Abstract
The Peak Stress Method (PSM) is an engineering, FE-oriented application of the notch stress intensity factor (NSIF) approach to fatigue design of welded joints, which takes advantage of the singular linear elastic peak stresses from FE analyses with coarse meshes. Originally, the PSM was calibrated to rapidly estimate the NSIFs by using 3D, eight-node brick elements, taking advantage of the submodeling technique. 3D modelling of large-scale structures is increasingly adopted in industrial applications, thanks to the growing spread of high-performance computing (HPC). Based on this trend, the application of PSM by means of 3D models should possibly be even more speeded up. To do this, in the present contribution the PSM has been calibrated under mode I, II and III loadings by using ten-node tetra elements, which are able to directly discretize complex 3D geometries without the need for submodels. The calibration of the PSM has been carried out by analysing several 3D mode I, II and III problems. Afterwards, an applicative example has been considered, which is relevant to a large-scale steel welded structure, having overall size on the order of meters. Two 3D FE models, having global size of tetra elements equal to 5 and 1.66 mm, have been solved by taking advantage of HPC, being the global number of degrees of freedom equal to 10 and 140 millions, respectively. The NSIFs values estimated at the toe and root sides according to the PSM have been compared with those calculated by adopting a shell-to-solid technique.
Highlights
On the basis of the fundamental contributions of Williams [1], who studied two-dimensional notch problems under mode I and mode II loadings, and Qian and Hasebe [2], who analysed the notch problem under mode III loading, the singular linear elastic stress distributions in the neighborhood of a sharp V-notch tip, see the example of a toe side in a welded joint in Fig. 1, can be written as functions of the notch stress intensity factors (NSIFs), which quantify the intensity of the asymptotic stress fields
In order to overcome this issue, an engineering and rapid technique, the so-called Peak Stress Method (PSM), has been proposed, which allows to speed up the calculation of the NSIFs by adopting coarse FE analyses, the element size being some orders of magnitude larger than that required to apply definitions (1a)-(1c)
The NSIFs K1, K2 and K3 can be readily estimated according to the PSM by adopting the singular, linear elastic, opening, sliding and tearing peak stresses σθθ,θ=0,peak, τrθ,θ=0,peak and τθz,θ=0,peak, respectively, which are referred to the V-notch bisector line, according to Fig. 2, and calculated at the V-notch tip from FE analyses with coarse meshes
Summary
On the basis of the fundamental contributions of Williams [1], who studied two-dimensional notch problems under mode I (opening) and mode II (sliding) loadings, and Qian and Hasebe [2], who analysed the notch problem under mode III (tearing) loading, the singular linear elastic stress distributions in the neighborhood of a sharp V-notch tip, see the example of a toe side in a welded joint in Fig. 1, can be written as functions of the notch stress intensity factors (NSIFs), which quantify the intensity of the asymptotic stress fields. In order to overcome this issue, an engineering and rapid technique, the so-called Peak Stress Method (PSM), has been proposed, which allows to speed up the calculation of the NSIFs by adopting coarse FE analyses, the element size being some orders of magnitude larger than that required to apply definitions (1a)-(1c). The NSIFs K1, K2 and K3 can be readily estimated according to the PSM by adopting the singular, linear elastic, opening (mode I), sliding (mode II) and tearing (mode III) peak stresses σθθ,θ=0,peak, τrθ,θ=0,peak and τθz,θ=0,peak, respectively, which are referred to the V-notch bisector line, according to Fig. 2, and calculated at the V-notch tip from FE analyses with coarse meshes.
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