The hot spot stress can be obtained by finite element (FE) analysis. The simplest way of FE modeling is offered by shell elements which have to be arranged in the mid-plane of the structural components. It is also generally accepted that FE models with shell elements could be used for the hot spot stress calculation of welded joints in ship and offshore structures. However, for fatigue strength assessment of complex welded joints, it is very important to accurately calculate the complex stress states in the vicinity of critical sites and consider the complex physics of multiaxial fatigue. Some research work have shown that it was difficult to get good agreement between the calculated stress using shell elements and measured stress for complex welded joints, because it is hard to describe the local geometry of the joints by shell elements. In this paper, FE analysis for the hot spot stress estimation of some welded joints is carried out for investigating the difference of stress results between shell and solid models. A new hot spot stress approach using solid elements is also proposed, which can be applied in conjunction with critical plane approach for multiaxial fatigue strength assessment. Numerical results show that the new approach has high accuracy in hot spot stress estimation compared with traditional surface stress extrapolation approach.
The hot spot stress analysis approach had been successfully used in design of offshore structures for many years. Gradually this methodology was also being used for the fatigue analysis of plated structures (Fricke, 1992). Although the scientific basis for using the hot spot type approach was somewhat weak, this methodology, combined with different refinements of fatigue analysis techniques, has been included in guidelines for fatigue assessment of ship and offshore structures developed by classification societies (ABS, 2003; DNV, 2005).
