PSI - Issue 13

Yoshiki Mikami et al. / Procedia Structural Integrity 13 (2018) 1804–1810 Author name / Structural Integrity Procedia 00 (2018) 000–000

1807

4

a

b

c

Longitudinal,

Transverse,

σ y Transverse, Point: experiment Line: simulation Distance along thickness, z (mm) 0 10 20 30 40 50 On line B

A

A

A

A

σ x Longitudinal,

Line B

Line B

Residual stress, σ x and σ y (MPa) −500 0 500

Cross section A-A

Cross section A-A

Fig. 4. Residual stress distribution; (a) longitudinal residual stress, σ x ; (b) transverse residual stress, σ y ; (c) through-thickness distribution.

a

b

Notch part (initially meshed)

B = 50

Duplicated nodes

2 45

Notch root radius: 0.1

60°

4.5 W = 450

Notch part (initially meshed)

213581 nodes 201669 elements

W = 2 B = 100

(unit: mm)

5

Fig. 5. Finite element model of a CTOD specimen; (a) overall view; (b) detail in notch root.

3.2. CTOD test simulation considering residual stress distribution In order to model a specimen in which residual stress distribution exists, the result of the residual stress simulation was mapped to the finite element mesh of the CTOD specimen shown in Fig. 5 (a). The model has B × 2 B dimension, a standard three-point bend CTOD test specimen (where B is the thickness of the multipass welded joint and is 50 mm in this study). The elements corresponding to the machined notch part initially exists and is meshed as shown in Fig. 5. In front of the notch root, duplicated nodes were generated and initially tied to model the introduction of the pre-crack. The transition of residual stress distribution was simulated according to the following steps: 1. Cutting out a specimen from the multipass welded joint: The residual stress distribution and strain components in the multipass welded joint were mapped to the specimen before notch machining. 2. Notch machining: Elements involved in the notch part were deactivated and the redistribution of the residual stress was calculated. 3. Reverse bending: This is applied with a four-point bend configuration. The load applied during reverse bending was 1.0 P L = 167.6 kN, where P L is the limit load for the SENB (single edge notched bend) specimen. 4. Precracking: The nodes tied in front of the notch root were released to model the precracking, and the redistribution was calculated. In this study, fatigue loading was not considered, and the tied nodes were released without loading. 5. CTOD testing: Bending was applied using a three-point bend configuration. The result of residual stress mapping (step 1) is shown in Fig. 6. The size of the specimen is smaller than that of the multipass welded joint; therefore, the residual stress that exists in the extra part of the welded joint is neglected. This corresponds to cutting off the extra part. The reinforcement of the weld metal was also removed. After mapping, the redistribution of residual stress in the remaining specimen is calculated. The simulation results after mapping the residual stress distribution following the above simulation steps are presented in Fig. 7.