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Characterization of the fatigue behaviors of offshore hyperbarik welds

Başlık çevirisi mevcut değil.

  1. Tez No: 29096
  2. Yazar: ÇINAR YENİ
  3. Danışmanlar: DOÇ. DR. SEÇİL ERİM
  4. Tez Türü: Yüksek Lisans
  5. Konular: Makine Mühendisliği, Mechanical Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1993
  8. Dil: İngilizce
  9. Üniversite: Dokuz Eylül Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Makine Mühendisliği Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 93

Özet

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Özet (Çeviri)

SUMMARY The use of arc welding process in repair and montage of the underwater steel structures depends strongly to the fracture toughness and fatigue properties of the welded joints. Presence of the pressure at greater sea-water depths affects the welding process and may further deteriorates the mechanical properties of the underwater welded joints. Therefore, this present study has been carried out to determine the effect of pressure on the fatigue life of small scale specimens (width=15 mm, thickness=5 mm). A large number of butt-welded specimens, in as- welded condition have been obtained from 15 mm wide offshore steel plates with V preparation welded with MIG/MAG processes under atmospheric (1 bar), 15 bar and 27 bar dry conditions. In the experimental part of the study, constant amplitude fatigue tests in air have been performed at the hydraulic testing machine by keeping the stress ratio (tfmin/smax)» R=0.1 constant The applied load values were varied between a maximum of 32 kN and a minimum of 12 kN. The results are plotted on logS-logN diagrams. The bi-linear S-N curve fitting method developed by Japanese scientists, which is based on a statistical approach of fitting data to a bi linear type of curve comprising inclined and horizontal lines, is used in the study. Weld toe angle versus fatigue life diagrams are constructed to determine whether the fatigue life gets shorter as the toe angle at which the crack initiates decreases. In the second part of this study, a statistical analysis of the scatter of the fatigue life data has been carried out. The results of fatigue tests for each pressure level are statistically compared to decide whether there is significant difference between the results or whether they can be treated as one set of data. Calculations were carried out to determine the confidence limits and 10%, 50%, 90% survival curves associated with the test results. The test results show that fatigue cracks in the butt welded joints always initiate at the weld region, mostly at one corner of the weld toes. From the weld toe angle versus fatigue life diagrams, though not clearly defined due to data scatter, it is observed that there exists a direct relationship between the weld toe angle of crack initiation site and the fatigue life of the specimen. Also it is clear that the scatter of fatigue lives tends to increase as the applied stress level is decreased. From the statistical analysis it is determined that the data obtained for three pressure levels were not significantly different and could be treated as one set of data. In other words, no effect of pressure can be observed on fatigue life of the hyperbaric butt-welds. This may be due to the fact that the effect of similar toe geometry, that is the change of section at the weld region, overcomes the differences in the mechanical properties of the welds.

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