Stochastic Aspects of Crack Propagation: Experiments and Cohesive-zone Modeling

Thin films;Crack velocity;Kinetics;Channeling;Cohesive-zone model;Stick-slip;Mechanical Engineering;Engineering;Mechanical Engineering

Meng, FanboDasgupta, Neil P ;

University of Michigan

关键词: Thin films;    Crack velocity;    Kinetics;    Channeling;    Cohesive-zone model;    Stick-slip;    Mechanical Engineering;    Engineering;    Mechanical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/146082/fanbo_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Crack behaviors with stochastic characteristics have been studied in this dissertation. Kinetic crack growth is known as a thermally-activated process associated with statistical mechanics.Techniques to measure the relationship between crack velocity and energy-release rate for kinetic channeling cracks in thin films and coatings are presented in Chapter 2.These approaches were used to analyze a multi-layer system consisting of a polymeric, colloidal-silica nano-composite layer and a primer layer coating a polycarbonate substrate.In Chapter 3, a stochastic cohesive-zone model has been developed in which the probability of a cohesive element breaking depends on the level of the work done against the tractions, above a equilibrium value.This concept has been used to model a kinetic crack growth using a cohesive-zone.The cohesive length combining with a parameter associated with the activation energy becomes the characteristic dimension for the fracture.If the cohesive length is sufficiently small such that the requirements of linear-elastic fracture mechanics are satisfied, the cohesive-zone model gives an good representation of a classical kinetic-crack growth model controlled by the energy-release rate.However, for large cohesive-length scales, the crack advance is controlled by the cohesive strength rather than the energy-release rate.A cohesive-zone model is demonstrated in Chapter 4 to explore the rate-dependent instabilities in crack growth in rubber-toughened polymers.Quasi-static crack growth was interrupted by stochastic occurrences of dynamic crack jumps, which was owing to a competition between the rate of toughening, driven by rubber cavitation, and the crack velocity.By coupling the classical void nucleation theory to a cohesive-zone model, in which the cohesive elements were allowed to make a re-selection of traction-separation law if a toughened mode was triggered, the crack exhibited similar behavior as that was experimentally observed.