Author/Authors :
J.L. Feng، نويسنده , , A.G. Varias، نويسنده , , Y.K. Sui، نويسنده ,
Abstract :
Delayed hydride cracking, which is observed in hydride-forming metals, due to the precipitation of hydrides near the
crack tip, is investigated under conditions of constant temperature and crack velocity, plane strain and small-scale
hydride-precipitation. The coupling of the operating physical processes of hydrogen-diffusion, hydride precipitation
and material deformation is taken into account. The material is assumed to be an elastic composite made of hydrides
and solid solution, with properties depending locally on the volume fraction of the hydrides. In the present analysis, the
composite elastic properties have been derived by a generalized self consistent model for particulate composites. With
respect to hydride-precipitation, two cases have been considered: (i) precipitation in a homogeneous medium with elastic
properties, equal to the effective properties of the composite and (ii) precipitation in an inhomogeneous medium,
where the expanding hydride has different elastic properties than those of the surrounding solid solution. The differences
between the near-tip field distributions, produced by the two precipitation models, are relatively small. The effect of the
hydrogen concentration far from the crack tip, on the near-tip field is also studied. It is shown that for small crack
growth velocities, near the threshold stress intensity factor, the remote hydrogen concentration weakly affects the normalized
stress distribution in the hydride-precipitation zone, which is controlled by the thermodynamically required
hydrostatic stress, under hydrogen chemical equilibrium. However, for values of the applied stress intensity factor
and the crack tip velocity, away from the threshold stress intensity factor and crack arrest, the effect of remote hydrogen
concentration on the normalized near-tip stress field is strong. Reduction of the remote hydrogen concentration generally
leads to reduction of the hydride-precipitation zone and increase of the near-tip stresses. Also reduction of the
remote hydrogen concentration leads to distributions closer to those under hydrogen chemical equilibrium.
Keywords :
hydride , hydrogen , Crack growth , Delayed hydride cracking