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Fast and robust procedures for fatigue analysis of welded structures


VTT has practiced computational stress and fatigue analyses, weld simulation, field measurements and fatigue testing for decades, and we continue to develop fast and robust procedures for industrial applications.




The computational methods developed at VTT are validated against measurements and structural testing. This ensures the reliability of the methods and the ability for us to interpret the analysis results, and let us help our customers to find the correct answers and solutions for their challenges.

Overview of methods for fatigue design 

We offer field measurements for wide range of applications, with long history of ships, offshore structures, airplanes, rolling stock, mobile work machines, and rotating machinery. From VTT you get the expertise needed for your trouble shooting and product development needs.

We currently develop fast analysis procedures for parametric design, analysis and optimisation of welded structures. The popular trend is to use large and extremely detailed solid element models, but such dense meshed models are typically slow to update for design changes. The alternative is to use traditional, relatively coarse shell or solid models, and model the welds in a hierarchical manner. This kind of approach allows parametric modelling and fast analyses that support the design process troughout the product development.

Fast reliable fatigue design of large welded structures 

The effective notch stress approach 

Lead time of stress and analysis can be shortened by automatic post processing of FE-analyses. The automatic post processing also helps to decrease human errors in fast pace projects with multiple design iterations and repeated analyses. Parametric analysis and automatic post processing enable us also to optimise structures, and help you develop competitive, lightweight products without compromising the product safety and durability.

For fatigue testing we offer standard small specimen tests, component and full scale tests, and in addition to these a novel approach of using mock-up fatigue test components. The mock-up components can be tailored to mimic the loading conditions and weld types of your structure. The benefit of the mock-up components is that the number of fatigue test results needed to determine for example the fatigue class of a weld (FAT) is achieved at much lower cost than if the actual components were tested. Misalignments and realistic welding and loading conditions can be included in the mock-up fatigue test components.  

We have developed at VTT tools for automatic classification of measured weld geometries. The procedure runs in MATLAB and is linked to FEA, from which the fatigue classes (FATs) related to the measured weld geometries are obtained.
3D-laser scanning can be used to determine the fatigue critical locations and FAT-class of welds

The weld profiles can also be synthesised to study the effect of variation of weld quality on the fatigue strength. The approach developed at VTT can be used for defining acceptance limits and in-house weld classes.
The synthetic weld profile approach can be used also for studying the effect of smooth defects on the fatigue class. For example a smooth undercut that is not allowed in weld class B and is limited to max. 0.5 depth in weld class C, is actually not very significant at thicker plates and often deeper smooth undercut does not affect the fatigue strength significantly. So for example this common defect could be accepted by controlled fatigue design process resulting to less repair welding. The simulated weld profiles can be screened as target profiles for welding procedure tests and fatigue testing, based on which the case specific acceptance limits can be defined.

 Fatigue classes

The main benefits of the novel methods are shortened lead time of structural and fatigue analyses, possibility of structural and weld optimisation, reliability of analysis results by validation, possibility to study the effect of misalignments and defects, and possibility to define in-house acceptance criteria and weld classes, and increase the overall quality of welding. By this our customers can decrease weight of their welded structures and achieve high fatigue strength for their products.