Numerical study on the effect of the Lüders plateau on the ductile crack growth resistance of SENT specimens

Abstract

The increasing demand of energy prompts the petroleum industry exploitation activities to the Arctic region where the low temperature is a strong challenge, both for structural design and material selection. For structural materials exhibiting Lüders plateau, it has been reported that lowering temperature will increase the Lüders plateau length. In order to obtain a deep understanding of the Lüders plateau effect on ductile crack growth resistance, we performed numerical analyses with SENT specimens and the Gurson damage model. The Lüders plateau was simplified by keeping the flow stress constant and varying the plateau length. The results show that the existence of Lüders plateau does not influence the initiation toughness, however, will alter the material's fracture resistance significantly. It is found that the Lüders plateau effect is in general controlled by the stress triaxiality level in front of the crack tip. Both the strain hardening and the crack depth effects on resistance curves are alleviated due to the Lüders plateau. For materials with very small initial void volume fraction the Lüders plateau effect is more pronounced. Since the Lüders plateau intensifies the crack driving force and may lower down crack resistance curve, special attention should be paid for the application of materials with Lüders plateau in the Arctic.

Computational fracture mechanics: An overview from early efforts to recent achievements

“…Finally, we present just a fragment of an extensive study on the effect of Lüders plateau on crack resistance curve with sent specimens. 166 Material behaviour has been modelled as shown in Figure 38, with hardening exponent n = 0.05, damage parameter f 0 = 0.005, crack length a/w = 0.1, and crack length increment δa = 0.5 mm. The stress triaxiality distribution ahead of crack tip for different levels of strain at Lüders plateau, ε l , is shown in Figure 38B, indicating that the stress triaxiality scales ductile crack growth, depending on the Lüders plateau length.…”

“…A, Lüders plateau. B, The stress triaxiality distribution ahead of crack tip [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…In this chapter, numerical methods, used for simulation of ductile fracture process, are presented as a compilation of previously accomplished research, followed by an overview of more recent results. [158][159][160][161][162][163][164][165][166]…”

“…More details are presented in Tu et al, 166 including effects of hardening exponent, n, damage parameter, f 0 , crack length a/w, and crack length increment δa, while here, we just emphasise 1 important conclusion, that the CTOD at crack initiation is insensitive to the Lüders plateau length.…”

“…On one hand side, it was relatively simple model for brittle fracture, ie, cleavage, whereas more complex mechanisms of ductile fracture were modelled as a process of void nucleation, growth, and coalescence, which is the focus here. In this chapter, numerical methods, used for simulation of ductile fracture process, are presented as a compilation of previously accomplished research, followed by an overview of more recent results …”