Effect of contact pressure on fretting fatigue of austenitic stainless steel

The effect of contact pressure on fretting fatigue in solution-treated austenitic stainless steel was studied. With an increase in contact pressure, fretting fatigue life was almost unchanged at low contact pressures, however it decreased drastically at high contact pressures. At low contact pressures, stress concentration due to fretting damage occurred at the middle portion of the fretted area and the main crack responsible for failure was initiated there. At high contact pressures, concavity was formed at the fretted area without accompanying heavy wear. The main crack was initiated at the outer edge corner of the concavity which probably acted as a notch. Plain fatigue prior to the fretting fatigue test increased the fretting fatigue life at high contact pressures since the concavity formation was suppressed by the cyclic strain hardening.     

Mechanism of reduction of fretting fatigue limit caused by hydrogen gas in SUS304 austenitic stainless steel

The fretting fatigue strength of pre-strained SUS304 is reduced in hydrogen gas. The mechanism of the reduction is discussed. In hydrogen gas, local adhesion between contacting surfaces occurred and many small cracks were formed at the adhered spots. The major crack propagated from one of the small cracks. The roles of the adhesion in relation to the initiation and propagation of the small cracks were examined by a two-step environment test. When adhesion was prevented by an oxidized film, no failure of the specimen occurred. It can be presumed that the stress conditions were more severe in hydrogen gas than that in air due to local adhesion.     

Microstructure sensitivity of fretting fatigue based on computational crystal plasticity

Three-dimensional finite element simulations are conducted to study the effects of microstructure on the fretting fatigue behavior of duplex Ti-6Al-4V. These fretting simulations involve a rigid cylindrical indenter pressed on the half space of Ti-6Al-4V with different realizations of microstructure. The deformation behaviors of the primary α and α/β lamellar phases at room temperature are described by three-dimensional crystal plasticity constitutive relations. Microstructure attributes considered in this sensitivity study include crystallographic texture, grain size, and grain size distribution. Voronoi tessellation is used to construct the three-dimensional finite element models with various grain size distributions. The plastic strain behaviors and the distribution of the average maximum plastic shear strain among grains are analyzed and contrasted. The relative susceptibility for crack formation, including effects of various microstructure features, is determined using the Fatemi-Socie parameter. The results suggest that both average grain size and especially crystallographic texture have more influence on the plastic deformation and fretting fatigue behavior than grain size distribution for the fretting condition considered.     

Prediction of the fretting fatigue resistance of various surface-modification layers on 1045 steel: the role of fretting maps

In this work, fretting maps of various surface modifications were established based on the friction logs of fretting experiments. The fretting fatigue resistance of the coatings was analyzed according to the features of the fretting maps of the coatings. The results showed clearly that fretting maps of materials are effective tools to predict the fretting fatigue properties of substrates and surface-modification coatings. It was also demonstrated that the fretting fatigue resistance of a 1045 steel substrate could be improved to different extents through surface modification. The fretting fatigue resistance of solid lubricating coatings was the best and the tendency for initiation and propagation of cracks in the substrate material could also be restrained by depositing hard coatings.     

A study on fretting fatigue characteristics of Inconel 690 at high temperature

Inconel 690 alloy is used in nuclear power plant steam generator tubes. Fretting fatigue experiments were performed on Inconel 690 specimens at room temperature and at the nuclear power plant operating temperature of 320 °C. By comparing the fretting fatigue test data at room temperature and 320 °C, this study analyzed the change in characteristics related to the fatigue limit at 10⁷ cycles. In addition, this study attempted to measure changes in the friction force for repetitive cycles in fretting fatigue tests, and analyzed the mechanism of fretting fatigue by observing the fracture surfaces and performing spectrum analysis.     

Some observations on the CLNA model in fretting fatigue

Using the Atzori–Lazzarin criterion, the author has recently proposed a unified model for Fretting Fatigue denominated Crack-Like Notch Analogue—CLNA model, considering only two possible behaviours: either “crack-like” or “large blunt notch”. In a general FF condition, the former condition is treated with a single contact problem corresponding to the MIT Crack Analogue (CA) improved in some details also by the author. The latter, with a simple peak stress condition, i.e. a simple Notch Analogue model, simply stating that below the fatigue limit, infinite life is predicted for any size of contact. In the typical condition of constant normal load and in phase oscillating tangential and bulk loads, both limiting conditions are immediately written, and the CLNA model permits to collapse the effect of the contact loads on a single closed form equation (differently from many other models which do not permit this flexibility). For not too large contact areas (“crack-like” contact) no dependence at all on geometry is predicted, but only on 3 load factors (bulk stress, tangential load and average pressure) and size of the contact. Only in the “large blunt notch” region occurring typically only at very large sizes of contact does size-effect disappear, but the dependence on all other factors including geometry remains. The model compares favourably with some experimental results in the literature. In this paper, some aspects of the CLNA model are further elucidated.     

Fretting fatigue properties of plasma nitrided AISI 316 L stainless steel: Experiments and finite element analysis

This study investigates the effects of thickness, hardness and composition of modified layer on the plain and fretting fatigue properties of the nitrided 316 L steel plasma nitrided under various processing conditions. Fretting fatigue behaviour of untreated and nitrided material is also analysed with the finite element method. Experimental and theoretical fatigue life results are compared. The result indicates that the nitriding process improved the fretting fatigue properties of 316 L stainless steel. The experimental test results are close to theoretical fretting fatigue life results, thus it yields that the established model in the numerical analysis is consistent in this regard.     

Effect of contact load on fretting fatigue behaviour of steel wires

Abstract

The tension–tension fretting fatigue tests of steel wires were performed on a self-made fretting fatigue test equipment under contact loads ranging from 40 to 70 N and a strain ratio of 0·8. The results showed that when the contact load increased, the fretting regime of steel wires transformed from gross slip regime to mixed fretting regime. The fretting fatigue life in the mixed fretting regime was significantly lower than that in the gross slip regime. The main fretting wear mechanisms in the gross slip regime, where there were serious fretting damage and a lot of wear debris, were abrasive wear and fatigue wear. Microcracks were observed in the fretting scar of the mixed fretting regime, and the main fretting wear mechanisms were adhesive and fatigue wears. The fretting wear scar was the fatigue source region, and the fatigue fracture surface could be divided into three regions.     

An experimental study torsional fretting behaviors of LZ50 steel

Four simple fretting modes are defined according to relative motion: tangential, radial, rotational, and torsional fretting. This paper presents a new test rig that was developed from a low-speed reciprocating rotary system to show torsional fretting wear under ball-on-flat contact. Torsional fretting behavior was investigated for LZ50 steel flats against AISI52100 steel balls under various angular displacement amplitudes and normal loads. The friction torques and dissipation energy were analyzed in detail. Two types of T–θ curves in the shape of quasi-parallelograms and ellipticals were found that correspond to gross and partial slips, respectively. The experimental results showed that the dynamic behavior and damage processes depend strongly on the normal loads, angular displacement amplitudes, and cycles. In this paper, the debris and oxidation behaviors and detachment of particles in partial and gross slip regimes are also discussed. Debris and oxidation are shown to have important roles during the torsional fretting processes. The wear mechanism of torsional fretting was a combination of abrasive and oxidative wear and delamination before third-body bed formation. The mechanism was then transformed into third-body wear after a great amount of debris formed.     

Progress in standardization of fretting fatigue terminology and testing

This paper reviews the current ASTM, ISO, and other standards that pertain in part to fretting fatigue and fretting wear testing. A historical perspective gives some background on why there still are relatively few standards for fretting fatigue and fretting wear testing. Current standards on the books tend to be application specific. In the past few years, there have been some new activities in standardization. These developments along with future needs in standardization are discussed.     

Subsurface damage development during fretting fatigue of high strength steel

The results of fretting fatigue experiments performed on two high-strength structural steels, PH 13-8 Mo stainless steel and quenched and tempered 4340 steel, are evaluated. Observations regarding the subsurface deformation and cracking behavior of the steels are compared and contrasted. It was found that the fretting stresses influenced early crack growth to a greater depth in PH 13-8 Mo stainless steel than in 4340 steel. In addition, experiments on PH 13-8 Mo led to the development of a region below the fretting scar that underwent a microstructural transformation, while experiments on 4340 steel did not. Likely reasons for this discrepancy are suggested. Differences in the formation of oxide layers and the occurrence of adhesion between the two materials are also discussed.     

An experimental study on radial fretting behaviour

A new test apparatus has been developed for radial fretting test. Main experimental conditions are as follows: the amplitude of normal load from 200 to 800N, the number of cycles from 1 to 3×10⁵ cycles. Three contact pairs (a 52100 ball against 52100, 1045, 1045 steel with TiN coating) were used for the test. Variations of normal load vs indentation depth between two contact surfaces have been analyzed as a function of cycles. Contact degradation was examined through metallographic expertise on the flat specimen and radial fretting behaviour was compared in the paper.     

Modeling of geometry effects in fretting fatigue

The stress field that results from two bodies in contact is an important aspect that governs the fretting fatigue behavior of materials. Applied loads as well as contact geometries influence the contact stresses. The profile of an indenter and the boundary conditions provide sufficient information from which the surface tractions and the corresponding subsurface stresses have been calculated in a semi-infinite halfspace using singular integral equations. In this investigation, a numerical subroutine was developed to calculate the surface tractions and the corresponding surface and subsurface stresses of an arbitrary finite thickness infinite plate subjected to loading through a random indenter. The results from the detailed stress analysis of the contact region are required by both an initiation and fracture mechanics approach. While initiation criteria involving stress gradient fields, such as sharp notches and edges of contact in fretting fatigue, are not well established or agreed upon, stress intensity factor calculations using tools such as weight functions are more reliable. The stress intensity analysis, which is used to determine whether an initiated crack will continue to grow if it is above the threshold, depends on many variables in the stress analysis such as pad and specimen geometry, loading configuration and friction coefficient. The contact stress analysis has been used to determine equivalent stress parameters that are related to the initiation of a crack. Similarly the numerical subroutine for the contact stresses is used in conjunction with the stress intensity analysis to determine the influence of the geometry, loading configuration and friction coefficient on the stress intensity factor. Results from high-cycle fretting fatigue experiments are used to determine the threshold stress intensity factor for a given configuration. The combination of the numerical and experimental analysis is then used to develop a tool for high-cycle fretting fatigue based on a threshold approach involving a go–no go criterion.     

Influence of surface-coatings on titanium-alloy resistance to fretting fatigue in cryogenic environment

Fretting damage, also known as small amplitude oscillatory sliding motion, can lead to catastrophic failure in many industrial applications. The understanding of fretting fatigue and its reproduction in laboratory tests have enable us to evaluate the fretting resistance of homogeneous substrate. To reduce the damage caused by fretting fatigue increasing use has been made of coatings or heat treatments which result in non homogeneous solids. From a theoretical point of view, ascertaining the mechanical behaviour of materials so modified is quite complex due to insufficient definition of the contact parameters. This present study seeks to analyse a layered medium undergoing fretting fatigue and the improvement of its fatigue criterion.     

Quantitative analysis of fretting fatigue degradation in 7075-T6 aluminum alloy

Fretting fatigue failures are commonly observed in the aviation industry. The objective of this study was to understand the fretting fatigue mechanism by characterization of fretting fatigue degradation to gain insight into the process of crack formation from pits in 7075-T6 aluminum alloy. This paper focuses on the quantitative analysis of fretting fatigue degradation in terms of pit depths and dominant crack formation. For 60 percent of the specimens, the dominant crack nucleated from a pit other than the maximum-depth pit observed on the fracture surface.     

The effect of fretting on the fatigue behaviour of plasma nitrided stainless steels

The plain fatigue and fretting fatigue behaviour of a plasma nitrided dual phase stainless steel known as 3CR12 and an AISI 316 austentic stainless steel have been studied in the present work, using a modified Wohler rotating-bending configuration. Test specimens were produced at two nitriding temperatures, namely 400 and 520 °C, representing low temperature and conventional nitriding temperature, respectively. The test results demonstrate that both nitriding processes can enhance the plain fatigue limit of these steels by approximately 10-25%, with the high temperature process being slightly more effective. Under fretting fatigue conditions, the beneficial effect of plasma nitriding is even more significant and the fretting fatigue limit is increased between 50 and 100% for 3CR12 and at least 50-150% for the AISI steel as the nitriding temperature is raised from 400 to 520 °C.     

车轴轮座微动损伤对车轴疲劳寿命的影响

使用有限元软件ANSYS计算轮座损伤对车轴疲劳寿命的影响.首先计算车轴的稳态受力,这时主要考虑两种栽荷:过盈应力和额定载重应力,关键是考虑两种载荷的复合作用效应.采用外推方法获得车轴材料的S-N曲线,然后将其导入有限元程序进行计算.计算结果表明:有微动损伤的车轴疲劳寿命比无微动损伤的疲劳寿命明显减少.     

Finite element analysis of shot-peening effect on fretting fatigue parameters

Shot peening is widely used to improve the fretting fatigue strength of critical surfaces. Fretting fatigue occurs in contacting parts that are subjected to fluctuating loads and sliding movements at the same time. This paper presents a sequential finite element simulation to investigate the shot peening effects on normal stress, shear stress, bulk stress and slip amplitude, which are considered to be the controlling parameters of fretting damage. The results demonstrated that among the modifications related to shot peening, compressive residual stress has a dominant effect on the fretting parameters.     

Torsional fretting fatigue strength of a shrink-fitted shaft with a grooved hub

Fretting causes considerable reduction in the fatigue strength of a shrink-fit assembly and failures through fretting are as numerous as failures from normal fatigue. The purpose of this investigation was to determine the effect of contact pressure and slip amplitude on the fatigue limit, and a favourable value for overhang of hub and fillet radius with constant diameter ratio, at which fretting failure can be avoided and the maximum normal fatigue strength will be obtained. The torsional fatigue strength of shrink-fitted shaft couplings was estimated by tests performed by varying the overhang of the hub, the fillet radius of the shaft and the contact pressure of the shrink-fitted assembly. Press-fitting of the hub overhanging the shoulder was used to increase the contact pressure. The tests were performed using a grooved hub. These experiments showed that fretting was reduced with an increase in contact pressure, because the slip amplitude decreased. The shaft was fractured just inside the end of the fit by fretting fatigue with low contact pressure, but if the contact pressure was very high, the shaft fractured at the fillet by normal fatigue. The fretting fatigue limit at a constant diameter ratio increases with an increase in the fillet radius, and reaches its maximum value at a certain radius using the grooved hub.     

An improved method to identify grain boundary creep cavitation in 316H austenitic stainless steel

Inter-granular creep cavitation damage has been observed in an ex-service 316H austenitic stainless steel thick section weldment. Focused ion beam cross-section milling combined with ion channelling contrast imaging is used to identify the cavitation damage, which is usually associated with the grain boundary carbide precipitates in this material. The results demonstrate that this technique can identify, in particular, the early stage of grain boundary creep cavitation unambiguously in materials with complex phase constituents.