SEDL / STP / STP770-EB / STP32433S

Prediction Capability and Improvements of the Numerical Notch Analysis for Fatigue Loaded Aircraft and Automotive Components

Nowack, H
Department Head and Research Fellows, Deutsche Forschungs- und Versuchsanstalt für Luft- und Raumfahrt (DFVLR), Institut für Werkstoff-Forschung, Köln,

Hanschmann, D
Department Head and Research Fellows, Deutsche Forschungs- und Versuchsanstalt für Luft- und Raumfahrt (DFVLR), Institut für Werkstoff-Forschung, Köln,

Foth, J
Department Head and Research Fellows, Deutsche Forschungs- und Versuchsanstalt für Luft- und Raumfahrt (DFVLR), Institut für Werkstoff-Forschung, Köln,

Lütjering, G
Professor, Technische Universität Hamburg-Harburg, Hamburg,

Jacoby, G
Professor, Schenck AG, Darmstadt,

Pages: 27    Published: Jan 1982

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Abstract

Because they combine minimum experimental expenses with a maximum flexibility regarding their application areas and objectives, numerical notch analysis methods have attained special importance among the presently available crack initiation life prediction methods.

The first part of this study gives the results of an evaluation program in which the prediction capability of the numerical notch analysis concept using the Neuber approach for the consideration of the notches was investigated. The loading histories considered are standard flight loading histories (TWIST and FALSTAFF), automotive histories, and simple, systematically varied loading histories. The test specimens were center notched and angle type, and the materials were high-strength aluminum alloys, Ti6-4, and others. The test results showed satisfactory predictions in many cases; however, unacceptable deviations occurred, especially under long-term random loading, after high peak loads, and under a high amount of compressive loads.

The second part of this study investigates the reasons for the deviations in the predictions. The main reasons are (1) inadequate consideration of the sequence effects on the damage accumulation, and (2) differences in the stress states and crack initiation processes at the stress raisers of the notched specimens and at the unnotched specimens.

A new damage evaluation procedure is proposed that is based on these test results. A more adequate definition of the crack initiation stage is attempted and a consideration of short cracks is provided.