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The main objective of the project was to predict fracture of welded high-strength steel structures using a newly developed failure assessment method for use in the transition region. This incorporates the Local Approach and J-Q-M concept for brittle fracture combined with the Gurson model for ductile crack extension.

For fracture toughness testing the SE(T) specimen, loaded under clamped conditions, turned out to be a good candidate due to a constraint level comparable to flawed structural components. Analytical equations to determine J or CTOD values have been established.

For the numerical calculations of Weibull stresses an appropriate mesh size and element type have to be chosen for FE modelling to avoid the impact of stress oscillations on calculated failure probabilities. To analyse brittle failure preceded by ductile crack growth a damage model should be applied.

The investigations revealed that the JQM concept and the Local approach method are tools to ensure transferability of fracture mechanics results from small-scale test results to full-scale structural components, despite some accuracy problems of Weibull stress calculations from FE results.

The yield strength class of 690 MPa is best used in structures that require very large conventional plate thicknesses and where weight savings are essential. A basic requirement to the application of new high-strength steels in welded structures is weldability. The lowest toughness is generally achieved in the intercritically reheated HAZ. The steels with higher alloy content showed better HAZ toughness than the former investigated 500 MPa steels. HAZ toughness was improved by low carbon content and increasing nickel content.

Additional information

Authors: HORN A, CORUS UK, Rotherham (UK);MEMHARD D, FH-IWM Fraunhofer-Institut fûr Werkstoffmechanik, Freiburg (DE);STUREL T, IRSID, Maizières-lès-Metz (FR)
Bibliographic Reference: EUR 20882 EN (2003), 50pp. Euro: 15
Availability: EUR-OP reference: KI-NA-20882-EN-S Available from EUR-OP sales agents URL:
ISBN: ISBN: 92-894-6307-4
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