Dynamic Property and Fatigue Crack Propagation Research on Tire Sidewall and Model Compounds

Abstract

Research was conducted to define appropriate compound loading conditions and energy parameters required to properly control and analyze fatigue crack propagation experiments for tire sidewall applications. The effects of strain level, pulse frequency, overall cycle frequency, sample thickness, and oven temperature were screened, and strain level was shown to be the dominant variable in the region of interest. Designed experiments further confirmed that frequency (i.e., strain rate) effects upon strain energy are small at normal rates of tire deformation (equivalent to 40 Hz). However, at typical laboratory test frequencies (≤5 Hz), strain rate effects on strain energy are large, and the differences vs. results under tire conditions depend heavily on polymer type as well as test temperature. Thus, the use of strain level, strain rate, and temperature conditions which simulate the tire service environment are critical to give representative results in laboratory testing. A constitutive equation was defined which provides an excellent model for strain energy in pure (or simple) shear as a function of the principal extension ratio (i.e., strain level) at constant frequency. Therefore, computer modeling of such experiments appears straightforward using an on-line minicomputer. Fatigue crack propagation studies showed major effects of pure-shear sample thickness, processing prior to molding, different types of reference compounds, and different polymer types. Halobutyl compounds and halobutyl/EPDM/NR blends were shown to provide superior FCP resistance at a given strain or strain energy level. These results were consistent with earlier tire and laboratory data.

Fatigue crack nucleation and growth in filled natural rubber

“…This is true for linear elastic material behaviour, as well as nonlinear elastic behaviour of rubber, due to the fact that the effect of crack growth is merely to translate the crack tip fields in this specimen. As the energy release rate is independent of crack size, the fatigue crack growth rate is also constant, on average, and the crack length varies linearly with applied cycles 8 , 20,21 . Crack growth at a constant rate may therefore be observed until a statistically converged measurement of the crack growth rate is obtained.…”

Multiaxial deformation and strain-induced crystallization around a fatigue crack in natural rubber

“…The geometry of the samples is a classical "pure shear" geometry (also known as planar tension samples), commonly employed for fatigue crack growth tests [9][10][11]. The dimensions are reported in Fig.…”

Effects of the interaction of hardness, resilience, and fatigue properties on the abrasion properties of rubber blends

“…The fatigue times were recorded, and the dynamic fatigue fracture parameters (m) can be calculated by the following equation 19 : The fatigue times were recorded, and the dynamic fatigue fracture parameters (m) can be calculated by the following equation 19 :…”

“…The dynamic fatigue fracture parameters were measured using strain-fatigue life curves (S-N curves) methods which was put forward by D. G. Young, 19 based on the superposition principle of viscoelasticity and fracture mechanics of rubberlike materials. The k 2 lg N curves (k is draw ratio and N is fatigue life) of a series of samples pre-cut with different size were obtained using tensile fatigue model according ASTM D4482.…”

“…The samples were respectively pre-cut with 0, 1.0, 1.2 and 1.4 mm in length (C i ), and tested by using tensile fatigue model with different k value. The fatigue times were recorded, and the dynamic fatigue fracture parameters (m) can be calculated by the following equation 19 :…”