PSI - Issue 13

A. Prokhorov et al. / Procedia Structural Integrity 13 (2018) 1521–1526 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

1522

2

obtain the structure with indefinite strength and fatigue durability. For this reason, many research groups involve an investigation on the physical properties of joints, character of their fracture, diagnostic of welded joints and theoretical explanation of fracture evolution under various types of loading [4-7]. In this work, the passive infrared thermography is applied to the investigation on the temperature evolution under fracture of the specimen manufactured from two dissimilar stainless steels using a laser welding. Infrared thermography (IRT)was applied for noncontact temperature monitoring during the experiments. IRT is popular method for nondestructive testing, which allows one to study fracture localization, evaluation of fatigue damage, estimation of thermomechanical properties of material etc. [9-10]. In this paper, experimental result of temperature evolution obtained by IRT is confirmed by numerical simulation and mathematical model of heat dissipation in laser-welded specimen during the quasi-static loading is proposed.

2. Experimental condition

The specimen manufactured from two dissimilar stainless steels (P91 and 316LN) welded by laser-welding technique. The mechanical experiments were performed on 100 kN servo hydraulic testing machine under different strain rates from 2 to 8 mm/min. The geometry of the specimen is shown in figure 1a. Chemical composition of the materials under investigation is given in Table 1.

Table 1. Chemical composition of joined steels

Name

C

Si

Mn

P

S

Cr

Mo

Ni

V

P91

0.05 0.03

0.26 0.75

0.37

0.01 0.25

<0.01

9.14 18.0

0.96

0.42 12.5

0.25

316LN

2.0

0.1

2.7

-

The stress-strain curves for P91 steel and 316LN steel are presented in figure 1b. As it can be seen from figure 1, the 316LN steel has a lower yield stress and ultimate tensile strength than P91 steel. The mechanical and physical properties of these steels are given in table 2.

Table 2. Physical and mechanical properties of materials

Young’s modulus, Pa

Name

Density, kg/cm3

Specific heat, J/(kg*K)

Yield stress, Pa

P91

7760 7990

622 485

2E+11

4.77E+08 2.49E+08

316LN

1.6E+11

Fig. 1. (a) Specimen geometry (all sizes are in mm); (b) Stress-strain curves.