Effect of prestrain on ductility and toughness in a high-strength line pipe steel

Yazid Madi (1, 2) , Yasuhiro Shinohara (1, 2, 3) , Jacques Besson (2)

1 Mines Paris - PSL (École nationale supérieure des mines de Paris)
2 CDM - Centre des Matériaux
3 Nippon Steel Corporation

Fracture properties of a mother plate for API grade X100 line pipe after pre-straining up to 6% are investigated using tensile notched bars and CT pre-cracked specimens. The material has an anisotropic plastic and damage behavior due to the thermo-mechanical control rolling process. Experiments evidence a decrease in both ductility and toughness for both rolling and long transverse direction with increasing prestrains. This effect is however more pronounced at low prestrain levels (0 → 2%) than at higher levels (2 → 4 → 6%). The modified GTN model proposed by Shinohara et al. (2016) is used to represent the database. A good agreement is obtained provided some damage model parameters are modified so as to obtain a slightly higher damage rate for the prestrained materials. This represents the fact that void growth tends to be faster for materials with a lower work hardening rate as evidenced by unit cell calculations. In addition, stress/strain distributions in test specimens are modified for reduced hardening so that stress triaxiality is increased at failure initiation points. This further lowers measured mechanical properties.

Domaines: Mécanique des matériaux [physics.class-ph]; Mécanique des structures [physics.class-ph]; Matériaux

Yazid Madi, Yasuhiro Shinohara, Jacques Besson. Effect of prestrain on ductility and toughness in a high-strength line pipe steel. International Journal of Fracture, 2020, ⟨10.1007/s10704-020-00442-6⟩. ⟨hal-02636866⟩