Stress triaxiality based transferability of cohesive zone parameters

• Published in: Engineering fracture mechanics 2020-02, Vol.224, p.106789, Article 106789
• Main Authors: Vanapalli, Viswa Teja, Dutta, B.K., Chattopadhyay, J., Jose, Nevil Martin
• Format: Article
• Language: English
• Subjects: Axial stress; Bend ductility; Cohesion; Cohesive zone model; Computation; Computer simulation; Confidence intervals; Crack tips; Ductile fracture; Multi-axiality quotient; Nuclear engineering; Nuclear safety; Parameters; Piping; Quotients; Statistical analysis; Steel; Structural steels; Transferability of cohesive parameters
• ISSN: 0013-7944; 1873-7315
• DOI: 10.1016/j.engfracmech.2019.106789

•Analysis of cracked pipes to predict cohesive parameters using experimental data.•Peak stress cohesive parameter is a strong function of stress triaxiality.•Sigmoidal variation of peak stress with multiaxiality quotient is suggested.•Normal variation of peak stress is proposed for a given multiaxiality quotient value.•Present methodology is useful for safety analysis of cracked components. Present study is to investigate the dependency of cohesive zone parameters on crack tip stress triaxiality for SA333 Grade 6 steel. An exponential cohesive law is used to simulate ductile fracture behavior of 14 three-point bend specimens made of SA333 Gr. 6 steel. Cohesive parameters are determined by varying peak stress to match experimental results with the computed data. To extend the validity of parameter peak stress as a function of triaxiality, experimental results of six piping components with through-wall circumferential crack made up of SA333 Grade 6 steel are used. A confidence interval band is then plotted to study the transferability of cohesive parameters. The variation in peak stress for a single value of multiaxiality quotient is attributed to the micro structural variation in material during manufacturing near the crack tip, which is statistical in nature. A normal variation of peak stress is assumed for a given value of multiaxiality quotient. To test the accuracy of the cohesive parameters with such normal variation, experimental results of six piping components are again used. Significant match of computed results with the measured values shows transferability of the present material parameters. The methodology presented in this work can be applied to other structural steels to find out cohesive zone parameters. Such material parameters will be useful to the designers to carry out safety analysis of piping components of nuclear and other installations.