UO2 micron scale specimen fracture: Parameter identification and influence of porosities

Abstract

Bending of micron-scale cantilevers with or without initial notch is simulated by finite element and their fracture is assessed using either the coupled criterion or a cohesive zone model.The fracture toughness and strength of UO 2 single grain specimens with several crystal orientations are determined by means of inverse identification based on experimental tests at the micron-scale. Irradiation causes a decrease in fracture toughness from around 10 J/m 2 to around 5 J/m 2 , whereas the strength variation remains in the order of magnitude of the measurement uncertainty. Premature fracture may occur in presence of a pore provided it is located close enough to the specimen surface undergoing tension, the resulting failure force decreasing with increasing pore size. A network of small porosities located on the fracture surface induces a decrease in the failure force which magnitude mainly depends on the total surface fraction and on the porosity locations rather than on the porosity size.

Molecular dynamics study of UO2 symmetric tilt grain boundaries around [001] axis

“…Experimental measurements on grain boundaries are common on nonradioactive materials such as metals or yttria stabilized zirconia (YSZ) 6,7 . Concerning UO2, far fewer results are available, 10 but our Institute recently proposed the first measurements of formation energies and toughness of grain boundaries in UO 2 8‐10 . Numerical simulations are a good alternative to this small amount of experimental data.…”

Brittle material strength and fracture toughness estimation from four-point bending test

“…The application of the CC allows a correct prediction of the failure force and demonstrates that in such configuration, failure is driven by the energy condition involving the platelet fracture toughness (Doitrand et al 2020a). The efficiency of the CC to predict crack initiation at small-scale was also recently illustrated on silicon nanoscale cantilevers (Gallo and Sapora 2020) and UO 2 micro-cantilevers loaded in flexion (Doitrand et al 2020b).…”

Finite fracture Mechanics at the micro-scale. Application to bending tests of micro cantilever beams

“…where G is the Energy Release Rate (ERR). However, it is well-known that if there is no preexisting crack G = 0, hence, the onset of a crack at a stress concentration point which is not a crack tip cannot be predicted using (6).…”

“…Among the latest developments are the evolution of the microelectronics industry, with the manufacture of small size components [1], such as inter-layer dielectric and chip passivation films [2]. Furthermore, the nuclear industry is also in demand for a better knowledge of the behaviour of fuels such as UO2 in pressurized water reactors [5,6]. It is also important to highlight the tendency to mimic natural materials like mother-of-pearl to create nacre-like inorganic materials [7,8].…”