Cohesive zone model for carbon nanotube adhesive simulation and fracture/fatigue crack growth.

摘要

The Cohesive Zone Model (CZM) describes material separation with a traction-separation law and links the micro-structural failure mechanism to the continuum deformation field. The evolvement of the CZM and its specific features were introduced in the first Chapter of this dissertation and followed by applications for interface decohesion and crack growth study.;Chapter II adopted a bilinear CZM for description of the decohesion properties of the innovative carbon nanotube (CNT) dry adhesive. Macroscopic modeling of the uncoupled normal and shear adhesive behaviors were implemented using finite element method. The cohesive zone model completes a multi-scale modeling scheme together with coarse grained molecular dynamics (CGMD).;Three-dimensional simulations of quasi-static fracture process were studied next by formulating an exponential cohesive law. Crack growth under monotonic loading was modeled and cohesive parameters were calibrated by comparing with experiments. The CZM simulation captured the crack initiation as well as the process of crack propagation.;A damage-updated irreversible cohesive law was formulated in Chapter IV for simulations of cyclic crack growth. Material degradation was described with a damage evolution mechanism, revealing the history dependence of fatigue crack growth. The irreversible CZM was verified through one-element model under load-controlled and iv displacement-controlled fatigue loading and was further validated with fatigue crack growth simulations for different specimen modes. Simulation results captured the gradual damage accumulation and stable fatigue crack propagation, consistent with the power law method.;Further application of the irreversible CZM for overload effect during fatigue crack propagation was presented in Chapter V. Stress redistribution caused by the overload in a compact-tension-shear (CTS) specimen was investigated. Fatigue crack growth retardation was studied in terms of overload ratios and the mode of the overload. A damage extrapolation scheme was formulated for the high-cycle fatigue loading and greatly reduced the computation cost.;The last chapter investigated crack path deviation phenomena with possible CZM simulation approaches. Numerical issues and mesh-related convergence problem were referred for future investigation.