PSI - Issue 14

Vijay Sai et al. / Procedia Structural Integrity 14 (2019) 491–498 Ch. Vijay Sai/ Structural Integrity Procedia 00 (2018) 000–000

493

3

Fig . 1. (a) Geometric modeling of plate butt weld joint; (b) Geometrical modeling of pipe butt weld joint.

2.2. Material modeling Temperature dependent material properties were used from Satish K.Velaga et al. (2015) and Zubairuddin et al. (2017) to accurately determine the temperature and stress fields, during the welding process. Significant differences are observed in the conductivity, coefficient of thermal expansion and yield strength of the two base materials. The properties of a given element, at a given time are attained by weighing the properties of its constituent phases as per their percentages. Martensite start and end temperature are 375 0 C and 200 0 respectively. The formation of martensite results in volumetric expansion of the element. Ramberg Osgood relationship between strain and stress and isotropic hardening were considered. The stress-strain curves at higher temperatures are obtained by extrapolating the yield strength, as per Ramberg-Osgood parameters. This gives a reasonable approximation for high temperature mechanical properties. 2.3. Heat input fitting The parameters of the Goldak’s double ellipsoidal heat source were obtained using heat source fitting. The parameters used for the two simulations are given in Table 1. Heat input fitting gives the approximate size of the fusion and heat affect zone part of the joint. The shape and size of the fusion zone help in determination of the correct heat input required for welding the base materials. The amount of heat input plays a critical role in the evolution of residual stress as observed by Zhao et al. (2014).

Table 1. Heat source parameters for plate and circumferential pipe weld joints. Parameter Plate weld

Circumferential weld

Heat Input (J/mm) Velocity (mm/s)

435

445

1

1

Efficiency

0.7

0.7

Q f / Q r

0.25

0.25

a f , a r ,b,c

2,4,2,3

2,4,2,3

3. Results and discussion 3.1. Thermo-metallurgical analysis

The simulations were carried out for 1500 seconds allowing the complete formation of martensite. Fig. 2 and Fig. 3 portray the peak temperature profile attained during the welding process in plate butt weld and circumferential pipe weld joints respectively.