A unique crack growth rate curve method for fatigue life prediction of steel structures

In this paper, a unique crack growth rate curve method, which is based on the equivalent stress intensity factor range (ESIFR) as the driving force, has been proposed and examined with crack growth rate data of base metals and as welded joints of some structural steels under constant amplitude external loading. By expressing the crack growth rate data with ESIFR instead of stress intensity factor range (SIFR) make it possible to establish a concise model for crack growth data under different R-ratios to the curve corresponding to R=0 both for base metals and welded joints. The most commonly tested crack growth rate constants under R=0 ∼0.1 are sufficient in fatigue crack growth life prediction of components subjected to tensile-tensile, tensile-compressive loading. Only two equations, one for Mean curve, and the other for Mean + 2SD curve replace the recommended crack growth rate curves in BS7910 for most structural steels. The phenomena that crack growth rates of as-welded joints under different applied loading ratios behaves independent of the applied loading ratio can be explained and the crack growth rate in residual stress field can be predicted well by the present model. The unique crack growth rate curve method does not only allow us to estimate the fatigue life of specimens of base metal and weld joints, but also the fatigue life of structural components under complex loading conditions.

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