On the crack propagation and fracture properties of Cr-coated Zr-4 alloys for accident-tolerant fuel cladding: In situ three-point bending test and cohesive zone modeling

The cracking behavior of a Cr-coated Zr-4 alloy for accident-tolerant fuel cladding at room temperature was investigated using an in situ three-point bending test and finite element (FE) analysis. The initiation and propagation of vertical and interfacial cracks were captured in real time. Moreover, the fracture properties of the Cr-coated Zr-4 alloy were evaluated by in situ observations and FE simulations based on the cohesive zone model. The results indicated that vertical cracks were generally initiated from the interface and promptly penetrated through the coating thickness at a small deflection. Under continuous external loading, the vertical crack density increased rapidly and finally reached a plateau. Additionally, interfacial cracks were initiated from the vertical crack tips and propagated gradually along the interface, which was driven by large local interfacial peeling and shear stresses. Through FE analyses, the fracture toughness of the Cr coating was estimated to be 65 J/m2, and the interfacial fracture strength and toughness were evaluated as 150 MPa and 200 J/m2, respectively.