PSI - Issue 13

Florian Fehringer et al. / Procedia Structural Integrity 13 (2018) 932–938 Fehringer, F., Schuler, X., Seidenfuß, M. / Structural Integrity Procedia 00 (2018) 000 – 000

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1. Introduction

To rule out failure in case of unforeseeable environmental caused incidents, which may exceed the design limits of nuclear power plant components, the evaluation of safety margins is an important task. Usually, for the assessment of components stress based criteria are used (KTA 3201.2 (2013), KTA 3211.2 (2013), ASME BPVC III (2013)). Even though some criteria allow small plastic strains (DIN EN 13445-3 (2015), ASME BPVC VIII (2013), FKM (2012), CSA-Z662-2007 (2007), DNV-OS-F101 (2012)), still these criteria mostly ignore the large deformation capability of the materials usually used for power plant components. To overcome this disadvantage, different limit strain concepts were developed in the past (i.e. Krieg and Seidenfuß (2003), Bao and Wierzbicki (2004), Simatos et al. (2011), Herter et al. (2012)). Most of the limit strain concepts define tolerable plastic strain values depending on the stress triaxiality. Stress triaxiality is not the only influence factor on limit strains, so for example Kucharczyp and Münstermann (2013) defined critical strains values as a function of stress triaxiality and Lode angle (Lode (1926)). With the new strain based structural integrity assessment concept the aim is to quantify the influence of stress triaxiality, size, Lode angle, loading history and multiple loading in limit strains.

2. Strain based structural integrity assessment concept

In current research work, a limit strain concept is developed, as shown in Fig. 1.

Fig. 1. Limit strain concept.

Based on a large experimental program, the different influences of stress triaxiality, size, non-proportional loading and multiple loading on limit strains are investigated. To ensure that the limit strain concept is later widely applicable, two different materials (ferritic steel 20MnMoNi5-5 and austenitic steel X6CrNiNb18-10) are used for the experimental investigations. As the concept is based on damage mechanics simulations, the experimental results are also used to extend the standard Rousselier model (Rousselier (1987)) for low stress triaxialities, a Lode angle dependency and kinematic hardening.