LIFE PREDICTION FOR HEAVY STRUCTURES BASED ON FATIGUE CRACK INITIATION AND GROWTH
The main goal for this thesis has been to perform fatigue life predictions on large components.
Dierent methods were to be chosen and reviwed critically. Experimental data
for girth welded pipes was assessed by means of a version of BS7910 which were modeled
from scratch. This version was veried with results from CrackWise, and used to predict
the fatigue life for loade cases matching the selected experimental data. The fatigue assessment
tool P-FAT was used to predict the fatigue life for the same experimental data,
and the results were compared. Except for some deviations recorded for embedded cracks,
a generally good agreement was found between the two tools.
Both the modeled BS7910 and P-FAT predicted conservative but accurate fatigue lives
for the experimental data that had signicant defects. They predicted non conservative
results for specimens that did not have signicant defects, when the initial crack depth
was set to 0.1 mm. When the initial crack depth was set to 0.5 mm the modeled version
predicted fatigue lives in agreement with the experimental results.
Fatigue life predictions were also performed by assistance of S-N curves provided by DNVRP-C203.
The results from these predictions were in agreement with the experimental
data, except for four specimens. These four specimens had signicant
aws, which reduced
the fatigue life signicantly.
A review of a two-phase fatigue assessment model was made. This model uses a strained
based approach to assess the fatigue crack initiation phase, and the fracture mechanic
approach suggested in the BS7910 to assess fatigue crack growth. This method have
shown promising results for fatigue assessment of llet welds in the literature, but the
model needs further investigation and calibration to be used to predict fatigue life of
girth welded structures. A specic area to investigate is the proposed transition depth of
0.1 mm. This depth is dubious based on the results
Place, publisher, year, edition, pages
Institutt for produktutvikling og materialer , 2012. , 68 p.
ntnudaim:7381, MIPROD Produktutvikling og produksjon, Produktutvikling og materialer
IdentifiersURN: urn:nbn:no:ntnu:diva-19001Local ID: ntnudaim:7381OAI: oai:DiVA.org:ntnu-19001DiVA: diva2:566393
Härkegård, Gunnar, ProfessorHron, Agnes MarieOsen, Vidar