Study of the fracture behavior of natural rubber and polybutadiene based compounds : structure to properties correlation (original) (raw)
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Rubber Chemistry and Technology, 2014
Material anisotropy induced by strain in filled vulcanized rubbers strongly affects fracture toughness. The influence of carbon black content on fracture phenomenology and fracture toughness was investigated by performing video-recorded tests adopting a suitable grooved notched pure shear test specimen. In such a way, it was possible to analyze the so-called ''knotty tearing'' deformation mechanism occurring at the crack tip: sideways cracks perpendicular to the notch plane develop before the onset and propagation of a forward crack parallel to the notch plane. The J-integral fracture mechanics approach was adopted and digital image correlation analysis was performed to measure the strain at the crack tip. The presence of carbon black modifies the maximum chain extensibility and strain-induced crystallizability of the rubber matrix in the compound. The formation of sideways cracks occurred in all filled compounds and resulted in a link to the maximum chain extensibility. Nevertheless, toughness enhancement was observed only when strain-induced crystallization took place at the crack tip before the onset of the forward crack.
Journal of Polymer Science Part B: Polymer Physics, 2010
The fracture behavior of carbon black-filled natural rubber compounds, differing in filler content, was studied performing tensile tests in biaxial loading conditions, using a central notched cross-shaped specimen. The test consisted of two steps: a drawing step was initially performed loading the specimen in the direction parallel to the notch plane, up to different draw ratios, and then the specimen was loaded in the direction normal to the notch plane up to fracture. Using a fracture mechanics approach, the fracture toughness was evaluated as a function of the draw ratio applied in the drawing step. A correlation between the fracture phenomenology observed and molecular orientability and orientation was attempted. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1509-1515, 2010
Journal of Applied Polymer Science, 2000
An investigation of the influence of different types of carbon black on fatigue crack-growth behavior was undertaken. Fatigue tests were carried out on edge-notched specimens under cyclic tension loading. A power-law dependency between the crack-growth rate and tearing energy was obtained. Natural rubber (NR) filled with N330 (the mean diameter is 30 nm) carbon black possessed the lowest values of exponent b and constant B (the two crack growth parameters determined from cyclic crack growth testing), which denoted the strongest resistance to crack growth at a given tearing energy. Strain-induced crystallization was investigated by the modified Mooney-Rivlin equation and showed the earliest appearance and strongest ability of the crystallization of the NR/N330 composite at the largest amount of bound rubber. The study on the viscoelastic properties by dynamic mechanical analysis confirmed that the NR/ N330 composite had the largest viscoelastic contribution, which was attributed to the viscoelastic dissipation in the viscoelastic region in front of the crack tip. All of these results confirm the best crack-propagation resistance of NR filled with N330. V
2012
The fracture resistance of different rubbers containing various nanofillers, such as multiwall carbon nanotube (MWCNT), organoclay, silica and carbon black (CB), was determined by the J-integral making use of the single edge notched tensile loaded (SEN-T) single specimen approach. The elastomeric matrices were natural (NR), ethylene propylene diene (EPDM) and hydrogenated nitrile rubbers (HNBR). Moreover, the strain softening (Payne effect) of selected rubbers with 30 part per hundred rubber (phr) filler content was also investigated by dynamic mechanical thermal analysis (DMTA) in shear mode. DMTA results indicated that the Payne effect follows the ranking: MWCNT(fibrous)!>!organoclay(platy)!> silica(spherical). J-resistance (J R) curves were constructed by plotting the J value as a function of the crack tip opening displacement (CTOD !), monitored during loading. CTOD ! = 0.1 mm was considered as crack initiation threshold and thus assigned to the critical value J Ic. J Ic increased with increasing filler loading, whereby MWCNT outperformed both silica and CB. On the other hand, J Ic did not change with filler loading for the NR/organoclay systems that was traced to straininduced crystallization effect in NR. The tearing modulus (T J) also increased with increasing filler loading. The related increase strongly depended on both rubber and filler types. Nonetheless, the most prominent improvement in T J among the fillers studied was noticed for the fibrous MWCNT.
SPE Polymers, 2023
The J-integral approach manifests itself in an efficient way to determine the crack growth and failure mechanism of tread and sidewall compounds used in tyres. Therefore, for a pure shear (PS) specimen of carbon black filled natural rubber, the J-integral formula was vivisected, and the material parameters were defined using the concepts of solid mechanics considering the planar stress conditions. Theoretical calculations, experimental observations, and finite element analysis were executed to calculate the J value for different strain percentages. Different hyperelastic material models were used to understand the hyperelastic behavior of the test compound, but Yeoh model was found to be the best fit with the least error against the experimental test data. The frequency sweep dynamic mechanical analyzer test was done to observe the viscoelastic response of the material. It was observed that the J value decreased with decreasing contour radius and had exhibited stark difference with the global tearing energy values, indicating the effects of stress softening and the dependence of J value on the elastic characteristics of the material. Further, the J value attained from finite element methods for a random strain 22% was used to predict the crack growth rate of the pre-notched PS specimen.
Toughness of natural rubber compounds under biaxial loading
Engineering Fracture Mechanics, 2015
Strain induced molecular orientation effect on the fracture toughness of natural rubber based compounds was studied under biaxial loading conditions, using non-linear elastic fracture mechanics. The J-integral at fracture was evaluated using the finite element method. Fracture toughness can be severely influenced by strain induced molecular orientation up to a material dependent threshold, above which toughness becomes constant. The effect of the fracture phenomenology shown by two carbon black filled compounds, for which propagation is preceded by branching at the tip (sideways crack propagation), is shown to remove any significant stress concentration at the original crack tip, enhancing the apparent fracture resistance.
Polymer Testing, 2009
In this experiment, various types of carbon black (CB) were employed to partially substitute the calcined clay for preparing natural rubber (NR) compounds of similar hardness. At similar hardness, the compounds containing both clay and CB give the better tensile strength, edge-cut tensile strength, tear strength and thermal ageing resistance compared to the control, but the control had better gas barrier property. In addition, the cracking behaviour of the vulcanizate has a transition from simple lateral growth to oblique crack with partial substitution of the clay with CB, and the vulcanizate containing N330 exhibits the greatest longitudinal cracking corresponding to its highest edge-cut tensile strength. This means the presence of N330 causes the greater orientation of the NR chains along the applied force. Furthermore, the vulcanizate containing N330 yields the highest tensile and tear strength, and lowest resilience, although it has the lowest volume fraction of filler. The explanation is given as the higher reinforcing efficiency of N330 and the better filler dispersion shown in SEM micrographs.
Journal of Physics: Conference Series
This study aims to determine the mechanical properties of natural rubber compounds with variations of OPBA nanoparticle fillers and carbon black. Preparation methods for natural rubber compounds using Open Mill. Indonesian rubber standard -20 (SIR-20) mixed with anti-oxidants, activators, curing agents, accelerators and OPBA nanoparticle fillers size 56.31 nm and commercial Carbon black type (N330) with variations (0,2,4,6 and 8)% wt. The results showed that tensile strength increased with the increase in the composition of OPBA nanoparticles and carbon black, as well as the elongation of break and hardness. The best composition of OPBA filler 8% wt showed a hardness of 52 Shore A, a tensile strength of 1.7 MPa, an elongation of break 150%. The best composition of carbon black 8% wt filler with a hardness of 55 Shore A, a tensile strength of 2.5 MPa, elongation breakdown of 140%.
Theoretical and Applied Fracture Mechanics, 1989
This paper presents an investigation of examining the effects of crack propagation and strain rate on the fracture resistance of carbon black reinforced rubber. The strain rates chosen for the investigation are 10, 30, 50, 100, 200, 300 and 500 mm/min. The method of analysis is based on a quasistatic energy approach. The specimen geometry used is basically a double cantilever beam specimen (DCB) which satisfies the criteria of the stability of crack propagation, an essential requirement of producing subcritical crack growth. Due to low bending stiffness of the rubber, the DCB specimen is reinforced to circumvent the specimen buckling upon loading. The results indicate that there is no effect of the strain rates chosen on the fracture toughness of the carbon black reinforced rubber. The magnitude of the measured fracture toughness for crack propagation is, however, found to be about 40 times larger than that for crack initiation. The observation appears in agreement with those reported by earlier investigators.
Properties of Natural Rubber Reinforced by Carbon Black-Based Hybrid Fillers
Polymer-Plastics Technology and Engineering, 2014
Properties of natural rubber (NR) filled with hybrid fillers were compared. Loading of the primary filler, carbon black (CB), was fixed whereas that of the secondary fillers, carbon nanotube (CNT) and conductive carbon black (CCB), was varied. The increase of secondary filler loading results in loss of elasticity but the increases of viscosity, vulcanization rate, cross-link density, hardness, modulus, thermal and electrical conductivities and tan d. Obviously, CNT gives stronger effect than CCB. However, CCB gives improvement in tensile and tear strengths when added up to 3 phr whereas the addition of CNT shows no significant effect on the strengths.