Jaap Schijve

Fatigue of Structures and Materials in the 20th Century and the State of the Art

The paper surveys the historical development of scientific and engineeringknowledge about fatigue of materials and structures in the 20th century. This includesfatigue as a material phenomenon, prediction models for fatigue properties ofstructures, and load spectra. The review leads to an inventory of the present state ofthe art. Some final remarks follow in an epilogue.

FATIGUE CRACK PROPAGATION IN LIGHT ALLOY SHEET MATERIAL AND STRUCTURES

Several test series on crack propagation in light alloy specimens were performed at a positive mean stress and axial loading. Results are presented on the following aspects: (1) The frequency effect was studied by comparing the crack rate at a low and a high frequency, viz. about 20 and 2000 c/min respectively. Some fractographical observations were made. (2) The effect of varying the stress amplitude and applying high peak loads on the crack propagation was studied in comparison with constant-amplitude data. (3) The results of stiffened panels were compared with the results of a complete structure and the results of small sheet specimens. At the end of the paper the conclusions are summarized.

Biaxial Fatigue of Metals

Problems of fatigue under multiaxial fatigue loads have been addressed in a very large number of research publications. The present paper is primarily a survey paper of biaxial fatigue under constant amplitude loading on metal specimens. It starts with the physical understanding of the fatigue phenomenon under biaxial fatigue loads. Various types of proportional and non-proportional biaxial fatigue loads and biaxial stress distributions in a material are specified. Attention is paid to the fatigue limit, crack nucleation, initial micro crack growth and subsequent macro-crack in different modes of crack growth. The interference between the upper and lower surfaces of a fatigue crack is discussed. Possibilities for predictions of biaxial fatigue properties are analysed with reference to the similarity concept. The significance of the present understanding for structural design problems is considered. The paper is completed with a summary of major observations.