Fatigue Investigation of Elastomeric Structures

Abstract

Fatigue crack growth can occur in elastomeric structures whenever cyclic loading is applied. In order to design robust products, sensitivity to fatigue crack growth must be investigated and minimized. The task has two basic components: (1) to define the material behavior through measurements showing how the crack growth rate depends on conditions that drive the crack, and (2) to compute the conditions experienced by the crack. Important features relevant to the analysis of structures include time-dependent aspects of rubber’s stress-strain behavior (as recently demonstrated via the dwell period effect observed by Harbour et al.), and strain induced crystallization. For the numerical representation, classical fracture mechanical concepts are reviewed and the novel material force approach is introduced. With the material force approach at hand, even dissipative effects of elastomeric materials can be investigated. These complex properties of fatigue crack behavior are illustrated in the context of tire durability simulations as an important field of application.

Durability prediction of an ultra-large mining truck tire using an enhanced finite element method

“…Similarly, delamination is observed to be likely at the interface of the second and third working belts (Figure 10(c)). Consistent with Na¨ser et al 5 proposition, the life predictions when SIC effects are considered tend to improve significantly with increasing inflation loads. They attributed the non-relaxing loads (R .…”

“…0. 5 In Figure 4(a), a representative plot of maximum and minimum strains measured at a predefined number of cycles is shown for one of the crack growth rates considered in the test. As shown in Figure 4(b), the crack grows steadily at the beginning when fully relaxed loads are applied until after 40,000 cycles when the ramped up minimum strains cause the growing crack to retard.…”

“…Next, equation (3) is rearranged to yield equation (4) for plotting F as a function of R-ratio, as shown in Figure 5. A cubic polynomial function was then fitted to the experimental data such that F(R) could be represented in the form given in equation (5). Note that F o is the fully relaxing power-law slope, which is approximately 2 for most NR compounds Figure 6 shows plots of FCGR curves for different R-ratios.…”

“…Considering that filled natural rubber (NR) used in the belt region of the tire strain-crystallizes upon application of non-relaxing loads, 5 FCG measurements were taken under fully relaxing and non-relaxing conditions in a static tearing energy experiment. A PT specimen with a pre-cut length of 25 mm was cycled through varying strain levels and the crack length measured at the end of each cycle.…”

“…For a known crack of relatively large size, an explicit crack feature can be introduced in a finite element (FE) model to obtain the propagation life based on the crack tip strain energy release rate using the theory of fracture mechanics. [1][2][3][4] Although approximate, Na¨ser et al 5 have shown that tire durability predictions cannot solely be dependent on fracture mechanics parameters but also on other factors, such as strain-induced crystallization (SIC).…”