TWI Industrial Member Report Summary 955a/2010
By S Smith, S Maddox, W He, D Zhou and R Saraswat
The present GSP has two overlapping aims. First, finite element analysis (FEA) of structures is being done to find accurate and robust schemes for calculating the structural stress (SS). Second, the analysis results are being used to redefine the weld fatigue categories of BS 7608 by plotting them in terms of the SS rather than a local nominal stress (NS). The SS and NS are the same for some specimen types, so it is assumed that the S-N curve of these specimens might represent the curve achieved when all specimen results are presented in terms of their SS.
The work done to address the combined aims described above is being undertaken to generate methods of FEA stress calculation that make weld fatigue assessments using BS 7608 practical for engineering design.
The overall project objectives are summarised below:
- Investigate current procedures for obtaining the SS for fatigue assessment of welded structures to clarify modelling issues such as choice of element type and mesh sensitivity.
- Create SS-based design curves from available fatigue data, including TWI's extensive databank of fatigue test results.
- Recommend practical procedures for fatigue assessments of a wide range of structural details by the use of fewer fatigue design curves than at present.
- Encourage adoption of the new design procedure by Standards bodies, by establishing an International Steering Committee of representatives from these organisations.
The present report has the following objectives:
- Further study methods of calculating the structural stress for welds on a flange above a web.
- Use the current structural stress calculation methods on a tubular intersection test specimen and therefore assess their potential for this type of geometry.