Fretting fatigue in engineering alloys

The experimental procedures which have been used to carry out fretting fatigue tests are reviewed and the preferred specimen and contact pad geometries and method of testing are identified. The S–N curves generated with and without fretting and subsequent analysis have been used to satisfy a number of objectives: (1) to establish the important variables which can significantly affect fretting fatigue behaviour; (2) to increase our fundamental understanding of the fretting fatigue process; and (3) to give a ranking of a diverse range of materials in terms of their resistance to fretting fatigue. The analytical methods which have been used to predict fretting fatigue crack initiation are briefly discussed. With some specimen/fretting pad material combinations, small fretting fatigue cracks are introduced at a very early stage in life and fracture mechanics methods are developed in order to model their growth. Analytical procedures for fretting fatigue based on either S–N endurance or fracture mechanics methodologies are discussed.     

Determination of fatigue fracture toughness by conventional rotary bending specimen

Determination of fatigue fracture toughness,K _fc, is made by rotary bending specimen considering partial contact of fatigue cracked surfaces in the compression side of the beam specimen. It is shown thatK _fc is a material constant independent of the nominal stress at the notch section, the specimen geometry, and the shape of the final fracture area.

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Résumé On détermine la ténacité à la rupture par fatigueK _fc à l'aide d'éprouvetes soumises à flexion rotative, en considérant le contact partiel entre les surfaces fissurées par fatigue, au cours de la phase de compression. On montre queK _fc est une constante du matériau, indépendante de la tension nominale au droit de la section entaillée, de la géométrie de l'éprouvette, et de la forme de la surface finale de rupture.

     

Fretting fatigue in AISI 1015 steel

A small oscillatory movement between two contacting surfaces is termed as fretting and on many occasions it acts as the crack initiation site leading to catastrophic failure of the overall structure. The occurrence of fretting is observed in many engineering structures such as shaft flanges, gas turbines, steel ropes etc. An experimental facility, which can simulate the fretting fatigue in many engineering applications, is the primary requirement of the research program. A laboratory fretting fatigue test facility capable of varying many influencing parameters of fretting fatigue such as slip amplitude, frequency, contact pressure, etc is designed and developed. Preliminary investigations on plain and fretting fatigue behaviour of AISI 1015 structural steel are reported in this paper. A strength reduction factor of about 1.30 was obtained due to fretting for the test material under the present experimental conditions. Influence of contact load on fretting was also studied. Increasing fretting contact load decreased the fatigue life in the range investigated. Failure analysis showed typical stage I oblique crack growth followed by stage II straight crack perpendicular to the fretting zone.     

Fretting corrosion and fatigue of gears

We describe the fretting and fatigue fracture of gears with guaranteed clearance. The results of a study of macro- and micro-reliefs of surfaces damaged by fretting and the results of X-ray analysis of products of wear and the oxide film are presented. The dependence of the joint operating conditions on the state of the working surfaces of slot teeth is analyzed.Chubar Institute of Mechanical Engineering, Zaporozh'e. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 6, pp. 112–114, November–December, 1993.     

Fretting fatigue test analysis of contact

Fretting fatigue tests conducted by Nowell and Szolwinski are analysed accurately by introducing several modifications needed to the classical formulation. With the total state of stress established, the crack‐tip stress intensity factor for a crack growing inward from the trailing edge of the contact is determined by the distributed dislocation technique. Finally, the results are correlated with local solutions for the contact stress field that enable an estimate of the crack nucleation life, and hence a characteristic material property quantifying initiation, to be found.     

Fretting fatigue limit as a short crack problem at the edge of contact

This paper proposes a local stress concept to evaluate the fretting fatigue limit for contact edge cracks. A unique S–N curve based on the local stress could be obtained for a contact edge crack irrespective of mechanical factors such as contact pressure, relative slip, contact length, specimen size and loading type. The analytical background for the local stress concept was studied using FEM analysis. It was shown that the local stress uniquely determined the ΔK change due to crack growth as well as the stress distribution near the contact edge. The condition that determined the fretting fatigue limit was predicted by combining the ΔK change due to crack growth and the ΔK_th for a short crack. The formation of a non‐propagating crack at the fatigue limit was predicted by the model and it was experimentally confirmed by a long‐life fretting fatigue test.     

Fretting fatigue behaviour of Ni-free high-nitrogen stainless steel in a simulated body fluid

Abstract

Fretting fatigue behaviour of Ni-free high-nitrogen steel (HNS) with a yield strength of about 800 MPa, which was prepared by nitrogen gas pressurized electroslag remelting, was studied in air and in phosphate-buffered saline (PBS(-)). For comparison, fretting fatigue behaviour of cold-rolled SUS316L steel (SUS316L(CR)) with similar yield strength was examined. The plain fatigue limit of HNS was slightly lower than that of SUS316L(CR) although the former had a higher tensile strength than the latter. The fretting fatigue limit of HNS was higher than that of SUS316L(CR) both in air and in PBS(-). A decrease in fatigue limit of HNS by fretting was significantly smaller than that of SUS316L(CR) in both environments, indicating that HNS has better fretting fatigue resistance than SUS316L(CR). The decrease in fatigue limit by fretting is discussed taking into account the effect of friction stress due to fretting and the additional influences of wear, tribocorrosion and plastic deformation in the fretted area.     

Fretting fatigue failure mechanism of automotive shock absorber valve

Fretting fatigue is a complex mechanical failure phenomenon, in which two contact surfaces undergo a small relative oscillatory motion due to cyclic loading. This study proposes a methodology to analyze the fretting fatigue failure mechanism of automotive shock absorber valve by means of experimental and numerical approaches. A servo hydraulic test set-up is used to simulate fretting fatigue under real working conditions. Moreover, a 3-D finite element model is developed to analyze the contact status and stress distribution at contact interface between connected components, i.e. washer-disc contact. The experimental test results depict that fretting damage appears at contact interface between washer and disc, which causes the initial crack nucleation and advancing the crack up to the final fracture of valve disc. Stress field, obtained by numerical simulation, is used to monitor some fretting fatigue features such as the distribution of relative slip amplitude, contact pressure and different stress fields at contact interfaces. Eventually, the crack initiation site is estimated by monitoring variation of equivalent multiaxial damage stress at contact interface.     

Corrosion fatigue life prediction of a steel shaft material in seawater

Corrosion fatigue behaviour of a medium strength structural material was studied in air and in 3.5% NaCl solution. Emphasis was placed on the study of corrosion pit formation and the development of cracks from pits. Pitting and crack propagation were quantified throughout the fatigue loading thereby allowing a model to be developed that included the stages of pitting and the pit-to-crack transition in order to predict the fatigue life. The results showed that a large number of corrosion pits with small size form at a very early stage in the fatigue lifetime. The number of pits and subsequent cracks was found to be higher at higher stress levels leading to multiple crack development and coalescence. When compared to air, fatigue life in a corrosive environment was significantly reduced at low stress levels due to pitting damage, indicating a dominant role of corrosion over that of mechanical effects. The corrosion fatigue model proposed shows good agreement with the experimental test data at lower stress levels but predicts more conservative lifetimes as the stress increases. Kitagawa–Takahashi diagram was produced for both test environments where it is indicated that the fatigue limit can be eliminated in a corrosive environment.     

罐式煅烧炉后期使用的管理和维护

包铝炭素分厂二车间所采用煅烧设备是八层五组二十室顺流式罐式煅烧炉,其中1#、2#煅烧炉处使用已达10年,超过设计使用寿命进入后期管理使用阶段。在此期间1#炉经历4次烘炉,2#炉经历2次烘炉,使得煅烧炉炉体变形严重,挥发份直接从罐内溢入火道,影响煅烧炉的正常使用。本文主要介绍炭素分厂二车间通过调整工艺参数,改进操作方式,改善煅烧炉使用情况,减缓煅烧炉老化趋势,从而确保煅烧炉的正常运行。     

FEM investigation of global mechanisms affecting brick lining stability in a rotary kiln in cold state

Severe degradation of refractory lining in a rotary kiln often leads to very costly production delays. Use of finite element analysis for understanding the mechanisms behind the failure of the lining is poorly reported in this field. To increase the knowledge and to update the field a simplified model of a kiln and a new methodology for studying stability of the lining are suggested. Behaviour of the lining in cold state – in static and dynamic cases – is studied. Influence of ovality, brick's Young's modulus and friction coefficient on stress and brick displacement are evaluated at two rotational speeds. It was found that the induced loads in the lining are harmless regardless of the tested conditions — challenging the traditional beliefs. On the other hand, recorded brick displacements were found to be significantly affected by rotational speed and ovality. Gaps as large as 80 mm could be observed between the bricks and the casing in a worst case scenario. An integrity coefficient was defined in order to quantify overall integrity of the lining.     

航空垃圾焚烧回转窑电气自动控制系统

介绍首都机场垃圾焚烧站航空垃圾焚烧系统电气自动控制系统的构成，并论述其PLC系统、变频调速系统、上位监控系统的特点。该系统配置合理、自动化及可靠性高。     

Fretting fatigue behavior of high-strength steel monostrands under bending load

In this paper, the fretting fatigue behavior of pretensioned high-strength steel monostrands is investigated. To measure the local deformations on the strands, a novel method based on the digital image correlation (DIC) technique was used to quantify the relative movement between individual wires along the length of the monostrand. Information about the monostrand bending stiffness and the extent of relative displacement between core and outer wires of a monostrand undergoing flexural deformations is provided. From the series of dynamic fatigue tests, a fretting fatigue spectrum is derived and compared with the localized bending fatigue spectrum. The presented spectra can be used for the estimation of monostrand bending fatigue life. The results presented herein form the basis for the development of a fretting failure criterion for monostrand cables experiencing transverse displacements and are of special interest for the fatigue analysis of modern stay cable assemblies where fretting constitutes a major mechanism of the fatigue life reduction.     

Fretting fatigue of a shrink-fit pin subjected to rotating bending: Experiments and simulations

Fretting fatigue initiation was studied for a shrink-fit pin at rotating bending. Eight assemblies with four different grips were manufactured from soft normalized steel and tested at loads well below bending endurance. All pins displayed rust-red fretting oxides deep into the contact and black oxidised fretting scars with fretting fatigue cracks at the rim. The slip evolution was simulated in a three-dimensional FE model including assembly, bending and sufficiently many rotations to reach a steady-state. The extension of cyclic slip agreed with the black oxidised scar. Deeper into the contact a monotonic slip developed to the positions with rust-red oxides. Asymmetric slip and traction on the interface sides together with a slight twist of the pin in the hub and the slip development process, illustrated that a three-dimensional analysis was required for the interface. Both the stress amplitude and the Findley multi-axial criterion predicted fretting fatigue of the pin although the rotating bend stress was well below the endurance limit.     

On the anelasticity and fatigue fracture entropy in high-cycle metal fatigue

The concept of thermodynamic entropy generation in a degradation process is utilized to study the high-cycle fatigue of medium carbon steel 1018. Uniaxial tension–compression fatigue tests are carried out with tubular dogbone specimens at different stress levels and loading frequencies. It is shown that a phase lag between the stress and the strain caused by the internal friction includes a considerable amount of non-damaging anelastic energy in a hysteresis loop when the amplitude of cyclic load is substantially smaller than the yield strength of the material. A methodology is proposed to determine the anelastic energy associated with metal fatigue at a stress level lower than the yield strength of a material. Finite element simulations are carried out with a 3-D model of the specimen to determine the validity of the proposed methodology. The evolutions of the plastic strain energy and temperature are discussed and utilized to calculate the entropy accumulation. It is shown that the accumulation of entropy generation in the HCF of the material—beginning with a pristine specimen and ending at fatigue fracture—is nearly constant within the experimental and loading conditions considered. The concept of tallying entropy is useful for the prediction of the fatigue life evolution of a material undergoing cyclic loading.     

新型干法水泥回转窑可吸入颗粒物计量检测研究

采用冲击式尘粒分级仪对某台5 000 t/d新型干法水泥回转窑的颗粒物排放进行了研究,以掌握颗粒物排放浓度和粒径分布情况.测试结果表明,窑头和窑尾除尘器出口排放的总颗粒物浓度分别为66.87 mg/Nm3和41.69 mg/Nm3,不能满足2010年新修订的国家标准.年排放颗粒物总量为227 t,其中PM2.5和PM10排放量分别为33.5 t和113 t.对回转窑排放颗粒物的粒径分布进行分析,发现非常符合对数正态分布规律,线性相关系数均大于0.99,窑头和窑尾排放颗粒物的中位直径分别为4.4μm和6.2μm.