A cohesive zone model, taking full account of finite geometry changes, is used to provide a unified framework for describing the process of void nucleation from in­itial debonding through complete decohesion. A boundary value problem simulating a periodic array of rigid spherical inclusions in an isotropically hardening elastic-viscoplastic matrix is analyzed. Dimensional considerations introduce a characteristic length into the formulation and, depending on the ratio of this characteristic length to the inclusion radius, decohesion occurs either in a "ductile" or "brittle" manner. The effect of the triaxiality of the imposed stress state on nucleation is studied and the numerical results are related to the description of void nucleation within a phenomenological constitutive framework for progressively cavitating solids. 1 Introduction The nucleation of voids from inclusions and second phase particles plays a key role in limiting the ductility and toughness of plastically deforming solids, including structural metals and composites. The voids initiate either by inclusion cracking or by decohesion of the interface, but here attention is confined to consideration of void nucleation by interfacial decohesion. Theoretical descriptions of void nucleation from second phase particles have been developed based on both continuum and dislocation concepts, e.g., Brown and Stobbs (1971), Argon et al. (1975), Chang and Asaro (1978), Goods and Brown (1979), and Fisher and Gurland (1981). These models have focussed on critical conditions for separation and have not explicitly treated propagation of the debonded zone along the interface. Interface debonding problems have been treated within the context of continuum linear elasticity theory; for example, the problem of separation of a circular cylindrical in­clusion from a matrix has been solved for an interface that supports neither shearing nor tensile normal tractions (Keer et al., 1973). The growth of a void at a rigid inclusion has been analyzed by Taya and Patterson (1982), for a nonlinear viscous solid subject to overall uniaxial straining and with the strength of the interface neglected. The model introduced in this investigation is aimed at describing the evolution from initial debonding through com­plete separation and subsequent void growth within a unified framework. The formulation is a purely continuum one using a cohesive zone (Barenblatt, 1962; Dugdale, 1960) type model for the interface but with full account taken of finite geometry

A continuum model for void nucleation by inclusion debonding

The mechanisms of hydrogen-related fracture are briefly reviewed and a few evaluative statements are made about the stress-induced hydride formation, decohesion, and hydrogen-enhanced localized plasticity mechanisms. A more complete discussion of the failure mechanism based on hydrogen-enhanced dislocation mobility is presented, and these observations are related to measurements of the macroscopic flow stress. The effects of hydrogen-induced slip localization on the measured flow stress is discussed. A theory of hydrogen shielding of the interaction of dislocations with elastic stress centres is outlined. It is shown that this shielding effect can account for the observed hydrogen-enhanced dislocation mobility.

Hydrogen-enhanced localized plasticity—a mechanism for hydrogen-related fracture

Atomistic modeling of interfaces and their impact on microstructure and properties

An HVEM study of hydrogen effects on the deformation and fracture of nickel

https://www2.lbl.gov/ritchie/Library/PDF/2012_Martin_ActaMat_Hydrogen.pdf

Hydrogen-induced intergranular failure in nickel revisited

Hydrogen embrittlement and grain boundary fracture

This paper describes the relationship between intergranular and transgranular fracture modes of hydrogen embrittlement. The interaction of a transgranular crack, propagating under constant stress in a gaseous hydrogen environment of 40kPa with a grain boundary, is shown. Transgranular fracture is observed when the hydrogen distribution is enhanced at the tip of a notch because either that is the point at which hydrogen enters from the gas phase or concentrates from the solid solution due to the stress field. Intergranular fracture is alternately observed when there is a hydrogen concentration at the grain boundary higher than at other places in the solid. Higher hydrogen concentrations have been observed at grain boundaries in Ni-H alloys using a Secondary Ion Mass Spectrometer technique. The presence of segregated S at the grain boundaries was also shown to enhance the concentration of hydrogen there.

W. Wei

Papers

Hydrogen embrittlement and grain boundary fracture

Hydrogen embrittlement and grain boundary fracture