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Residual stress fields and fracture mechanics assessment via FEAs

  • 1.  Residual stress fields and fracture mechanics assessment via FEAs

    Posted 07-30-2020 07:44

    Hi guys and girls! 

    I am currently trying to learn how to do fracture mechanics assessments via FEAs and API 579 (fitness for service). The first challenge I have come across is implementing a stress field to simulate the residual stresses present near weldments. 

    What is the best way to implement a residual stress field for fracture mechanics assessments via FEAs? Thermal analysis? Other ways?

    As a simple case, I've created a sample problem (quarter section shell with head, semi elliptic inside crack). A region of the shell is to be assigned residual stresses. To start, I'd like to assign a small value of tension in this section (say, about 50 MPa). What is the best way to do this, conceptually?

    If you want to tag along; I'm using ANSYS. I've created a simple example file here:
    ANSYS file

    Cheers



    ------------------------------
    Julian Løvlie
    Engineer
    Pressura
    Kristiansand
    +4746640677
    ------------------------------


  • 2.  RE: Residual stress fields and fracture mechanics assessment via FEAs

    Posted 07-31-2020 08:15
    Edited by David Segletes 07-31-2020 13:42
    There are numerous AMSE PVP papers that discuss this.  Many are published by my former co-workers at Structural Integrity Associates (Chris Tipple, DJ Shim, Rich Bax, and others).  There are also some commercial packages that can do this.  I believe there have been developed some standard equations in the literature for the residual stress vs wall thickness.  FE modelling of the weld residual stress can be done using a kinematic model, but details of the welding process are required for the best accuracy.  

    Steve McCracken at EPRI would also be a good point of contact.

    Here are some papers
     https://link.springer.com/article/10.1007/BF03266579
    https://www.sciencedirect.com/science/article/abs/pii/S0308016118301765
    https://www.nrc.gov/docs/ML1219/ML12192A016.pdf
    https://asmedigitalcollection.asme.org/PVP/proceedings-abstract/PVP2016/50435/V06BT06A076/285359

    ------------------------------
    David Segletes
    Materials and Process Engineer
    Blue Origin
    Taft TN
    (803) 487-2368
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  • 3.  RE: Residual stress fields and fracture mechanics assessment via FEAs

    Posted 08-03-2020 08:20

    @David Segletes

    Thank you so much for your answer.

    Indeed, there are numerous papers in the literature on the topic with great depth and detail to how to compute residual stresses. My impression from the research papers is that they are just that (research papers), and delve into great detail etc. However, what I am looking for is a more practical approach to solve fracture mechanical problems. API 579-1 indeed provides normative through-wall stress distributions to be used. I'm more on the lookout for how to actually solve a given problem. But maybe there is none other than a comprehensive welding simulation? Maybe I can contact one of the people you mentioned to delve deeper?

    Thank you for your time.

    Julian



    ------------------------------
    Julian Løvlie
    Engineer
    Pressura
    Kristiansand
    +4746640677
    ------------------------------



  • 4.  RE: Residual stress fields and fracture mechanics assessment via FEAs

    Posted 08-04-2020 09:02
    @Julian Løvlie - in nuclear power plants, weld overlay repairs have been used for two decades to provide an effective alternative to replacement due to PWSCC and IGSCC of dissimilar metal welds.  The ASME B&PVC Code Cases N-504 and N-740 describe the details.  Weld residual stresses from the original fabrication and the WOL are both considered in the fracture mechanics assessment.   ​These are typically developed using FEA. You could also delve into the bibliography of API-579 and ASME FFS-1 for detail.  Here is another good paper - https://energyresources.asmedigitalcollection.asme.org/PVP/proceedings-abstract/PVP2019/58929/V001T01A092/1068754

    The ASME PCC meets 2x a year and is a good place to interact with the experts - at least once we get past COVID-19.

    ------------------------------
    David Segletes
    Materials and Process Engineer
    Blue Origin
    Huntsville AL
    (803) 487-2368
    ------------------------------