Characterizing the Intrinsic Strength (Fatigue Threshold) of Natural Rubber/Butadiene Rubber Blends

Abstract

Tires require rubber compounds capable of enduring more than 108 deformation cycles without developing cracks. One strategy for evaluating candidate compounds is to measure the intrinsic strength, which is also known as the fatigue threshold or endurance limit. The intrinsic strength is the residual strength remaining in the material after the strength-enhancing effects of energy dissipation in crack tip fields are removed. If loads stay always below the intrinsic strength (taking proper account of the possibility that the intrinsic strength may degrade with aging), then cracks cannot grow. Using the cutting protocol proposed originally by Lake and Yeoh, as implemented on a commercial intrinsic strength analyzer, the intrinsic strength is determined for a series of carbon black (CB) reinforced blends of natural rubber (NR) and butadiene rubber (BR) typical of tire applications. The intrinsic strength benefits of the blends over the neat NR and BR compounds are only observed after aging at temperatures in the range from 50 to 70 °C, thus providing fresh insights into the widespread durability success of CB-filled NR/BR blends in tire sidewall compounds and commercial truck tire treads.

About the Influence of Materials Parameters on the Ultimate and Fatigue Properties of Elastomers

“…The reduction of the dissipation zone can be obtained by pushing an ultra-sharp blade into the open crack. This inspired a new efficient protocol to rapidly evaluate G0 [36,37].Values are found between 20 and 100 J / m 2 [38][39][40][41][42]. According to Lake and Thomas [43], they corresponds to the breaking energy of the chains that cross the fracture plane.…”

Fatigue Crack Growth Behavior of Carbon Black–reinforced Natural Rubber

“…The tearing energy below which no crack growth occurs is termed the fatigue threshold, T 0 , and is typically of the order of 0.04-0.10 kJ/m 2 . 9,10,13,14 At very high tearing energies, the failure process transitions from crack growth to catastrophic tearing. 15,16 The tearing energy at which this transition occurs is the critical tear energy, T c , of the order of 10-50 kJ/m 2 for compounds typically used in tire applications.…”

“…The nucleation or initiation of cracks within the rubber article (or at the article surface) from crack precursors 2. The intrinsic crack growth resistance of the rubber compound, which defines the rate at which cracks originating from precursors can grow to the critical length required for catastrophic mechanical failure [1][2][3][4][5][6][8][9][10] Reinforcing rubber with particulates such as carbon black (CB) plays a key role in extending the lifetime of rubber components. Reductions in fatigue crack growth (FCG) rates and an improved resistance to catastrophic tearing are characteristic features of CB reinforcement, but the exact mechanisms underpinning these phenomena are still incompletely understood.…”

Future trends in predicting the complex fracture behaviour of rubber materials

“…[5,14] A crack operating at an energy release rate below the intrinsic strength can be projected to operate indefinitely without growing, since there is simply not enough energy supplied to break polymer chains at the crack tip. [15,16] Therefore, this endurance limit T0 or mechanical fatigue limit is very useful in product design and in fatigue analysis. [17].…”