size is 13.8 {micro}m and the {alpha}subgrain size is 15.6 {micro}m. The {l_brace}001{r_brace} initially-oriented regions, by contrast, do not recrystallize even in the coarse initial structure. These results indicate that they recrystallization of the {alpha} matrix in ({alpha} + {gamma}) microduplex structures strongly depends on the initial orientation of {alpha} as well as the size of initial structure.

Effect of initiator structure on physical and thermal properties of nylon‐6

AbstractNylon‐6 is synthesised from ε‐caprolactam by an anionic polymerisation method, through a two‐step process using sodium metal as a catalyst and diisocyanate‐caprolactam block initiator. Two different aliphatic diisocyanates are used. The effects of diisocyanate structure and concentration on percentage cryslallinity, molecular weight, density and thermal properties of nylon are discussed.

Effect of initial structure on the deformability of structural steels

Effect of initial structure on the deformability of structural steels

Effect of Initial Structure on the Residual Strength of Kaolinitic Clay

The effect of initial structure on the residual shear strength of a saturated kaolinite clay is studied by using reversal-shear box technique. An attempt has been made to study the variation of structure with deformation by employing Direct Current conductivity (σs) dispersion characteristics. Residual strength is found to be practically independent of the initial structure for a given effective normal pressure (σ') and so also the shrinkage ratio. The conductivity reduced with increase in deformation and constancy attained when the total deformation reached the residual state. There is no significant variation in the strength ratio (tan ϕ'/tan ϕ'r) and the conductivity ratio (σs initial/ σs at residual) for a given initial structure.

The effect of structure on the strain rate sensitivity of 3003 AlMn alloy

The effect of initial structure on the strain rate sensitivity of 3003 commercial aluminum alloy was studied as a function of strain at temperatures of 25° C and −196° C. The strain rate sensitivity was found to be critically dependent on the initial structure, test temperature and strain, and thus on the instantaneous structure. The change of flow stress with an increase in strain rate resulted in positive, K > 0[K = ( dσ/ d log dot ε ) T] , negative, K < 0, and insensitive, K = 0, strain rate effects depending on the initial structure and the test temperature used. The parameter K was found to increase as the strain increased. To explain the variation in the character of K with structure, strain and test temperature, structural arguments are invoked associating the observed strain rate effects with a stress/strain induced solute disposition instability. A model is proposed relating the strain rate effects to the inherent stability of the initial structure and to the dynamic deformation conditions.

Effect of initial structure on the transformations in high-carbon steels during heating

1. For hypereutectoid steels the duration of the α→γ transformation in parts and the intensive isothermal solution time of excess carbides during heating to quenching temperature are linear functions of the dispersity of the initial structure as characterized by the hardness HRA. 2. The temperature dependence of the intensive isothermal solution time of excess carbides in austenite has an exponential character for hypereutectoid steels. 3. The data obtained make it possible to calculate the effect of the initial structure and the temperature on the transformation during heating of high-carbon steels and more precise calculation of the soaking time. 4. The monographs facilitate the technical calculations of the intensive isothermal solution time of carbides in U12A steel with different initial structures.