scholarly journals Microstructurally small fatigue crack initiation behavior of fine and coarse grain simulated heat-affected zone microstructures in low carbon steels

2021 ◽  
Author(s):  
Hide-aki Nishikawa ◽  
Yoshiyuki Furuya ◽  
Manabu Enoki ◽  
Manabu Enoki
Keyword(s):  
Grain Size ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Initiation ◽  
Fatigue Crack Initiation ◽  
Coarse Grain ◽  
Shear Mode ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Prior Austenite Grain Size

Successive observation of fatigue crack initiation process was conducted on six types of thermally simulated HAZ microstructures to clarify the physical significance of fatigue life difference between coarse grain (CG) and fine grain (FG) heat-affected zone (HAZ) microstructures. The results showed the fatigue life-decreasing mechanism in the CGHAZ to be successfully explained by acceleration of the shear mode fatigue crack growth rate provided the crack is smaller than the prior austenite grain size, based on the following experimental results. In other words, the fatigue cracks initiated along the shear stress plane. In addition, the prior austenite grain size of crack initiation life with the FG and CGHAZ were comparable, since the shear mode fatigue crack growth rate of the CGHAZ was faster than that of the FGHAZ. As a result, the remaining fatigue life after the grain size crack initiation of the CGHAZ become shorter than that of the FGHAZ as a function of grain size difference.

scholarly journals A New Systematic Approach Based on Dilatometric Analysis to Track Bainite Transformation Kinetics and the Influence of the Prior Austenite Grain Size

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 324
Author(s):  
David San-Martin ◽  
Matthias Kuntz ◽  
Francisca G. Caballero ◽  
Carlos Garcia-Mateo
Keyword(s):  
Heat Treatment ◽  
Grain Size ◽  
Prior Austenite ◽  
Bainitic Transformation ◽  
Transformation Rate ◽  
Transformation Kinetics ◽  
Austenite Grain Size ◽  
Austenite Grain ◽  
Prior Austenite Grain Size ◽  
Prior Austenite Grain

This investigation explores the influence of the austenitisation heat treatment and thus, of the prior austenite grain size (PAGS), on the kinetics of the bainitic transformation, using as A case study two high-carbon, high-silicon, bainitic steels isothermally transformed (TIso = 250, 300, 350 °C), after being austenised at different temperatures (γTγ = 925–1125 °C). A methodology, based on the three defining dilatometric parameters extracted from the derivative of the relative change in length, was proposed to analyse the transformation kinetics. These parameters are related to the time to start bainitic transformation, the time lapse for most of the transformation to take place and the transformation rate at the end of the transformation. The results show that increasing the PAGS up to 70 µm leads to an increase in the bainite nucleation rate, this effect being more pronounced for the lowest TIso. However, the overall transformation kinetics seems to be weakly affected by the applied heat treatment (γTγ and TIso). In one of the steels, PAGS > 70 µm (γTγ > 1050 °C), which weakly affects the progress of the transformation, except for TIso = 250 °C, for which the enhancement of the autocatalytic effect could be the reason behind an acceleration of the overall transformation.

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.

scholarly journals A fatigue crack initiation and growth life estimation method in single-bolted connections

2019 ◽  
Vol 54 (2) ◽  
pp. 79-94 ◽  
Author(s):  
Arash P Jirandehi ◽  
TN Chakherlou
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Crack Initiation ◽  
Multiaxial Fatigue ◽  
Estimation Accuracy ◽  
Life Estimation ◽  
Lower Error ◽  
Fatigue Life Estimation

Fatigue life estimation accuracy of mechanical parts and assemblies has always been the source of concern in different industries. The main contribution of this article lies in a study on the accuracy of different multiaxial fatigue criteria, proposing and investigating the accuracy of four optimized fatigue crack initiation life estimation methods—volume, weighted volume, surface and point, thereby improving the multiaxial fatigue life estimation accuracy. In order to achieve the goal, the fatigue lives of bolt clamped specimens, previously tested under defined experimental conditions, were estimated during fatigue crack initiation and fatigue crack growth and then summed together. In the fatigue crack initiation part, a code was written and used in the MATLAB software environment based on critical plane approach and the different multiaxial fatigue criteria. Besides the AFGROW software was utilized to estimate the crack growth share of fatigue life. Experimental and numerical results showed to be in agreement. Furthermore, detailed study and comparison of the results with the available experimental data showed that a combination of Smith–Watson–Topper approach and volume method results in lower error values, while a combination of Fatemi–Socie criterion and surface or point method presents estimated lives with lower error values. In addition, the numerical proposed procedure resulted in a good prediction of the location of fatigue crack initiation.

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