Modeling Dislocation-Mediated Hydrogen Transport and Trapping in Fcc Metals

The diffusion of hydrogen in metals is of interest due to the deleterious influence of hydrogen on material ductility and fracture resistance. It is becoming increasingly clear that hydrogen transport couples significantly with dislocation activity. In this work, we employ a coupled diffusion-crystal plasticity model to incorporate hydrogen transport associated with dislocation sweeping and pipe diffusion in addition to standard lattice diffusion. Moreover, we consider generation of vacancies via plastic deformation and stabilization of vacancies via trapping of hydrogen. The proposed hydrogen transport model is implemented in a physically-based crystal viscoplasticity framework to model the interaction of dislocation substructure and hydrogen migration. In this study, focus is placed on hydrogen transport and trapping within the intense deformation field of a crack tip plastic zone. We discuss the implications of the model results in terms of constitutive relations that incorporate hydrogen effects on crack tip field behavior and enable exploration of hydrogen embrittlement mechanisms.

Crack Tip Field of a Double-Network Gel: Visualizing Covalent Bond Scission by Mechanoradical Polymerization

Quantitative characterization of the energy dissipative zone around the crack tip is the central issue in fracture mechanics of soft materials. In this research, we present a mechanochemical technique to visualize the bond scission of the first network in the damage zone of tough double-network hydrogels. The mechanoradicals generated by polymer chain scission are employed to initiate polymerization of a thermoresponsive polymer, which is visualized by a fluorophore. This technique records the spatial distribution of internal fracturing from the fractured surface to the bulk, which provides the spatial profiles of stress, strain, and energy dissipation around the crack-tip. The characterized results suggest that, in addition to the dissipation in relatively narrow yielded zone which is mostly focused in the previous works, the dissipation in wide pre-yielding zone and the intrinsic fracture energy have also significant contribution to the fracture energy of a DN gel.

Crack Tip Field of a Double-Network Gel: Visualizing Covalent Bond Scission by Mechanoradical Polymerization

Quantitative characterization of the energy dissipative zone around the crack tip is the central issue in fracture mechanics of soft materials. In this research, we present a mechanochemical technique to visualize the bond scission of the first network in the damage zone of tough double-network hydrogels. The mechanoradicals generated by polymer chain scission are employed to initiate polymerization of a thermoresponsive polymer, which is visualized by a fluorophore. This technique records the spatial distribution of internal fracturing from the fractured surface to the bulk, which provides the spatial profiles of stress, strain, and energy dissipation around the crack-tip. The characterized results suggest that, in addition to the dissipation in relatively narrow yielded zone which is mostly focused in the previous works, the dissipation in wide pre-yielding zone and the intrinsic fracture energy have also significant contribution to the fracture energy of a DN gel.

The Interaction Problem Between a Crack and a Wedge Disclination Dipole With Irwin Plastic Zone Correction

In this work, the multiple defects interaction problem is studied. A crack located near an inclusion is influenced by a wedge disclination dipole. Stress field induced by the disclination affects the crack tip field and yield behavior of the crack. With varying the wedge disclination dipole properties, including strength, position to the crack tip, arm length, etc., the plastic zone size (PZS), the crack tip opening displacement (CTOD) and the stress intensity factor (SIF) are estimated with the generalized Irwin model. Numerical results showed that the wedge disclination dipole arm length and strength can significantly increase or decrease the values of the CTOD and PZS, depending the disclination dipole positions. The maximum values of the CTOD and the PZS were explored with the change of disclination position.

Numerical Investigations on the Effects of T-Stress in Mode I Creep Crack

The effects of [Formula: see text]-stress on the stress field, creep zone and constraint effect of the mode I crack tip in power-law creeping solids are presented based on finite element (FE) analysis in the paper. The characteristics of the crack tip field in power-law creep solids by considering low negative [Formula: see text]-stress and high positive [Formula: see text]-stress are studied in the paper. The differences of [Formula: see text]-stress effect on the crack tip field between power-law creeping solids and elastoplastic materials are also clarified. A modified parameter is proposed to characterize the influence of [Formula: see text]-stress on creep zone. The constraint parameter [Formula: see text] under both small-scale creep and large-scale creep with various [Formula: see text]-stresses for the modified boundary layer (MBL) model and various specimens with different crack depths are given. The applicability and the limitation of the MBL model for creep crack are also investigated. The inherent connection between [Formula: see text]-stress and [Formula: see text]-parameter is discussed. The investigations given in this paper can further promote the understanding of [Formula: see text]-stress effect and constraint effect on the mode I creep crack.