Journal of Thermoplastic Composite Materials current issue

Predicting the Alignment of Ferromagnetic Particles in a Thermoplastic Matrix

Streilen, D., Yarlagadda, S., Gillespie, J. W. — 2008-06-30

This study investigates the use of an external magnetic field to cause the magnetic and physical alignment of ferromagnetic particles in a thermoplastic polymer matrix. The composite selected provides the best alignment involving rare-earth ferromagnetic particles in a polystyrene matrix. The rare-earth particles are able to be effectively aligned due to their high magnetic and physical anisotropy. The time-to align the particles ranged from <5 s at 498 K to approximately 60 s at 398 K. Composites with weight percents ranging from 5 to 25% are studied. A model is developed in order to predict the alignment, and is validated against experimental data. This model predicts the time-to-align based on magnetic torque balancing that would cause alignment with the viscous drag that acts to slow the particle rotation. It is found that the model describing the polymer as a Newtonian fluid follows the same trends and form as the experimental data. Potential sources of differences that prevents close fit to the data are attributed to particle interactions, sample variations, and especially the shear thinning behavior of polystyrene.

Dielectric Relaxation and Thermal Stability of Polycarbonate Doped with MnCl2 Salt

Ayesh, A.S. — 2008-06-30

Polycarbonate (PC)/MnCl₂ composites have been prepared in order to study the influence of MnCl₂ salt on the dielectric properties (resistivity , permittivity ^', dielectric loss ^'', dielectric relaxation time `' and dielectric relaxation process) and thermal stability of PC/MnCl₂ composites. The dielectric study was carried out over a frequency range from 10 Hz to 306 kHz at room temperature as a function of frequency and salt concentration. Permittivity data was fitted in the frequency domain using Yan and Rhodes model in order to estimate the relaxation times for PC composites. As expected, the resistivity of the composites decreases with increasing of salt concentration and frequency. Also, it was found that, addition of MnCl₂ salt to PC host changes the dielectric properties of PC, mainly, broadening dielectric spectra, increases permittivity and dielectric loss, shortening relaxation time and reduces thermal stability of PC and PC composites. Results reveal that the relaxation process of these composites is due to ionic conductivity relaxation with a single relaxation time and not due to viscoelastic relaxation, while in case of pure PC is due to viscoelastic relaxation.

Thermal and Mechanical Properties of PAN- and Pitch-Based Carbon Fiber Reinforced PEEK Composites

Qiang Yuan, , Bateman, S. A., Friedrich, K. — 2008-06-30

Thermal and mechanical properties of different short carbon fibers (CF) reinforced polyether-ether-ketone (PEEK) composites are investigated, where CF is made from polyacrylonitrile (PAN-CF) and pitch (Pitch-CF). The thermal properties of both composites are studied using differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The crystallinity of PEEK increases with the content of PAN-CF, but it is independent of Pitch-CF content. At the isothermal condition, the crystallite rate of Pitch-CF/PEEK composite is faster than that of PAN-CF/PEEK composites. Dynamic tensile modulus of PAN-CF/PEEK increases with the CF content. An increase of glass transverse temperature with an increase in CF content is found in PAN-CF/PEEK, but not in Pitch-CF/PEEK. The fracture toughness of PAN-CF/PEEK composites increases with CF contents; whereas it remains the same value for Pitch-CF composite. The fracture surface of both composites is analysed using scanning electron microscopy.

Improved Approximations of the Rayleigh Wave Velocity

Pham Chi Vinh, , Malischewsky, P. G. — 2008-06-30

In this article we have derived some approximations for the Rayleigh wave velocity in isotropic elastic solids which are much more accurate than the ones of the same form, previously proposed. In particular: (1) A second (third)-order polynomial approximation has been found whose maximum percentage error is 29 (19) times smaller than that of the approximate polynomial of the second (third) order proposed recently by Nesvijski [Nesvijski, E. G., J. Thermoplas. Compos. Mat. 14 (2001), 356—364]. (2) Especially, a fourth-order polynomial approximation has been obtained, the maximum percentage error of which is 8461 (1134) times smaller than that of Nesvijski's second (third)-order polynomial approximation. (3) For Brekhovskikh—Godin's approximation [Brekhovskikh, L. M., Godin, O. A. 1990, Acoustics of Layered Media: Plane and Quasi-Plane Waves. Springer-Verlag, Berlin], we have created an improved approximation whose maximum percentage error decreases 313 times. (4) For Sinclair's approximation [Malischewsky, P. G., Nanotechnology 16 (2005), 995—996], we have established improved approximations which are 4 times, 6.9 times and 88 times better than it in the sense of maximum percentage error. In order to find these approximations the method of least squares is employed and the obtained approximations are the best ones in the space L²[0, 0.5] with respect to its corresponding subsets.

Thermomechanical Simulation of Infrared Heating Diaphragm Forming Process for Thermoplastic Parts

Labeas, G.N., Watiti, V.B., Katsiropoulos, Ch. V. — 2008-06-30

An innovative methodology for the thermomechanical simulation of the infrared heating diaphragm forming (DF) process is proposed. In the first section of the paper, the heat transfer mechanisms between the infrared (IR) heating lamps and the thermoplastic plate are simulated, and the effect of the various preheating parameters on the heating time and temperature distribution is investigated. In the second section, the mechanical deformation of the thermoplastic component is simulated to enable prediction of heat losses due to the plate contact with the mold. Based on the developed simulation methodology, the main process parameters — e.g., the number, location, and power of IR lamps for optimal preheating; the heat losses during plate deformation; and the minimum required mold temperature throughout the forming phase — are derived for five different thicknesses. The optimization results show that the forming parameters considered influence the heating of the plate in a complex and interactive way; in addition, it is found that with increasing plate thickness, the heating time required to reach the desired temperature also increases.