摘要:

AbstractIn order to form long fiber‐reinforced plastic sheets into angled parts, a new process called the Laminate‐Bending Process was recently developed. The process consists of preforming a prepreg into semi‐cured stable shapes having various sharp bending radii, followed by laminating the preforms into a fully cured thick angle product having high strength and rigidity. A sharp 90°V‐angled product of five lay‐ups of preform was test fabricated under various preforming and laminating conditions by using a continuous glass fiber reinforced epoxy resin, and it was confirmed to be excellent in delamination resistance and specific strength. Also, the process is quite practical in productivity, handling, and applicability to other advanced composite materials, and it can expand the use of such brittle materials for wider ap

ISSN:0032-3888    

DOI:10.1002/pen.760331702

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe objective of this effort has been to investigate the relationship between polymer structure and microwave absorptivity. Dielectric loss factor, ε″, loss tangent, tan δ, and oscillator strength, (εS−‐ ε∞), were used to evaluate potential material processability under applied microwave radiation. Numerous polymeric materials varying in chemical and physical structures were irradiated in a low power (≤ 100W) electric field at 2.45 GHz. Electromagnetic radiation was applied as either traveling or resonant wave modes in cylindrical and rectangular waveguides. In general, heatability was found to be a direct function of the dielectric loss dispersion dependence on temperature and frequency. The dielectric loss factor obtained at low frequency measurements was found to be directly proportional to the heatability of polymers. A WLF plot was used to predict the shift of dielectric loss maxima into or out of the microwave fr

ISSN:0032-3888    

DOI:10.1002/pen.760331703

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe dielectric behavior of glassy thermoplastic polymer in the microwave frequency range was investigated. Specifically, the relationship between energy absorption and temperature for several thermoplastic systems was examined to test the theoretical basis for heating under microwave irradiation. Irradiation under traveling and standing wave conditions were explored. The heating rate versus temperature data at a frequency of 2.45 GHz yielded a microwave calorimetry procedure for examination of the dielectric and relaxation behaviors. Correlations were drawn between (a) the apparent activation energy and the critical temperature, and (b) the shape of the dielectric spectra at 2.45 GHz and its shape in the kHz region. WLF relationships were examined for glassy thermoplastics to show the difference in changing activation energy with temperature.

ISSN:0032-3888    

DOI:10.1002/pen.760331704

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe overall objective of these studies was to investigate the relationship between polymer structure and microwave absorptivity. In this paper, the microwave processing of semicrystalline polymers such as poly(ether ether ketone) (PEEK), nylons, and poly(ethylene terephthalate) (PET), via a cylindrical resonance wave cavity and a rectangular standing wave applicator is described. These polymeric materials were irradiated in low power (<50W) electric fields at 2.45 GHz. Silicone flexible molds were necessary for improved processing of nylons and PEEK at temperatures below theirTcRapid heating rates were observed between the glass transition temperature,Tg, and the melting temperature,Tm, for all these polymers provided thatTcwas exceeded. Both dynamic mechanical thermal analysis (DMTA) and dielectric thermal analysis (DETA) spectra were utilized to predict the heating phenomena between amorphous and semicrystalline materials and to explain the rapid crystallizing rate of PEEK. above its glass transition temperature. Correlations were drawn between (a) the apparent activation energy and the critical temperature (Tc) and (b) the shape of the dielectric spectra at 2.45 GHz and its shape in kHz region.

ISSN:0032-3888    

DOI:10.1002/pen.760331705

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractStoichiometric mixtures of DGEBA (diglycidyl ether of bisphenol A)/DDS (diaminodiphenyl sulfone) and DGEBA/mPDA (meta phenylene diamine) have been isothermally cured by electromagnetic radiation and conventional heating using thin film sample configurations. Fourier transform infrared spectroscopy (FTIR) was used to measure the extent of cure. Thermal mechanical analysis (TMA) was used to determine the glass transition temperatures directly from the cured thin film samples. Well‐defined glass transitions were observed in the TMA thermograph for both thermal and microwave cured samples. Significant increases in the reaction rates have been observed in the microwave cured DGEBA/DDS samples. Only slight increases in the reaction rates have been observed in the microwave cured DGEBA/mPDA samples. Higher glass transition temperatures were obtained in microwave cured samples compared to those of thermally cured ones after gelation. The magnitude of increases of glass transition temperature is much larger for the DGEBA/DDS system than DGEBA/mPDA system. The microwave radiation effect was much more significant in DGEBA/DDS system than in DGEBA/mPDA system. DiBenedetto's model was used to fit the experimentalTgdata of both thermal and microwave cured epoxy resin

ISSN:0032-3888    

DOI:10.1002/pen.760331706

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractDynamic mechanical and tensile properties were investigated for blends of poly(styrene‐co‐acrylonitrile) and bisphenol‐A polycarbonate prepared by the solution process. It is apparent from the dynamic mechanical properties that the as‐blended sample has a phase separated structure and the structure changes further with heat treatment. The phase structures of as‐blended and heat‐treated samples were estimated using the theories of Kerner and Davies for the modulus of two‐phase materials and the dynamic mechanical data. The tensile properties obtained at room temperature are not inconsistent with the phase structure estimated for the as‐blended and heat

ISSN:0032-3888    

DOI:10.1002/pen.760331707

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractFusion simulation is one of the key techniques used in designing and producing electrofusion joints for gas distribution and in evaluating fusion joint integrity. This paper describes the results of numerical simulation of the thermal fusion process, using the finite element method. A nonlinear heat transfer computer program was used to obtain the temperature profile of an electrofusion joint at fusion. It was found that the temperature experimentally measured at the fusion interface by insertion of a thermocouple agreed with the temperature computed by fusion simulation. In addition, as both the temperature at the fusion interface and the resin temperature close to the wire corresponding to the mechanical strength of the fusion part were measured, it was confirmed that the proper heating conditions for each joint could be determined based on the results of the fusion simulation.

ISSN:0032-3888    

DOI:10.1002/pen.760331708

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe effect of molecular weight on the spherulite growth rate of poly(ethylene terephthalate) (PET) has been determined using a real‐time small angle light scattering (RTSALS) device equipped with a two‐dimensional position‐sensitive detector. This detector, the design of which was previously reported, incorporates a CCD camera, a personal computer, and an imaging board as the major hardware components. The device performs real‐time analysis of the light scattering pattern and calculates the average spherulite radius as a function of time during the crystallization experiment. Growth rate data were obtained for PET having number‐average molecular weights of 18,000, 24,700, and 33,100. Samples were crystallized isothermally following a temperature jump from the glass at room temperature to the desired crystallization temperature, which ranged from 130 to 200°C. Both the temperature and molecular weight dependence were found to be well described by the Hoffman equation. The temperature dependence agrees well with that found by previous workers, but the molecular weight dependence is somewhat

ISSN:0032-3888    

DOI:10.1002/pen.760331709

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY

ISSN:0032-3888    

DOI:10.1002/pen.760331701

出版商:Society of Plastics Engineers    

年代:1993

数据来源: WILEY