Effect of Crack Closure on the Fatigue Limit of Material Containing Small Defect

Accession number;03A0817506
Title;Effect of Crack Closure on the Fatigue Limit of Material Containing Small Defect
Author;KASHIWAGI MASAHIRO(Kyushu Univ., Graduate School, JPN)   KUDO TAKAO(Kyushu Univ., Graduate School, JPN)   KUBOTA MASANOBU(Kyushu Univ., Graduate School of Engineering, JPN)   SAKAE CHU(Kyushu Univ., Graduate School of Engineering, JPN)   KONDO YOSHIYUKI(Kyushu Univ., Graduate School of Engineering, JPN)   
Journal Title;Journal of the Society of Materials Science, Japan
Journal Code:F0385A
ISSN:0514-5163
VOL.52;NO.11;PAGE.1345-1350(2003)
Figure&Table&Reference;FIG.16, TBL.2, REF.13
Pub. Country;Japan
Language;Japanese
Abstract;It has been recognized that the threshold stress intensity factor range .DELTA.Kth of short crack is dependent on many factors. Fatigue tests were performed on materials containing small defects under a wide range of mean stress for three grades of steels with different hardness. Strong dependencies of .DELTA.Kth on material hardness, mean stress and defect size were observed. Major tendencies such that softer material had lower .DELTA.Kth and smaller defect had lower .DELTA.Kth were obtained, which were quite different from those of long cracks. The causes of these effects were investigated based on the crack closure behavior of short crack. The crack closure measurement on a very shallow crack was done. Test results showed that softer material and shorter crack had lower crack closure stresses. It was shown that the threshold effective stress intensity factor range (.DELTA.Keff)th was a unique value for defects deeper than 0.1 mm. The crack closure was the major cause of the abovementioned effects of material hardness and mean stress for defects deeper than 0.1 mm. On the contrary, (.DELTA.Keff)th significantly decreased compared with that for long cracks when the defect was shallower than 0.1 mm. This is another short crack effect which could not be explained only by the crack closure. It was shown that (.DELTA.Keff)th was no more a unique value when the defect depth was shallower than 0.1 mm. (author abst.)