scholarly journals Effect of the Depth of Decarburized Layer in SKL15 Tension Clamp on Fatigue Strength

2021 ◽  
Vol 11 (9) ◽  
pp. 3841
Author(s):  
Yeun-Chul Park ◽  
Chang-Beom An ◽  
Mancheol Kim ◽  
Hyoung-Bo Sim
Keyword(s):  
Fatigue Crack ◽  
Fatigue Strength ◽  
Fatigue Failure ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Initial Crack ◽  
Spring Steel ◽  
Urban Transit ◽  
Linear Elastic ◽  
Decarburized Layer

The surface of a quenched and tempered spring steel may have a decarburized layer from which the carbon component has been reduced. The fatigue strength of the decarburized layer is low compared to the base metal, which can easily develop fatigue cracks. Recently, fatigue failure was reported in the tension clamp (SKL 15) of the DFF-300 rail fastening system during use on one urban transit route in South Korea. As a result of measuring the depth of the decarburized layer of the SKL 15 tension clamp where the fatigue failure occurred, a decarburized layer thinner than the manufacturer’s maximum allowable decarburized layer was found in one of the eight tension clamps. To check the depth of the decarburized layer where the fatigue crack may have initiated, the decarburized layer was assumed to be the initial crack, and fatigue crack initiation was assessed based on the linear elastic fracture mechanics. The manufacturer’s maximum allowable decarburized layer depth of 0.2 mm may result in fatigue cracks.

Plastic Slip and Early Stage of Fatigue Damage in Polycrystals: Comparison between Experiments and Crystal Plasticity Finite Elements Simulations

2014 ◽  
Vol 891-892 ◽  
pp. 1711-1716 ◽  
Author(s):  
Loic Signor ◽  
Emmanuel Lacoste ◽  
Patrick Villechaise ◽  
Thomas Ghidossi ◽  
Stephan Courtin
Keyword(s):  
Fatigue Crack ◽  
Finite Elements ◽  
Crack Initiation ◽  
Fatigue Damage ◽  
Crystal Plasticity ◽  
Early Stage ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Plastic Slip

For conventional materials with solid solution, fatigue damage is often related to microplasticity and is largely sensitive to microstructure at different scales concerning dislocations, grains and textures. The present study focuses on slip bands activity and fatigue crack initiation with special attention on the influence of the size, the morphology and the crystal orientation of grains and their neighbours. The local configurations which favour - or prevent - crack initiation are not completely identified. In this work, the identification and the analysis of several crack initiation sites are performed using Scanning Electron Microscopy and Electron Back-Scattered Diffraction. Crystal plasticity finite elements simulation is employed to evaluate local microplasticity at the scale of the grains. One of the originality of this work is the creation of 3D meshes of polycrystalline aggregates corresponding to zones where fatigue cracks have been observed. 3D data obtained by serial-sectioning are used to reconstruct actual microstructure. The role of the plastic slip activity as a driving force for fatigue crack initiation is discussed according to the comparison between experimental observations and simulations. The approach is applied to 316L type austenitic stainless steels under low-cycle fatigue loading.

scholarly journals Fatigue Strength Analysis and Fatigue Damage Evaluation of Roller Chain

Metals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 847 ◽  
Author(s):  
Ryoichi Saito ◽  
Nao-Aki Noda ◽  
Yoshikazu Sano ◽  
Jian Song ◽  
Takeru Minami ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Strength ◽  
Fatigue Damage ◽  
Fatigue Crack Initiation ◽  
Strength Analysis ◽  
The Finite Element Method ◽  
Roller Chain ◽  
Press Fitting ◽  
The Press ◽  
Static Tensile

This paper deals with the roller chain commonly used for transmission of mechanical power on many kinds of industrial machinery, including conveyors, cars, motorcycles, bicycles, and so forth. It consists of a series of four components called a pin, a bush, a plate, and a roller, which are driven by a sprocket. To clarify the fatigue damage, in this paper, the finite element method (FEM) is applied to those components under three different types of states, that is, the press-fitting state, the static tensile state, and the sprocket-engaging state. By comparing those states, the stress amplitude and the average stress of each component are calculated and plotted on the fatigue limit diagram. The effect of the plastic zone on the fatigue strength is also discussed. The results show that the fatigue crack initiation may start around the middle inner surface of the bush. As am example, the FEM results show that the fatigue crack of the inner plate may start from a certain point at the hole edge. The results agree with the actual fractured position in roller chains used in industry.

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 Performance Evaluation of a Carbon Nanotube Sensor for Fatigue Crack Monitoring of Metal Structures

Sensors ◽  
2020 ◽  
Vol 20 (16) ◽  
pp. 4383
Author(s):  
Shafique Ahmed ◽  
Thomas Schumacher ◽  
Erik T. Thostenson ◽  
Jennifer McConnell
Keyword(s):  
Fatigue Crack ◽  
Carbon Nanotube ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Real Time ◽  
False Positive ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Resistance Change ◽  
Metal Structures

This article describes research that investigated the ability of a carbon nanotube (CNT) sensor to detect and monitor fatigue crack initiation and propagation in metal structures. The sensor consists of a nonwoven carrier fabric with a thin film of CNT that is bonded to the surface of a structure using an epoxy adhesive. The carrier fabric enables the sensor to be easily applied over large areas with complex geometries. Furthermore, the distributed nature of the sensor improves the probability of detecting crack initiation and enables monitoring of crack propagation over time. Piezoresistivity of the sensor enables strains to be monitored in real time and the sensor, which is designed to fragment as fatigue cracks propagate, directly measures crack growth through permanent changes in resistance. The following laboratory tests were conducted to evaluate the performance of the sensor: (1) continuous crack propagation monitoring, (2) potential false positive evaluation under near-threshold crack propagation conditions, and (3) crack re-initiation detection at a crack-stop hole, which is a commonly used technique to arrest fatigue cracks. Real-time sensor measurements and post-mortem fractography show that a distinguishable resistance change of the sensor occurs due to fatigue crack propagation that can be quantitatively related to crack length. The sensor does not show false positive responses when the crack does not propagate, which is a drawback of many other fatigue sensors. The sensor is also shown to be remarkably sensitive to detecting crack re-initiation.

Mode II Fatigue Crack Behavior in Compact Tension Shear Specimen

2005 ◽  
Vol 297-300 ◽  
pp. 1592-1597 ◽  
Author(s):  
Sam Hong Song ◽  
Jeong Moo Lee
Keyword(s):  
Fatigue Crack ◽  
Crack Surface ◽  
Notch Root ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Load Condition ◽  
Compact Tension ◽  
Initial Crack ◽  
Shear Loading ◽  
Mode Ii

The need for research on fatigue behavior of mechanical element under mixed-mode loading has been increasing as the user environment today becomes more and more complicated. However there haven’t been enough investigations on behavior in shear loads comparing to those under tensile loading conditions. So, for this paper, we investigated the characteristics and properties of initiation and propagation behavior for fatigue crack observed for different shapes of the initial crack and magnitudes of load in the modified compact tension shear (CTS) specimen subjected to mode II load. In the low-load condition, the secondary fatigue crack was created in the notch root due to friction on the pre-crack surface grew to a main crack. In the high-load condition meanwhile, fatigue crack under shear loading propagated branching from the pre-crack tip. Influenced by the shear loading condition, fatigue crack propagation was retarded in the initial propagation region due to the decrease in crack driving force and friction on the crack surface. In both cases, however, fatigue cracks grew in tensile mode. The propagation direction of fatigue crack under mode II loading was approximately at a 70 degree angle from the initial crack, regardless of its shape and load magnitude.

Effect of Pre-Strain on Fatigue Properties of NHH Rail

2004 ◽  
Vol 261-263 ◽  
pp. 1239-1244
Author(s):  
Wen Xian Sun ◽  
S. Nishida ◽  
Nobusuke Hattori ◽  
X.L. Yue
Keyword(s):  
Fatigue Crack ◽  
Fatigue Strength ◽  
Fatigue Test ◽  
Fatigue Cracks ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Slip Lines ◽  
Propagation Behavior ◽  
Strain Process ◽  
Initiation And Propagation

In the present study, fatigue tests have been performed to study the effect of pre-strain on fatigue properties of NHH (New Head-Hardened) rail. The objectives of this study were: (1) to observe the microscopic behavior of specimens during pre-strain process, (2) to research the influence of pre-strain on fatigue strength of NHH rail and (3) to investigate initiation and propagation behavior of the fatigue crack. The results showed that plastic pre-strain decreased the fatigue strength of NHH rail; fatigue limits had no obvious variation among the different pre-strain ratios. Fatigue cracks initiated in the microscopic cracking or slip lines that were originated in the pre-strain process and propagated from these sites in the later fatigue test.

The Influence of Notch Geometric Size in the Fatigue Strength of Steel

2014 ◽  
Vol 602-605 ◽  
pp. 167-171
Author(s):  
Yong Zhuang Yuan
Keyword(s):  
Fatigue Strength ◽  
Fatigue Behavior ◽  
Stress Gradient ◽  
Fatigue Crack Initiation ◽  
Estimation Method ◽  
Size Factor ◽  
Linear Elastic ◽  
Factor Effect ◽  
Geometric Size ◽  
Elastic Fracture

The fatigue behavior of notch specimens has been investigated in this manuscript. It is shown that notch geometric size has apparent effect for fatigue strength of specimens. The blunt notch is used in test. It is concluded that geometric size effect depends on the stress gradient and can be estimated with the help of the linear elastic fracture mechanics. The influence of notch size for fatigue strength can be explained with geometric factor. The plastic strain play an important role in fatigue crack initiation with notch gets sharper reach certain magnitude limit, and fatigue strength is lower than the predicted by geometric size factor effect. The method does not apply fatigue strength of the sharper notch. Another estimation method shall be used to that kind of notches.

Interior-Induced Fracture Mechanism of High Cleanliness Spring Steel (JIS SWOSC-V) in Very High Cycle Regime

2015 ◽  
Vol 664 ◽  
pp. 209-218 ◽  
Author(s):  
Taku Miura ◽  
Takayuki Sakakibara ◽  
Takanori Kuno ◽  
Akira Ueno ◽  
Shoichi Kikuchi ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Fracture ◽  
Fracture Mode ◽  
Fracture Mechanism ◽  
Fatigue Crack Initiation ◽  
Fatigue Tests ◽  
Spring Steel ◽  
Topographic Analysis ◽  
Very High

In order to investigate the interior-induced fatigue crack propagation behavior of high cleanliness valve spring steel (JIS SWOSC-V), rotating bending fatigue tests were performed for various kinds of specimens with different hardness or surface finishings. The harder specimen with higher compressive residual stress showed longer fatigue life. The electrochemical polished specimen pre-treated with shot peening showed almost same fatigue life as the shot-peened specimen in spite of the difference in surface roughness. After fatigue tests, fracture surfaces were observed using a scanning electron microscope (SEM) to evaluate the fatigue fracture mechanism. Most specimens failed in surface-induced fracture mode due to high cleanliness; however, some specimens failed in interior-induced fracture mode in the very high cycle regime. Although non-metallic inclusions were not observed at interior fatigue crack initiation sites, 2 types of significant microstructures (with smooth surface or granular surface) were observed. EBSD analysis, profile analysis and computational simulation using a fracture surface topographic analysis (FRASTA) method were performed to investigate the mechanism of the interior-induced fatigue fracture caused by the microstructure at defect without any inclusion.

Research on the Mechanism of Fatigue Crack Initiation of X60 Pipeline Steel after Per-Tension Deformation

2012 ◽  
Vol 197 ◽  
pp. 798-801
Author(s):  
Yu Rong Jiang ◽  
Mei Bao Chen
Keyword(s):  
Fatigue Crack ◽  
Cyclic Loading ◽  
Brittle Fracture ◽  
Crack Initiation ◽  
Pipeline Steel ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Fracture Characteristics ◽  
Metallic Inclusions ◽  
The Matrix

It is impossible to keep pipelines free from defects in the manufacturing, installation and servicing processes. In this paper, pre-tension deformation of X60 pipeline steel was employed to experimentally simulate the influence of dents and the mechanism of fatigue crack initiation of X60 pipeline steel after per-tension deformation under cyclic loading were investigated. The results indicate that the mechanism of fatigue crack initiation is the typical cleavage fracture characteristics and the cracks mainly initiates from the non-metallic inclusions which was the local brittle fracture materials such as MnS inclusion. With the pre-tension deformation increase, the yield strength of the matrix was increased and the toughness decreased due to the work-hardening effect. With the effects of the non-metallic inclusions larger, the fatigue cracks initiated from the non-metallic inclusions easier.

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