Transcript Liberty Ships - Brittle Fracture_powerpoint_Group 23.ppt

Project 23
Liberty Ships - Brittle Fracture
4A6 (1) - Structure
Neil Bonner
Maxime Gonzalez
Stephanie Luquet
Sylvain Ruggi
Liberty Ships
• Steel vessels built in the US during the second World War
• 2700 produced between 1942 and 1945
• 442 feet long, carried 10,000 tons, 12 MPH
• All welded construction
What happened
At the start of the programme 30% of Liberty Ships suffered
catastrophic fracture
What happened
• Most of the failure occurred during the winter months
•
Failures occurred both when the ships were in heavy seas and
when they were anchored at dock
These calamities focused attention on the fact that normally
ductile mild steel can become brittle under certain conditions
Basic factors
•
Low temperature
•
Triaxial state of stress
•
High strain rate or rapid rate of loading
•
Effect of stress concentrations due to notches and
cracks
Temperature effects
Other factors
• All- welded construction: eliminated crack- arresting
plate boundaries which are present in riveted joints
• Presence of crack- like flaws in welded joints performed
by inexperienced operators
• Use of low resistance materials
Preventing Brittle Fracture
• Material used : adequate toughness for anticipated
loading and low temperature
• Methods used in construction : Ensure that the welds
have no imperfections
• Structure design : eliminate sharp changes in cross
section
Conclusion
• Fracture Mechanics was relatively unknown at the time
failures