► 3D FE implementation of continuum damage mechanics for multiaxial fatigue. ► Validation for uniaxial and notched fatigue and fretting fatigue for Ti–6Al–4V. ► Automatic incrementation scheme for ...efficient computation of damage accumulation. ► Captures effect of contact slip on fatigue life for round-on-flat fretting geometry. ► Comparisons with critical-plane multiaxial fatigue approach for fretting.
The three-dimensional finite element implementation of a continuum damage mechanics formulation for multiaxial fatigue is presented, incorporating elastic modulus reduction due to fatigue damage. The implementation is validated against theoretical and published experimental results for uniaxial and notched multiaxial fatigue under different combinations of mean and alternating stresses for Ti–6Al–4V. An automatic incrementation scheme is developed for efficient computation of damage accumulation and hence stress redistribution. The method is also implemented in two-dimensional, plane strain for fretting fatigue and is shown to successfully capture the effect of contact slip on fatigue life for a round-on-flat fretting geometry. Comparisons are also made with a critical-plane multiaxial fatigue approach for fretting. The work is a first step towards a more general fatigue damage approach to unify wear and fatigue prediction for fretting.
•Influence of varying aluminum alloys on mechanical characteristics of self-piercing riveting joints.•The microstructure, fracture behavior and failure mechanism of the joints was analyzed from macro ...and micro perspectives.•The mechanical properties of low ductility material Al7075 self-piercing riveting joint were studied.•The fatigue failure mechanism of 7075 self-piercing riveting joint under different load levels was investigated.•The fatigue life of 7075 self-piercing rivet joints was estimated using Paris law.
In order to investigate the mechanical properties of self-piercing riveting (SPR) joints in low ductility aluminum alloys, the study utilized three different types of aluminum alloy sheets: 7075, 6061, and 5754. These sheets were joined together using self-piercing riveting technology. The research compared the geometric parameters, microhardness, quasi-static mechanical properties, and fatigue properties formed with the joints of the three aluminum alloys. Additionally, the fatigue life of the self-piercing riveting joint in the 7075 aluminum alloy was analyzed using the Paris law and its corollary. The findings revealed that effective connections were established in all three aluminum alloys, although the expansion of the rivet was comparatively lower in the 7075 alloy. Plastic deformation resulted in an increase in microhardness of joined sheets. The hardness of the joined sheets followed the order: 7075 > 5754 > 6061. Furthermore, the 7075 alloy exhibited superior static mechanical and fatigue properties due to its inherent material. However, despite its lower material strength, the 5754 alloy outperformed the 6061 alloy at low fatigue load levels as a result of work hardening. The failed joints exhibited black oxide, and fretting damage under fatigue loading exacerbated the fatigue failure of the joint, serving as the primary cause. In the case of the 7075 alloy, three types of failure occurred due to fretting damage, which was influenced by the unique nature of the lower die. Fretting between the lower sheet and the rivet leg primarily caused lower sheet fracture and rivet failure, while fretting wear between the rivet head and the upper sheet or between the two sheets mainly led to upper sheet fracture failure. The fatigue life estimation method employed in the study, based on the Paris law, demonstrated good agreement with the experimental results.
Fretting wear occurring on the roller and raceway of rolling bearings is prone to reduce the reliability of bearings. In this study, fine particle bombardment (FPB) under different air pressures (0.3 ...and 0.6 MPa) was performed on GCr15 bearing steel, and the microstructure and fretting wear properties of GCr15 bearing steel modified by FPB were systematically investigated. The results show that the surface structure of the samples underwent severe plastic deformation, which led to surface grain refinement and increased in dislocation density. Also, the martensite bundle size decreased, and the densities of low-angle grain boundaries (LAGBs) and high-angle grain boundaries (HAGBs) increased. Moreover, the FPB improved the microhardness and thickness of the deformed layer. The enhancement was positively correlated with the air pressure of FPB. Compared with the untreated sample, the wear volume of the FPB samples increased by 10.1% (0.3 MPa) and 19.0% (0.6 MPa), respectively. Thus, the fretting wear resistance was significantly improved. The main wear mechanism changed from severe adhesive wear, abrasive wear, and fatigue wear to slight adhesive wear owing to the application of FPB.
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•Electrochemical behaviour in saliva solution under fretting conditions was investigated.•Effect of anodic formed TiO2 and electrodeposited hydroxyapatite film were studied.•EIS and ...open circuit potential were employed to test the tribocorrosion resistance.•Nanoporous TiO2 and hydroxyapatite layers enhance Ti alloy resistance to tribocorrosion.
The comparative tribo-electrochemical behaviour of both untreated Ti–6Al–4V alloy surface and the modified surface by forming nanoporous titania layer followed by electrodeposition of hydroxyapatite coatings into nanoporous titania layer have been investigated in physiological fluid solution. The in situ electrochemical techniques used for investigation of tribo-electrochemical degradation were the open circuit potential (OCP) and the electrochemical impedance spectroscopy (EIS) measurements performed before, during and after fretting tests. The results show that both surface modification techniques applied can significantly enhance the tribo-electrochemical performances of Ti–6Al–4V alloy surface for biomedical applications.
Diamond-like carbon (DLC) film is undoubtedly one excellent self-lubricating solid film to improve the fretting behavior due to its ultralow friction as well as high-hardness. Investigating the ...evolution laws of fretting running state with operating condition and the friction reduction mechanism of DLC film under fretting is vital for reducing friction and wear. Here, the fretting performance of self-mated hydrogen-containing DLC (H-DLC) and Cr-doped DLC (Cr-DLC) was studied under different normal loads and amplitudes. In addition, the mechanism of friction reduction for transfer film and the cause of discrepancy in fretting behavior were clarified through a control experiment. The results demonstrate that as the normal load increases, the relative slip decreases, the elastic deformation increases, and the fretting regime develops towards the partial slip regime, while the increasing amplitude moves the fretting regime towards slip regime. During fretting, the third body layer will transfer to the counterface, and form a uniform and graphitized transfer film. The difference in the length of run-in period and the sp2/sp3 hybrid carbon content of DLC films influences the formation rate and the graphitized degree of the transfer film, which induces the discrepancy of fretting behavior of H-DLC and Cr-DLC films. Thus, this study not only clarifies the evolution on fretting regime of DLC film with changes in working conditions, but also demonstrates the key role of highly graphitized transfer film in fretting performances of self-mated DLC films. This work demonstrates the controllability and potential of self-mated DLC films in the field of fretting.
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•The evolution of fretting regime can be completed by adjusting the operating conditions, which can realize the reduction of friction and wear.•The control experiment explained the formation mechanisms of transfer film, and proved the relationship between graphitization and the fretting behavior.•The doping elements of DLC film will affect the hybrid carbon content of sp2/sp3 and the length of run-in period under fretting.
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•The fretting fatigue (FF) mechanism of gradient-nanostructured steel was revealed.•Decreased FF initiation angle and increased FF propagation path were explained.•The nanolamellar ...martensite can inhibit FF crack propagation.•The influence mechanism model of 40CrNiMoA steel fretting fatigue was established.
In this research, a gradient nanostructure (GNS) of 40CrNiMoA steel prepared by the ultrasonic surface rolling process (USRP) is investigated. The results show that the USRP sample surface is equiaxial nanocrystalline and has a high-density nanolamellar gradient structure, and excellent compressive residual stress (CRS) and hardness gradient distribution are observed. In this study, the fretting fatigue (FF) limit of the USRP-treated specimen is 550 MPa, which is about 67 % higher than that of the untreated specimen. It is found that the equiaxed nanocrystalline top layer can effectively delay FF crack initiation. The high-density nanolamellar martensite structure is almost parallel to the surface, reduces the FF crack initiation angle, and increases the crack propagation path. High-strength CRS increases the crack growth resistance and changes the crack growth path. In addition, the improvement in surface hardness, CRS, and surface quality enhances the resistance to fretting wear and FF crack initiation. It is concluded that these factors effectively improve the FF limit of the material.
In this work, the role of the contact stiffness in the measurement of principal variables in fretting wear tests is assessed. Several fretting wear tribometers found in the literature, including one ...developed by the authors, are analysed and modelled using numerical methods. The results show the importance of the tribosystem stiffness and tangential contact stiffness in the displacement sensor calibration and in the correct numerical modelling of fretting wear tests, especially for flat-to-flat contact configuration. The study highlights that, in most cases, direct comparisons between fretting results with severe wear obtained with different tribometers cannot be performed if the contact stiffness is not properly considered during the development of the experiments.
In this investigation, a new model for dry fretting wear of similar materials in Hertzian contact is proposed. The wear law which is dependent on material properties, applied load and sliding ...distance is proposed for similar materials under dry fretting wear conditions. Based on this law, a stress based damage mechanics equation for wear is formulated and a finite element model is developed to determine wear rates and wear coefficients. The modeling approach proposed is based on wear at the level of material microstructure and thus Voronoi tessellation is used to configure the microstructure of the bodies in contact. To simulate fretting wear, fatigue crack initiation and propagation along the grain boundaries, and grain removal technique is developed. Two distinct regions – wear initiation and wear propagation are observed from the results of the simulation. The results of the simulation are compared with the Archard wear law and the calculated wear coefficients are of the same order as suggested in the literature. Wear volume measurements for partial slip regime in fretting wear are obtained using the model and the effects of coefficient of friction, hardness and Young's modulus on fretting wear is studied. It is found that the wear rate is significantly influenced by hardness and Young's modulus while the applied coefficient of friction has little to no effect on the wear rate. A regression analysis of the results and a wear map technique to predict wear rates based on material parameters is also presented.
•Dry fretting wear (partial slip regime) of similar materials in Hertzian contact is modeled.•A wear law independent of experimental constants is proposed.•Damage mechanics is used to simulate crack propagation and element deletion.•Wear coefficients are calculated and compared to Archard's wear law.•Wear rate depends significantly on Hardness and Young's modulus.
In this paper, ultrasonic surface rolling (USRP) and laser heating-assisted USRP (Laser-USRP) techniques are employed to enhance the fretting fatigue strength of TC11 titanium alloy. Furthermore, the ...surface deformation mechanism and fretting fatigue behavior are investigated. The properties of the reinforced surfaces were observed using transmission electron microscope (TEM), microhardness test, residual stress test and fretting fatigue experiments. The results showed that laser-USRP led to a remarkable enhancement in the fretting fatigue life of TC11 titanium alloy compared to traditional USRP. This was mainly due to the fact that laser heating improved the plasticity of TC11 titanium alloy, contributed to the formation of a smoother surface and increased the degree of surface oxidation, which could improve surface lubrication. Under high temperature, more slip systems were activated and more stable dislocations were formed, which resulted in larger compressive residual stress (CRS) with higher stability. The superposition of the elevated temperature field and the kinetic energy of the ultrasonic vibration produced an annealing effect in localized regions, resulting in the formation of more stable gradient nanograins. This study demonstrated the immense potential of laser-assisted plastic deformation in improving the surface properties of titanium alloys.
Grid-to-rod fretting (GTRF) is the main factor leading to the failures of fuel rods in reactor. The oxide layer formed on pre-wear stage has a significant impact on the wear resistance of zirconium ...(Zr) alloys fuel cladding. In this research, Zr alloy was immersed in high-temperature water conditions for 30 days,110 days,145 days, and 195 days. The characterization and fretting wear behavior of oxide layer on Zr alloy were investigated. Results show that the oxide layer consists of t-ZrO2, m-ZrO2, and metal Zr. The thickness and hardness of oxide layer increases with the corrosion time increase. The fretting running region and F-D curve are dependent on the oxide layer. Compared with Zr alloy, the wear volume of oxide layer on Zr alloy is significantly reduced because the structure of oxide layer is dense with a high hardness, leading to that the oxide layer is not easy to be destroyed during the fretting. The wear mechanism of Zr alloy is adhesive wear, and the wear mechanism of oxide layer is abrasive wear.
•The fretting wear behavior of pre-oxidized Zr alloy cladding was investigated.•The wear volume of oxide layer on Zr alloy decreases with the corrosion time increase.•The fretting running region and F-D curve are significantly dependent on the oxide layer.
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