Setup for studying the kinetics of crack growth in cyclic bending tests

2020 ◽  
Vol 86 (7) ◽  
pp. 59-64
Author(s):  
V. N. Pustovoit ◽  
S. A. Grishin ◽  
V. V. Duka ◽  
V. V. Fedosov
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Fatigue Tests ◽  
Computer Processing ◽  
Crack Development ◽  
Potential Difference ◽  
Fatigue Crack Development ◽  
Kinetics Of

The goal of the study is analysis of the features of fatigue cyclic fracture of steels. An installation has been designed to induce fatigue cracks and to study the kinetics of fatigue crack development. Crack growth is recorded by the method of potential difference. The data on the crack growth kinetics were processed on a computer using LGraph2 programs and Excel spreadsheets. When studying the kinetics of the fatigue crack development, the electrodes were soldered to the edges of the initial notch of the sample and time dependence of the potential difference was recorded on a computer during crack growth. To interpret the experimental data, a calibration chart in the coordinates «potential difference (U) – the crack length (Lcr)» constructed on the basis of the millivoltmeter readings was used, with due regard for the size of the sample section, current flow and length of the fatigue crack. Cyclic loading of the sample resulted in a stepwise character of the crack growth: first occurred zone of plastic deformation of the metal is then followed by accumulation of stresses of a certain size, their relaxation in the form of a crack and sudden crack growth. An abrupt crack growth is clearly visible on a graph of the fatigue crack growth rate obtained upon computer processing of experimental data. Using a graphical editor KOMPAS, a graph was constructed which characterized the growth of the fatigue crack against the number of cycles of fatigue tests for bending. The experimental setup provides the possibility of fatigue crack formation for impact tests, determination of the work of crack propagation, as well as studying of the kinetics of crack development and computer processing of experimental data.

A Method for the Analysis of the Growth of Short Fatigue Cracks

1995 ◽  
Vol 117 (4) ◽  
pp. 408-411 ◽  
Author(s):  
A. J. McEvily ◽  
Y.-S. Shin
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Material Constant ◽  
Plastic Zone Size ◽  
Surface Cracks ◽  
Zone Size ◽  
Short Cracks

A method for the analysis of the fatigue crack growth rate for short cracks has been developed and is applied to the case of fatigue crack growth of short surface cracks in a 1045 carbon steel. The method entails three modifications to standard LEFM procedures. These modifications include the use of a material constant to bridge between smooth and cracked specimen behavior, consideration of the plastic zone size to crack length ratio, and incorporation of the development of crack closure. Comparisons are made between calculations based upon this approach and experimental data.

Fatigue crack growth at stress concentrators under spectrum loading

2005 ◽  
Vol 40 (2) ◽  
pp. 117-127
Author(s):  
R. V Prakash
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Crack Growth ◽  
Surface Defects ◽  
Fatigue Cracks ◽  
Mapping Technique ◽  
Critical Dimensions ◽  
Small Cracks ◽  
Stress Raisers ◽  
Kinetics Of

Fatigue cracks initiate at stress raisers such as notches, discontinuities, and surface defects. Many of the field failures that indicate the presence of a fatigue crack at failure can be traced to crack initiation from one or more crack initiation sites and merger of cracks over a period of service. Substantial service life is spent in the growth of small cracks from an initial size of few micrometres before they coalesce and grow to critical dimensions that cause fracture. This paper summarizes research that was carried out in order to understand the kinetics of crack growth of small cracks at notches under simulated FALSTAFF service loading. This paper also presents a method used to understand crack growth kinetics in a pin-loaded lug joint through a crack-front-mapping technique.

Methodical approach for studying kinetics of short and long fatigue cracks growth for irradiated reactor materials. Part 1. Statement of problem. The effect of the initial notch acuity on the fatigue crack rate on small-sized specimens

2019 ◽  
pp. 191-204 ◽  
Author(s):  
V. I. Smirnov ◽  
A. J. Minkin ◽  
B. Z. Margolin ◽  
V. I. Kokhonov
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth ◽  
Growth Kinetics ◽  
Fatigue Cracks ◽  
Stress Concentration Zone ◽  
Concentration Zone ◽  
Methodical Approach ◽  
Reactor Materials ◽  
Kinetics Of

The paper considers methodical issues in the experimental research of fatigue crack growth kinetics when testing irradiated small-sized specimens. The effect of the initial notch acuity is studied on the long crack growth rate. The stress concentration zone sizes are estimated for notches of various types. A brif literature review of the main problems in the study of the growth kinetics of short fatigue cracks has been performed. The tasks of further research are formulated. 

PREDICTION FOR FATIGUE CRACK GROWTH IN NOTCHED PLATES

2012 ◽  
Vol 06 ◽  
pp. 269-274
Author(s):  
K. SHOJIMA ◽  
K. YANASE ◽  
M. ENDO
Keyword(s):  
Fatigue Crack ◽  
Fatigue Strength ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Cracks ◽  
Fatigue Tests ◽  
Crack Growth Behavior ◽  
Plastic Behavior ◽  
Short Cracks ◽  
Major Factors

The notch is usually unavoidable in designing various mechanical components. As well known, those notches significantly influence the fatigue life and fatigue strength of materials. In addition, most fatigue cracks spend the vast majority of their lives as short cracks, and the behavior of such flaw is of significant importance in determining the fatigue lifetime of notched components. Correspondingly, in this research, we investigate the fatigue crack growth behavior and fatigue strength of notched plates. For the proposed method, the elastic-plastic behavior, the Kitagawa effect and the crack closure are taken into account as the major factors responsible for the peculiar behavior of small fatigue cracks emanating from notches. Regarding the experiment, the fatigue tests were conducted using the plates with a circular notch under uniaxial loading condition. The proposed approach is validated by comparing the predicted results to the experimental data.

Evaluation of the threshold for the development of fatigue cracks in a railway steel under harmonic and operational loading

2021 ◽  
Vol 87 (12) ◽  
pp. 42-47
Author(s):  
S. G. Lebedinsky ◽  
O. V. Naumov
Keyword(s):  
Fatigue Crack ◽  
Fatigue Fracture ◽  
Fatigue Cracks ◽  
Crack Opening ◽  
Experimental Studies ◽  
Crack Development ◽  
Railway Track ◽  
Harmonic Loading ◽  
Loading Process ◽  
Fatigue Crack Development

The results of experimental studies of the fatigue crack development in 20GFL steel specimens cut from a cast bolster of a freight car are presented. The ratio of the threshold stress intensity coefficient Kth determined from the kinetic diagram of fatigue fracture and from the average parameters of the operational loading process is considered using the experimental results with a simulation of operational loading. Tests were carried out upon the development of permanent blocks of crack opening in the specimen (in a rigid loading mode). The operational process is presented in the form of a block of consecutive loading cycles recorded during the test of the car frame in conditions typical for a straight section of the railway track. The threshold operational level is determined by the algorithm of gradual reduction of the loading similar to the original process. The regularities in a decrease of the rate of crack development and corresponding decrease in the load were determined. Subsequent extrapolation of the obtained experimental regularities to zero value of the crack propagation rate provided estimation of the threshold loading level, similar to the initially specified value. It is shown that the value of the threshold level of the fatigue crack development in low-alloy steel 20GFL obtained from the fatigue fracture diagram (i.e., under harmonic loading) is significantly higher than that obtained from the estimate based on the average values of the operational loading process. The considered model of operational loading gives greater damage compared to harmonic loading, on the basis of which the survivability of structural elements is usually assessed.

Guided Wave Acoustic Emission from Fatigue Crack Growth in Aluminium Plate

2006 ◽  
Vol 13-14 ◽  
pp. 23-28 ◽  
Author(s):  
C.K. Lee ◽  
Jonathan J. Scholey ◽  
Paul D. Wilcox ◽  
M.R. Wisnom ◽  
Michael I. Friswell ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Elastic Waves ◽  
Fatigue Cracks ◽  
Guided Wave ◽  
Experimental Results ◽  
Multiple Reflections ◽  
Alloy Plate

Acoustic emission (AE) testing is an increasingly popular technique used for nondestructive evaluation (NDE). It has been used to detect and locate defects such as fatigue cracks in real structures. The monitoring of fatigue cracks in plate-like structures is critical for aerospace industries. Much research has been conducted to characterize and provide quantitative understanding of the source of emission on small specimens. It is difficult to extend these results to real structures as most of the experiments are restricted by the geometric effects from the specimens. The aim of this work is to provide a characterization of elastic waves emanating from fatigue cracks in plate-like structures. Fatigue crack growth is initiated in large 6082 T6 aluminium alloy plate specimens subjected to fatigue loading in the laboratory. A large specimen is utilized to eliminate multiple reflections from edges. The signals were recorded using both resonant and nonresonant transducers attached to the surface of the alloy specimens. The distances between the damage feature and sensors are located far enough apart in order to obtain good separation of guided-wave modes. Large numbers of AE signals are detected with active fatigue crack propagation during the experiment. Analysis of experimental results from multiple crack growth events are used to characterize the elastic waves. Experimental results are compared with finite element predictions to examine the mechanism of AE generation at the crack tip.

Effect of Processing Layer on Fatigue Strength of Extruded AZ61 Magnesium Alloy

2013 ◽  
Vol 577-578 ◽  
pp. 429-432 ◽  
Author(s):  
Yukio Miyashita ◽  
Kyohei Kushihata ◽  
Toshifumi Kakiuchi ◽  
Mitsuhiro Kiyohara
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Magnesium Alloy ◽  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Crack Initiation ◽  
Fatigue Tests ◽  
Crack Growth Resistance ◽  
Az61 Magnesium Alloy

Fatigue Property of an Extruded AZ61 Magnesium Alloy with the Processing Layer Introduced by Machining was Investigated. Rotating Bending Fatigue Tests were Carried out with the Specimen with and without the Processing Layer. According to Results of the Fatigue Tests, Fatigue Life Significantly Increased by Introducing the Processing Layer to the Specimen Surface. Fatigue Crack Initiation and Propagation Behaviors were Observed by Replication Technique during the Fatigue Test. Fatigue Crack Initiation Life of the Specimen with the Processing Layer was Slightly Longer than that of the Specimen without the Processing Layer. Higher Fatigue Crack Growth Resistance was also Observed when the Fatigue Crack was Growing in the Processing Layer in the Specimen with the Processing Layer. the Longer Fatigue Life Observed in the Fatigue Test in the Specimen with the Processing Layer could be Mainly due to the Higher Crack Growth Resistance. it is Speculated that the Fatigue Strength can be Controlled by Change in Condition of Machining Process. it could be Effective way in Industry to Improved Fatigue Strength only by the Cutting Process without Additional Surface Treatment Process.

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