A phase field finite element study and evaluation of sulfide stress cracking in DCB specimen testing

The challenges presented by sour environments rich in hydrogen sulfide (H₂S) underscore the necessity for a comprehensive understanding of material behavior under such conditions. The cracking susceptibility of metals and alloys used for subsurface equipment in downhole oil and gas exploration operations is particularly concerning. The NACE Double Cantilever Beam (DCB) test has emerged as a widely used quality assurance tool in the petroleum industry, leveraging fracture mechanics principles to assess the environment-assisted cracking (EAC) resistance of metals and alloys. The DCB test evaluates the fracture toughness <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>K</mml:mi></mml:mrow> <mml:mrow><mml:mi>ISSC</mml:mi></mml:mrow> </mml:msub> </mml:math> of materials in H₂S-containing environments via assessment of the crack arrest, which serves as a vital parameter in structural integrity assessments to mitigate the risk of service-related failures from sulfide stress cracking (SSC). However, various studies suggest that different test parameters, such as arm displacement and initial notch, significantly influence <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>K</mml:mi></mml:mrow> <mml:mrow><mml:mi>ISSC</mml:mi></mml:mrow> </mml:msub> </mml:math> . This work presents a detailed numerical investigation on a comprehensive simulation of the DCB test, examining the effects of different test parameters on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>K</mml:mi></mml:mrow> <mml:mrow><mml:mi>ISSC</mml:mi></mml:mrow> </mml:msub> </mml:math> prediction. A coupled deformation-diffusion phase field framework is adopted to simulate SSC in DCB specimens arising from a complex interplay between material deformation, hydrogen diffusion, and fracture. The numerical results show good agreement with experimental results reported in the literature and provide deeper insights into the factors affecting crack growth and arrest in DCB testing.