PSI - Issue 66

B. (Bo) van Schuppen et al. / Procedia Structural Integrity 66 (2024) 412–418

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Author name / Structural Integrity Procedia 00 (2025) 000–000

Fig. 2. Broken wire electronic binary sensor method in test-setup

3. The Failure Assessment Diagram The assessment is graphically shown in Fig. 3, consisting of a curve indicating the locus of failure in the K r -L r plane, where K r is defined as the ratio between the stress intensity factor, K , and the material fracture toughness including constraint correction K c mat , and L r , is defined as the ratio between the applied load, P , and the plastic collapse load, P c , defined by a limit load analysis on the cracked section. When the assessment point is inside the locus of failure, failure is not deemed to occur, i.e. the inner area denotes a safe zone. The stress intensity factor is calculated considering the measured geometry of the specimen, the load type, and the size of the crack at failure, as found on the fracture surface of the specimens. In particular, it turned out that cracks were essentially of two types: (1) through the thickness cracks, and (2) corner cracks at the hole. The stress intensity factor formula used in this study are those reported in BSI (2013). The material fracture toughness in terms of stress intensity factor including constraint correction, K c mat , is estimated through correlation with the Charpy impact energy, using the Master Curve ��� � 20 �� 11 � 77exp � 0.019 � � � � � ���� 25 � � . � � ln � 1 1 �� � �� � . �� (5) where T is the temperature at which K mat is to be determined, T 0 = T 27J − 18 is the temperature for a median toughness of 100MPa √ m in 25 mm thick specimens, T k = 25 describes the scatter in the Charpy vs fracture toughness correlation, B is the thickness for which an estimation of the toughness is required, and P f is the probability level for K mat . To correct K mat for low constraint level, i.e. for T stress < 0, a correction formula is provided in BSI (2013), which is based on the Master curve method �� �� � 20 � MPa √ m ��� ��� � 20 � exp � 0.019 �� ������ 10 � MPa � �� (6) where T stress is the second-order expansion of the Williams series describing the stress field in the vicinity of the crack tip Anderson (2017), calculated using the formula reported in BSI (2013). The interaction curve, K r = f( L r ), defining the locus of failure is here based on Option 1 provided in BSI (2013), which is a function of f y , E , and f u . When the assessment point is inside the locus of failure, failure is not deemed to occur, i.e. the inner area denotes a safe zone.

Fig. 3. Crack configurations and Failure Assessment Diagram