Title

Dynamic Models for Low Cycle Fatigue

Report Number

RTD-TDR-63-4197 Part I, p. 511

Creator

Roberts, W. H.

Walker, K.

Corporate Author

Northrup Corporation

Laboratory

Air Force Flight Dynamics Laboratory

Date

1964

Date Issued

1964-03

Extent

40

Abstract

Aeroelastic and dynamic models are a practical way to improve aerospace and vehicle safety and reliability while providing significant economies in resources and reduction in full scale ground and flight testing. Progress in applying the models to fatigue problems of two types, specimens and complex structures, is presented. The nature of present fatigue probems is explored, in particular, the link between fatigue and dynamic loads of both high and low frequency. Fatigue damage has been severe and the problem requires complete reassessment. The failures experienced are not because the state-of-the-art is misapplied, but because it is inadequate. The problem contains several layers of complexity beyond the present methods. The probability of failure increases radically in the early life of a part when a typical load history is considered. High frequency dynamic load components added to slowly varying static loads lead to a further increase in probability of failure. Because of this, the structural dynamicist has a key role to play and must adopt this problem area as a major responsibility since his inadequacies appear to be a factor in lack of reliability. For low cycle fatigue, the models may be applied in real time or in scaled time. The accuracy required for dynamic response is very high, but that required for fatigue scaling is higher still. Principal advantage of the models is their capability to handle all aspects of the static and dynamic loads simultaneously, including thermal loads. The models represent an engineering design tool available for application in the early design stage. That structural load paths are not available in exact detail is not a problem since equal fatigue quality in terms of the stress concentrations can govern the approach. Model shortcomings for fatigue scaling are brought
out, and ways to circumvent these are discussed.

Distribution Classification

1

Distribution Conflict

No

DTIC Record Exists

No

Illinois Tech Related

No

Photo Quality

Complete

Report Availability

Full text available

Type

article

Is Part Of

Proceedings of Symposium on Aeroelastic & Dynamic Modeling Technology

Provenance

Bombardier/Aero