In this study, Ti-6Al-4V dovetail joint specimens which highly simulate the attachment between the blade and disk of fan stages in a certain gas turbine engine were designed and used in fretting ...fatigue experiments. The fretting wear mechanism was characterized using a bench level experimental method. The effect of shot-peening on both fretting wear mechanism and fretting fatigue property was evaluated. The results indicated that shot-peening transformed the fretting wear behavior, altered the dominant crack initiation mechanism and dramatically promoted the fretting fatigue performance of Ti-6Al-4V dovetail joint specimens. Different reinforcement mechanisms of the multiple surface modifications created by shot-peening were also analyzed and summarized in this study.
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•The fretting behaviors of Ti-6Al-4V dovetail joint specimens were investigated.•Shot-peening prevented the adhesion behavior in the preliminary fretting period.•Shot peening gives a significant improvement on fretting fatigue life.•Parameters induced by shot-peening played different roles in the promoting effect.
The failure of the aircraft spline shaft was attributed to overstressing, cyclic bending loads, and other complex conditions. This study investigates the bending fretting fatigue behaviours and ...failure mechanisms of 15–5PH stainless steel. The study analysed the residual stress, microstructure, morphology, and chemical state of the worn surface and the fatigue failure mechanisms. The results showed that fretting wear significantly reduces the bending fatigue life. The surface residual stress transitions from compressive to tensile stress states. The value of residual stress increased, and the oxygen content of the worn surface was higher in the mixed fretting regime. Fatigue fractures occur at a depth of 50–100 µm below the surface in the present experiment.
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•The S-N curve for bending fretting fatigue of 15-5PH stainless steel is established.•The fretting wear contributes to the evident reduced bending fatigue life.•Bending fretting fatigue fracture sources are forms at 50-100 µm below the surface.•The surface residual stress changes from compressive to tensile stress states.
In this paper, a global-local fretting design methodology for the pressure armour layer of flexible marine risers is outlined. This includes global dynamic riser analysis, geometrical and analytical ...sub-models and local nub-groove contact finite element analysis. Furthermore, a fretting test rig is developed and utilised to quantify coefficient of friction and wear coefficient under representative nub-groove loading conditions. The combination of the global-local computational methodology and experimental characterisation of pressure armour wire material allows for the development of running condition fretting maps. This identifies design criteria for critical riser global curvatures that are associated with minimum number of cycles to failure. The design methodology presented in this paper is applied to a realistic riser design study, using extreme sea-state loading conditions. In this case study, the predicted pressure armour fretting fatigue lives are found to be in the same range as the plain fatigue lives of the tensile armour layer.
•Global-local fretting design methodology for the pressure armour layer of flexible marine risers.•Global dynamic riser analysis, geometrical and analytical sub-models and local nub-groove contact finite element analysis.•Development and utilisation of a fretting rig to quantify friction and wear coefficients under representative nub-groove loading conditions.•Identification of design criteria for critical riser global curvatures associated with minimum number of cycles to failure.•Realistic riser design study, using extreme sea-state loading conditions.
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•Highly porous Ti was presented as a highly potential bone substitute.•Fretting-corrosion behaviour between highly porous Ti and Ti alloy was studied.•A load- and amplitude-dependent ...response was obtained.•Structure integrity of porous Ti was preserved after 16 h of fretting-corrosion.
Highly porous Ti was investigated under fretting-corrosion conditions as a function of load and amplitude. To obtain a correlation between mechanical and electrochemical responses according to amplitude, a new representative master curve was suggested: the A ratio (dissipated energy over total energy) vs. 1st OCP drop that fitted well the fretting-corrosion behaviour. Fretting-corrosion mechanisms were presented and a fretting map was illustrated. There was a significant load- and amplitude-dependent response, showing gross slip and partial slip regimes can occur with expected OCP variations. The promising structure of highly porous Ti was preserved after 16 h of fretting-corrosion under severe solicitations.
•Torsional deformation can affect the fretting fatigue behavior between wires.•The torsion of pearlite sheet is the key factor affecting fretting fatigue.•Fretting fatigue damage can change the ...contact form of rope strand steel wire.
Fretting wear and torsional deformation of steel wire can reduce the performance of wire rope and threaten the safety of mine hoisting system. In this study, to explore the influence of different torsional deformation on the fretting fatigue wear behavior under multi-wire spiral contact, an experimental study was conducted on a self-made test apparatus. The results show that the increase of torsional deformation can reduce the breaking force of steel wire by about 2.6%, and reduce the bending fatigue performance by about 36.4%. In addition, the maximum wear depth, wear amount and coefficient of wear increase with the increase of torsional deformation. The torsion and deformation of the pearlite lamellae parallel to the tensile stress direction are the main reasons for the decrease of the wear resistance of the main steel wires. More torsional deformation makes the steel wire produce less furrow morphology in fretting fatigue wear. The main wear mechanism of steel wire with small torsional deformation is abrasive and tribochemical reactions, and the main wear mechanism of steel wire with large torsional deformation is surface fatigue and tribochemical reactions.
Predicting fretting fatigue in engineering design Sunde, Steffen Loen; Berto, Filippo; Haugen, Bjørn
International journal of fatigue,
December 2018, 2018-12-00, 20181201, Letnik:
117
Journal Article
Recenzirano
Odprti dostop
•The progress in fretting fatigue understanding and predictability is reviewed.•Applicability to engineering applications is especially considered.•Asymptotic approaches for fretting fatigue ...assessments are reviewed.•The use of multiaxial fatigue criteria to determine fretting fatigue crack nucleation life is considered.
The progress in fretting fatigue understanding and predictability is reviewed, with engineering applications in mind. While industrial assessments often relies on simple empirical parameters, research in fretting fatigue should allow the design engineer to improve confidence in the fretting fatigue analysis.
Fretting fatigue cracks often form in multiaxial stress fields with severe gradients under the contact area, and are inherently difficult to predict.
By describing the fretting stress gradients using comparisons with the mechanical fields surrounding cracks and notches, crack nucleation threshold conditions and finite life can efficiently be determined. Also, non-local stress intensity multipliers provide promising tools for the industrial finite element analysis, often involving complex geometries and loading conditions.
The use of multiaxial fatigue criteria to determine fretting fatigue nucleation life is also reviewed. Researchers have shown that critical plane calculations with some stress-averaging method can predict fretting fatigue crack initiation. However, the frictional interface causes non-proportional loading paths, and the application of critical plane methods is not straight forward.
•FE model was proposed to predict fretting fatigue crack initiation in railway axle.•The effect of stress redistribution due to fretting wear was considered.•The role of stress relief groove on the ...fretting wear and fatigue was studied.•The simulation results agree with the published experimental results.
In this paper, a finite element model for the prediction of fretting fatigue crack initiation in the full-scale railway axle was proposed, which took into account the influence of the stress redistribution due to fretting wear on the fretting fatigue. Then, this model was used to investigate the influence of stress relief groove on the fretting wear and fatigue of the railway axle. The simulation results show that the stress concentration at the contact edge is gradually relieved with an increase in fretting cycles due to the fretting wear, while a new stress concentration appears at the edge of fretting wear scar, which gradually increases and moves towards the inner side of the contact area. The stress concentration in the inner side is considered to cause the fatigue crack initiation. Either the increase in groove depth or the decrease in groove radius can reduce the fretting wear and improve the fretting fatigue strength through relieving the stress concentration. Accompanying the improvement of fretting fatigue strength, the potential site of crack initiation gradually moves towards the contact edge. The simulation results stated above agree with the published experimental results.
•The fretting damage mechanism of aero-engine involute spline couplings is proposed: During the aircraft ground taxiing stage, the fretting wear was slight, almost no fatigue crack was observed in ...the adhesion center, and the fatigue crack sprouted only at the contact edge. During the aircraft take-off stage, the spline coupling changed from two-body contact to three-body contact, the fretting wear was severe, the fatigue crack was suppressed, and the fretting fatigue was slight. In the cruise phase, the contact surface was in dynamic equilibrium, and the fretting wear was slight. With an increase in the number of load cycles, the fatigue cracks sprouted and expanded rapidly. In the declining phase, the influence of three-body contact decreased, the friction increased, the fretting wear was slight, and the fatigue cracks began to sprout and expand rapidly at the contact surface wear. The contact surface was elastic contact, and the fretting wear was slight, with the exception of fatigue cracks sprouting at the contact edge, which accelerated expansion.•A novel fretting damage prediction method was proposed. The Archard model was optimized to obtain a novel fretting wear model and combined with the calculation results of the finite element software. The SWT critical plane method was used to calculate the location at which the fatigue crack exhibited the greatest chance of sprouting and expanding and combined with the XFEM in the finite element software to prefabricate the crack at this location. The final verification results are consistent with the proposed fretting damage mechanism of aero-engine involute spline couplings.•The influence mechanism of various factors on the fretting damage of aero-engine involute spline couplings was investigated by a combination of finite element simulations and experiments. In the future, these conclusions can be used as a reference for the design of splines and for the prediction of fretting damage and design of other parts against fretting damage.
Aiming at the serious fretting damage and failure of aviation involute spline couplings, this work proposes the fretting damage mechanism of involute spline couplings of aero-engine based on previous theories. The optimized Archard wear volume model and Smith-Watson-Topper critical surface method are used to establish the fretting damage prediction model of involute spline couplings of aero-engine. On this basis, the law of fretting damage is analyzed and its mechanism is verified by finite element simulation and experiment. The results show that the fretting damage failure mode of involute spline couplings of aero-engine is mainly fretting wear, fretting fatigue and fretting wear compete and influence each other. With the increase of contact stress and sliding distance, the fretting damage degree increases, but when it reaches a certain critical value, the fretting damage degree decreases. The fretting damage degree increases with the increase of angle mismatch and friction coefficient. The theory is in good agreement with the actual results, which provides a feasible way to study the fretting damage mechanism of other spline couplings.
Boron dipyrromethene (Bodipy) is one of the most extensively investigated organic chromophores. Most of the investigations are focused on the singlet excited state of Bodipy, such as fluorescence. In ...stark contrast, the study of the triplet excited state of Bodipy is limited, but it is an emerging area, since the triplet state of Bodipy is tremendously important for several areas, such as the fundamental photochemistry study, photodynamic therapy (PDT), photocatalysis and triplet-triplet annihilation (TTA) upconversion. The recent developments in the study of the production, modulation and application of the triplet excited state of Bodipy are discussed in this review article. The formation of the triplet state of Bodipy upon photoexcitation,
via
the well known approach such as the heavy atom effect (including I, Br, Ru, Ir,
etc.
), and the new methods, such as using a spin converter (
e.g.
C
60
), charge recombination, exciton coupling and the doubly substituted excited state, are summarized. All the Bodipy-based triplet photosensitizers show strong absorption of visible or near IR light and the long-lived triplet excited state, which are important for the application of the triplet excited state in PDT or photocatalysis. Moreover, the methods for switching (or modulation) of the triplet excited state of Bodipy were discussed, such as those based on the photo-induced electron transfer (PET), by controlling the competing Förster-resonance-energy-transfer (FRET), or the intermolecular charge transfer (ICT). Controlling the triplet excited state will give functional molecules such as activatable PDT reagents or molecular devices. It is worth noting that switching of the singlet excited state and the triplet state of Bodipy may follow different principles. Application of the triplet excited state of Bodipy in PDT, hydrogen (H
2
) production, photoredox catalytic organic reactions and TTA upconversion were discussed. The challenges and the opportunities in these areas were briefly discussed.
The accessing of the triplet excited state of one of the most popular fluorophores, boron-dipyrromethene (Bodipy), was summarized.
More than 25 years ago, Vingsbo and Söderberg published a seminal paper regarding the mapping of behaviour in fretting contacts (O. Vingsbo, S. Söderberg, On fretting maps, Wear, 126 (1988) 131–147). ...In this paper, it was proposed that in the gross-slip fretting regime, the wear coefficient increased by between one and two orders of magnitude as the fretting displacement amplitude increased from around 20µm to 300µm (defined as the limits of the gross-slip regime).
Since the publication of this paper, there have been many papers published in the literature regarding fretting in the gross-sliding regime where such a strong dependence of wear coefficient upon fretting displacement has not been observed, with instead, the wear coefficient being shown to be almost independent of fretting amplitude. Indeed, many researchers have demonstrated that there is a good correlation between wear volume and frictional energy dissipated in the contact for many material combinations, with the additional insight that a threshold in energy dissipated in the contact exists, below which no wear is observed (experimental data relating to fretting of a high-strength steel is presented in the current paper which supports this concept).
It is argued that in deriving a wear coefficient in fretting, there are two key considerations which have not always been addressed: (i) the far-field displacement amplitude is not an adequate substitute for the slip amplitude (the former is the sum of the latter together with any elastic deformation in the system between the contact and the point at which the displacement is measured); and (ii) there is a threshold in the fretting duration, below which no wear occurs and above which the rate of increase in wear volume with increasing duration is constant (this constant may be termed the wear coefficient, ktrue). Not addressing these two issues results in the derivation of a nominal wear coefficient (knominal) which is always less than ktrue. A simple analysis is presented which indicates thatknominalktrue=1−A−B
where A is associated with erroneously utilising the far-field displacement amplitude in place of the contact slip amplitude in the calculation of the wear coefficient and B is associated with the failure to recognise that there is a threshold in fretting duration below which no wear occurs.
A and B are shown to depend upon the tractional force required to initiate sliding (itself dependent upon the applied load and coefficient of friction), the system stiffness, the applied displacement amplitude, the threshold fretting duration below which no wear occurs and the number of fretting cycles in the test. Using typical values of these parameters, the ratio of knominal to ktrue has been shown to be strongly dependent upon the applied displacement amplitude over the range addressed by Vingsbo and Söderberg (with the ratio rapidly decreasing by an order of magnitude over this range). As such, it is argued that ktrue shows no strong dependence on slip amplitude in fretting, and that the strong dependence of knominal upon displacement amplitude presented by Vingsbo and Söderberg does not imply a change in ktrue as is often inferred.
The routine recording of force–displacement loops in fretting is a major experimental advancement which has taken place since the publication of the paper by Vingsbo and Söderberg. It is argued that this technique must be routinely used to allow the correct interpretation of wear data in terms of the actual slip amplitude (or energy dissipated); moreover, a range of conditions should be experimentally examined to allow the threshold fretting duration below which no wear has occurred to be evaluated and its significance assessed.
•Assumptions made in derivation of the fretting wear coefficient have been analysed.•The measured wear coefficient is generally smaller than the true wear coefficient.•To minimise such discrepancies, the recording of fretting loops is essential.•The influence of the threshold for initiation of wear is also recognised.•The strong dependence of wear on fretting amplitude in gross sliding is questioned.
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