13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- form: ( ) T r r dr X T ef X xx ef ef . ( ). 1 0 Φ = ∫ (3) Kρc–Tef,c has been determined with [6] and without[2] the presence of hydrogen. Different specimens geometries (CT, SENT, RT and DCB) are used, all with a notch and a depth ratio of 0.5 (a/t = 0.5). Specimens have been submitted to hydrogen environment during 30 days. Fracture initiation is detected by acoustic emission and provides load for crack initiation Pi, more details are given in [12]. Results are compared with results of [2] and summarized in Figure 3. The material master curve is approximated by the following equation K aT b ef c c + = , ,ρ (4) -400 -300 -200 -100 0 100 200 60 80 100 120 Kρ,c=77.8317 -0.0741 Tef,c Material Failure Curve (with Hydrogen) Kρ,c=71.6785 -0.0843 Tef,c Material Failure Curve (without Hydrogen) APL 5L X52, a/t = 0.5 DCB RT CT SENT Notch Stress Intensity Factor, K ρ,c (MPa.m0.5) Effective T-stress, Tef,c(MPa) With hydrogen without hydrogen Linear fit Figure 3. The experimental assessment points ( c ef c K T , , , ρ ) and the material failure curve ( ) ef c c K f T , , = ρ for X52 pipe steel with and without hydrogen effect [6]. where a = -0.0843 and b =71.6785 for the X52 pipe steel without hydrogen embritlement and a =- 0.0741 and b = 77.83 for the X52 pipe steel with hydrogen embrittlement. One notes a small decreases of fracture toughness decreases in the range [5.8 %– 9.8 %] when Tef increases in the range [- 400 MPa- +100 MPa] with a small difference for SENT specimen and larger for DCB specimen (about 10 %). One note a parallel with the decrease of fracture resistance in term of master failure curve and increase of the yield stress after hydrogen introduction. A small increase of yield stress has been noted (2.5%), as an important reduction of elongation at failure (38%). Also one notes that increasing the yield stress increases the constraint parameter. 4. Hydrogen and Constraint Effect on Kinking Direction 4.1 Fracture under low constraint Fracture of pipe under internal pressure is performed under low constraint. Notched tubes were used for burst tests under pressure of hydrogen gas. Tubes were manufactured with steel X52, which
RkJQdWJsaXNoZXIy MjM0NDE=