The Research On The Damping And Sound Insulation Properties Of Long Glass Fiber Reinforce Polypropylene Composites

The fiber reinforced thermoplastic composite materials have been widely applied into automobile industry owning to the excellent properties such as lightweight, high specific strength, high specific rigidity, high damping, excellent sound absorption and insulation. In this thesis, a preparation technology of a kind of long glass fiber reinforced thermoplastic composite materials(LGF/PP) is proposed. It mainly includes the preparation technology of LGF/PP mixed felt, the improvement of heating scheme and the hot pressing molding technology. Then the damping and sound insulation properties are researched through the method of free vibration of cantilever beams and the method of insertion loss separately. Detailed contents are listed as follow:Firstly, the LGF/PP mixed felt is prepared through air-lay technology to improve the dipping effect. Air-lay technology is mainly realized by a double cage air-lay machine. The glass fiber and the PP fiber in the LGF/PP mixed felt are mixed mutually. The probability of the fiber distribution in each direction is equal and the LGF/PP mixed felt presents a three-dimensional structure. In view of the defect of the heating temperature instability of the traditional electric heating scheme, a hybrid contact heating scheme is proposed. The high efficiency of electric heating and the heating uniformity of the heating-oil are combined in this scheme to improve the heating uniformity of the LGF/PP mixed felt. The molding parameters are reasonably controled to heat and mold the the LGF/PP mixed felt.Secondly, the damping property of LGF/PP composites are tested through the method of free vibration of cantilever beams and the test system is built through the Lab VIEW program. The experiment results indicate that the damping ratio decrease with the increasing of density and glass fiber mass fraction, and that the dynamic elastic modulus increase with the increasing of density and glass fiber mass fraction.Thirdly, LGF/PP cavities are prepared to test the sound insulation property through the method of insertion loss. The experiment results indicate that the insertion loss of the LGF/PP cavity increases with the increasing of LGF/PP density and that the sound insulation property is effected little by the glass fiber mass fraction. The sound insulation property is effected by the sound type under the low frequency, but the effect becomes weak gradually with the increasing of sound frequency. The lowest resonant frequency of LGF/PP cavity is about 250 Hz and the critical frequency of coincidence effect is about 1250 Hz.In conclusion, the preparation technology of LGF/PP composites and its damping and sound insulation properties are studied through experiment in this thesis. It provides a reliable experimental basis and reference for the engineering application.