Design criteria for rolling contact fatigue resistance in back-up rolls

Abstract

This research centres on surface initiated damage on back-up rolls whereby rolling contact fatigue cracks can propagate into the rolls potentially reaching the internal stress fields and leading to catastrophic failure and has sought to establish design criteria for avoiding such failures. The project objectives have been achieved by examining field evidence, determining the loading and tribological conditions at the work roll/back-up roll interface and investigating both theoretically and experimentally the mechanisms involved in rolling contact fatigue in this case. The presented rolling contact, fatigue and fracture mechanics model includes criteria for crack branching either upwards (i.e.relative safety) or downwards (i.e.potentially catastrophic) and the link between these two cases is related, quantitatively, to the properties of the roll material. After linking mechanics to microstructure, the influence of work roll test disc surface roughness on both the surface wear of and the interaction between wear and rolling contact fatigue at the surface of back-up roll test discs has been quantified using the results obtained from experimental simulations carried out on a rolling–sliding testing machine. Finally practical quantitative recommendations are made for the mechanical and microstructural design of bainitic back-up roll materials, back-up roll redressing procedures and the surface roughness of both work rolls and back-up rolls presented to the mill.     

Tensile behavior of ren’e 95 in the thermomechanically processed and conventionally processed forms

A transmission and scanning electron microscope study has been conducted on the deformation and fracture behavior of Ren’e 95, an advanced superalloy developed for use as a disk material in gas turbine engines. In addition to the normal solid solution strengthening and precipitation strengthening mechanisms, Ren’e 95 derives part of its strength from thermomechanical processing. In this paper, the tensile mechanical properties, deformation structure and tensile fracture characteristics of Ren’e 95 are examined and related to the microstructure. The results are compared with those from the conventionally processed material (without TMP), and an attempt is made to account for the factors that influence the tensile characteristics of these two materials.     

Prediction of Surface Roughness in Turning of EN 353 Using Response Surface Methodology

In the present work, an attempt has been made to investigate the influence of cutting speed, feed, depth of cut and nose radius on surface roughness during wet turning of EN 353 steel using tungsten carbide inserts. Surface roughness prediction models in terms of speed, feed, depth of cut and nose radius is developed by using response surface methodology based on center composite rotatable design. A comparison of first order models with quadratic model was carried out on the basis of percentage mean absolute error and mean square error. The results clearly reveals that the predicted data using quadratic model is in close agreement to the experimental surface roughness values as compared to predicted data using first order model. In addition to this, it has been revealed that the speed is the main influencing factor affecting the surface roughness. The depth of cut has no significant influence on the roughness. Mathematical model for surface roughness shows that surface roughness decreases with increase in speed and nose radius, but increases with increase in feed. The percentage variation between the predicted and experimental values of the surface roughness during the confirmation experiments was found within 5 %. An attempt has also been made to obtain optimum cutting conditions for minimum surface roughness.     

Fe在铜基粉末冶金摩擦材料中的作用

研究了Fe在铜基粉末冶金航空摩擦材料中的摩擦磨损作用及机理。研究表明:Fe在铜基摩擦材料中起到了摩擦组分的作用,对材料的机械性能和摩擦磨损性能起到了重要的作用。Fe能提高铜基摩擦材料的强度、硬度;当Fe含量超过4%后,随Fe含量的增加,材料的摩擦系数及稳定性增加;高速摩擦条件下,Fe能促进摩擦面氧化膜的形成,减小材料的摩擦系数和磨损量。     

新型无银触头材料的研制

采用粉末冶金技术研制了一种新型无银触头材料。该材料的综合性能,如密度、硬度、电阻率、灭弧特性及温度特性与传统的银基触头材料接近。所研制的无银触头在许多应用中,如在电力机车上可替代银基材料,具有明显的经济效益和社会效益。     

粉末冶金结构零件材料的密度均匀化设计

根据零件性能要求，设计材料密度的大小。通过讨论零件形状对材料密度分布的影响，采取相应措施，用一次压制成形法可以生产较高密度和形状复杂的结构零件。     

Influence of porosity and sliding rate on the tribotechnical properties and features of deformation of the surface layers of copper-graphite materials during friction without lubrication

Conclusions The relationship of the intensity of wear of a copper-graphite material containing 10% graphite to porosity has an extreme character. The optimum antifriction properties are obtained with a porosity of 6–12%. In this interval of porosities the minimum degree of deformation of the surface layer in friction is observed. The minimum values of the intensity of wear and of the coefficient of friction of copper-graphite materials are observed in the 2.6–22 m/sec range of sliding rates, at which solid films of secondary structures distinguished by low roughness are formed on the surface.Translated from Poroshkovaya Metallurgiya, No. 8(296), pp. 81–85, August, 1987.     

直接热等静压粉末Udimet 720合金的组织与性能

铸锻U720合金已被广泛用作发动机涡轮盘材料.最近研究发现挤压加等温锻的粉末冶金U720也有很好的性能.本文研究了热等静压加热处理(即直接热等静压状态)粉末U720合金的拉伸、持久及低周疲劳性能.研究表明,直接热等静压粉末U720合金的性能与变形(挤压加锻造)合金的相当,可用于发动机涡轮盘.这种不需要挤压和锻造的近净尺寸成型工艺正适应了目前不断降低成本的要求.     

MoS2对铁基摩擦材料烧结过程的影响

研究了MoS2对铁基粉末冶金摩擦材料烧结过程的影响.研究结果表明,作为润滑组元广泛应用于粉末冶金摩擦材料中的MoS2,在氢气保护下的加压烧结过程中发生分解反应,分解后的Mo和S与材料中其他组元相互作用,影响摩擦材料的性能.     

The Effect of ITMT’s and P/M Processing on the Microstructure and Mechanical Properties of the X7091 Alloy

The influence of microstructure and texture on the monotonic and cyclic properties of X7091-T651 was investigated. The various structures were developed from conventional ingot metallurgy (I/M), powder metallurgy (P/M) and intermediate thermal mechanical treatments (ITMT). Powder metallurgy produced a finer grain structure and particle distribution than I/M. Intermediate thermomechanical treatment produced a recrystallized, coarse grain structure with a weak texture, compared to the unrecrystallized grain structure and sharp texture obtained with conventional processing (CP). All materials had comparable monotonic properties. The resistance to fatigue crack initiation (FCI) increased with both a reduction in grain size and a finer particle distribution. Smaller grain sizes and finer particle distributions reduced the degree of cyclic strain localization. The CP-P/M alloy had the poorest ductility and FCI resistance of all the materials, although the slip was fairly homogeneous. This may be due to the presence of oxides at the grain boundaries and a sharp texture. The threshold stress intensity, ΔK_th, and the fatigue crack growth rate (FCGR) roughly follow a grain size dependence with the resistance of fatigue crack propagation (FCP) increasing with increasing grain size. It appears that large grains allow more reversible slip and reduce the amount of accumulated plastic strain within the reverse plastic zone. It is also believed that a greater degree of fatigue crack closure, which may be associated with large grains and a rough FCP surface, results in a lower FCGR in the lowΔK region. The intermediate thermomechanical treatment of P/M X7091 produced the optimum microstructure giving the best combination of mechanical properties. The important features include a small recrystallized grain structure, a fine particle distribution, a weak texture, and a low concentration of oxides at grain boundaries. Formerly Director, Fracture and Fatigue Research Laboratory, Georgia Institute of Technology, Atlanta, GA.     

金属纤维增强作用对固体润滑材料性能的影响

本文介绍了金属纤维增强复合固体润滑材料部件的制造工艺;着重研究了金属纤维增强作用对固体润滑材料性能的影响。试验表明,金属纤维基体有高的强度和塑性,良好的渗透性(纤维基体的断裂极限σ_b和冲击韧性α_k分别为粉未冶金同类产品的2~15倍和5~17倍)。它与固体润滑剂复合而成的材料,不仅机械性能好,还由于纤维体通孔多和具有蜂窝结构,有利于润滑剂渗透、贮存和分泌。并且还为材料提供理想的润滑源,同时明显改善材料的耐磨性、磨合效果及加工性能。所研制的部件经过试验证实,已达到预期的目的和效果,是一种有发展前途的新型材料。     

Effects of the surface roughness of rolls on the powder rolling process

Conclusions A study was made of the effects of the surface roughness of rolls on the properties (thickness, density, and forward slip) of roll-compacted strip and of the running-in of rolls in contact with the material being rolled. It was established that the surface condition of rolls has a strong influence on the properties of strip. Increasing the height of roll surface irregularities from 2.8 to 7.0 increases the strip thickness from 0.38 to 0.65 mm in the rolling of a coarse copper powder and from 0.43 to 0.68 mm in the rolling of an iron powder. Further increase in the height of microirregularities produces very little change in strip thickness and density. The study revealed that, during the running-in of the roll surfaces as a result of contact with the material being rolled, the thickness and density of the strip change, and the rolling process thus takes place under non steady-state conditions. The time required for the stabilization of the process depends on the composition of the mixture being rolled and the hardness of the material of the rolls. The findings of laboratory investigations have been confirmed by data yielded by experiments carried out under industrial conditions. As a method of treatment of roll surfaces, the rolling of electrocorundum abrasive cloths of No. 10–20 grain size, to GOST 3647-71 standard, is recommended. As a result of this treatment, rolls acquire a class 5 surface finish.Translated from Poroshkovaya Metallurgiya, No. 7 (139), pp. 15–21, July, 1974.     

Comparative Study of Surface Chemical Composition and Oxide Layer Modification upon Oxygen Plasma Cleaning and Piranha Etching on a Novel Low Elastic Modulus Ti25Nb21Hf Alloy

Metals are widely employed for many biological artificial replacements, and it is known that the quality and the physical/chemical properties of the surface are crucial for the success of the implant. Therefore, control over surface implant materials and their elastic moduli may be crucial to avoid undesired effects. In this study, surface modification upon cleaning and activation of a low elastic modulus Ti alloy (Ti25Hf21Nb) was investigated. Two different methods, oxygen plasma (OP) cleaning and piranha (PI) solution, were studied and compared. Both surface treatments were effective for organic contaminant removal and to increase the Ti-oxide layer thickness rather than other metal-oxides present at the surface, which is beneficial for biocompatibility of the material. Furthermore, both techniques drastically increased hydrophilicity and introduced oxidation and hydroxylation (OH)-functional groups at the surface that may be beneficial for further chemical modifications. However, these treatments did not alter the surface roughness and bulk material properties. The surfaces were fully characterized in terms of surface roughness, wettability, oxide layer composition, and hydroxyl surface density through analytical techniques (interferometry, X-ray photoelectron spectroscopy (XPS), contact angle, and zinc complexation). These findings provide essential information when planning surface modifications for cleanliness, oxide layer thickness, and surface hydroxyl density, as control over these factors is essential for many applications, especially in biomaterials.     

Influence of Mandrel's Surface and Material on the Mechanical Properties of Joints Produced by Electromagnetic Compression

Electromagnetic compression of tubular profiles with high electrical conductivity is an innovative joining process for the manufacturing of lightweight structures. The mandrel's material has an influence on the transferable loads which is affected by the Young's modulus as well as the strength of the material. This was investigated, on the one hand, by changing the mandrel's material and, on the other hand, by using the same mandrel material with differing strength. Furthermore, taking conventional interference fits into account, the contact area's influence on the joint's quality seems to be of significance, as e.g. the contact area and the friction coefficient between the joining partners proportionally determine an allowed axial load or torsional momentum. Therefore, different contact area surfaces were prepared by shot peening and different machining operations and strategies. The mandrel's surfaces were modified by shot peening with glass beads and Al₂O₃ particles. An alternative preparation was performed using simultaneous five‐axis milling, because potential joining partners in lightweight frame structures within the Transregional Collaborative Research Centre SFB/TR10 would be manufactured similarly. After that, the manufactured surfaces were characterized by measuring the surface roughness and using confocal whitelight microscopy. Afterwards the modified mandrels were joined by electromagnetic compression. The influence of different mandrel's surface conditions on the joint's mechanical properties was analysed by tensile tests. Finally, conclusions and design rules for the manufacturing of joints by electromagnetic compression are given.     

The development of two texture variants and their effect on the mechanical behavior of a high strength P/M aluminum alloy,X7091

The influence of texture on the deformation behavior and monotonic and cyclic properties of two recrystallized P/MX7091-T651 plates was investigated. Thermal mechanical treatments were used to produced two different textures which varied in intensity by a factor of four. The two plates had similar grain and precipitate structures. The deformation behavior and mechanical properties were correlated with grain orientation and grain boundary misorientation. Differences in fracture surface roughness and crack deflection frequencies were observed for the two texture variants during fatigue crack propagation studies. Deformation behavior, crack closure, and crack deflection affected the fatigue crack growth rates. A small but measurable improvement in tensile strength, fatigue strength, and fatigue crack growth resistance was obtained in the sharply textured material when compared with the weakly textured counterpart.     

Production of Tailored High Strength Hybrid Sandwich Structures

This project deals with the manufacturing and subsequent treatment of partially strengthened, three layered, symmetrical sandwich structures. Those sandwich materials have the advantages to combine the properties of the used mono‐materials. Additionally, they have a good damping behaviour because of the soft core and good stiffness and a good corrosion resistance if stainless steel sheets are used as cover. The characteristics of such structures are even more improved by the specific local influence of partial reinforcement within the sandwich material. With this type of strengthening, complex material properties can be developed, e.g. high strength with high stiffness, good thermal joining properties at the place of strengthening, as well as an improved strength and strength absorbing ability. The forming behaviour of such composite materials is still unknown. In this research project different sandwich materials ‐ with and without reinforced elements ‐ are analysed in bending tests and in deep‐drawing investigations.     

粉末冶金摩擦材料综述

本文简要地综述了为提高并稳定粉末冶金摩擦材料摩擦系数,提高耐磨性、耐热性、抗腐蚀能力和改进导磁性、降低成本而作的配方试验与所得到的性能;并介绍了粉末冶金摩擦材料的各种制造方法,包括现行的与正在试验的制造方法;导后综述了关于粉末冶金摩擦材料发展前景的若干评价。     

粉末冶金制品（硬质合金,过滤器除外）表面粗糙度评定方法分析

表面粗糙度是反映粉末冶金制品(硬质合金、过滤器除外)质量的重要指标之一。现有的国标GB1031-83不适合粉末冶金制品表面粗糙度的评定。本文介绍了使用斧刃形触针测头定量评定粉末冶金制品表面粗糙度的方法。     

Metallothionein content increased in the liver of mice exposed to magnetic fields

OBJECTIVES: The aim of this investigation was to evaluate the significance of selected surface texture parameters used to describe and quantify the effect of tooth brushing with various "tooth whitening" dentifrices on a resin composite surface in vitro. METHODS: Specimens of a microfil resin composite were brushed with selected dentifrices. Surface texture profiles were acquired and analyzed both pre- and post-brushing using a contact diamond stylus. The selected parameters chosen to describe the surface texture were Ra, Rz, Rpm and the Rpm:Rz ratio. Differences between toothpastes were assessed using an ANOVA and a multiple comparisons test, the Student Newman-Keuls procedure. P and t values were calculated to determine if any of the surface roughness parameters were significantly changed by brushing. RESULTS: The results indicate that there were significant changes in the surface texture of the resin composite following tooth brushing with the selected dentifrices. For example, the use of Clinomyn significantly increased the surface roughness of the resin composite, as measured by the Rz parameter, from 2.19 +/- 1.67 microns to 10.02 +/- 2.57 microns (p < 0.05). In addition, the surface texture parameters chosen to describe the properties of the surface should reflect a knowledge of profile shape such as Rpm:Rz ratio, and care should be taken if measurements of surface texture of dental restorative materials are to be used as predictors of clinical performance. SIGNIFICANCE: All the toothpastes chosen for this investigation left a surface on the resin composite which may be prone to crack propagation during "vertical barrelling" movements generated during mastication. However, this may be more of a function of the rigidity of the restorative material rather than the surface left after tooth brushing.     

Effect of Roughness and Surface Hardening on the Mechanical Properties of Three-Layered Brass/IF Steel/Brass Composite

In this research, three-layered brass/IF steel/brass composite produced by cold roll bonding (CRB) process was investigated. The effect of roughness and surface hardening of each layer on the mechanical properties of three-layered composite were separately examined. For this purpose, five rotatory wire brush models were used in order to prepare the surfaces for CRB process. The peeling and shear punch tests were also used to evaluate the mechanical properties of samples. Finally, optical and scanning electron microscopes were used to evaluate the fracture surfaces. The chemical compositions were analyzed at the joint interface by an energy dispersive X-ray analysis. It was observed that, decreasing the diameter of the brush enhanced the roughness and surface hardening. However, the increase in roughness and surface hardening of brass were less than that of IF steel due to different wear mechanisms. The results showed that, at the same reduction, the bond and shear strengths of composite were enhanced by increasing the surface roughness of each layer. Also, increasing the brass surface roughness had more effect on the bond strength of the strips due to its vital role in bonding formation in CRB processing. Moreover, rising the surface roughness of IF steel in comparison to brass had more influence on the shear strength of the composite.