For further clarification of the mechanisms leading to featureless crack initiation fibcross sections perpendicular to the crack initiation site were performed, see fig. Atomistic simulation methods including largescale molecular dynamics simulations with classical potentials, density functional theory calculations and advanced concurrent multiscale methods have led to new insights e. Very high cycle fatigue of duplex stainless very high. Crack initiation mechanisms in aa6082 fatigued in the.
On fatigue crack initiation in the matrix in very high. Influence of grain size and precipitates on the fatigue lives. Fatigue is one of the primary reasons for the failure of structural components. The grain where the fatigue crack initiated on the. Detailed analysis on crack initiation site has shown different types of subsurface crack initiation.
A discernible area called rough zone observed around the initiation site has been closely characterized. The mechanisms for fatigue crack initiation and short crack growth were investigated using electron microscopes. Fatigue damage behaviors of four metal materials in the very high cycle. Crack initiation and propagation in a stainless duplex. At lower stress amplitudes in the vhcfregime, subsurface cracks in the form of socalled. Deepdyve is the easiest way to get instant access to the academic journals you need. Formation of micro cracks of a duplex stainless steel dss in the very high cycle fatigue vhcf regime was studied and discussed. Fatigue strength of vdsicr spring steel under cyclic torsion and cyclic axial loading at different load ratios in the vhcf regime r. Design and life management of fracture critical components are made difficult by small scale deformation responses to low applied stresses in the very high cycle fatigue vhcf regime, where the number of cycles exceeds 107 and fatigue life is dominated by crack initiation and the growth of.
This raises the question of can dislocation multiplication and rearrangement also be the fracture mechanism in high. Processes at the atomic scale therefore critically influence the toughness and overall fracture behavior of materials. Cleaning, fatigue and cluster analysis researchgate, the professional network for. The life of a fatigue crack has two parts, initiation and propagation.
Characterization of microstructural effects on small fatigue crack growth mechanisms in ti6242s. Stress ratio and notch effects on the very high cycle. Talks of the 24 th colloquium on mechanisms on fatigue cyclic deformation and low cycle fatigue 1 plasticity from low to gigacycle fatigue pdf c. Damage accumulation is dominated by microstructure related slip localization, grain morphology and microstructural flaws.
For type ii materials the fatigue cracks in the vhcf regime mainly originate at non. Computational micromechanics of fatigue of microstructures in the hcf vhcf regimes. However, crack initiation in the interior without forming typical fish eye type fracture and without any clear influence of. For type ii materials the fatigue cracks in the vhcf regime mainly originate at. Crack initiation characteristics and fatigue property of a highstrength steel in veryhighcycle fatigue vhcf regime under different stress ratios were investigated in this paper.
Abstract the fatigue strength and crack initiation mechanisms of veryhighcycle fatigue vhcf for two low alloy steels were investigated. For the col d rolled stainless steels crack initiation and early growth occurred through the formation of the fine granular area fga observed on the fracture surface and in tem. This hypothesis was tested by starting from the coffinmanson fatigue life law. Fatigue behavior of 316 l stainless steel weldment up to. Study of crack initiation or damage in very high cycle fatigue using. Research on the fatigue behavior and mechanism of impeller material in the vhcf regime is beneficial to fatigue design and the remanufacturing of impellers, and it. Read mean stress sensitivity and crack initiation mechanisms of spring steel for torsional and axial vhcf loading, international journal of fatigue on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. The evolution of surface roughening was investigated with light, scanning electron and atomic force microscopy. New and basic results on the fatigue mechanisms of high strength steels in the vhcfregime can be achieved. Sem observations of the fracture surface indicate that fatigue crack initiates from the surface of specimen in lowcycle regime and initiates mostly from the inclusion in the interior of specimen in highcycle and vhcf regimes, which is irrespective of the state of stress ratio. In the vhcf regime cracks still initiate at subsurface inclusions, but the inclusion at the crack origin is additionally surrounded by a fine granular area fga inside the fisheye that cannot. Crack initiation of the aluminium alloy en aw6082 on the one hand depends on. Castelluccio, gustavo m musinski, william d mcdowell.
Goken, influence of grain size and precipitation state on the fatigue lives and deformation mechanisms of cp aluminium and aa6082 in the vhcfregime, int. Stress levels of 40 to 60% of the yield strength of this alloy have been examined. Lifetime and cyclic slip of copper in the vhcfregime. Dislocation tangles rearranged themselves to form well. In the present paper the aluminum alloys en aw6082 peakaged and overaged and en aw5083 solution annealed were investigated regarding the long fatigue crack growth behavior in the range of very. Interior crack initiation and growth behaviors and life. In view of the good agreement between the predicted and experimental results, the theoretical modeling method based on crack initiation and growth can be well used to. Hong, effects of stress ratio on highcycle and veryhighcycle fatigue behavior. However, for a nickelbased superalloy and a wrought aluminium alloy it will be shown, that the vhcf behavior cannot solely be explained by the precipitation morphology.
A general scenario of fisha eye crack initiation on the. Some fatigue cracks were found to be initiated in the gaps between inclusions al 2 o 3, mgoal 2 o 3 and the matrix, while other cracks. Mean stress sensitivity and crack initiation mechanisms of. Crack initiation mechanisms in aa6082 fatigued in the vhcfregime. If a fatigue crack initiates at an inner inclusion a ringlike smooth fracture surface in the vicinity of the inclusion is build, the so called fisheye. Mainly two subsurface crack initiation mechanisms were found. Fatigue behavior and mechanism of fv520b in very high. Fatigue strength of vdsicr spring steel under cyclic torsion. However, crack initiation in the interior without forming typical fish eye type.
Vhcf regime can be different in different metals due to the mechanisms for. Mechanisms of strain localization, crack initiation and fracture of polycrystalline copper in the vhcf regime. Fatigue behaviour of twophase titanium alloy in vhcf regime. Some fatigue cracks were found to be initiated in the gaps between inclusions al 2 o 3, mgoal 2 o 3 and the matrix. The effects of microstructure and axial tension on the fatigue behavior of tc4 titanium alloy in high cycle hcf and very high cycle vhcf regimes are discussed in this paper. However, the variation tendency of the sn data from lowcycle fatigue to vhcf regime is similar for the four cases. Influence of grain size and precipitation state on the. Lcf behavior, the prediction of cyclic strength in the vhcf regime requires a. Fatigue life variability and its dependence on microstructure variability in the very high cycle regime. Fatigue tests were performed at stress ratios of 1, 0. Thus, the vhcf life prediction approach related to the crack initiation mechanism need to be further discussed. The fatigue strength and crack initiation mechanisms of veryhighcycle fatigue vhcf for two low alloy steels were investigated. Initiation and earlystage growth of internal fatigue.
Studies have shown that the vhcf regime is associated with characteristic crack initiation mechanisms. Dislocations play a major role in the fatigue crack initiation. Effects of the heterogeneous microstructure of a 7050t7451. This work aims to investigate the effect of main inclusions on crack initiation in bearing steel in the very high cycle fatigue vhcf regime. Effect of main inclusions on crack initiation in bearing. Goken, crack initiation mechanisms in aa6082 fatigued in the vhcfregime, international journal of fatigue, 60 2014 2327. Crack initiation mechanisms in aa6082 fatigued in the vhcf. Effect of corrosion on the fatigue life and fracture mechanisms of. High cycle fatigue hcf and very high cycle fatigue vhcf induced by wake flow and other causes are the main failure modes of impellers which are the key component of centrifugal compressors. The major feature of vhcf is its loading stress lower than the traditional fatigue limit and fatigue life longer than that of highcycle. Pdf crack growth behaviour of aluminium wrought alloys in the. Ultrasonic fatigue tests up to 10 10 cycles were performed on a turbine engine titanium alloy ti8al1mo1v at the stress ratio r of. Results indicate that the fatigue crack initiates from an area consisting of many distributed facets, while the region of early crack propagation is characterised by parallel traces, based on a fractographic analysis. Crack initiation mechanisms in aa6082 fatigued in the vhcf regime.
Atomistic simulation methods including largescale molecular dynamics simulations with classical potentials, density functional theory calculations and advanced concurrent multiscale methods have led to new. In the case of subsurface crack initiation several fatigue life controlling mechanisms of crack initiation were found. However, in the vhcf regime, crack initiation can also emanate. In this study, the vhcf property of a crniw gear steel was experimentally investigated under axial loading with the stress ratio of r. Characterization of microstructural effects on small. Probabilistic lifeprediction in the longlifetime regime. Influence of grain size and precipitates on the fatigue. Mechanism of fatigue crack initiation and propagation in the very high cycle fatigue regime of highstrength steels. Bitzek, atomicscale modeling of elementary processes during the fatigue of metallic materials.
Request pdf crack initiation mechanisms in aa6082 fatigued in the vhcfregime over the last decades research activities in the field of very high cycle fatigue vhcf have strongly increased. Vhcf, cr steel, turbine blade steel, mean stress, fatigue damage. In the experimental part, ultrasonic fatigue testing at 20 khz of cold rolled and hot rolled stainless steel grades was conducted and fatigue strengths in the vhcf regime were obtained. Fau erlangennurnberg werkstoffwissenschaften allgemeine. Internal crack characteristics in veryhighcycle fatigue. For the aa6082 alloy it is shown that a heattreatment significantly affects the crack initiation mechanism. In the case of extruded vt31 the crack initiation is related to the fracture of alphaphase platelets agglomeration. Fatigue behavior of precipitation hardening alloys in the lcf and. In the vhcf regime, the crack initiation life associated with the fga size is almost equivalent to the total fatigue life, whereas the crack growth life only occupies a tiny fraction.
Crack initiation mechanisms in the very high cycle fatigue vhcf regime of nickelbased singlecrystal sx superalloys have been investigated at high temperature c and under fully reversed conditions r. Influence of microstructural inhomogeneities on the fatigue. Crack initiation mechanisms in aa6082 fatigued in the vhcfregime article in international journal of fatigue 60. As a result, with increase of fatigue life, the source of reduced fatigue life caused by multipoint surface crack initiation changes from crack propagation stage to crack. Fatigue lifetimes in the range of 10 to the 6th to 10 to the 9th cycles are observed and fatigue cracks initiate from. Fatigue behavior of precipitation hardening alloys in the. Both surface and subsurface crack initiations were observed. It can be shown that the stress amplitude, leading to first irreversible changes in the microstructure, strongly depends on the depth position within the original wheel rim. The importance of the crack initiation stage in the vhcf regime is emphasized by the fact that more than 90% of the total fatigue life is spent in this stage 2. The research of veryhighcycle fatigue vhcf, which is fatigue failure beyond 10 7 cycles of loading, is a hot topic in structural integrity because engineering structures require greater than 10 7 cycles of safe performance 1,2,3,4,5,6.
Highstrength bolt corrosion fatigue life model and application. The significant differences in morphology around the crack. Often, depending on the material, the longlifetime regime is accompanied by a step in the stress vs. Fatigue of materials at very high numbers of loading cycles experimental techniques, mechanisms, modeling and fatigue life assessment ed. The cracks either initiated at inclusions and other defects or at nondefect initiation sites 8. Crack initiation in vhcf regime on forged titanium alloy under tensile and torsion loading modes a. Microstructural influences on very high cycle fatigue.
Materials free fulltext the effect of microstructure. Microstructural influences on veryhighcycle fatigue. Fatigue cracks preferred to initiate from the specimen surface in both high cycle fatigue and vhcf regime and multiple crack initiation sites were commonly observed in 316 l weldment. Abstractthe aim of this paper is to assess the veryhighcycle fatigue vhcf behaviour of a magnesium alloy zk60. Mechanism of fatigue crack initiation and propagation in. The reasons for the formation of these socalled featureless crack initiation sites. Any fracture process ultimately involves the rupture of atomic bonds.
The unexpected failures of structural materials in very high cycle fatigue vhcf regime have been a critical issue in modern engineering design. Deepdyve is the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. The mechanism of the fatigue crack initiation in the hcf and vhcf ranges was noteworthy because the. Very high cycle fatigue of copper archive ouverte hal. Veryhighcycle fatigue crack initiation and propagation.
Crack initiation mechanisms of ti6a14v in the very high. The paper focuses on the fatigue mechanisms in the vhcfregime of type ii materials. Crack initiation in vhcf regime on forged titanium alloy. As described above, the aa6082 alloy contains two different types of precipitates which differ in size and composition, compare also 22. Mechanisms controlling the crossslip annihilation distance and the cyclic saturation stress in f. Crack initiation mechanisms during very high cycle fatigue. Initiation and early crack initiation and early crack. Very high cycle fatigue damage mechanisms high frequency testing. In cases in which a particular fatigue crack initiation mechanism governs fatigue life, it could be proposed that a unique relationship between irreversibility p and fatigue life n f exists. For a peakaged condition the fatigue crack starts at the surface whereas for the asreceived condition a featureless crack initiation is obtained. Tensile tests were carried out with two different stress ratios.
Effect of variable amplitude loading on high cycle fatigue hcf damage. In the initiation stage, the crack is small compared. In fractography, the fatigue crack initiation site is surrounded by a semicircular flat zone, of which the formation in vhcf regime accounts for more than 98% of the total fatigue life. Influence of grain size and precipitates on the fatigue lives and. Microplasticity and energy dissipation in very high cycle fatigue. Abstract this paper is focused on the vhcf behavior of aeronautical titanium alloy under tensile and torsion fatigue loadings. Fatigue strength and crack initiation mechanism of very. This paper provides a study on the fatigue crack initiation mechanisms at subsurface nondefect matrix origin in two metallic materials using electron backscatter diffraction and electron channeling contrast imaging. Cyclic plastic zone is the region ahead of a growing fatigue crack in which slip takes place. Department of materials science, university erlangennurnberg martensstr. Mechanisms of crack initiation and crack propagation at very long lifetimes and the role of microstructure, defects and environment on these phenomena. The results show that the fatigue crack initiation in vhcf regime could.
In the case of forged titanium alloy both flat and rough fractured facets were found under tension loads. For type ii materials the fatigue cracks in the vhcf regime mainly originate at nonmetallic inclusions located in the interior, the socalled fisheye fracture, often reported for high strength steels and other alloys. Lcfhcf strength of precipitation hardening alloys is primarily controlled by its heat treatment condition. Influence of grain size and precipitates on the fatigue lives and deformation mechanisms in the vhcfregime heinz werner hoppel, michaela prell, lilia may, mathias goken institute i. Mughrabi, specific features and mechanisms of fatigue in the ultrahighcycle regime.
Microstructural mechanisms of cyclic deformation, fatigue. Crack initiation mechanism of bearing steel in very high cycle fatigue. For all nibased sx alloys tested, a discernible area called rough zone has been identified around the crack initiation site on the fracture surface and is for the first time described. Bach j, hoppel h w, prell m and goken m 2014 crack initiation mechanisms in aa6082 fatigued in the vhcfregime int. On the mechanism of fatigue failure in the superlong life regime n 10 7 cycles, part 1. For high strength steels with high crack propagation rate and low fracture toughness, the fatigue life in the vhcf regime should be governed by the crack initiation. There was little frequency effect of 20 khz on fatigue lives when compared with 100 hz, nor did the deformation and fracture mechanisms. The size and type of inclusions in the steel were quantitatively analyzed, and vhcf tests were performed. Dr aleksandar sedmak, faculty of mechanical engineering, university of belgrade. While on the subject of dislocations, it is appropriate to briefly discuss fatigue. Thus, whether the vhcf fatigue property can be improved by the layer of gs is still questioning as the crack initiation mechanism in vhcf differs.
In most cases, this change in mechanism has been reported to be. Fatigue lifetimes in the range of 106 to 109 cycles are observed, and fatigue cracks initiate from both surface. The predicted crack initiation life tends to increase with the decrease of stress amplitude. Several highresolution techniques were applied to fatigued specimens, identifying the mechanical properties of the dss and relating them to the mechanisms of the micro crack initiation. On the origin of crack initiation in duplex stainless. Its size relative to the microstructure determines the behavior of the fatigue crack, i. Crack initiation characteristics and fatigue property of a.