| The relationship between strain distribution near crack tip and fracture resistance of rubber products undergoing cyclic loading has recently been of great interest. This thesis focuses on the influence of different type and amount of filler to the strain distribution status near crack tip, and thus the evaluation of anti-crack initiation and propagation properties of filler reinforced styrene-butadiene rubber composites. The filler systems that are studied include carbon black (CB), carbon nanotube (CNT), and CNT/CB hybrid filler system.Firstly, for styrene-butadiene rubber (SBR) filled with four different types of carbon black, the strain distribution at the crack tip of the single-edge notched tension (SENT) specimens are investigated using Digital Image Correlation (DIC) and Finite Element Analysis (FEA). Both DIC and FEA results demonstrate that the larger carbon black particle size, the less strain amplification at the crack tip of SBR. However, the strain amplification region obtained from FEA simulation is much smaller than the one observed from DIC and the reasons are discussed. Critical J integral (JIC) and tearing modulus (TR) are calculated via J integral method, and are connected to crack initiation and propagation resistance of the SBR, respectively. With increasing carbon black particle size, both JIC and TR decrease. These results are in agreement with the prediction based on strain amplification at the crack tip.Then 5 phr of CNT,20 phr and 40 phr of CB are mixed with SBR respectively, the strength of filler network and the strain distribution near crack tip are compared. Although the internal network of 5 phr of CNT exhibits similar stiffness with that of 40 phr of CB, the mechanical and fracture resistance properties of the CNT filled composite is not as well as those of 20 phr CB filled one, not to mention 40 phr CB due to the poor interaction between CNT and rubber matrix. If the filler network strength of CNT is controlled and is similar with that of CB filled SBR, the rod-like CNT would probably play an important role in the resistance proccess of crack initiation and propagation.Finally, with CB filled SBR as a reference, effects of hybrid filler network of CNT and CB on fracture resistance are investigated via two filling strategies:1 phr CNT replacing 1 phr CB and 1 phr CNT replacing 4 phr CB. JIC and TR are calculated. Both JIC and TR decrease along with the rising CNT amount for SBR composites with the replacing ratio 1/1; whereas they increase for the ones with replacing ratio 1/4. DIC results demonstrated that, for the case of 1/1 replacement, higher concentration of CNT led to stronger strain amplification effect, yet the opposite trend was found for the 1/4 replacement. Taking the stiffness of hybrid filler network and the specific geometry of CNT into consideration, the relationship between CB/CNT replacement and fracture resistance of CB/CNT reinforced SBR is discussed in detail. |
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