Issue 35

X.C. Arnoult et alii, Frattura ed Integrità Strutturale, 35 (2016) 509-522; DOI: 10.3221/IGF-ESIS.35.57 509 Short review: Potential impact of delamination cracks on fracture toughness of structural materials X.C. Arnoult, M. Růžičková, K. Kunzová Centrum Výzkumu Řež s. r. o., Husinec-Řež, Czech Republic A. Materna Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering Prague, Czech Republic A BSTRACT . The current energy policy envisages extended lifetime for the current nuclear power plants (GEN II NPP). This policy imposes a large research effort to understand the ageing of power plant components. In this goal, it is necessary to improve knowledge about safety, reliability and components’ integrity for more than forty years of operation. In Central and Eastern Europe, the majority of NPPs are VVER types, where some of the components are produced from austenitic steel 08Ch18N10T. Irradiated 08Ch18N10T may exhibit brittle behavior, namely delamination cracks are found in some cases on the fracture surface of irradiated 08Ch18N10T with elongated δ-ferrite. Delamination cracks have also been observed on the fracture surface of high-strength steels or aluminum-lithium alloys. This article presents a state-of-the art review to provide a detailed analysis of the influence of delamination cracks on the toughness of metal alloys. In general, the delamination cracks are present in metal alloys having a high texture and microstructure anisotropy. Three types of delamination cracks have been observed and are classified as crack arrester delamination, crack divider delamination and crack splitting delamination. The microscopy characterization, 3D fracture theories and computational studies explaining possible causes and effects of delamination cracks on the mechanical properties of metal alloys are presented. K EYWORDS . Delamination cracks; Fracture Mechanics; Steels; Ferrite. I NTRODUCTION elamination cracks, i.e. secondary cracks parallel to the rolling plane, have been observed on high strength steels [1-10], aluminum-lithium alloys [11-15], Ti-stabilized stainless steels [16, 17] and ultrafine-grained steels [18]. Different types of delamination cracks in combination with different orientations of the specimen direction had been identified [13, 19]. The delamination cracks have been classified (a) as crack divider, (b) crack arrester and (c) crack splitting as shown on the Figure 1. In the last 4 decades, some researcher noticed the existence of delamination cracks and tried to understand the origins, mechanisms and consequences on the fracture toughness, impact toughness and tensile properties. Some delamination cracks are shown on the fracture surfaces of irradiated 08Ch18N10T with elongated δ-ferrite [16, 17], the 304 L and the 316 L after exposure in PWR [20] environments and degraded by hydrogen embrittlement [21]. D