摘要:

AbstractIn order to provide nw experimetnal facts required for constructing a nonlinear constitutive equationfor solid polymers, some tests wee conducted on amorphous pojymers of polycarbonate and poly(methyl methacrylate) and for a crystalline polymer of polyxymethylene under varous strain paths such as comprssion, torsion and combined tension‐torsion. It is shown that (1) the stress‐strain behavior for the strain paths without strain reversal is described well not only for amorphous polymers, but also for crystalline polymers by an overstess theory proposed by Krempl, and (2) at the strain paths wth stran reversal, the stress responses are considerably differetn from what is expected for the fstress responses of metals and their all

ISSN:0032-3888    

DOI:10.1002/pen.760352202

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe flow‐induced and thermally induced residual stresses during injection molding of a thin part with complex geometries are predicted. The injection molding precess was considered to consist of a filling and a post‐filling stage (packing coupled with cooling). Additionally, the analysis were applied to successive stages of the process. The model takes into account the viscoelasticity of the molding polymer, which has been neglected in most previous works, because of the complexity of its inclusion. A unified K‐BKZ viscoelastic constitutive model, capable of modeling both the fluid‐rubbery state and the glass state of amorphous polymers, was employed for simulating this problem. For the flow‐induced residual stress predictions of the filling stage, a quasi‐steady state approximation was employed for each element of the part, for the calculation of stress profile and subsequent stress relaxation after cessation of flowf. Stress calculations were provided for the thermally induced residual stress predictions of the post‐filling stage. These explicit calculations led to the results of pressure and temperature distributions of the part during the post‐filling stage into the viscoelastic constitutive model. Additionally, the pressure and asymmetric temeprature profiles of the post‐filling stage were based on finite element packing analysis coupled with a boundary element cooling analysis of the molding process. Finally, the total residual stress in the part was obtained via superposition of the flow‐induced and thermally induced residual stresses. An example is provided to demonstrate the entire concept. The results indicate that thermally induced residual stress is higher than the flow‐induced residual stress by one to tw

ISSN:0032-3888    

DOI:10.1002/pen.760352203

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractA hybrid FEM/FEM computer model was employed n this studyfor simulating the non‐newtonian, nonisothermal polymr melt fielt in the inetering section of a single‐screw extruder. The pressure distribution in the screw surface was obtained by solving the generalized Reynolds equation. Instead of using the energy equation in Eulerian frame, a Lagrangian expression ws involved for stabilizing the numerical scheme. The temperature profiles wee obtained by finite difference discretizaton for the energy equation in such element. The screw surface with the screw channels and the flight lands could be modeled as a surface divided into small shell elements. To demonstrate aplicability, the results provided by the hybrid FEM/FDM were found to be similar to those of the 2D FDM for the trhermally developing flow, through Fenner's example. It can also ilustrate the leakage flow and the cross‐channel effect in the screw pumping problem. The results from the Hybrid FEM/FDM revealed that if the clearance becomes too large, the volumetric flow rate would considerably decrease and the exist melt temperature would increase. In addtion, when the clearance is close to the normal design clearance, the leakage flow through the flight lands was found to be small. These computational results were observed to correlate with those of other experimental studies. Finally, the hybrid FEM/FDM approach can in principle be extended to the non‐Newtonian, nonisothermal flow in a complex screw surface such as the barrier screw and the Maddock mixi

ISSN:0032-3888    

DOI:10.1002/pen.760352204

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractA numerical implementation of the Volume of Fluid (VOF) free surface technique, applied to a filling process governed by a potential flow, is introduced. The implementation is based on a finite element control volume space discretization and uses an implicit time integration. This allows for the accurate tracking of the filling front using large simulation time steps in molds with complex geometries. The approach is validated on comparision with the analytical solution for filling a one‐dimensional tube and with two‐dimensional results obtained with previously‐presented filling algorithms. Examples of the application of the approach in the analysis of structural resin transfer molding (SRTM) are presented. The capability of the method is demonstrated on predicting “race tracking” and “dry spotting” phenomena. The CPU requirement for a typical analysis is on the order of 1 to 20 s on peso

ISSN:0032-3888    

DOI:10.1002/pen.760352205

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThe development of multiphase liquid‐liquid morphologies during mixing at small Reynolds numbers has been modeled. The mixing process is divided into (i) stretching of dispersed drops. (ii) breakup of the liquid threads formed, and (iii) coalescence of the final droplets upon collision. Rules and criteria of the distinct processes are presented and combined to a general 2‐zone mixing model simplifying the flow field into a sequence of alternating “strong and weak zones.” In a “strong zone,” dispersed drops and threads are stretched unless their radius is too small; meanwhile, the stretching threads might break up into droplets. In the subsequent “weak zone,” the remaining threads may disintegrate while any drops present may coalesce. After passing a number of zones, stretching, breakup, and coalescence lead to a dynamic equilibrium that could be considered as the “final” morphology. Using the 2‐zone mixing model, the influence of material parameters and processing conditions on the morphology has been studied. Interestingly, increasing either viscosity (dispersed or continuous phase) yields a finer morphology due to the delay of thread breakup, allowing for further stretching and suppr

ISSN:0032-3888    

DOI:10.1002/pen.760352206

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractA specially designed falling body viscometer has been used to obtain low shear viscosities of dilute solutions of high molecular weight polyethylene in decalin and for detecting phase transitions at high pressures. The method provides valuable rheological data at pressures that correspond to those I lubrication and some extrusion processes. In addition, the method enables detection of phase transitions, such as crystallization, that result in detectable changes in rheology. The influence of pressure as high as 0.6 GPa ( ∼ 80.000 psi) is illustrated here through a study of crystallization, with verification from light scattering and calorimetr

ISSN:0032-3888    

DOI:10.1002/pen.760352207

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractThis research addresses the wear properties and processes of 10 vol% polytetrafluoroethylene (PTFE) filled ultra‐high molecular weight polyethylene (UHMWPE) composites and their relationship to mechanical properties. The addition of the PTFE micropowder results in a slight increase in modulus and a significantly lower strain at break. This is due to a quasi‐brittle failure mechanism. Crosslinking the UHMWPE reduces both the modulus and the ultimate properties. Polymer wear studies against SiC abrasive paper can be divided into initial and steady‐state processes. The initial wear, polymer‐SiC wear, is dominated by microcutting and the formation of a transfer film. A single‐pass wear rate (R1) can be derived from a power‐law description of the initial wear. The steady‐state wear eventually achieved, called polymer‐film wear, is dominated by sliding against a self‐generated. A steady‐state multiple‐pass wear rate (Rx) can be derived from a linear description of steady‐state wear. The relationships between the wear of UHMWPE and the wear of PTFE can be predicted through their ultimate and deformation properties and through an understanding of the wear mechanisms. These relationships cannot be used to relate composite and UHMWPE wear due to their different failure mechanisms. The lowerRxand coefficient of friction of the composite may be related to the PTFE flakes found on the worn and wearing surface. Crosslinking the UHMWPE yields little change in the worn and wearing surfaces and inRx. The increase inR1on addition of PTFE and decrease inR1on crosslinking may be related to the respective increase

ISSN:0032-3888    

DOI:10.1002/pen.760352208

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractA torque rheometer method has been developed to evaluate the melt behavior of biopolyesters. The main features of this technique include: (i) a modified equipment configuration, so as to maintain the melt temperature within ± 1°C pf the set temperature after the first few minutes of polymer melting and thermal equilibration, and (ii) a kinetic equation that can be used to determine the melt behavior from the torque‐time data. Applying this methology to a poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerte) copolymer shows that the degradation kinetics follow Arrhenius behavior with temperature, that the degradation rate increases with increasing hear, and that the activation energy for random chain scission is independent of shear rate. This effect of shear on the degradation process may be a result of viscous heating. The degradation rate is increased because of the increased internal energy of the polymer chains as a result of the mechanical deformation. There is no evidence of direct mechanical degradation. Last, the viscosity values obtained with the torque rheometer are consistent with those obtained by capillar

ISSN:0032-3888    

DOI:10.1002/pen.760352209

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractBlends prepared from poly(ethylene 2,6‐naphthalate) (PEN) and poly(butylene 2,6‐naphthalate) (PBN) show only partial miscibility judged from their glass transition temperatures. Two distinct mechanical behaviors are observed: brittle for the blends20 wt% of PBN. The experimental modulus and strength values of the blends are within the predicted values according to Kleiner and Paul models, respectively. This means that PEN/PBN blends are somewhat compatible based on their tensile properties. Especially for 20 wt% of PBN blend, the high modulus and strength are observed. The viscosity of the blend is high, which may imply a somewhat entangled morphology in the amorphous st

ISSN:0032-3888    

DOI:10.1002/pen.760352210

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY

摘要:

AbstractA perspective of adhesion is offered using average property indices such as dielectric constant, dipole moment, and thermal conductivity. These indices have been derived by comparisons of dielectric theories of adhesion and cohesion with comparisons to experimental data found in the literature. For example, it was found that adhesion generally increases with increased dielectric constant, or with the inverse of the thermal conductivity, for metal substrates. It was also found that ranges in the experimental data found were primarily caused by changes in surface roughness, which meant that interaction densities were not predictable.

ISSN:0032-3888    

DOI:10.1002/pen.760352211

出版商:Society of Plastics Engineers    

年代:1995

数据来源: WILEY