Fretting wear of iron, nickel, and titanium under varied environmental conditions

Fretting wear experiments were conducted on high purity iron, nickel and titanium in air under conditions of varied humidity and temperature, and in nitrogen. For iron and titanium, maximum fretting occurred at 10 and 30 percent relative humidity respectively. Nickel showed a minimum in fretting wear at about 10 percent relative humidity. With increasing temperature, all three metals initially showed reduced fretting wear, with increasing wear observed as temperatures increased beyond 200-300 C. For titanium, dramatically reduced fretting wear was observed at temperatures above 500 C, relatable to a change in oxidation kinetics. All three metals showed much less fretting wear in N2 with the presence of moisture in N2 having a proportionally stronger effect than in air

Fretting of titanium at temperatures to 650 C in air

Fretting wear experiments were conducted on high-purity titanium at temperatures up to 650 C. Results indicate that up to about 500 C, the fretting wear increases with temperature. A further increase in the temperature up to 650 C results in decreasing fretting wear. This change in trend of fretting wear with temperature is shown to be associated with a change in oxidation rate. Additional experiments at 650 C showed a transmission from a low rate of fretting wear to a higher rate occurred after exposure to a number of fretting cycles; the number of cycles required to cause this transition was dependent on the normal load. Scanning electron microscopy studies revealed that this transition was marked by cracking and disruption of the surface oxide film. A model was proposed that coupled the oxidation rate kinetics of titanium at 650 C with the occurrence of wear at the surface of the oxide film

Delamination-fretting wear failure evaluation at HAp-Ti-6Al-4V interface of artificial hip implant

Osteoarthritis due to rapid aging population in Malaysia and developed countries leads to an extensive application of titanium artificial hip implants. However, titanium alloys (Ti-6Al-4V) cannot directly adhere with human bone due to bio-compatibility issue. Thus, Hydroxyapatite (HAp:Ca10(PO4)(OH)2) coating which consists of main composition of human bone is plasma sprayed on titanium implants to maintain fixations during bone in-growth process. HAp coatings are susceptible to fail due to brittle fractures (coating through thickness crack) to initiate delamination which promotes fretting wear behaviour. Fretting wear particles are concerned for activating inflammations at surrounding organs, which lead to loosening of implants or subsequent failures. Present research aims to develop a finite element model to examine delamination-fretting wear behaviours that can suitably mimic actual loading conditions at HAp-Ti-6Al-4V interface of hip implant femoral stem component to formulate maximum wear depth predictive equation as a novel and fast failure prediction tool. Three simple finite element contact configuration models subjected to different mechanical and tribological properties consist of contact pad (bone), HAp coating and Ti-6Al-4V substrate are developed using contact modelling, cohesive zone modelling (CZM) and adaptive wear modelling (UMESHMOTION) approaches to be examined under static simulation. The developed finite element models are validated and verified with modified Hertzian theoretical solution and reported literatures. The findings revealed that significant delamination-fretting wear is recorded at contact edge (leading edge) as a result of substantial contact pressure and contact slip driven by stress singularity effect. Tensile-compressive condition (R = -1 ) experiences most significant delamination-fretting wear behaviour (8 times higher) compared to stress ratio R = 0.1 and R = 10. Finally, maximum delamination-fretting wear depth predictive equations are successfully formulated with significant goodness of fit and reliability as a fast failure prediction tool

A numerical study on the effect of debris layer on frettingwear

Fretting wear is the material damage of two contact surfaces caused by micro relative displacement. Its characteristic is that debris is trapped on the contact surfaces. Depending on the material properties, the shapes of the debris, and the dominant wear mechanisms, debris can play different roles that either protect or harm interfaces. Due to the micro scale of the debris, it is difficult to obtain instantaneous information and investigate debris behavior in experiments. The Finite Element Method (FEM) has been used to model the process of fretting wear and calculate contact variables, such as contact stress and relative slip during the fretting wear process. In this research, a 2D fretting wear model with a debris layer was developed to investigate the influence of debris on fretting wear. Effects of different factors such as thickness of the debris layer, Young's modulus of the debris layer, and the time of importing the layer into the FE model were considered in this study. Based on FE results, here we report that: (a) the effect of Young's modulus of the debris layer on the contact pressure is not significant; (b) the contact pressure between the debris layer and the flat specimen decreases with increasing thickness of the layer and (c) by importing the debris layer in different fretting wear cycles, the debris layer shows different roles in the wear process. At the beginning of the wear cycle, the debris layer protects the contact surfaces of the first bodies (cylindrical pad and flat specimen). However, in the final cycle, the wear volumes of the debris layers exhibit slightly higher damage compared to the model without the debris layer in all considered cases

A combined wear-fatigue design methodology for fretting in the pressure armour layer of flexible marine risers

This paper presents a combined experimental and computational methodology for fretting wear-fatigue prediction of pressure armour wire in flexible marine risers. Fretting wear, friction and fatigue parameters of pressure armour material have been characterised experimentally. A combined fretting wear-fatigue finite element model has been developed using an adaptive meshing technique and the effect of bending-induced tangential slip has been characterised. It has been shown that a surface damage parameter combined with a multiaxial fatigue parameter can accurately predict the beneficial effect of fretting wear on fatigue predictions. This provides a computationally efficient design tool for fretting in the pressure armour layer of flexible marine risers

Fretting wear of bolted joint interfaces

Under vibration loading, fretting wear between bolted joint interfaces may change the dynamic characteristics of structures. Even the reliability of long-lasting assembly structures could be affected. This paper focuses on an experimental study on the fretting wear behavior of bolted joint interfaces under tangential loading. A recently developed fretting test apparatus was used to measure the hysteresis loops and the bolt preload at different fretting wear cycles. Changes of tangential contact stiffness and friction coefficient were estimated from the measured hysteresis loops. Experimental results showed a large change in bolt preload, contact stiffness, and friction coefficient due to fretting wear. The effect of surface roughness on fretting wear behavior of bolted joint interfaces was discussed. A modified Iwan model, comprehensive of wear effects, was proposed to simulate the hysteresis loops. Comparison between simulations and experimental results was performed to validate the proposed method. Results achieved in this research can provide the basis for the dynamic analysis of long-lasting joint structures in which wear plays a fundamental role in modifying the contact parameters

AN ANALYTICAL APPROACH TO THE THIRD BODY MODELLING IN FRETTING WEAR CONTACT: A MINIREVIEW

In fretting wear contact, the third body is defined as the wear debris bed between two contacting bodies. The problem of third-body modelling is considered from a point of view of contact mechanics. This paper is restricted to a discussion of recent developments in analytical modelling of fretting wear contact

Prediction of fretting wear in spline couplings

The original contribution of this work is modeling of fretting wear in aero-engine spline couplings widely used in aero-industry to transfer power and torque. Their safe operation is very critical with respect to flight safety. They consist of two components namely hub and shaft. As they are of light weight, usually it is difficult to realize a perfect alignment. To allow for misalignment, their teeth are designed to be of crowned shape. The crowing allows a degree of misalignment without concentration of stresses which is otherwise inevitable if a misalignment is introduced in case of straight teeth. However, crowing results in another problem of fretting wear and fretting fatigue owing to kinematic constraints imposed as a result of misalignment. The focus of this work is development of mathematical models for prediction of fretting wear and not fretting fatigue. The spline couplings under consideration are industrial scale and made up of nitrogen hardened 42CrMo4. The aero industry requires a reliable method to model and predict fretting wear to be able to optimize the design of spline coupling and reduce the maintenance costs. Wear tests on crowned spline couplings on a dedicated test bench have been conducted and analyzed. Empirical, artificial neural network based and analytical models have been de- veloped to analyse, predict and formulate fretting wear in spline couplings. The empirical and artificial neural netwrok based models are specific to the given case of spline couplings and tribological conditions. However, the analytical model developed has been found to be quite general. Incremental fretting wear formulation both in terms of wear volume and wear depth has been realized. Some novel findings regarding effect of roughness parameters in conjunction with applied torque and misalignment angles with respect to fretting wear are also reported. It has been observed that the evolution of wear depth accelerates with increased applied torque or misalignment angle. Changes in roughness parameters are also found to be increasing with torque and misalignment angle in most of the cases. Preliminary tests for frequency effects on fretting wear have also been conducted

An ad-hoc fretting wear tribotester design for thin steel wires

Steel wire ropes experience fretting wear damage when the rope runs over a sheave promoting an oscillatory motion between the wires. Consequently, wear scars appear between the contacting wires leading to an increase of the stress field and the following rupture of the wires due to fatigue. That is why the understanding and prediction of the fretting wear phenomena of thin wires is fundamental in order to improve the performance of steel wire ropes. The present research deals with the design of an ad-hoc fretting wear test machine for thin wires. The test apparatus is designed for testing thin wires with a maximum diameter of 1.0 mm, at slip amplitudes ranging from 5 to 300 μm, crossing angle between 0-90º, and contacting force ranging from 0,5 to 5 N. The working principle of displacement amplitude and contacting force as well as the crossing angle between the wires are described. Preliminary studies for understanding the fretting wear characteristics are presented, analysing 0.45 mm diameter cold-drawn eutectoid carbon steel (0.8% C) wires (tensilestrength higher than 3000 MPa)