Craze band

Further, electron micrographs such as those of Matsuo (25) indicate that matrix craze bands are as wide as rubber particle diameter. Thus, energy absorption in the rubber during the important craze phase is... 

PEELS was utilized to measure the variation in density inside the craze band. Because the thin sections are prepared from the DN-4PB damage zone of a bulk sample, the thickness of the thin sections is believed to be approximately uniform throughout. Therefore, the variations in the measured PEELS spectra intensities must be due to local density differences instead of deviations in thickness. 

When the PEELS measurement was conducted, an abrupt drop in density was observed at the interface between the matrix and the craze bands (Figure 4). In addition, a drop of approximately 50% in density was found at the base of the already unloaded craze band. This observation implies that an extension ratio of at least 2 exists for the craze fibrils. This phenomenon is not uncommon for thermoplastic crazes (5, 10). To ensure that the PEELS method gives reasonable results, the density of the craze band inside a polystyrene tensile specimen was measured (Figure 5) using the same sample-preparation procedures described in the section Experimental Details. The measured density of the craze band in the unloaded polystyrene was found to be about 0.62 g/cm3, which is in good agreement with the number reported in the literature (5,10, 24). 

Figure 4. PEELS line scan of the craze bands observed in BCB-MI. A sharp transition in density is detected at the boundaries between the dilatation bands and the matrix. The slight increase in density at the center region of the bands may result from the stretched molecules inside the dilatation bands partially snapping back after unloading.

Figure 8. Three-stage mechanism of multiple crazing (a) stage 1 stress concentration and craze initiation at rubber particles (b) stage 2 superposition of stress fields (small interparticle distance, high rubber volume content) and formation of broad craze bands and (c) stage 3 limitation of crack length and crack stopping at rubber particles.

Stage 2 (superposition effect). At a rubber-particle content of more than 15 vol%, the stress concentration directly at the particle surface is increased by the stress fields of neighboring particles (Figure 9). This fact favors the formation of broad crazes and long craze bands. 

Superposition effect Stress fields around the rubber particles overlap when the particle distance is smaller than half the particle diameter (i.e., particle content larger than about 15 vol.%) higher stress concentrations create thicker crazes and long craze bands, so large material volumes contribute to toughness. 

SPS shows a lower impact strength than APS. The study of the failure and deformation behavior of SPS revealed that the breakage of SPS occurs with a slow and controlled crack growth at a much lower energy level than APS. During the deformation, many craze bands appear in the AI, while no visual evidence of crazing was observed in SPS before the break [12], The critical stress intensity factor, A ic, and the fracture energy, Gu, of SPS are smaller than those of APS. These results show that SPS is more brittle compared with APS. 

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