Seam weld fatigue life analysis

Specialist Durability provides a unique method for detecting and calculating seam welds. This methodology is user-friendly in the detection of the seam welds and not only more flexible but also more accurate than any method available in commercial software. The flexibility is guaranteed by handling any type of loading and the ability of adding user-defined types of welds.

Introduction

The fatigue of seam welds became a topic in the off-shore industry first. State-of-the-art methods have been developed and validated for fatigue of welds and got incorporated in the Eurocode 3 recommendations. The validation area of the methods is restricted to defined loading conditions and relatively thick sheet structures. However, the real life loading conditions are multi-axial and changing with time. Furthermore, the sheet thickness used in the automotive industry gets thinner and thinner due to weight reduction requirements. The development of new welding techniques, like arc or laser welding, also needs to be taken into account.

The general work flow for calculating the durability behavior of welds in a CAE process starts with modeling the welds in the finite element model. Due to the fact that the real geometry of a weld is on one hand very complicated and on the other hand dependent on the actual welding process and therefore not completely known, the finite element modeling is a key issue. In most cases the structure is modeled as welded sheets that are represented as shell elements in a FE-structure. Here the welds are simple connections between the sheets. For the durability analysis the welds need to be identified in the structure. The problem arising is that the geometry of the welds are not completely 3D-modeled. Even if this would be done for real structures, computational restrictions in the finite element structure would soon occur. Therefore a state-of-the-art process was developed that reads the shell stress results in the neighborhood of the weld. From this point in the process there exist several possibilities in literature and real life application on how to evaluate the durability behavior. In principle we get a nominal stress for both the weld as the sub-component. You can apply these stresses directly to a refined model of the weld structure which is the most accurate but also the most costly way.

Opposite to these approaches there exist catalogs of test results for a variety of weld structures. In this approach, you have to identify the right geometry and loading condition in the catalog. Very often the remarks from the latter paragraph also apply to this approach. Next to these considerations there is also the problem that a lot of structures that are used today are not included in the current catalogs. For an efficient seam weld fatigue analysis it is therefore key to find a better and automated method that combines both approaches.

The idea implemented in Specialist Durability is based on using a database of detailed models. Based on these detailed models a set of potentially critical elements is selected. The models are then used to analyze the influence of a well-chosen load cases on these critical locations. The number of critical elements depends on the configuration itself. The forces at the nodes of the seam weld are chosen to be the quantities representing the loading situation. These forces are calculated for all load cases. Considering both the forces and the local stresses in the detailed model a transition matrix from the forces to the local stresses can be derived. Each transition matrix, corresponding to a specific type of seam weld can then be stored in a database, similar to the idea of using a catalog. In what follows an overview of all the methods that are implemented in Specialist Durability will be presented.

Learn more

Structural stress methods

Notch stress methods

Definition by the extended master connection file (XMCF)

Automatic seam weld recognition

Seam weld fatigue life analysis bibliography

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Seam weld fatigue life analysis, Simcenter 3D 2021.1 Series

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