Research On Natural Rubber Crack Tip Morphology Evolution By A Real-time Monitoring Method

This topic focuses on the crack tip morphology evolution and its relationship with the crack growth rate. For this purpose, a real-time monitoring platform is employed to capture the crack tip morphology during standard fatigue testing. Combined with the characterization of microstructure analysis, we studied the natural rubber(NR) cracking morphology evolution rules in details and discussed the effects of conventional filler for NR crack tip morphology. Finally, we explored the influence of styrene butadiene rubber(SBR) / NR blends for NR crack tip morphology. Based on the above research, we set up a bridge between the crack morphology and fatigue property.There are two stages of NR in the crack propagation rate corresponding with two characteristic cracking morphologies. We defined this two kinds as "peeling" and "breaking-up". "Peeling" will result in the appearance of secondary crack which could share stress concentration, so the crack growth rate is low; "breaking-up" ligament is irregular. It cannot generate secondary crack, so the crack growth rate is high.Three kinds of filler have been chosen as object of filler influence research, there are carbon black, silica and silica-Si69(silane coupling agent). We found that filler could decrease the crack-growth rate effectively because of its ability of making ligaments with homogeneous distribution. This ability is related to filler own property. By using Si69, silica particles can be well dispersed and a filler-matrix network can be formed, which leads to lower crack growth rate. Results indicate that a dosage of 5 wt%(with respect to silica loading) is the optimal content.By exploring the impact of NR / SBR blend morphology of the crack tip, we found proportional blending structure will reduce the crack resistance of NR and increase the crack growth rate at low tearing energy region. The "sea-island" structure which is formed by continuous phase NR and dispersed phase SBR could make the ligaments with homogeneous distribution and create more surface energy dissipation to improve the energy required for cracking.