scholarly journals Crack Initiation and Propagation Fatigue Life of Ultra High-Strength Steel Butt Joints

2019 ◽  
Vol 9 (21) ◽  
pp. 4590 ◽  
Author(s):  
Markus J. Ottersböck ◽  
Martin Leitner ◽  
Michael Stoschka ◽  
Wilhelm Maurer
Keyword(s):  
Fatigue Life ◽  
Crack Initiation ◽  
Welded Joints ◽  
High Strength Steel ◽  
High Strength ◽  
Crack Initiation And Propagation ◽  
Butt Joints ◽  
Fatigue Assessment ◽  
Initiation And Propagation ◽  
Ultra High Strength Steel

The division of the total fatigue life into different stages such as crack initiation and propagation is an important issue in regard to an improved fatigue assessment especially for high-strength welded joints. The transition between these stages is fluent, whereas the threshold between the two phases is referred to as technical crack initiation. This work presents a procedure to track crack initiation and propagation during fatigue tests of ultra high-strength steel welded joints. The method utilizes digital image correlation to calculate a distortion field of the specimens’ surface enabling the identification and measurement of cracks along the weld toe arising during the fatigue test. Hence, technical crack initiation of each specimen can be derived. An evaluation for ten ultra high-strength steel butt joints reveals, that for this superior strength steel grade more than 50% of fatigue life is spent up to a crack depth of 0.5 mm, which can be defined as initial crack. Furthermore, a notch-stress based fatigue assessment of these specimens considering the actual weld topography and crack initiation and propagation phase is performed. The results point out that two phase models considering both phases enable an increased accuracy of service life assessment.

Study on Micro-Mechanism of Crack Initiation and Propagation Induced by Inclusion in Ultra-High Strength Steel

2007 ◽  
Vol 353-358 ◽  
pp. 1185-1190 ◽  
Author(s):  
Yan Ping Zeng ◽  
Hong Mei Fan ◽  
Xi Shu Wang ◽  
Xi Shan Xie
Keyword(s):  
Crack Initiation ◽  
High Strength Steel ◽  
Harmful Effect ◽  
High Strength Steels ◽  
High Strength ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Crack Initiation And Propagation ◽  
Initiation And Propagation ◽  
Ultra High Strength Steel

Specially designed SEM in-situ tensile and fatigue tests have been conducted to trace the entire process of crack initiation and propagation till fracture in an ultra-high strength steel MA250. TiN is a typical inclusion and its average size is in the range of 8~10μm in MA250 steel. The micro-mechanism of the effect of TiN inclusion on crack initiation and propagation at tensile and fatigue tests both have been studied in detail. Experimental results show the harmful effect of TiN on tensile and fatigue properties both. This work is helpful to establish the practical life prediction model for the characteristic inclusion parameters in ultra-high strength steel components. It also enlightens us to eliminate TiN in the further development of ultra-high strength steels.

Fatigue Crack Initiation and Propagation Life of Welded Joints

2005 ◽  
Vol 297-300 ◽  
pp. 781-787 ◽  
Author(s):  
Jeong Woo Han ◽  
Seung Ho Han ◽  
Byung Chun Shin ◽  
Jae Hoon Kim
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Initiation ◽  
Welded Joints ◽  
Fatigue Crack Initiation ◽  
Welding Residual Stress ◽  
Multiple Cracks ◽  
Weld Toes ◽  
Crack Initiation And Propagation ◽  
Initiation And Propagation

The fatigue life of welded joints is associated with crack initiation and propagation life. Theses cannot be easily separated, since the definition of crack initiation is vague due to the initiation of multiple cracks that are distributed randomly along the weld toes. In this paper a method involving a notch strain and fracture mechanical approach, which considers the characteristics of welded joints, e.g. welding residual stress and statistical characteristics of multiple cracks, is proposed, in an attempt to reasonably estimate these fatigue lives. The fatigue crack initiation life was evaluated statistically, e.g. the probability of occurrence in 2.3, 50 and 97.7%, in which the cyclic response of the local stress/strain in the vicinity of the weld toes and notch factors derived by the irregular shape of the weld bead are taken into account. The fatigue crack propagation life was simulated in consideration of the Mk-factor and the mechanical behavior of mutual interaction/coalescence between two adjacent cracks. The estimated total fatigue life as a sum of crack initiation and propagation life was found to be in good agreement with the experimental results.

scholarly journals Autofrettage of component-like ultra high Strength Steel Specimens with intersecting Holes

2021 ◽  
Vol 349 ◽  
pp. 04004
Author(s):  
Carl Fällgren ◽  
Thomas Beier ◽  
Michael Vormwald ◽  
Andreas Kleemann
Keyword(s):  
Residual Stress ◽  
Fatigue Life ◽  
Stress Distribution ◽  
Crack Initiation ◽  
Crack Propagation ◽  
High Strength Steel ◽  
High Strength ◽  
Crack Arrest ◽  
Residual Stress Distribution ◽  
Ultra High Strength Steel

This work is primarily concerned with the fatigue life of high-pressure-bearing components with intersecting holes, typically used in Diesel engine fuel injection systems. The investigation focuses on specimens with intersecting holes that have undergone the process of Autofrettage (single mechanical overload), which is typically used to extend the fatigue life of components loaded by cyclic internal pressure. The resulting residual stress distribution thus influences the fatigue failure and especially the crack propagation behaviour of the components. In previous works, results showed that besides crack initiation, crack arrest behaviour has to be taken into account when calculating fatigue lives of autofrettaged specimens as the endurance limit is otherwise underestimated. In order to achieve reliable results, material testing with samples made of the ultra high strength steel W360 was performed. The resulting test data were used to simulate the Autofrettage process with finite-element analysis. Calculated residual stress distributions were used to determine at which levels of subsequent cyclic loading crack initiation would occur. For predicted crack initiation, the simulated residual stress distribution was used to investigate the crack propagation behaviour with fracture mechanics based approaches of different complexity in order to identify possible crack arrest or crack propagation. Calculated results were compared to experimental test data from component-like specimens. The comparison showed that the fracture mechanics based approaches are capable of describing the crack arrest and propagation behaviour reliably.

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