Qiang Yuan

Effect of cavitations on brittle–ductile transition of particle toughened thermoplastics

In this study, we established a correlation between cavitations volume and the brittle-ductile transition (BDT) for particle toughened thermoplastics. The brittle-ductile transition temperature (T-BD) was calculated as a function of T* and interparticle distance (ED), respectively, where T* was a parameter related to the volume of cavitations. The results showed that the smaller the cavitations volume, the higher the brittle-ductile transition temperature. The calculations correlated well with the experimental data. With respect to rubber particle, the rigid particle was too hard to be voided during deformation, thereby the TED of the blend was much higher than that of rubber particle toughened thermoplastic. This was a main reason that rubber particle could toughen thermoplastics effectively, whereas rigid particle could not.

Brittle–ductile transition in PP/EPDM blends: effect of notch radius

Abstract The toughness of polypropylene (PP)/ethylene–propylene–diene monomer (EPDM) blends was studied over wide ranges of EPDM content and temperature. In order to study the effect of notch radius ( R ), the toughness of the samples with different notch radii was determined from Izod impact test. The results showed that both toughness and brittle–ductile transition (BDT) of the blends were a function of R , respectively. At test temperatures, the toughness tended to decrease with increasing 1/ R for various PP/EPDM blends. Moreover, the brittle–ductile transition temperature ( T BT ) increased with increasing 1/ R , whereas the critical interparticle distance (ID c ) reduced with increasing 1/ R . Finally, it was found that the different curves of ID c versus test temperature ( T ) for different notches reduced down to a master curve if plotting ID c versus T BT m – T , where T BT m was the T BT of PP itself for a given notch, indicating that T BT m – T was a more universal parameter that determined the BDT of polymers. This conclusion was well in agreement with the theoretical prediction.

Effect of annealing on the viscoelastic and viscoplastic responses of low-density polyethylene

Two series of tensile tests with constant crosshead speeds (ranging from 5 to 200 mm/min) and tensile relaxation tests (at strains from 0.03 to 0.09) were performed on low-density polyethylene in the subyield region of deformations at room temperature. Mechanical tests were carried out on nonannealed specimens and on samples annealed for 24 h at the temperatures T = 50, 60, 70, 80, and 100 degreesC. Constitutive equations were derived for the time-dependent response of semicrystalline polymers at isothermal deformations with small strains. A polymer is treated as an equivalent heterogeneous network of chains bridged by temporary junctions (entanglements, physical crosslinks, and lamellar blocks). The network is thought of as an ensemble of mesoregions linked with each other. The viscoelastic behavior of a polymer is modeled as a thermally induced rearrangement of strands (separation of active strands from temporary junctions and merging of dangling strands with the network). The viscoplastic response reflects sliding of junctions in the network with respect to their reference positions driven by macrostrains. Stress-strain relations involve five material constants that were found by fitting the observations.