SynopsisMechanical properties of rubber-modified polymers are not single-valued functions of rubber/ matrix type and rubber content, but also vary with processing conditions. The variations in mechanical properties with processing conditions arise mainly from changes in rubber-phase dispersion. In our past work, by lightly crosslinking the rubbers to increase their melt tenacity and strength, we have succeeded in producing fine and consistent dispersions despite diverse processing conditions. In this study, mechanical properties of polypropylenehghtly crosslinked rubber blends are compared with those of polypropylene/uncrosslinked rubber blends. The results indicate that, like dispersion, mechanical properties of polypropylene/crosslinked rubber blends also appear to be consistent and independent of process variables. The influences on mechanical behavior of degree of crosslinking, rubber content, and rubbedmatrix type are also discussed.
An impact facility has been designed and constructed to produce and measure large amplitude one-dimensional compression and shear waves in solids. Design considerations and experimental details to produce the necessary impact configuration and to measure the particle velocity profiles resulting from compression and shear waves are described. Experimental results are presented to show that the impact facility was satisfactorily constructed. After a brief discussion of shear wave measurements, the experimental measurements made under compression and shear loading in polymethyl methacrylate and polycrystalline aluminum oxide are presented. These results are expected to provide new information on material response at high strain rates.
The evolution of particle‐impact‐induced fracture damage in hot‐pressed (HP) silicon nitride was established by accelerating single 2.4‐mm‐diameter tungsten carbide spheres against polished HP Si3N4 surfaces. Threshold velocities for ring, cone, and radial cracks were determined and the corresponding threshold stress for ring cracking was obtained from an elastic stress analysis. Particle size had significant effects on the threshold velocities for the inelastic impression and the various crack types. Loading rate had little effect on the threshold stress for ring cracks; rate effects on other crack types could not be assessed because the quasistatic indenter failed at stresses less than those required to invoke other crack types. A 20‐μm‐thick oxide scale had little influence on morphology and extent of damage but was removed easily at low velocities, suggesting higher erosion rates for Si3N4 in oxidizing environments. Damage phenomenology in 85% dense reaction‐bonded Si3N4 was similar to that in HP material; however, all stages of damage occurred at substantially lower velocities.
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