Dynamic Behavior to Fatigue Crack Initiation of a Glass/Epoxy Laminate

2013 ◽  
Vol 577-578 ◽  
pp. 677-680
Author(s):  
S. Lecheb ◽  
A. Nour ◽  
A. Chellil ◽  
R. Lechani ◽  
H. Kebir
Keyword(s):  
Crack Initiation ◽  
Cyclic Load ◽  
Fatigue Testing ◽  
Fatigue Crack Initiation ◽  
Laminate Plate ◽  
Mode Shapes ◽  
Element Analysis ◽  
Plate Specimen ◽  
Initiation Condition ◽  
Fast Fracture

This paper based to study of the dynamic and fatigue behaviors with numerical and experimental parts of a composite material manufactured by stacking two layers of E-glass fiber in different angle orientations (0°/90°) immersed in polyester resin with total thickness 1.39mm. In Finite Element Analysis (FEA) using ABAQUS was used to evaluate the maximal (displacement, strain and stress) and the natural frequencies (mode shapes) of composite behavior under crack initiation condition. In the experimental part the laminate plate specimen with two layers is tested under one types of cyclic load in fully reversible tensile at (R=0), the fast fracture occur phenomenon and the fatigue life are presented , the fatigue testing exerted in INSTRON 8801 machine.

Thermal Fatigue Testing and Analysis of a Thick Perforated Ring

2007 ◽  
Author(s):  
T. M. Damiani ◽  
J. E. Holliday ◽  
M. J. Zechmeister ◽  
R. D. Reinheimer ◽  
D. P. Jones
Keyword(s):  
Crack Initiation ◽  
Thermal Fatigue ◽  
Fatigue Testing ◽  
Fatigue Crack Initiation ◽  
Three Dimensional ◽  
Fatigue Cracking ◽  
Forced Flow ◽  
Test Loop ◽  
Rapid Changes ◽  
Oxygenated Water

Thermal fatigue cracking has been observed for thick perforated spacer rings used as part of a thermal fatigue test loop operating at Bechtel Bettis, Inc. The perforated rings are used for instrumentation access to the fluid flow at the test specimen inlet and outlet, and are subject to alternating hot and cold forced flow, low oxygenated water every three minutes so that rapid changes in water temperature impart a thermal shock event to the inner wall of the rings. Thermal and structural three dimensional elastic and elastic-plastic finite element analyses (FEA) were conducted for the ring and the results used to predict fatigue crack initiation using strain-based fatigue-life algorithms. Predicted cycles-to-crack initiation agreed well with the observed cracking when alternating shear strain intensity analogous to the Tresca stress was used. This analysis qualifies the use of FEA for thermal fatigue assessments of complicated three-dimensional components.

scholarly journals Fatigue behaviour of corrosion pits in X65 steel pipelines

2018 ◽  
Vol 233 (5) ◽  
pp. 1771-1782 ◽  
Author(s):  
Farnoosh Farhad ◽  
Xiang Zhang ◽  
David Smyth-Boyle
Keyword(s):  
Finite Element ◽  
Crack Initiation ◽  
Stress Ratio ◽  
Fatigue Crack Initiation ◽  
Local Stress ◽  
Fatigue Behaviour ◽  
Stress And Strain ◽  
Element Analysis ◽  
X65 Steel ◽  
Corrosion Pits

Corrosion pits are a form of geometrical discontinuity that lead to stress and strain concentration in engineering components, resulting in crack initiation under service loading conditions and ultimately fracture and failure. Initiation and propagation of cracks in offshore pipelines can lead to loss of containment and environmental and commercial impacts. In order to prevent such failures, tools to predict the structural integrity of pipelines need to be improved. This work investigates the fatigue behaviour of corrosion pits in API-5L X65 grade steel pipeline utilising numerical and analytical methods. Firstly, load-controlled fatigue tests were carried out on smooth X65 steel samples to establish S–N data. Secondly, local stress–strain behaviour at corrosion pits and its effect on fatigue crack initiation were investigated using elastic-plastic finite element analysis of samples containing a single corrosion pit under cyclic loading. Analysis of stabilised stress–strain hysteresis loops at corrosion pits showed that the local stress ratio at the pit changes from 0.1 to −0.4 while the applied stress amplitude increases with the same stress ratio of 0.1. Analytical methods were also used to predict the local maximum stress and strain at the pit, which showed a similar local stress ratio to the finite element analysis result but lower stress and strain ranges. Finally, fatigue crack initiation life was predicted using the combination of finite element stress and strain analysis and the Smith–Watson–Topper strain–life approach. An advantage of this method for life estimation is that this approach considers the local stress and strains at corrosion pits rather than applied stress.

scholarly journals Fatigue crack initiation and propagation of 100Cr6 steel under torsional loading in very high cycle regime

2018 ◽  
Vol 165 ◽  
pp. 20003
Author(s):  
Hongqian Xue ◽  
Tao Gao ◽  
Zhidan Sun ◽  
Xianjie Zhang
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Fatigue Testing ◽  
Fatigue Cracks ◽  
Maximum Shear Stress ◽  
Testing Machine ◽  
Fatigue Crack Initiation ◽  
Longitudinal Direction ◽  
Torsional Fatigue ◽  
Very High

Cyclic torsional fatigue properties of a high strength steel 100Cr6 are investigated using an ultrasonic torsional fatigue testing machine, and the results are compared with those obtained with fatigue tests under axial loading. Fatigue crack initiation and growth under torsion loading are observed in the very high cycle regime. Results show that fatigue cracks initiated from specimen surface as well as subsurface inclusions under torsion loading. However, subsurface MnS inclusions play a dominant role in crack initiation under torsion loading in the very high cycle regime. The initiation and early propagation of fatigue cracks are mostly controlled by the direction of the maximum shear stress. For surface crack initiation, cracks initiated in parallel to the longitudinal direction of the specimens. Once the shear crack propagated to a crack length of about 20-30 μm, crack branched to the angle close to the direction perpendicular to the remote maximum principal stresses. As for the subsurface fatigue crack initiation, the cracks parallel to the longitudinal direction of the specimens could not be observed, and crack propagation followed a spiral shape on a plane with an orientation of 45° with respect to the loading direction, which corresponds to the maximum principal stress plane.

Damage Evaluation of Ferrite and Ferrite-Pearlite Steel during Fatigue Crack Initiation by EBSD

2014 ◽  
Vol 891-892 ◽  
pp. 410-415 ◽  
Author(s):  
Mamoru Hayakawa ◽  
Masayuki Wakita ◽  
Eisuke Nakayama
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Fatigue Testing ◽  
Electron Backscatter Diffraction ◽  
Fatigue Crack Initiation ◽  
Ferrite Matrix ◽  
Fatigue Tests ◽  
Before And After ◽  
Ferrite Steel ◽  
Orientation Deviation

Orientation changes during fatigue crack initiation in ferrite and ferritepearlite steel were evaluated by electron backscatter diffraction (EBSD). Ferrite steel with different grain sizes and ferritepearlite steel with different carbon contents were prepared. EBSD measurements and fatigue tests were alternately performed using a small specimen. The tests on both ferrite and ferritepearlite steel suggest that the initial cracks were observed in the ferrite matrix. Thus, crystal rotation induced by fatigue in ferrite matrix is quantitatively evaluated by two misorientation parameters: grain reference orientation deviation, which is the misorientation between measuring points and the average orientation in each grain, and crystal misorientation at the same point before and after fatigue testing.

Investigating the effect of cold expansion process on the fatigue behavior of aluminum alloy 7075-T6 in double-lap shear joints

2018 ◽  
Vol 233 (8) ◽  
pp. 1645-1660 ◽  
Author(s):  
Z Emami Geiglou ◽  
TN Chakherlou
Keyword(s):  
Finite Element ◽  
Aluminum Alloy ◽  
Crack Initiation ◽  
Fatigue Behavior ◽  
Fatigue Crack Initiation ◽  
Angular Position ◽  
Expansion Process ◽  
Element Analysis ◽  
Cold Expansion ◽  
Lap Shear

In this paper, the effect of cold expansion process on the fatigue behavior of 7075-T6 aluminum alloy has been investigated both by numerical modeling and conducting experimental tests. In the experimental part, one batch of the specimens without cold expansion and two other batches after being subjected to cold expansions of 1.5% and 4.7% were subjected to cyclic loading in a double-lap shear joint. In the numerical part, finite element simulations of the cold expansion process and loading of the joint were performed and the effect of this process on the stress distribution and the location of the critical zone of the fatigue crack initiation were surveyed. Tangential stresses at different angles around the hole were extracted from the finite element analysis, and after determining the angular position of the surfaces with maximum stresses, crack initiation location in the thickness direction is predicted with an acceptable approximation. The S–N diagrams obtained from the experiments show that the cold expansion process increases fatigue life, and this increase is much more pronounced in lower loads. Also by increasing the percentage of cold expansion from 1.5% to 4.7%, this increase is more appreciable.

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