IBESS - Crack propagation investigations on longitudinal stiffeners to validate the IBESS-Procedure [IGF-Nr. 17519 N]

AiF-DFG-Cluster-Project

Responsible research centres: TU Hamburg-Harburg (Prof. Fricke)

Time period: 01.05.2012 to 31.10.2015


Motivation / Background

The crack propagation concept is rarely used in practice, although it is the only suitable approach to assess the fatigue strength of any welded structures. In addition to the higher effort related to the computation of stress intensities and the behavior of short cracks, other reasons such as the uncertainties regarding the initial assumed crack length, the development of the crack shape in geometrically complicated cases, the influence of the local weld geometry, the production-related residual stresses and the mean stresses could be mentioned.

The uncertainties concern significantly complex welded structures, such as they occur for example in steel construction, in shipbuilding, in offshore structures, as well as in crane constructions. The influences mentioned, being related to the local geometry, the residual and mean stresses are to be considered in the crack-critical areas of these constructions and lead to a considerable need for research.

 

Summary of planned objectives

The project includes eight partners. According to the research approach, the aim of the project is to develop a concept through which the fatigue strength of welded joints based on fracture mechanics could be determined. In practice, this concept will allow the evaluation of the S-N curve for a given weld configuration.

The main goal of the present sub-project includes experimental and numerical investigations to determine the influences of the local weld geometry and residual stresses on the crack propagation behavior in complex welded structures.  Relatively thick-walled (10 mm) welded plate structures from structural steel S355 are considered, as it is typical in shipbuilding and in offshore structures. The chosen specimens are longitudinal stiffeners with the focus on their welded ends, as they often occur in these complex structures, whereby they will be used to test the developed calculation IBESS procedure.

A concept is expected to predict the lifetime of welded structures that is experimentally validated and may take into account the production-related and geometrical influences of complex structures more accurately. For this purpose, results regarding the influences of the local weld geometry, the welding-induced residual stresses and possible early defects are expected. Based on the numerical investigations and their comparison to the experimental ones, recommendations for the calculation procedure to be incorporated in guidelines and software products will be given.

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