Experimental Observations of Dominant Effective Short Fatigue Crack Behavior for Railway LZ50 Axle Steel

2010 ◽  
Vol 118-120 ◽  
pp. 54-58 ◽  
Author(s):  
Bing Yang ◽  
Yong Xiang Zhao
Keyword(s):  
Crack Initiation ◽  
Evolutionary Process ◽  
Crack Size ◽  
Short Crack ◽  
Structural Barriers ◽  
Banded Structure ◽  
Crack Behavior ◽  
Growing Crack ◽  
Two Stages ◽  
Hardness Values

, was experimentally investigated by a replica technique to seven smooth hourglass shaped specimens for railway LZ50 axle steel. Character of two-stages, i.e. the micro-structural short crack (MSC) stage and the physical short crack (PSC) stage, was revealed for the crack initiation and growth. Most importantly, the crack growth rate exhibited decelerations twice in MSC stage. This behavior was corresponding to the ferrite grain boundary firstly and then to the pearlite banded structure. The boundary appeared a barrier because there were pearlites around with significant higher micro-hardness values. The banded structure appeared a barrier because each band was rich in hard layered pearlites for the crack to cross. In PSC stage, the crack propagated with a decreasing resistance of micro-structural barriers as the crack length increased. The two barriers are inherent in the material and the crack initiation and growth are subjected to an evolutionary process under competition between the inherent resistances from the barriers and the increasing driving force from the growing crack size. This provides a prehensive understanding of the crack initiation and growth.

Study on the Influence of Strain Rate on Crack Initiation and Growth in Simulated Reactor Coolant Environment of Type 316 Stainless Steel

2018 ◽  
Author(s):  
Takahisa Nose ◽  
Takao Nakamura ◽  
Takanori Kitada
Keyword(s):  
Crack Initiation ◽  
Strain Rate ◽  
Nuclear Power ◽  
Power Plants ◽  
Fatigue Crack Initiation ◽  
Crack Size ◽  
Strain Rates ◽  
3 Dimensional ◽  
Reactor Coolant ◽  
Cumulative Fatigue Damage

In order to conduct effective and rational maintenance activity of components in nuclear power plants, it is proposed to manage fatigue degradation based on crack size corresponding to an extent of cumulative fatigue damage. The purpose of this study focuses on the influence of strain rate in simulated reactor coolant environment for fatigue crack initiation and growth. 3-dimensional replica observations were conducted for environmental fatigue test specimens in different strain rates. Crack initiation and growth were observed in the experiments. It is clarified that low strain rate influences crack propagation and coalescence and increases crack growth rate that finally decrease fatigue life.

Local Investigation of Microstructure-Induced Fatigue Damaging

2009 ◽  
Vol 417-418 ◽  
pp. 521-524
Author(s):  
Michael Marx ◽  
Wolfgang Schäf ◽  
Markus T. Welsch ◽  
Horst Vehoff
Keyword(s):  
Electron Microscope ◽  
Crack Initiation ◽  
Scanning Electron Microscope ◽  
Crack Propagation ◽  
Focused Ion Beam ◽  
Fatigue Cracks ◽  
Ion Beam ◽  
Short Crack ◽  
Beam Technique ◽  
Scanning Electron

From the emission of dislocations till short crack propagation fatigue is a local process determined by the microstructure. In this paper we present experiments based on refined applications of the scanning electron microscope and focused ion beam technique, which give detailed information about crack initiation and the interaction of short fatigue cracks with microstructural elements.

Damages Identification in the Cantilever-based on the Parameters of the Natural Oscillations

2016 ◽  
Vol 66 (1) ◽  
pp. 44 ◽  
Author(s):  
A. V. Cherpakov ◽  
A. N. Soloviev ◽  
V. V. Gritsenko ◽  
O. U. Goncharov
Keyword(s):  
Parametric Identification ◽  
Crack Size ◽  
Crack Identification ◽  
Natural Oscillations ◽  
Crack Location ◽  
Diagnostic Signs ◽  
Cantilever Construction ◽  
Two Stages ◽  
Local Extreme

<p>An approach to parametric identification of damages such as cracks in the rod cantilever construction is described. The identification method is based on analysis of shapes of the natural oscillations. The analytic modelling is performed in the Maple software on the base of the Euler-Bernoulli hypothesis. Crack is modelled by an elastic bending element. Transverse oscillations of the rod are considered. We take into account first four eigen modes of the oscillations. Parameters of amplitude, curvature and angle of bends of the waveforms are analysed. It was established that damage location is revealed by ‘kink’ on corresponding curves of the waveforms. The parameters of oscillation shapes are sensitive to the crack parameters in different degree. The novelty of the approach consists in that the identification procedure is divided into two stages: (a) it is determined the crack location, and (b) it is determined the crack size. Based on analytical modelling, an example of determination of dependence of the crack parameters on its size in the cantilever rod is presented. Study of features of the waveforms during identification of the fracture parameters shows that the features found in the form of ‘kinks’ and local extreme a of the angle between the tangent and curvature of waveforms for different modes of bending oscillations, define the crack location in cantilever. They can serve as one of diagnostic signs of crack identification and allow us to determine its location.</p><p><strong>Defence Science Journal, Vol. 66, No. 1, January 2016, pp. 44-50, DOI: http://dx.doi.org/10.14429/dsj.66.8182</strong></p><p> </p>

scholarly journals Short crack initiation and growth at 600°C in notched specimens of Inconel718

2003 ◽  
Vol 340 (1-2) ◽  
pp. 139-154 ◽  
Author(s):  
T Connolley ◽  
P.A.S Reed ◽  
M.J Starink
Keyword(s):  
Crack Initiation ◽  
Short Crack ◽  
Notched Specimens

A Probabilistic Micromechanical Code for Predicting Fatigue Life Variability: Model Development and Application

2005 ◽  
Vol 128 (4) ◽  
pp. 889-895 ◽  
Author(s):  
K. S. Chan ◽  
M. P. Enright
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Initiation ◽  
Crack Growth ◽  
Model Development ◽  
Fatigue Crack Initiation ◽  
Crack Size ◽  
Crack Initiation Life ◽  
Variability Model

This paper summarizes the development of a probabilistic micromechanical code for treating fatigue life variability resulting from material variations. Dubbed MICROFAVA (micromechanical fatigue variability), the code is based on a set of physics-based fatigue models that predict fatigue crack initiation life, fatigue crack growth life, fatigue limit, fatigue crack growth threshold, crack size at initiation, and fracture toughness. Using microstructure information as material input, the code is capable of predicting the average behavior and the confidence limits of the crack initiation and crack growth lives of structural alloys under LCF or HCF loading. This paper presents a summary of the development of the code and highlights applications of the model to predicting the effects of microstructure on the fatigue crack growth response and life variability of the α+β Ti-alloy Ti-6Al-4V.

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