PSI - Issue 13

Primož Štefane et al. / Procedia Structural Integrity 13 (2018) 1895 – 1900 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

1896

2

SE(B)

Single edge notched bend specimen Width of the SE(B) specimen (mm) Thickness of the SE(B) specimen (mm)

W B S a 0 a p L 0

Span between support roller pins of SE(B) specimen (mm)

Sharp fatigue crack length (mm)

Final crack length (mm)

Distance from fusion line to sharp fatigue crack front (mm)

R

Load ratio

SIF

Stress intensity factor

Stress intensity factor (MPa×m 1/2 )

K

Maximum applied stress intensity factor (MPa×m 1/2 )

K max

Young’s modulus (GPa)

E

Engineering yield strength (MPa) Engineering ultimate tensile strength (MPa) Crack tip opening displacement (mm) Crack mouth opening displacement (mm) Normalization data reduction technique J-integral (kJ/m 2 )

R p0,2

R m

J

CTOD CMOD NDRT

AWMTT

All weld metal tensile testing

Neck diameter of round bar tensile test specimen (mm) Gage length of tensile test specimen (mm)

D G

FEA FEM

Finite element analysis Finite element model

1. Introduction

Pronounced heterogeneity in mechanical and fracture toughness properties is common in case of repair welds, dissimilar welded joints and functionally graded materials. It can ha ve a strong impact on structure’s capacity to withstand the imposed loads during service. However current engineering critical assessment (ECA) methods (e.g. BS7910:2015) provide procedures for fitness-for-service (FFS) assessment which are generally based on assumption of homogeneity. Therefore, it is necessary to characterize fracture behavior of described material configurations and to develop methods for the characterization of crack driving force. Focus of this work is dedicated to repair welds where a crack propagates from one type of weld material to another through an interface. Such weld configuration is produced when weld repair is performed with consumables different from the original weld as reported by Brinckmann et al. (2000). Several studies addressing the described topic were conducted in the past. Predan et al. (2007) conducted a comprehensive study of a crack in a double mismatched weld using the principle of configuration forces. Finite element analysis (FEA) showed that stress concentration close to the interface caused additional internal stress or relaxation along the interface in the vicinity of the crack tip which causes an accelerated crack growth rate or a pop-in when the crack is growing towards an overmatched-undermatched (OM-UM) interface and a reduced crack growth rate or crack arrest when the crack is growing towards UM-OM interface. This additional internal stress (positive or negative) can be calculated by using an inhomogeneous crack driving force parameter. Similarly, Kozak et al. (2009) performed extensive FEA of limit load solutions of welds with half UM and OM weld material. Results revealed that material in front of crack propagation has a predominant role on the limit load solution. While OM material in terms of yield stress in front of the crack tip effectively increased limit load, the opposite was observed in case of UM material in front of the crack tip. Additionally, results revealed a reduction of limit load when the width of the weld was increased due to easier yield zone spreading. Considering that additional internal stress in front of the crack tip has a strong impact on CDF, limit load and fracture toughness, the question arises whether T-stress and st ress biaxiality coefficient β could be considered when determining fracture toughness of heterogeneous welds. This is because these parameters represent stress in front of the crack tip and ratio of T-stress to crack tip opening stress. An overview of studies focusing on T-stress and β is provided by Gupta et. al (2015). Due to T-stress being valid in the case of small scale yielding, only crack initiation is investigated in this case.