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This study investigates the surface changes and fretting phenomena at neck-head interface of Ti6Al4V alloy. In particular, hip necks subjected to burnishing process are the objective of the experimental campaign. Ti6Al4V is a widely used material in orthopedic implants due to its excellent biocompatibility and mechanical properties. However, the potential for fretting fatigue is a common concern in hip implants requiring the exploitation of surface modification techniques to enhance the implant's performance and durability. Burnishing process involves the controlled application of mechanical pressure to the implant's surface, which can generate residual stresses and changes in surface topography. By employing advanced surface characterization techniques, including micrograph and profilometry, the surface modifications induced by burnishing were evaluated. Furthermore, fretting fatigue assessment was carried out through mechanical testing, simulating the conditions encountered in the hip joint during typical daily activities. Finally, an emerging sensing technology in the field of non-destructing optical testing, phase-based motion estimation (PBME) was employed in order to assess the surface gradual degradation before failure. [ABSTRACT FROM AUTHOR]

In this study, a new model is developed for fretting fatigue crack initiation life prediction based on the slip amplitude as a macroscopic feature of the contact interfaces. The main difference between the presented model and many other fretting fatigue life prediction models is the focus on the fretting specific characteristics. In this model, a damage parameter is combined with a damage severity factor to obtain a new fretting fatigue crack initiation life prediction parameter. To investigate the accuracy of this new parameter, a series of fretting fatigue tests were conducted. Also, crack initiation life data from the literature were added to enhance parameter accuracy investigation. It was shown that the effective slip amplitude was an unbiased geometric-independent parameter in fretting fatigue crack initiation life prediction. Also, comparison of the prediction results from the effective slip amplitude with those of Smith-Watson-Topper and Ruiz parameters illustrated that the new parameter could outperform available fretting fatigue life prediction parameters. [ABSTRACT FROM AUTHOR]

In studies on a material fretted with different contact pad materials having different hardness values, there will be effect of both chemical composition and hardness. In the present work, the effect of hardness was studied by keeping the chemical composition of the contact pad material the same. Test samples were made of Ti–6Al–4V and fretting pads were made of Alloy 718. By heat treatments (annealing and ageing), the hardness of the pads was changed. The effect of hardness of pads was observed only at higher contact pressure of 175 MPa and lower cyclic stresses, where annealed pads restricted the life of Ti–6Al–4V samples compared to aged pads. This is because the relatively softer Alloy 718 pads in annealed condition had relatively higher adhesion to the Ti–6Al–4V samples leading to higher tangential force coefficient values compared to that of harder pads in the aged condition. [ABSTRACT FROM AUTHOR]

Saddle systems have been used on recent projects to support the cables in cable-stayed and extradosed bridge structures. A major design consideration for these anchorage systems is the in-service fretting fatigue behaviour of the cables within the pylon saddle. In order to better understand the fatigue behaviour of these anchorage systems, a research project was undertaken, wherein fatigue tests were performed on saddle test specimens, analytical models for calculating displacements and contact forces were developed, and a multiaxial stress-based fretting fatigue model was developed for calculating fatigue life. In the current paper, it is shown how the developed models can be used to perform probabilistic analysis of fretting fatigue life for the purpose of assessing the fatigue reliability of saddle systems, using two approaches – fretting maps, in conjunction with Monte Carlo simulation (MCS) or the multiplicative dimensional reduction method (MDRM). [ABSTRACT FROM AUTHOR]

This paper analyses the phenomenon of fretting and fretting wear to the classical and modular total hip prostheses. Theoretical and experimental manifestations are studied, at the interface of the femoral stem with the bone cement mantle, at the taper junction between the femoral stem and the femoral head of the prosthesis, as well as at the tapering of the connections of the femoral neck adapter with the stem and the femoral head. The aim of the paper is to highlight the implications of modularisation of the total hip prosthesis femoral component, especially its tribological implications (fretting wear of modular junctions, fatigue and corrosion by fretting), which can contribute to increasing ion concentrations of the metal in the blood and the possibility of femoral stem fracture at the femoral head - neck junction. Experimental laboratory studies focused on the analysis of the tribological phenomena occurring at the taper junctions between the femoral head and neck, as well as the neck and femoral stem, highlighting the relevant qualitative tribological aspects. For this purpose, experimental junctions were fabricated and tested on a universal MTS mechanical machine, equipped with an Instron® fatigue testing device. The importance of the materials used for the taper (or trapezoidal) junction components and the measures to reduce the micro-motion, which reveal the phenomena of fretting, corrosion and fretting fatigue, are highlighted. The influence of tapering on tribological phenomena is also analyzed. [ABSTRACT FROM AUTHOR]

The objective of this work is to conduct an experimental campaign to evaluate the effects of the catenary parameter ( H/w ) on the fatigue life of overhead conductors, being H the horizontal tensile load of the power line and w the weight per unit length of the conductor. A battery of twenty seven (27) fatigue tests was carried out on three types of conductors, an AAAC 900 MCM, an AAC Orchid and an ACSR Tern. For this study, all tests were conducted using the value of H/w = 2144 m. Fatigue damage, one of the major problems affecting power line conductors around the world, is caused by Aeolian vibration, characterised by high frequency and low amplitude movements. Based on field observations, the H/w parameter has recently been proposed as a fatigue design criterion for different families of cables. However, there is little experimental data available in the literature to assess the impacts of this hypothesis. Comparison between the generated S-N curves proved that an ACSR Tern conductor could sustain a significantly higher number of cycles before fatigue failure than the AAAC 900 MCM for this level of H/w . Meanwhile, the AAC Orchid presents a fatigue life situated between the AAAC 900 MCM and the ACSR Tern conductors. Failure analysis of the broken samples revealed not only that cracks initiated in the fretted areas of the aluminium wires but also that their morphology presented clear evidence of fatigue failure, such as observable beach marks and secondary cracks. Additionally, a failure map has been raised to determine the precise layer and the position from the clamp mouth where the wires broke. Furthermore, the provided information could be helpful for planning the maintenance of power lines. [ABSTRACT FROM AUTHOR]

This paper presents a real case study of a generator that successfully passed testing in one environment; although, the rotor shaft failed mechanically when the testing environment had been customized. So, to design a robust rotor shaft, major factors that affect the life time of the rotor shaft should be addressed and considered. These major factors which are addressed in this paper are fundamental geometry driven stress concentration factors, fretting driven fatigue stress concentration effects and vibration natural frequency. Finite elements analysis and extensive mechanical vibration tests were used to achieve a robust shaft design. [ABSTRACT FROM AUTHOR]

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This paper presents a comparative study for the fatigue behavior between an All Aluminium Alloy Conductor (AAAC) and a Aluminum Conductor Steel Reinforced (ACSR). These cables use Aluminium Alloys (AA) 6201-T81 and 1350-H19, respectively. This test program was carried out at a resonant fretting fatigue bench for overhead conductors at the University of Brasília. The results showed that the ACSR conductor fails by fatigue when is subjected to bending amplitude stress levels which are in average more than 1.25 times greater than that sustained by AAAC conductors (for the life ranges studied). In terms of durability, the ACSR has a fatigue life 5 times greater than the AAAC. A notch sensitivity analysis using Neuber's approach was invoked to try to explain this “anomalous behavior” for the cables fatigue performance, considering that the AA 6201-T81 has a significantly higher fatigue limit than the AA 1350 -H19. [ABSTRACT FROM AUTHOR]

Fretting fatigue is a critical load that appears on many structures, such as the blade/disk contact of aircraft engines, train wheel assemblies, etc. Predicting crack nucleation risk is essential for safety, but is particularly complex. Fretting contact stress is multiaxial, with severe stress gradients. To palliate this difficulty, a common approach consists in computing multiaxial fatigue at a critical distance, thus correcting the stress gradient effect and achieving stable pertinent predictions. However, this strategy is very costly in FEM computation due to very fine FEM mesh size, which may be <10 μm, and application needs to be limited in large 3D industrial contacts. Investigating the partial slip fretting crack nucleation boundaries of 35NCD16 steel (plane) fretted against 52100 steel cylinders, a new semi-empirical contact loading parameter was introduced, defined as the maximum shear stress generated in the interface (q max ) multiplied by the square-root of the sliding size (s) of the partial slip interface (i.e., ϕ = q max ×√s). Using this very simple parameter inspired by “crack analog strategy”, it was found that all the crack nucleation data obtained for a wide spectrum of contact pressures and cylinder radii were aligned along a single master curve. Scatter was very low, even less than for the costly “fatigue-critical distance method”. The approach was extended to various fretting-fatigue loading conditions, confirming stability of prediction. [ABSTRACT FROM AUTHOR]

Although cemented titanium alloy is not favored currently in the Western world for its poor clinical and radiography outcomes, its lower modulus of elasticity and good biocompatibility are instrumental for its ability supporting and transforming physical load, and it is more suitable for usage in Chinese and Japanese populations due to their lower body weights and unique femoral characteristics. Through various friction tests of different cycles, loads and conditions and by examining fretting hysteresis loops, fatigue process curves and wear surfaces, the current study investigated fretting wear characteristics and wear mechanism of titanium alloy stem–bone cement interface. It was found that the combination of loads and displacement affected the wear quantity. Friction coefficient, which was in an inverse relationship to load under the same amplitude, was proportional to amplitudes under the same load. Additionally, calf serum was found to both lubricate and erode the wear interface. Moreover, cement fatigue contact areas appeared black/oxidative in dry and gruel in 25% calf serum. Fatigue scratches were detected within contact areas, and wear scars were found on cement and titanium surfaces, which were concave-shaped and ring concave/ convex-shaped, respectively. The coupling of thermoplastic effect and minimal torque damage has been proposed to be the major reason of contact damage. These data will be important for further studies analyzing metal–cement interface failure performance and solving interface friction and wear debris production issues. [ABSTRACT FROM AUTHOR]

To date, only a few full-scale experimental investigations of the fatigue behavior of stay cables under axial loading and transverse displacements have been conducted. Modern cable anchorage systems often feature technologies that reduce local bending effects significantly and. therefore, interwire friction (fretting) may often constitute the main mechanism of the fatigue life reduction. However, the influence of transverse deformations and interwire movements at the critical locations on bending fatigue has not been measured and described in detail. The objective of the full-scale experimental investigation described herein was to study the structural response of a multi-strand stay cable to cyclic bending and to establish a correlation between the reversed cyclic flexural behavior of a single strand and that of a multi-strand stay cable. For this purpose, a digital image correlation (DIC) technique was employed as a tool for quantifying the deformations occurring on the surface of the strand and between wires. Moreover, the relationship between the transversal stiffness and the variation in tensile force of a single strand and that of a multi-strand specimen was studied. The novel application of the DIC technique for the measurement of local cable deformations provided valuable information on the internal state of displacement of the multi-strand stay cable under bending and resulted in the gaining of significant insight into the deformation and cyclic bending behavior of stay cable assemblies under axial and transverse loading. [ABSTRACT FROM AUTHOR]

Journal bearings as so sensitive parts of steam turbines are very susceptible to failure through different mechanisms of wear, fatigue and crush during service conditions. Failure occurring through these mechanisms lead to turbine completely shut down as a result of interfering in working conditions of bearing different parts. In this research, failed interfered part of a journal bearing related to a 320,000 kW steam turbine was examined. Failure analysis investigations were performed by utilizing of stereographic, optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) analysis and hardness test. Surface crush, large amounts of surface cracks, no noticeable changes of failed surface chemical composition and microstructure with significant hardness improvement were the main obtained results. The studies were revealed that the bearing part loosing and inappropriate clearance can produce relative displacements under cyclic gradient loading. This condition was detrimental for the service life of turbine journal bearing via failure through fretting fatigue mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Large bore four stroke diesel engines are widely employed in power demanding applications such as large ships and terrestrial power plants. Due to the extremely high number of cycles they are subject to (above 108), components are designed according to the infinite-life approach. Although fatigue cracks are well below the propagation threshold, concurring damage phenomena such as corrosion, wear, fretting, and overloads can trigger them, leading to failure in relatively short times and posing great challenges to an accurate root cause failure analysis. In this paper, the fatigue failure of connecting rods initiated by fretting damage is described. Fracture mechanics and Hertz theory were employed to assess the main parameters controlling the damage and to define thus appropriate corrective actions. Connecting rods which were considered to be susceptible to fatigue crack propagation were subsequently monitored through a tailored ultrasonic testing procedure. [Copyright &y& Elsevier]

Abstract: Fretting fatigue behaviour of solution treated and aged near a-titanium alloy Timetal 834 was investigated at a constant stress amplitude of ±800 MPa, and different contact stresses of 50, 63, and 75 MPa at cyclic frequency of 0.1 Hz, at room temperature. Also wear behaviour of the alloy was studied against EN31 steel counter body, under dry sliding condition, at different loads from 2 to 10 kg and sliding velocity of 1 ms−1, at room temperature. The fretting fatigue life of the alloy was found to decrease drastically with increasing contact stress above 50 MPa. Wear rate of the alloy was found to increase linearly up to the entire load range investigated. Fall in fatigue life, with increase in contact load, occurs due to early crack initiation at stress concentration sites. These sites form due to combined effect of wearing in localized regions and consequent increase in absorption of oxygen in those regions because of much higher degree of plastic deformation in them.The wear behavior is discussed in terms of the nature of the debris formed. [Copyright &y& Elsevier]

Abstract: Fretting fatigue is an important consideration in the design and optimization of mechanical systems and assemblies in the recent times. Empirical approaches, multi-axial fatigue considerations and fracture mechanics approaches are considered for assessing fretting fatigue damages at contact interfaces of assemblies. Ruiz criteria is an effective empirical approach for evaluation of Fretting Fatigue Damage Parameter (FFDP) and has been demonstrated in two dimensional fretting studies of a typical dovetail interface problem. The current paper considers the extension of Ruiz criterion for assessing fretting fatigue damage parameter for three dimensional problems. Two approaches viz. summation of FFDP computed independently along the two slip directions and combined maximum principal-shear stress approach have been proposed for the FFDP evaluation, considering three dimensional stress and slip components over contact interface. FFDP evaluation using maximum principal-shear stress approach is observed to be more appropriate for three dimensional problems [Copyright &y& Elsevier]

Abstract: Fretting fatigue generally leads to the degradation of the fatigue strength of a material due to cyclic micro-slip between two contacting materials. Fretting fatigue is regarded as an important issue in designing aerospace structures. The primary goal of this study was to characterize the fretting fatigue crack initiation behavior in the presence of plasticity. Experimental tests were performed using pad configurations involving elastic-plastic deformations. To calculate stress distributions under elastic-plastic fretting fatigue conditions, FEA was also performed. The critical distance methods, which are commonly used in notch analysis, were applied to the fretting fatigue problem. In conclusion, the effective strain range method when used in conjunction with the SMSSR parameter showed a good correlation of data points between the pad configurations involving elastic and elastic plastic deformations. [Copyright &y& Elsevier]

Abstract: Fretting fatigue generally leads to the degradation of the fatigue strength of a material due to cyclic micro-slip between two contacting materials. Fretting fatigue is regarded as an important issue in designing aerospace structures. The primary goal of this study was to characterize the fretting fatigue crack initiation behavior in the presence of plasticity. Experimental tests were performed using pad configurations involving elastic-plastic deformations. To calculate stress distributions under elastic-plastic fretting fatigue conditions, FEA was also performed. The critical distance methods, which are commonly used in notch analysis, were applied to the fretting fatigue problem. In conclusion, the effective strain range method when used in conjunction with the SMSSR parameter showed a good correlation of data points between the pad configurations involving elastic and elastic plastic deformations. [Copyright &y& Elsevier]