Search

The composition and sequence structure of a serial of ethylene-propylene diene (EPDM) were analyzed according to the 13C-NMR analysis. The stress-induced crystallization was occurred in EPDM 3080 which the segment chains of methylene were long enough. The mechanical properties of stress-induced crystallization of EPDM 3080 were increased rapidly when the extension ratio reached about 4.5. With the observation by the synchrotron two-dimensional wide angle X-ray diffraction, it confirmed that the increasing stress just begin at the extension ratio of 4.5, which can be attributed to the stress-induced crystallization. Based on the rubberlike network model with crosslinking, entanglement and stress-induced crystallization interaction points, the constitutive equation can be derived according to rubber statistical distribution function and the free energies of deformation. The modified constitutive equation was compared with the stress-strain experimental data. It showed that the deduced stress-induced crystallization constitutive equation of EPDM rubber was in good agreement with the experimental results, which offered a theoretical base for the prediction of the stress-induced crystallization rubber materials.

This paper presents a pneumatic energy absorption system which can extend the energy-absorption beam automatically just before crash. The system consists of thin-shell energy absorption structure, pneumatic equipment and control system. When the control system detectives a crash accident is unavoidable, the pneumatic equipment will extend the energy absorption beam which is fixed in thin-shell energy absorption structure immediately to increase energy absorption space. This system has been equipped on a mass produced bus, and it indicates that the length of energy absorption space can be increased more than 230 mm instantaneously before a crash accident occurs. The time used to extend the energy absorption beam is less than 100ms.

The compositions of a series of ethylene-propylene copolymers were quantitatively determined by13C-NMR at 300K in the solvent o-dichlorobenzene. The monomer composition and sequence distribution were analyzed. The glass transition temperatureTg, half temperature of decomposition and crystallinity were found to be closely related to the sequence structures of methylene. The Tg, half temperature of composition, and crystallinity appeared an abrupt change when the methylene length arrived 7~8 because of the movement of the ethylene segments. Also, theTgof copolymers were simulated according to the monomer compositions. The simulatedTgtended to decrease with the increasing methylene, which was opposite to that of experimented. That was due to the increased crystallization along with the growth of methylene length. While the polymer was amorphous constructed in the simulation, theTgtended to decrease with the increasing soft segment methylene.