13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- Fig.2 Equivalent stress nephogram of integral joint The crack toughness of Q345steel is: 1 2 207.91 cK Mpa mm = • . According to formula (4), we can get the critical crack size: 2 2 1 1 207.91 1.93 84.4 c c K a mm π σ π ⎛ ⎞ ⎛ ⎞ = = = ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ Initial crack size: 0 0.5 a mm = , material constant 3.0 m= , material constant C , average 13 2.12 10 cμ − = × , coefficient of variation 0.15 vC = [8]. According to formula (3), we can get the fatigue life is 2310340 times, 2123015 times, 1963789 times, 1826781 times and 1707643 times under different levels. 4.2 Create the factor set Considering the specific condition of truss structure, the influencing factors of fatigue life of integral joint plate are as follows: 1 2 3 ( , , ) C c c c = Among it, 1c means fabrication technology, 2c means material properties, 3c means environment for use. 4.3 Create the evolution set According to the trends consistency principle, five evolution indexes should be created which are shown in table1.
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