Fractographic analysis of the crack resistance of styrene–acrylonitrile/polybutadiene‐g‐styrene–acrylonitrile blends as evaluated by the essential work of fracture method

Abstract

The fracture surfaces and deformation micromechanisms of styrene-co-acrylonitrile (SAN)/polybutadiene-g-styrene-coacrylonitrile (PB-g-SAN) blends with the compositions ranging from 65/35 to 0/100 were studied with a scanning electron microscopy technique. The results were compared to the essential work of fracture parameters obtained in a previous study conducted on double-edge notched tension specimens. Different plastic damage mechanisms were observed, and they depended on the blend composition. For blends of 65/35 and 45/55, a high degree of rubber particle cavitation and multiple cracking followed by the massive shear yielding of the matrix were found to be the main source of energy dissipation during crack growth. Within this compositional range, more intense plastic damage in a larger volume of material, especially at the notched region, was observed as the concentration of the rubbery phase increased. For the 25/75 blend, the prevailing mechanism was pure shear yielding without any sign of cavitation inside the particles, and the fracture surface became relatively flat and was covered with aligned small microcracks. This sample showed the highest specific essential work (w e ) value among the blends examined in the previous study. For the samples containing concentrations of dispersed phase higher than 75%, the shear yielding process gradually became less important with the progressive importance of multiple crazing so that high-magnification micrographs revealed extensive microcracking/crazing both inside and between the rubber particles, as the only active deformation micromechanism for neat PB-g-SAN. The variation w e and specific plastic work of fracture with the PB-g-SAN phase content were successfully explained in terms of prevalent deformation mechanisms. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40072.

Tough salami-inspired Cf/ZrB2 UHTCMCs produced by electrophoretic deposition

“…In these weak matrix composites (WMCs) the matrix is subjected to multiple cracking whilst the fibers provide strength and crack tolerance, in this way after the matrix is completely fractured by multiple microcracking, the total fracture occurs with the failure of the fibers [18]. A further development for UHTCMCs in terms of toughness can be borrowed from strategy behind the solution-polymerized acrylonitrile-butadiene-styrene (ABS): the salami-like particles [19,20]. The dispersed salami-like particles consist in polybutadiene particles (PB) grafted (-g-) by acrylonitrile-styrene copolymer (SAN).…”

“…Hence, the aimed scenario is the promoting of extensive microcracking ahead of the crack tip, primarily between the bundles (in other words, along the weak matrix), which leaves uncracked-bundle bridges (the cross section should be appear like a slice of salami). The uncracked-bundle bridges (as the crazing and shearing phenomena activated by the salami-like particles [19,20]) will act as intact regions spanning the crack wake to inhibit its progress by further microcracking inside the bundles and crack deflection along the transverse orientation to the main fracture surface. At the end of the fracture processes, the salami-inspired UHTCMCs should fail under bundle pull-out mode.…”

Experimental analysis of tensile properties and essential work of fracture of fumed silica filled polypropylene toughened with thermoplastic polyolefin elastomer

“…6 On the other hand, by adding 20 wt.% of ethylene-based TPO to PP, white circles were observed, indicating the debonding and droplet of ethylene-based TPO particles, which would reduce the tensile strength and module of the compounds. 29 Figure 2(d), (d)´ indicates cavitation, by the addition of 20 wt.% of propylene-based TPO due to the homogeneity of the disperse phase. These cavities and their size were increased compared to the combination of PP with 10 wt.% of propylene-based TPO.…”

“…As a result, the resistance of the material to the onset and propagation of cracks subsequently rose by increasing the volume of material against the crack tip in energy absorption/dissipation processes. 29…”

“…6 On the other hand, by adding 20 wt.% of ethylene-based TPO to PP, white circles were observed, indicating the debonding and droplet of ethylene-based TPO particles, which would reduce the tensile strength and module of the compounds. 29 SEM micrographs of the broken blend nanocomposite surface of PP with 20 wt.% of TPOs (ethylene and propylene-based) and 3 wt.% of fumed silica with 3 wt.% of compatibilizer are indicated in Figure 3. To compare the influence of fumed silica in the blend nanocomposites including propylene-based and ethylene-based TPOs, the average diameter of holes is estimated employing ImageJ software and expressed in Figure 4.…”