Atomistic Modeling of Fatigue Crack Growth in Magnesium Single Crystals Under Cyclic Loading

2009 ◽  
Author(s):  
Tian Tang ◽  
Sungho Kim ◽  
Sebastien Groh ◽  
Mark F. Horstemeyer
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Cyclic Loading ◽  
Fatigue Crack Growth ◽  
Boundary Conditions ◽  
Strain Rate ◽  
Crack Growth ◽  
Periodic Boundary ◽  
Periodic Boundary Conditions ◽  
Initial Crack

The fatigue crack propagation behavior of magnesium single crystal was analyzed using molecular dynamics simulation. The inter-atomic potential used in this investigation is Embedded Atom Method (EAM) potentials. The studies of the influences of crystal orientation and strain rate were perfomred using CC (center crack) and EC (edge crack) specimen. For CC specimen, the periodic boundary conditions were assigned in the x and z direction, while for EC specimen, only z direction was allowed periodic boundary conditions. In order to study the orientation dependence of fatigue crack growth mechanism, ten crystal orientations of initial crack, namely, orientation A-(12¯10) [101¯0], orientation B-(101¯0)[12¯10], orientation C-(101¯0)[0001], orientation D-(12¯10)[0001], orientation E-(0001)[101¯0], orientation F-(0001)[12¯10], orientation G (101¯1)[1¯012], orientation H (101¯1)[12¯10], orientation I (101¯2)[101¯1], and orientaton J (101¯2)[12¯10] were analyzed and the simulation results reveal that the fatigue crack growth rate and the crack path vary significantly with the crystallographic orientations of initial crack. The growth rate of orientaton G is the highest and the resistance of fatigue crack growth of orientation B is the highest. A CC specimen was employed to demonstrate the fatigue damage caused by pyramidal slip band under increased maximum strain cyclic loading in the specimen of orientation E. The analysis of the influences of strain rate was carried out on the orientation C, D, F, and G and the results revealed that the growth rate of fatigue crack decreasing with increasig strain rate. Fatigue growth rate can be expressed by da/dN = cΔCTOD, where the constant c was determined by the present atomistic simulations. The values of the constant c are large and vary widely from on orientation to another.

Automatic Fatigue Crack Growth

2009 ◽  
Author(s):  
S. C. Mellings ◽  
J. M. W. Baynham
Keyword(s):  
Fatigue Crack ◽  
Cyclic Loading ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Initial Crack ◽  
Design Stage ◽  
Load Spectrum ◽  
Forensic Investigations ◽  
Crack Faces

One of the critical requirements of fatigue crack growth simulation is calculation of the remaining life of a structure under cyclic loading. This paper presents a method which predicts the remaining fatigue life of a part, and gives information on the eventual mode of failure. The path of a growing crack needs to be understood so that informed assessment can be made of the structural consequences of eventual fast growth, and the likelihood of leakage and determination of leakage rates. For these reasons the use of standard handbook solutions for crack growth is generally not adequate, and it is essential to use the real geometry and loading. The reasons for performing such simulation work include preventive investigations performed at the design stage, forensic investigations performed after failure, and sometimes forensic investigations performed during failure-when the results provide input to the planning of remedial work. This paper focuses on the 3D simulation of cracks growing in metal structures exposed to cyclic loading, and explains the techniques which are used. The loading might arise from transients of pressure or other mechanical forces, or might be caused by thermal-stress variations. The simulation starts from an initial crack which can be of any size and orientation. The relevant geometry of the cracked component is modelled, and the loading is identified using one or more load cases together with a load spectrum which shows how the loading cycles. The effects of the crack are determined by calculating stress intensity factors at all positions along the crack front (it would be called the crack tip if the modelling was performed in 2D). The rate and direction of crack growth at each part of the crack front are calculated using one of the available crack growth laws, together with appropriate material properties. The effects of such growth are accumulated over a number of load cycles, and a new crack shape is determined. The process is repeated as required. The use of multi-axial and mixed mode techniques allows the crack to turn as a result of the applied loading, and the resulting crack path is therefore a consequence of both the detail of the geometry and the loading to which the structure is subjected. Gas or other fluid pressures acting on the crack faces can have significant impact, as can the contact between opposing crack faces when a load case causes part of the crack to close.

Fatigue Crack Growth Rate of Reeled Pipe in Sour Environments

2015 ◽  
Author(s):  
Javad Safari ◽  
Ramgopal Thodla ◽  
Ian Merchant ◽  
John Hamilton
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Cyclic Loading ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Paris Law ◽  
Number Of Cycles ◽  
Corrosive Environments

Fatigue Crack Growth Rate (FCGR) of reeled pipe (strained & aged) in sour environments was investigated. FCGR frequency scans on different microstructures, i.e. heat affected zone (HAZ), and weld center line (WCL), revealed that, FCGR in corrosive environments increased with decreasing frequency and reached a plateau value at low frequencies of 10mHz to 3mHz. At these ‘plateau frequencies’, FCGR in the moderately sour environment that was investigated were found to be about 10–18× or 30× higher than the in-air values for the WCL and HAZ, respectively. There was no effect of the reeling cycles on the FCGR of the WCL or HAZ specimens. The FCGRs of the WCL were consistently lower than that of the HAZ by about a factor of 2–3× under various conditions. The reason for the lower FCGR of the WCL is not well understood. It is possible that it may be due to the higher yield strength (YS) of the overmatched welds, differing hydrogen concentration and/or diffusion coefficient or possibly due to the differences in the microstructure between the HAZ and WCL. Paris law curves, FCGRs as a function of ΔK (stress intensity factor range), were measured on the HAZ, and WCL (both intrados) at the plateau frequency (10mHz), representative of flowline cyclic loading. They were also measured at a higher frequency of 0.33Hz, representative of Steel Catenary Risers (SCR) cyclic loading associated with wave motion. Comparisons of measured Paris law curves in corrosive environments to those in air were consistent with the results of the frequency scans. There was no effect of number of cycles of reeling on the Paris law curves in the sour environment tested for WCL and HAZ specimens at both the plateau frequency and 0.33Hz. The results of the test program suggest FCGR of WCL and HAZ in the sour environment tested are not affected by number of cycles (up to 5) of straining on the intrados side for the strain level (1.93% per cycle) used in this study.

scholarly journals Fatigue Crack Growth Rate, Microstructure and Mechanical Properties of Diverse Range of Aluminum Alloy: a Comparison

2020 ◽  
Vol 22 (1) ◽  
pp. 329-340 ◽  
Author(s):  
Abdessamad Brahami ◽  
Benattou Bouchouicha ◽  
Mokhtar Zemri ◽  
Jamal Fajoui
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Microstructural Analysis ◽  
Initial Crack ◽  
Diverse Range ◽  
Secondary Element

AbstractIn practice for all metallic materials, damage by fatigue usually takes in two steps, the appearance of an initial crack which then grows as a function of the present microstructure. The objective of this study is to identify the elements influencing the fatigue crack growth rate on aluminum alloys of different microstructures. Characterization tests and microstructural analysis on 2024-T3, 5083-H22, 6082-T6 and 7075-T6 shades have been carried out. Based on the experimental results obtained, AA7075-T6 has the best fatigue crack rate resistance which is explained by its behavior as well as the nature and dispersive distribution of the secondary element.

scholarly journals Fatigue Crack Growth Under General-Yielding Cyclic-Loading

1986 ◽  
Vol 108 (3) ◽  
pp. 201-205 ◽  
Author(s):  
Zheng Minzhong ◽  
H. W. Liu
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Cyclic Loading ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
The Finite Element Method ◽  
General Yielding

In low cycle fatigue, cracks are initiated and propagated under general-yielding cyclic-loading. For general-yielding cyclic-loading, Dowling and Begley have shown that fatigue crack growth rate correlates well with the measured ΔJ. The correlation of da/dN with ΔJ has also been studied by a number of other investigators. However, none of these studies has correlated da/dN with ΔJ calculated specifically for the test specimens. Solomon measured fatigue crack growth in specimens in general-yielding cyclic-loading. The crack tip fields for Solomon’s specimens are calculated, using the finite element method, and the J-values of Solomon’s tests are evaluated. The measured crack growth rate in Solomon’s specimens correlates very well with the calculated ΔJ.

Evaluation of Crack Growth of Ni-Base Alloys Under Long Term Cyclic Loading in BWR Environment

2015 ◽  
Author(s):  
Masao Itatani ◽  
Takuya Ogawa
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Cyclic Loading ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Weld Metal ◽  
Crack Growth ◽  
Base Metal ◽  
Test Data

Crack growth test data of Ni-base alloys under cyclic loading in simulated boiling water reactor (BWR) environment including the effects of load rising time (tr) were evaluated in the view points of both fatigue and stress corrosion cracking (SCC). When the test data were plotted in the relationship between da/dt and Kmax, da/dt monotonically decreased with increasing tr and the stress ratio (R). For alloy 182 weld metal under short tr and/or low R, the crack growth rate assuming SCC is much lower than those of the test data. For alloy 182 under tr = 30 and 1000 s at R = 0.8, the crack growth rate assuming SCC almost coincided with test data. For heat affected zone (HAZ) of alloy 600 base metal (600HAZ), the crack growth rate assuming SCC had much different slope of da/dN-ΔK relationship compared with the test data in the tested range of tr up to 3000 s. From these observations, the contribution of SCC is relatively small and the main mechanism of crack growth is thought to be fatigue for the tested range (tr=1 to 1000 s for weld metal, tr=1 to 3000 s for base metal and R = 0.1 to 0.8). It was assured that the fatigue crack growth formula proposed by the authors accounts the effect of SCC adequately at long tr. Additionally, the applicability of the fatigue crack growth rate formula for austenitic stainless steels to the long term cyclic load was investigated and it was found that the formula can be applied to tr=30000 s.

Fatigue Crack Growth Rate, Microstructure and Mechanical Properties of Diverse Range of Aluminum Alloy: A Comparison

2020 ◽  
Vol 22 (4) ◽  
pp. 1453-1462
Author(s):  
Abdessamad Brahami ◽  
Benattou Bouchouicha ◽  
Mokhtar Zemri ◽  
Jamal Fajoui
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Microstructural Analysis ◽  
Initial Crack ◽  
Diverse Range ◽  
Secondary Element

AbstractIn practice for all metallic materials, damage by fatigue usually takes in two steps, the appearance of an initial crack which then grows as a function of the present microstructure. The objective of this study is to identify the elements influencing the fatigue crack growth rate on aluminum alloys of different microstructures. Characterization tests and microstructural analysis on 2024-T3, 5083-H22, 6082-T6 and 7075-T6 shades have been carried out. Based on the experimental results obtained, AA7075-T6 has the best fatigue crack rate resistance which is explained by its behavior as well as the nature and dispersive distribution of the secondary element.

Acoustic Fatigue Crack Growth Prediction in Coupled Air Structures

2010 ◽  
Vol 452-453 ◽  
pp. 293-296
Author(s):  
Hossein Hosseini-Toudeshky ◽  
M. Karimi ◽  
Bijan Mohammadi
Keyword(s):  
Finite Element Method ◽  
Growth Rate ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Initial Crack ◽  
Structure Modeling ◽  
Length Increment ◽  
Thin Walled ◽  
Acoustic Fatigue

In this paper, crack growth of thin-walled cylinders containing an initial crack under acoustic plane wave is analyzed. A coupled air-structure modeling is considered for the analyses. For this purpose, a methodology for computational modeling of the fatigue crack growth in cracked cylinders using finite element method is presented. Effects of various parameters such as crack length increment and boundary conditions on the crack growth rate are investigated.

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