Fracture mechanics based assessment of the fatigue strength: approach for the determination of the initial crack size

2015 ◽  
Vol 38 (9) ◽  
pp. 1066-1075 ◽  
Author(s):  
U. Zerbst ◽  
M. Madia
Keyword(s):  
Fatigue Strength ◽  
Fracture Mechanics ◽  
Crack Size ◽  
Initial Crack

Determination of Critical Crack Size Utilizing a Fracture Mechanics Test in Equipment Under Fatigue

2009 ◽  
Author(s):  
Irene Garcia Garcia ◽  
Radoslav Stefanovic
Keyword(s):  
Heat Treatment ◽  
Fracture Mechanics ◽  
Crack Size ◽  
Operational Experience ◽  
Element Analysis ◽  
Critical Crack ◽  
Circumferential Welds ◽  
Fea Model ◽  
Critical Crack Size

Equipment that is exposed to severe operational pressure and thermal cycling, like coke drums, usually suffer fatigue. As a result, equipment of this sort develop defects such as cracking in the circumferential welds. Operating companies are faced with the challenges of deciding what is the best way to prevent these defects, as well as determining how long they could operate if a defect is discovered. This paper discusses a methodology for fracture mechanics testing of coke drum welds, and calculations of the critical crack size. Representative samples are taken from production materials, and are welded employing production welding procedures. The material of construction is 1.25Cr-0.5Mo low alloy steel conforming to ASME SA-387 Gr 11 Class 2 in the normalized and tempered condition (N&T). Samples from three welding procedures (WPS) are tested: one for production, one for a repair with heat treatment, and one for repair without heat treatment. The position and orientation of test specimen are chosen based on previous surveys and operational experience on similar vessels that exhibited cracks during service. Fracture mechanics toughness testing is performed. Crack finite element analysis (FEA) model is used to determine the path-independed JI-integral driving force. Methodology for the determination of critical crack size is developed.

Effect of Uncertainties on the Reliability of Fatigue Damaged Systems

2004 ◽  
Author(s):  
Francisco L. Silva-Gonza´lez ◽  
Ernesto Heredia-Zavoni
Keyword(s):  
Fracture Mechanics ◽  
Failure Modes ◽  
Crack Size ◽  
Initial Crack ◽  
Wave Forces ◽  
Scale Parameters ◽  
Uncertain Variables ◽  
Mechanics Model ◽  
Distribution Of Stress

Fluctuating stresses and strains due to wave forces cause accumulated fatigue damage in tubular joints of marine platforms. Considering the uncertainties in the loads, material properties, initial crack sizes, and stress intensity factors, etc., may affect significantly the reliability assessment of marine jacket platforms. In this paper, we assessed the effect of uncertainties about such fatigue variables on the time evolution of the reliability of series and parallel systems considering correlation between failure modes. The fracture mechanics Paris-Erdogan model is used to model crack growth and a FORM method is used for computing the safety index. The uncertain variables analyzed are: initial crack size, material parameters C and m in the fracture mechanics model and the shape and scale parameters of the Weibull density function used for the long-term distribution of stress range.

The Application of Fracture Mechanics to Predict the Critical Initial Crack Length for Inspection

2003 ◽  
Author(s):  
C. T. Liu
Keyword(s):  
Composite Material ◽  
Fracture Mechanics ◽  
Crack Length ◽  
Particulate Composite ◽  
Crack Size ◽  
Initial Crack ◽  
Initial Crack Length ◽  
Particulate Composite Material

In this study, a method is developed based on fracture mechanics, for predicting the equivalent critical initial crack size, aic in a particulate composite material. The predicted aic is the crack size that should be used to develop an inspection criterion to determine the reliability of a structure made of the particulate composite material.

Structural Integrity Evaluation of Reactor Pressure Vessels During PTS Events Using Deterministic and Probabilistic Fracture Mechanics Analysis

2013 ◽  
Author(s):  
Kazuya Osakabe ◽  
Hiroyuki Nishikawa ◽  
Koichi Masaki ◽  
Jinya Katsuyama ◽  
Kunio Onizawa
Keyword(s):  
Fracture Mechanics ◽  
Structural Reliability ◽  
Structural Integrity ◽  
Probabilistic Approach ◽  
Crack Size ◽  
Initial Crack ◽  
Pressure Vessels ◽  
Probabilistic Fracture Mechanics ◽  
Main Steam Line ◽  
Main Steam

To assess the structural integrity of reactor vessels (RVs) during pressurized thermal shock (PTS) events, a deterministic fracture mechanics (DFM) approach has been widely used such as the procedure in JEAC4206-2007. On the other hand, the application of a probabilistic fracture mechanics (PFM) analysis method for the structural reliability assessment of RV has become attractive recently because uncertainties related to input parameters can be incorporated rationally. The probabilistic approach has already been adopted as the regulation on fracture toughness requirements against PTS events in the U.S. In this paper, in order to verify the applicability of a PFM method to JEAC4206-2007, deterministic and probabilistic analyses have been performed, and the effects of initial crack size defined in JEAC4206-2007 on the temperature margin obtained from DFM and the probability of crack initiation obtained from PFM have been evaluated. With regard to the PTS event variation, a stuck open valve scenario (SO) has been considered in addition to large- and small-break loss of coolant accident (LBLOCA, SBLOCA) and main steam line break (MSLB).

Development of Probabilistic Fracture Mechanics Method for Fatigue Life Prediction Based on EIFS Concept

2017 ◽  
Author(s):  
Guang Zou ◽  
Kian Banisoleiman ◽  
Arturo González
Keyword(s):  
Fracture Mechanics ◽  
Crack Initiation ◽  
Crack Size ◽  
Initial Crack ◽  
Mean Value ◽  
Flaw Size ◽  
Crack Evolution ◽  
Initiation And Propagation ◽  
The Mean ◽  
Crack Initiation Life

A problem with fracture mechanics (FM) based fatigue analysis is that reliable information on initial crack/flaw size is often hard to obtain. Also, FM method can’t be applied directly to welded joints with relatively small initial flaws and long crack initiation life. This paper proposes a novel probabilistic FM method based on the equivalent initial flaw size (EIFS) concept. The initial crack size is substituted with EIFS to take both the crack initiation and propagation life into account. Three methods are tested to obtain mean value of EIFS: calibrating to S-N curves, Kitagawa-Takahashi (KT) diagram and fitting to test data. The obtained EIFSs are evaluated by comparing the predicted fatigue lives and crack evolutions with S-N curves and test crack evolution data. The suggested procedure is to derive the mean value of EIFS from S-N curves and the coefficient of variation from KT diagram.

Evaluation of Fatigue Life of Cylindrical Geared Wheels

2013 ◽  
Vol 199 ◽  
pp. 93-98 ◽  
Author(s):  
Józef Drewniak ◽  
Jacek Rysiński
Keyword(s):  
Fatigue Life ◽  
Fatigue Strength ◽  
Boundary Element Method ◽  
Fracture Mechanics ◽  
Boundary Element ◽  
Analytical Methods ◽  
Dual Boundary Element Method ◽  
Methods Of Evaluation ◽  
Element Method

The main aim of the work is determination of numerical and numerical-analytical methods of evaluation of fatigue strength and life of geared tooth considering tooth breakage phenomenon. The discussed tasks were performed using the following tools: dual boundary element method, BEASY package as well as fracture mechanics

Method of Construction for High Cycle Fatigue Resistant Pressure Vessels in Hydrogen Service

2018 ◽  
Author(s):  
Pooya Mahmoudian
Keyword(s):  
Fatigue Crack ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Applied Pressure ◽  
Design Procedure ◽  
Fatigue Loading ◽  
Crack Size ◽  
Initial Crack ◽  
Pressure Vessels

Currently, pressure vessels that operate in hydrogen service and subjected to fatigue must be designed using a defect tolerant design procedure. This means that first the fracture mechanics properties of the material being considered must be measured in hydrogen at the maximum service pressure. The properties are fatigue crack propagation properties and threshold stress intensity factor for hydrogen embrittlement (KIHE). With these properties, a fatigue crack propagation life can be estimated assuming an initial crack size and geometry and growing this defect to failure. The property measurements are costly and can only be performed at a few laboratories. Furthermore, the resulting lives are usually very short because of the assumed initial crack size. These things limit the application of this design method to lower cycle or static loading applications. This work introduces a cost-effective method of design and construction of pressure vessels for high cycle use in hydrogen service at pressures below 40,000 psi that eliminates the need for determining fracture mechanics properties in hydrogen environment. The method uses shrink fit construction of a liner inside a jacket. The method requires that when the pressure is applied, the magnitude of the resultant stress at the pressure boundary of the liner is more compressive than the magnitude of the applied pressure and the maximum allowed size of defect in the jacket at the interface between the jacket and the liner is such that when the cyclic stress is applied the resultant fatigue loading of that defect at that location to be less than the threshold value for growth of that defect.

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