摘要:

AbstractA numerical simulation model for the analysis of the buildup and, the relaxation of molecular orientation in injection‐molded products has been developed. The constitutive equations of the material are described using an extended version of the viscoelastic material model developed by Leonov. The volumetric responses are described using two different equations of state, the Tait equation and an equation developed by Spencer and Gilmore. A WLF‐type of equation is used for the temperature and pressure dependence. Stresses calculated with the model are coupled to birefringence by means of the stress‐optical rule. Birefringence, in turn, is used to characterize the molecular orientation. The model is used to investigate the influence of the processing conditions, the mold elasticity, and the pressure dependence of the material functions on the pressure and birefringence profiles. The material data used are for polystyrene, PS 678E, and are determined experimen

ISSN:0032-3888    

DOI:10.1002/pen.760330402

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe numerical simulation of the injection molding process described in Part I is compared in the present paper with experimental results obtained with an instrumented test mold. Pressure and birefringence profiles are compared with corresponding predictions for an amorphous polymer. The influence of the melt temperature, the flow‐rate, and the packing pressure on the pressure profiles and the frozen‐in birefringence is investigated. It is demonstrated that the prescription of a specified packing pressure profile can reduce the frozen‐in birefringence. The shape and the tendencies of the predicted birefringence profiles agree well with the experimental ones. This leads to the conclusion that the, model can be used to optimize the processing conditions to mold high‐quality products with minimum frozen‐in or

ISSN:0032-3888    

DOI:10.1002/pen.760330403

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractFilled thermosetting resins used for adhesives, sealants, and coatings are two‐phase systems whose rheological behavior is determined by the properties of both phases as well as by the interactions between the matrix and the filler. The chemorheological changes during the crosslinking of an epoxy system (EPON 828 with curing agent Y from Shell Chemical Co.) were investigated. The influence of an untreated silica filler on the reaction kinetics and the Rheological behavior of the system were also analyzed. The concentration of the filler was varied between 0 and 17.25 vol%. The influence of the filler on the gel point was explained in terms of the accelerating effect of the filler on the reaction kinetic

ISSN:0032-3888    

DOI:10.1002/pen.760330404

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractUsing the Crack Layer Theory, differences in damage formation under different stress states during fatigue crack propagation in an ethylene‐butene copolymer were quantified and compared. Despite having vastly different stress states and crack propagation behaviors, arc specimens (28 mm thick) and single edge notched (SEN) specimens (2 mm thick) were shown to have the same specific enthalpy of damage, ∼300 J/g, a parameter in the Crack Layer Theory that is a measure of the material's intrinsic toughness. Damage in the SEN specimen consisted of crazing the significant material yielding; the latter damage type is associated with plane stress conditions. In the predominantly plane strain arc specimen, material yielding was minimal compared to crazing, the dominant damage form. After measuring these damage forms and applying the Crack Layer Theory, the constancy of the specific enthalpy of damage was established. Also the dissipation coefficient, β, a second parameter of the Crack Layer Theory, was shown to be a process‐dependent parameter, which was inversely proportional to the lifetime of the specimen: βSEN= 4.6 × 10−5, βarc= 1.1 × 10−4, which corresponds to lifetimes of 140,000 and 30,000 cycles to failure

ISSN:0032-3888    

DOI:10.1002/pen.760330405

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA laboratory prototype tester was used to systematically study the effects of geometrical and operational variables on the mixing of two immiscible polymer melts. Results verify that the number of passages is a dominant variable in dispersive mixing. The development of micromorphology in a controlled fashion was studied extensively and backed up with a finite element simulation of the flow in the tester geometry. Complex deformational fields in the laboratory mixer are evident from the highly deformed dispersed phase morphologies.

ISSN:0032-3888    

DOI:10.1002/pen.760330406

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe problem of excessive heat buildup in a heat diffusion supported thermosetting process may lead, especially in the case of thick composite profiles, to compromised quality or even thermal degradation of the final product. A computer simulation of a real manufacturing process demonstrates this intrinsic weakness of the conventional manufacturing process by showing nonuniformities in the degree of cure development and a temperature inversion at the end of the processing cycle. Those nonuniformities in thermal expansion and contraction may be avoided by heating the composite uniformly throughout the whole cross section. This can be achieved with the help of electromagnetic irradiation. The electric energy absorption and, hence, conversion to heat takes place uniformly in the whole bulk of the material, regardless of the position. In effect, one can expect that the uniformly fast cured composite features superior mechanical properties over that of a composite that is conventionally processed.

ISSN:0032-3888    

DOI:10.1002/pen.760330407

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractHeat deflection is often the only test used to determine a materials ability to withstand exposure to elevated temperatures under load. This test has its limitations, simply because not all materials operate under loads of 1820 kPa (264 psi) or 455 kPa (66 psi). Consequently, heat deflection cannot always give a true indication of a materials high temperature capabilities. The automotive industry has used the heat sag test to measure the deformation of elastomeric materials during the paint curing process. The heat sag test measures the sag of a molded bar. One end of the bar is clamped while the other end is free to sag or deflect. Samples are tested over a range of temperatures to determine the failure deflection point. This study examines the correlation of the heat sag to heat deflection and dynamic mechanical analysis (DMA) on polypropylene resins and compounds and polystyrene.

ISSN:0032-3888    

DOI:10.1002/pen.760330408

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760330401

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY