TY - BOOK

T1 - Novel fracture mechanics concepts in elastomer fatigue to model the influence of temperature

AU - Schieppati, Jacopo

N1 - no embargo

PY - 2022

Y1 - 2022

N2 - Failure of elastomers is often related to fatigue. In fact, the mechanical properties of these materials make them suitable in applications in which cyclic loading overlaps with large static loads. Due to the peculiar mechanical properties, namely hyperelasticity and viscoelasticity, the investigation of elastomers¿ mechanical and fatigue properties is not a trivial task. Temperature strongly influences the mechanical and fatigue behavior of elastomers. Despite the awareness of the effects of temperature dating back to the early studies of rubber fatigue, only little effort has been made to rationalize this behavior and develop a systematic model that allows this effect to be taken into account. Thus, this thesis aims to analyze the fatigue of a non-crystallizing elastomer and specifically to investigate the effect of temperature in order to create a model able to improve the fatigue predictions. At first, the influence of self-heating upon cyclic loading due to heat build-up was assessed considering different frequencies, and interesting observations about the temperature evolution during crack propagation were made. Furthermore, an equation for the evaluation of temperature in the thickness of samples was described. Second, the fatigue crack propagation of a filled elastomer was analyzed, considering several mechanical parameters and among them, the most influential for non-crystallizing elastomers was found to be frequency. Based on these findings, the influence of temperature on the mechanical behavior was investigated in terms of large and small deformations, evidencing a strong role of fillers on the overall mechanical properties. Moreover, the fatigue crack propagation at high temperatures was studied and a model to reduce the data to a fatigue master curve was developed. Finally, fatigue lifetime investigations were correlated with initial defect size and crack propagation results. This was possible by exploiting the fatigue master curve applied according to the surface temperature monitored in the fatigue tests as a consequence of heat build-up. These results were then verified through the particle size obtained from microtomography measurements. Finally, a hyperelastic J-integral equation for notched specimens was developed, correlating the fatigue lifetime independently of the geometry.

AB - Failure of elastomers is often related to fatigue. In fact, the mechanical properties of these materials make them suitable in applications in which cyclic loading overlaps with large static loads. Due to the peculiar mechanical properties, namely hyperelasticity and viscoelasticity, the investigation of elastomers¿ mechanical and fatigue properties is not a trivial task. Temperature strongly influences the mechanical and fatigue behavior of elastomers. Despite the awareness of the effects of temperature dating back to the early studies of rubber fatigue, only little effort has been made to rationalize this behavior and develop a systematic model that allows this effect to be taken into account. Thus, this thesis aims to analyze the fatigue of a non-crystallizing elastomer and specifically to investigate the effect of temperature in order to create a model able to improve the fatigue predictions. At first, the influence of self-heating upon cyclic loading due to heat build-up was assessed considering different frequencies, and interesting observations about the temperature evolution during crack propagation were made. Furthermore, an equation for the evaluation of temperature in the thickness of samples was described. Second, the fatigue crack propagation of a filled elastomer was analyzed, considering several mechanical parameters and among them, the most influential for non-crystallizing elastomers was found to be frequency. Based on these findings, the influence of temperature on the mechanical behavior was investigated in terms of large and small deformations, evidencing a strong role of fillers on the overall mechanical properties. Moreover, the fatigue crack propagation at high temperatures was studied and a model to reduce the data to a fatigue master curve was developed. Finally, fatigue lifetime investigations were correlated with initial defect size and crack propagation results. This was possible by exploiting the fatigue master curve applied according to the surface temperature monitored in the fatigue tests as a consequence of heat build-up. These results were then verified through the particle size obtained from microtomography measurements. Finally, a hyperelastic J-integral equation for notched specimens was developed, correlating the fatigue lifetime independently of the geometry.

KW - Elastomer

KW - Ermüdung

KW - Temperatur

KW - Wärmestauung

KW - Bruchmechanik

KW - Elastomer

KW - fatigue

KW - temperature

KW - heat build-up

KW - fracture mechanics

M3 - Doctoral Thesis

ER -