Fatigue life calculation of welded joints based on fracture mechanics Ahmed M. Al-Mukhtar* MSc. Materials and Manufacturing Engineering BSc. Aeronatical Engineering Supervisors: Prof. Dr.- Ing. habil. H. Biermann* Prof. Dr.- Ing. P. Hübner** *Institute of Materials Engineering, Technische Universität Bergakademie Freiberg, Germany **Fachhochschule Mittweida, Mittweida, Germany Institut of Materials Engineering PHD Programme
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Fatigue Life Calculation of Welded Joints Based on Fracture Mechanics
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Fatigue life calculation of welded joints based on fracture mechanics
Ahmed M. Al-Mukhtar*MSc. Materials and Manufacturing Engineering
BSc. Aeronatical Engineering
Supervisors: Prof. Dr.- Ing. habil. H. Biermann* Prof. Dr.- Ing. P. Hübner**
*Institute of Materials Engineering, Technische Universität Bergakademie Freiberg, Germany **Fachhochschule Mittweida, Mittweida, Germany
Institut of Materials Engineering
PHD Programme
Outlines
1) Aim of reaserch (Objectives) - Procedure
2) Introduction (Why fracture mechanics?)
3) Finite Element Analysis (FEA)
- Modelling- Crack path direction
4) Standard and fatigue design recommendations
5) Results (benchmarking)
- SIF calculation and comparison for some welded joi nts- Fatigue life calculation and comparison for some w elded joints- Case study not presented in the recommendation
6) Conclusions
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Aim
- Accurate SIF calculation
- Moreover, calculate the fatigue life, and the fatigue strength (FAT) of the welded joints with different geometries that not presented in recommendations
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Procedures
1) FE modeling which give accurate stress intensity factor.
2) With knowledge of the stress intensity factors KI at different crack depths (a), it was possible to make curve fits for KI(a) for the different loading and use Paris’law to integrate numerically and calculate the expected fatigue life for the specimens.
3) Case studies can be consulted, and the need for well thought out benchmarking of analytical results against experimental databases-IIW
1. Ziel – und Aufgabenstellung1. Aim and Proecdures
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1. Ziel – und Aufgabenstellung2. Introdcution - Why Fracure Mechanics?
- One of the most important deterioration mechanisms of Aircrafts, ships and steel bridge structures which occur in service condition is Fatigue .
- Fatigue Failure , accounts for at least 75% of all machines and structures failures
Goal: Calculate ai, which already existed and crack growth parameters
Fatigue life calculation and FAT
Safe life and lower cost consuming for experiments tests
- Crack normally existed! But may be accelerated due to environment and loading condition-A.A. Griffith (1893-1963)
Aloha Airlines.1988
De Havilland First commercial jet aircraftfatigue cracks initiated at square windows, 1954
• Seven of the Liberty ships built during the world war II has broken completely in two as a result of brittle fractures. (1943)
• However, larger safety factor !!
• Crack normally existed !! How long?
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2. Introdcution - Why Fracure Mechanics?
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2. Introdcution - Why Fracure Mechanics?
Ref.Ingraffea A R. Case Studies of Simulation of Fr acture in Concrete Dams. Eng. Fracture Mech., 35, 1 /2/3, 1990, 553-564.
Fontana Dam, North Carolina, USA
• FRANC2D is a FE based simulator for curvilinear crack propagtion planar structures. CASCA which used for the creating the meshes, is a preprocessor for genrating initial input file for FRANC2D.
-New Geometry not presenetd in IIW recommendations-Fatigue life calculation and comparison
5. Results
provided a new value of FAT could be considered as the design value or lower bound.The new case with fillet radius not consider in IIW and in BS. (FAT=71 Mpa.)
Radius R t
1
10
100
1000
1,E+04 1,E+05 1,E+06 1,E+07 1,E+08
Log N (Cycle)
Str
ess
Ran
g (M
pa.)
Experimental
FAT63.No toe radius.IIW
FRANC2D.C=5E-13.m=3.ai=0.1mm.with toe radius
C=1,85E-13.m=3.mean values
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1) Accurate SIF is calculated through FEM FRANC2D
2) Different weld geometries which are not yet listed in previous recommendations could be easily modeled to evaluate the fatigue life strength. Which means that,
2) The new approach saves the time and costs need for experimental testes