Evaluation of Plastic “Eta” Factor for Welds of SS316L(N) with High Strength Mismatch Ratio

  • R. Nikhil
  • S. A. KrishnanEmail author
  • G. Sasikala
  • B. Shashank Dutt
  • A. Moitra


Fracture testing standards of ASTM and ISO recommend expressions for plastic η factor of various fracture test specimen geometries to evaluate the fracture behavior of materials. These are intended for homogenous specimens, but according to ISO 15653, it can be extended for weldments up to a strength mismatch ratio (M) of 1.25. In practice, M > 1.25 is encountered in many applications. In the present study, η factor has been evaluated for welded compact tension specimens using a limit load-based approach. The η factors obtained using this approach for homogenous specimens with elastic–perfectly plastic material model are found to be within ± 4% of those from the ASTM E 1820-17a, thereby validating the procedure. For welds, the limit load is obtained from nonlinear (elastic–plastic) FE simulations. η factors for specimens with various crack lengths (a), weld width (h) and strength mismatch have been evaluated and found to be significantly influenced by these parameters. For M > 1.25, the estimated η values were found to be ~ 16% lower compared to that from the ASTM E 1820-17a. Thus, the use of the η values from the proposed method provides a conservative estimate of J–R curve for the welds. Further, it has been observed that depending on the slope of the blunting line, the JIc value may vary significantly with the estimated η values.


eta J–R curve limit load strength mismatch 



Crack length (mm)


Crack area, i.e., B*a (mm2)


Plastic area under the load–displacement plot (kJ)


Ligament length, i.e., W − a (mm)


Thickness of the specimen (mm)


Weld width (mm)


Elastic–plastic fracture mechanics parameter (kJ/mm2)


Plastic component of J-integral


Critical value of J-integral under mode I loading


Strength mismatch ratio, i.e., \(M = \sigma_{\text{y,wm}} /\sigma_{\text{y,bm}}\)


Limit load (kN)


Width of the specimen (mm)


Flow stress, i.e., \(\sigma_{\text{f}} = \frac{{\sigma_{\text{y}} + \sigma_{\text{u}} }}{2}\)


Ultimate tensile strength (MPa)


Yield strength (MPa)


Yield strength of base metal (MPa)


Yield strength of weld metal (MPa)


A non-dimensional geometric factor


Plastic displacement (mm)


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Copyright information

© ASM International 2018

Authors and Affiliations

  • R. Nikhil
    • 1
  • S. A. Krishnan
    • 1
    Email author
  • G. Sasikala
    • 1
  • B. Shashank Dutt
    • 1
  • A. Moitra
    • 1
  1. 1.Indira Gandhi Centre for Atomic ResearchHomi Bhabha National InstituteKalpakkamIndia

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