An Approach to Predicting the Growth to Failure of Fatigue Cracks Subjected to Arbitrary Uniaxial Cyclic Loading

2009 ◽  
pp. 122-122-22 ◽  
Author(s):  
TR Brussat
Keyword(s):  
Cyclic Loading ◽  
Fatigue Cracks

scholarly journals Structural and mechanical defects of materials of offshore and onshore main gas pipelines after long-term operation

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Pavlo Maruschak ◽  
Sergey Panin ◽  
Iryna Danyliuk ◽  
Lyubomyr Poberezhnyi ◽  
Taras Pyrig ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Quantitative Analysis ◽  
Stress Concentration ◽  
Cyclic Loading ◽  
Fatigue Cracks ◽  
Preliminary Deformation ◽  
Term Operation ◽  
Steel Pipes

AbstractThe study has established the main regularities of a fatigue failure of offshore gas steel pipes installed using S-lay and J-lay methods.We have numerically analyzed the influence of preliminary deformation on the fatigue life of 09Mn2Si steel at different amplitudes of cyclic loading. The results have revealed the regularities of formation and development of a fatigue crack in 17Mn1Si steel after 40 years of underground operation. The quantitative analysis describes the regularities of occurrence and growth of fatigue cracks in the presence of a stress concentration.

Fatigue Testing of Large-Scale Models of Submarine Structural Details

1965 ◽  
Vol 2 (03) ◽  
pp. 299-307
Author(s):  
Frank W. Dunham
Keyword(s):  
Cyclic Loading ◽  
Large Scale ◽  
Fatigue Testing ◽  
Fatigue Cracks ◽  
Pressure Variation ◽  
Test Tank ◽  
Initiation And Propagation ◽  
Scale Models ◽  
Structural Details

The conversion of a 30-ft-dia test tank to a facility for subjecting large-scale models of submarine structural details to cyclic loading is described. By means of automatically controlled valves, models were subjected to a pressure variation simulating a submarine diving to its test depth and returning to the surface. The cyclic rate was slightly less than one per minute. The system was so designed that the test tank itself was not subjected to the pressure variations. Details of a series of models designed to simulate particular structural details of interest in recent submarine construction are described. Results of the tests to date are summarized, and several observations relative to the initiation and propagation of fatigue cracks in submarine structural details are presented.

Research on the Mechanism of Fatigue Crack Initiation of X60 Pipeline Steel after Per-Tension Deformation

2012 ◽  
Vol 197 ◽  
pp. 798-801
Author(s):  
Yu Rong Jiang ◽  
Mei Bao Chen
Keyword(s):  
Fatigue Crack ◽  
Cyclic Loading ◽  
Brittle Fracture ◽  
Crack Initiation ◽  
Pipeline Steel ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Fracture Characteristics ◽  
Metallic Inclusions ◽  
The Matrix

It is impossible to keep pipelines free from defects in the manufacturing, installation and servicing processes. In this paper, pre-tension deformation of X60 pipeline steel was employed to experimentally simulate the influence of dents and the mechanism of fatigue crack initiation of X60 pipeline steel after per-tension deformation under cyclic loading were investigated. The results indicate that the mechanism of fatigue crack initiation is the typical cleavage fracture characteristics and the cracks mainly initiates from the non-metallic inclusions which was the local brittle fracture materials such as MnS inclusion. With the pre-tension deformation increase, the yield strength of the matrix was increased and the toughness decreased due to the work-hardening effect. With the effects of the non-metallic inclusions larger, the fatigue cracks initiated from the non-metallic inclusions easier.

Characteristics of Fatigue Cracks Propagating in Different Directions of FSW Joints Made of 5754-H22 and 6082-T6 Alloys

2014 ◽  
Vol 794-796 ◽  
pp. 371-376 ◽  
Author(s):  
Ákos Meilinger ◽  
János Lukács
Keyword(s):  
Fatigue Crack ◽  
Cyclic Loading ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Welded Joints ◽  
Fatigue Cracks ◽  
Research Work ◽  
Friction Stir ◽  
Base Materials ◽  
Welding Processes

The Friction Stir Welding (FSW) is a dynamically developing version of the pressure welding processes. High-quality welded joints can be created using this process for different engineering applications (e. g. automotive parts). Nowadays, the knowing of the properties and the behaviour of the welded joints is an important direction of the investigations, especially under cyclic loading. The research work aimed to demonstrate the behaviour of the friction stir welded joints under cyclic loading conditions. Fatigue Crack Propagation (FCG) experiments were performed on 5754-H22 and 6082-T6 aluminium alloys and their friction stir welded joints. The CT type specimens were cut parallel and perpendicular to the characteristic directions of the base materials and the welded joints, and the notch locations in the specimens of welded joints were different, too. Therefore, the propagating cracks represent the possible directions of the fatigue cracks both on the base materials and on the welded joints. The results of the fatigue crack propagation tests on the welded joints clearly demonstrate the different characteristics of the thermo-mechanically affected zone (TMAZ), the heat affected zone (HAZ), and the advancing (AS) and retreating sides (RS) of the weld nugget (WN). The investigations and their results were compared with each other and with the results can be found in the literature.

Assessment of Constraint Effects on the Local Behaviour of a Propagating Crack Under Cyclic Loading

2012 ◽  
Author(s):  
M. R. Goldthorpe ◽  
A. H. Sherry
Keyword(s):  
Cyclic Loading ◽  
Best Practice ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Crack Tip ◽  
Element Model ◽  
Compact Tension ◽  
Stress Constraint ◽  
T Stress ◽  
Constraint Effects

During operation, reactor components experience a range of static and cyclic loading that have the potential to result in environmental-fatigue crack initiation and growth. Recent experimental work has indicated that the ASME XI fatigue ‘in air’ design curves are non-conservative for fatigue cracks propagating in primary water environments at fixed temperatures of relevance to the plant. The approach adopted to assess these tests has, to date, followed current best practice: in which global Linear Elastic Fracture Mechanics (LEFM) loading parameters are used to quantify crack growth rates. To help establish an improved understanding of these data, and to assist in their application to assess plant components, a local crack-tip finite element model has been developed. The model incorporates material constitutive behavior that simulates cyclic deformation of austenitic steel, can take account of plasticity-induced crack closure and can take into consideration cracks in structurally-representative geometries via the T-stress constraint parameter. The results of studies using the model suggest that highly compressive values of the T-stress constraint parameter tend to promote less severe reverse loading of the crack tip compared with high constraint geometries such as pre-cracked compact tension and bend test specimens. These findings indicate that rates of corrosion-fatigue in actual structural geometries might be different from those observed in pre-cracked test specimens.

Effect of Pre-Strain on Fatigue Behaviour of AZ31 Mg Alloy

2012 ◽  
Vol 706-709 ◽  
pp. 3052-3056
Author(s):  
Gao Feng Quan ◽  
Ying Bo Zhang ◽  
Zhao Ming Liu
Keyword(s):  
Fatigue Life ◽  
Cyclic Loading ◽  
Evaluation Method ◽  
Fatigue Cracks ◽  
Fatigue Property ◽  
Fatigue Behaviour ◽  
Sem Analysis ◽  
Fatigue Tests ◽  
Mg Alloys ◽  
Critical Feature

Mg Alloys Are the Lightest Structural Alloys with Excellent Castability and Machinability as Well as Highest Specific Strength and Stiffness. According to their Hexagonal close Packed Crystal Lattice there Is an Urgent Requirement of Mechanical Property Evaluation Method for Industrial Application, Particularly to Wrought Mg Alloys. Cyclic Loading Is a Very Popular Mode for Most Structural Application Situations. Recent Development of Fatigue Examination of Extruded Profile Has Shown that Mg Alloys Show Not so Ideal Fatigue Property. so that the Further Detailed Study on Cyclic Loading for Plastic Deformed Mg Alloys Is Needed. Tension-Tension Fatigue Tests Were Conducted on Pre-Strained AZ31 Mg Alloys that Produced by Rolling and Extruding Procedures. the Results Show that the Compressive Plastic Deformation Leads to Reduction of Fatigue Life/limit Significantly. SEM Analysis on Fatigue Fracture Surfaces Indicates that the Fatigue Cracks Initiate in the Surface or Sub-Surface of Dramatically Deformed Zones. the Microstructure Analysis Reveals that the Pre-Strain Brings More Abundant Twinning Bands with the Increase in Pre-Strain. the Decrease in Fatigue Life Demonstrates Also some Critical Feature with the Pre-Strain Level.

Fatigue of structural materials in corrosive environments

2020 ◽  
pp. 56-60
Author(s):  
G.V. Pachurin ◽  
A. A. Filippov ◽  
D. A. Goncharova ◽  
A.N. Kuzmin
Keyword(s):  
Cyclic Loading ◽  
Structural Material ◽  
Fatigue Cracks ◽  
Metals And Alloys ◽  
Corrosive Environment ◽  
Deflection Curve ◽  
Operation Conditions ◽  
Factors Influencing ◽  
Corrosive Environments ◽  
Selection Of

The factors influencing the fatigue failure of metals and alloys are investigated. To increase the resource and reliability of products made of metals and alloys, taking into account their operation conditions and the presence of a corrosive environment, when justifying the selection of a structural material, it is proposed to take into account its deflection curve under cyclic loading. Keywords: structural material, corrosive environment, fatigue resistance, fatigue cracks, deflection curve, cyclic loading, durability. [email protected]

The Qualification of BWR Steam Dryer Weldments Exposed to Cyclic Loading Using Finite Element Methods

2013 ◽  
Author(s):  
Michael R. Breach
Keyword(s):  
Finite Element ◽  
Cyclic Loading ◽  
Stress Field ◽  
Finite Element Methods ◽  
Fatigue Cracks ◽  
Failure Process ◽  
Peak Stress ◽  
Point Of View ◽  
Nominal Stress ◽  
Number Of Cycles

The qualification of welds other than full penetration groove welds exposed to cyclic loading using finite element methods requires an understanding of the basis behind classical methodologies. These methodologies usually address nominal stresses. The nominal stress (S-N) method was the first approach developed to try to understand this failure process and is still widely used in applications where the applied stress is nominally within the elastic range of the material and the number of cycles to failure is large. From this point of view, the nominal stress approach is best suited to that area of the fatigue process known as high cycle fatigue. Cracks and discontinuities will cause stress redistribution and concentrations leading to secondary and peak stresses additive to the nominal stress when referencing the S-N curves. Therefore, fundamental to the qualification of weldments of components and structures is the determination of the nominal stress field; however, this can be problematic for several reasons: • Secondary, Peak stress arising from structural discontinuities can mask the actual nominal stress field. • There may be an insufficient number of elements and/or integration points through the thickness to rely on linearization techniques, to separate the nominal stresses from the secondary and peak stresses due to the high cost of using bricks or tetrahedrons. • In complex shell structures, the nominal stress field in weldments that satisfies equilibrium against externally applied loads is not readily distinguished; this is due to the shear preponderance of mesh sensitive discontinuities. Herein, is a summary of methods to address the aforementioned problem and guidance in determining the true peak stresses and their qualification. Methods documented in ASME BPV Code Section VIII Div. 2, and various papers are compared. These methods will be used to assess existing methods that may be used in the industry. ASME BPV Code Section III Subsections NG and NB will be used as a basis to classify and qualify the weldment stresses.

scholarly journals Observations and modelling of non-proportional mixed mode cyclic loading

2019 ◽  
Vol 300 ◽  
pp. 01002
Author(s):  
Michael Vormwald
Keyword(s):  
Cyclic Loading ◽  
Mixed Mode ◽  
Normal Force ◽  
Fatigue Cracks ◽  
Influence Factors ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Mixed Mode Loading ◽  
Prediction Tools ◽  
Engineering Environment

Under non-proportional mixed-mode loading conditions at the crack tip, some observations are reported. They are limited to cases of cylindrical specimens under normal force and torsion. The fatigue cracks have been initiated by the same loading for which the crack growth behavior has been studied. The observations are discussed against the background of a variety of influence factors on non-proportional mixed mode growth. Finally, a couple of modeling approaches are listed which are – according to the nature or the problem – not yet developed for providing prediction tools in an engineering environment.

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