Uncertainties of Crack Propagation Analysis in Ship Structures

2016 ◽  
Author(s):  
Wengang Mao ◽  
Jingxia Yue ◽  
Da Wu ◽  
Luis De Gracia ◽  
Naoki Osawa
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Fatigue Cracks ◽  
Estimation Methods ◽  
Ship Structures ◽  
Residual Fatigue Life ◽  
Propagation Analysis ◽  
Structural Details ◽  
Residual Fatigue

Fatigue cracks can be observed quite frequently on today’s ocean crossing vessels. To ensure the safety of ship structures sailing in the sea, it is important to know the residual fatigue life of these damaged ship structures. In this case, the fracture mechanics theory is often employed to estimate how fast these cracks can propagate along ship structures. However, large uncertainties are always associated with the crack prediction and residual fatigue life analysis. In this study, two uncertainties sources will be investigated, i.e. the reliability of encountered wave environments connected with shipload determinations and different fracture estimation methods for crack propagation analysis. Firstly, different available codes based on fracture mechanic theory are used to compute the stress intensity factor related parameters for crack propagation analysis. The analysis is carried out for both 2D and 3D cases of some typical ship structural details. The comparison is presented to illustrate the uncertainties of crack propagation analysis related with different codes. Furthermore, it is assumed that the structural details will undertake dynamic loading from a containership operated in the North Atlantic. A statistical wave model is used to generate wave environments along recorded ship routes for different years. The uncertainties of crack growth analysis related with encountered weather environments is also investigated in the study. The comparison of these two uncertainties indicated the requirement of further development for the fracture mechanics theory and associated numerical codes, as well as the reliable life-cycle encountered weather environments.

Fatigue Modeling of Friction-Stir-Welded (FSW) Butt-Joints for Aerospace Applications

2019 ◽  
Author(s):  
Muhammad A. Wahab ◽  
Vinay Raghuram
Keyword(s):  
Fatigue Life ◽  
Aluminum Alloys ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Fatigue Cracks ◽  
Strength Criterion ◽  
Fatigue Properties ◽  
Interface Element ◽  
Friction Stir ◽  
Stress Ratios

Abstract Among the recent research Friction-Stir-Welding (FSW) has been adopted worldwide as one of the dominant processes for welding lightweight aerospace Aluminum alloys. Al-2195 which is one of the new generation Aluminum alloys has been used in the external tank of the space shuttles. Aerospace fabricators are continuously pursuing FSW-technologies in its efforts to advance fabrication of the external tanks of the space shuttles. The future launch vehicles with reusable mandates require the structures to have excellent fatigue properties and improved fatigue lives. The butt-welded specimens of Al-2195 and Al-2219 are fatigue tested according to ASTM-E647. The effects of stress ratios, use of corrosion preventive compound (CPC), and the applications of periodic overloading on fatigue lives are investigated in this study. Scanning-electron-microscopy (SEM) is used to examine the criticality of the failure surfaces and the different modes of crack propagation that could have been initiated into the materials. It is found that fatigue life increases with the increase in stress ratio, and results show an increase in fatigue life ranging over 30% with the use of CPC, and the fatigue life increases even further with periodic overloading; whereas crack-closure phenomenon predominates the fatigue fracture. Fracture mechanics analysis and crack similitude was modified for fatigue cracks by Paris. Numerical studies using FEA has produced a model for fatigue life prediction scheme for these structures, where a novel strategy of the interface element technique with critical bonding strength criterion for formation of new fracture surfaces has been used to model fatigue crack propagation lives. The linear elastic fracture mechanics stress intensity factor is calculated using FEA and the fatigue life predictions made using this method are within 10–20% of the experimental fatigue life data obtained. This method overcomes the limitation of the traditional node-release scheme and closely matches the physics of the crack propagation.

Transitional Behavior of Residual Fatigue Life After Applying Overload During Fatigue Crack Growth With Constant Stress Amplitude

2004 ◽  
Author(s):  
Anindito Pumowidodo ◽  
Tatsujiro Miyazaki ◽  
Chobin Makabe ◽  
Arthur J. McEvily
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Propagation ◽  
Crack Growth ◽  
Critical Level ◽  
Stress Intensity Factor Range ◽  
Fatigue Crack Propagation Rate ◽  
Residual Fatigue Life ◽  
Residual Fatigue ◽  
Tensile Overload

It is well known that crack propagation is retarded after applying a tensile overload, and accelerated after applying a compressive overload. However, at a negative value of the baseline stress ratio, the fatigue crack propagation rate can accelerate after applying a tensile overload. To evaluate such crack propagation behavior, the effective stress intensity factor range has been employed. In the present study, the effects of a tensile overload followed by a compressive overload on crack propagation were investigated. The transition of residual fatigue life after applying these loads was observed and this behavior was dependent on the loading conditions. When the applied overload level was lower than a critical level, retardation of crack propagation was observed. However, when the applied overload level was higher than a critical level, the crack growth rate got higher. These phenomena are related to not only residual stress, but also crack opening behavior.

scholarly journals Determination of Residual Fatigue Life of Welded Structures at Bucket-Wheel Excavators through the Use of Fracture Mechanics

2018 ◽  
Vol 13 ◽  
pp. 79-84 ◽  
Author(s):  
M. Arsić ◽  
S. Bošnjak ◽  
N. Gnjatović ◽  
S.A. Sedmak ◽  
D. Arsić ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Fracture Mechanics ◽  
Welded Structures ◽  
Residual Fatigue Life ◽  
Residual Fatigue

Fatigue Crack Propagation of the Ship Structure in Random Sea Condition

2015 ◽  
Author(s):  
Niu Song ◽  
Cao Jun-wei ◽  
Ren Hui-long ◽  
Feng Guo-qing
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Random Load ◽  
Sea State ◽  
Ship Structures ◽  
Linear Effect ◽  
Fatigue Crack Propagation Life

Fatigue damage is one of the main causes responsible for the destruction of ship structures. The traditional methods of the fatigue strength check are based on S-N curves and Miner linear cumulative damage rules. But different fatigue lives of the same node are obtained, because the disadvantages of S-N curves could not be avoided, such as neglect of initial objection of material. The method of fracture mechanics to assess the fatigue life of ship structures has become a trend now. According to the relevant fracture mechanics theory, this paper brings forward a set of methods on the fatigue life of ship structures under random sea state. This method takes into account the non-linear effect of stress distributed along the crack surface, and the stress intensity factor is calculated through the weight function method. The crack extension is calculated in each cycle of stress according to the stress response history of ship in actual sea state so as to attain the fatigue crack propagation life of ship structures in the random load.

Residual Fatigue Life Determination of Anchor Bolts

1979 ◽  
Vol 101 (1) ◽  
pp. 47-52 ◽  
Author(s):  
B. Mukherjee
Keyword(s):  
Growth Rate ◽  
Fatigue Life ◽  
Crack Growth Rate ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Effect Of Temperature ◽  
Transmission Tower ◽  
Residual Fatigue Life ◽  
Anchor Bolts ◽  
Residual Fatigue

A project was conducted to determine residual fatigue life of transmission tower anchor bolts. Notched and fatigue precracked round bar specimens were used to simulate anchor bolt fatigue and to determine fatigue life experimentally. Fatigue precracked compact tension specimens were used to determine fatigue crack growth rate properties using a fracture mechanics approach. The effect of temperature on crack growth rate was also investigated. A method to estimate fatigue life of surface cracked round bars was developed and predictions were compared against experimental results. This paper shows how a fracture mechanics approach can be used to estimate residual fatigue life of cracked anchor bolts.

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