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  • FAQ: How can elevated ('dynamic') loading rates be taken into account in structural and fracture mechanics assessments?

How can elevated ('dynamic') loading rates be taken into account in structural and fracture mechanics assessments?

   

Frequently Asked Questions

For structural integrity assessment purposes, the effect of dynamic loading rate on the structural response has to be considered for determining the input stresses for the calculation. Finite element stress analyses can quantify the effect of inertia and stress waves on the structural stress state due to dynamic loading. Results can be validated using experimental methods (such as strain gauge techniques). The overall approach for both uncracked components and flaw-containing structures is outlined in Fig.1.

Once the actual stress state and applied loading rates for the component or structure to be assessed have been determined, appropriate input parameters (tensile and toughness properties) can be determined and the assessment can be carried out using assessment procedures such as BS 7910 [1] . The importance for consideration of loading rate effects is recognised in the text of BS 7910 which states in Clause 7 that 'fracture toughness tests should take account of (....) rate of loading (....) experienced in service'.

It should be noted that toughness requirements in some fabrication codes for bridge structures (Barsom, [2] ) do include consideration of dynamic loading, and whilst the above comments apply generically, the loading rate effects on the significance of potential fabrication flaws in bridges have been taken into account in the derivation of toughness requirements.

A Japanese procedure for assessment of fracture in steel weldments subjected to dynamic loading has been published by the Japanese Welding Engineering Society [3] .

References

  1. BS 7910:2005:'Guidance on methods for assessing the acceptability of flaws in metallic structures '. British Standards Institution, London, 2005.
  2. J M Barsom:'Development of the ASSHTO Fracture Toughness Requirements', Enggs, Frac. Mechs, 1975, Vol.7, pp605-618.
  3. WES TR2808:2000:'Method for assessment of brittle fracture in steel weldments subjected to cyclic and dynamic large straining'. The Japan Welding Engineering Society, Tokyo, 2000.

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