This experimental investigation is devoted to the hydride embrittlement of fuel cladding tubes and especially to the influence of the orientation of hydrides with respect to the applied stress on strain, damage and failure mechanisms. Ring tensile tests are performed on cladding tube material (unirradiated cold worked stress-relieved Zircaloy-4). The average hydrogen content of the material is about 200ppm, and orientations of hydrides are either "tangential" (hydride platelets parallel to the tensile direction) or "radial" (perpendicular to the tensile direction). Tangential hydrides are usually observed in cladding tubes, in particular because of the texture of the material. However, hydrides can be reoriented after cooling under stress and become radial and then trigger brittle behaviour. In this investigation, we first perform "macroscopic" tensile tests, on smooth rings, which give us the mechanical response of the material as a function of hydride orientation. Then, we perform SEM in-situ tensile tests, on rings with the same geometry, in order to observe damage and failure mechanisms. In both cases, digital image correlation techniques are used to estimate local and global strain levels. For macroscopic tests, airbrush speckle painting is used to mark the samples while 2μm-pitch micro-grids are used for in-situ tests. The "macroscopic" tests underline the strong influence of the hydrides orientation: the specimen with radial hydrides suddenly fails at 1700N, within the elastic domain, whiles the specimen with tangential hydrides reaches 4300N and develops macroscopic shear band. The SEM in-situ tests allow us to improve the understanding of failure mechanisms: with radial hydrides, a crack propagates along a path of aligned hydrides and leads to failure. With tangential hydrides, macroscopic shear bands lead to large plastic strain and final ductile failure; damage can only be observed in the very late stage of deformation.
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