Life Of Machine Parts Research Articles

Mproving the properties of steels by producing in their structure along with other components of metastable austenite and the following hardening

The relevance. Improving the mechanical properties of steels and their wear resistance makes it possible to increase the service life of machine parts, which is an important task of materials science. One of the promising directions in its solution is combined processing technologies of steels based on the principle of obtaining in them in various ways a structure containing, along with other components (various types of martensite, lower bainite, in some cases carbides) of an increased amount (³ 25 %) of metastable austenite, and subsequent strengthening. In this case, a certain amount of austenite transforms into deformation martensite, and the its remaining part undergoes dynamic deformation martensitic transformation (DDMT) – the effect of self-hardening under loading (SHL). Combined processing technologies include thermal (in some cases, chemical-thermal) and deformation effects on the metal, carried out in various combinations and sequences. Processing technologies for obtaining an increased amount of metastable austenite in the structure of steels can include: holding in the intercritical temperature interval (ICTI) with various hardening methods, plastic deformation stabilizing austenite with respect to the formation of cooling martensite, thermal cycling, etc. Strengthening of steels with an increased amount of metastable austenite is carried out by cold plastic deformation, after which tempering is carried out in some cases. However, the principle is currently being considered and the combined processing technologies that implement it are not used in industry. This excludes the use of metastable austenite, which is an internal resource of the material itself, and its transformation under loading, which increases its ability to self-defense against destruction during testing of properties and operation. In this regard, it is advisable to introduce the proposed combined processing technologies into practice, which will ensure resource saving. In work on a number of steels their effectiveness has been shown.
 Рurpose is to show the possibility of increasing the mechanical properties or wear resistance of the studied steels by using combined processing technologies based on the principle that provides for the production of an increased amount of metastable austenite in their structure and subsequent hardening, which preserves the possibility of DDMT and the implementation of the effect SHL.
 Research methods. Durometric, metallographic and X-ray research methods were used. The tensile properties and impact strength, as well as abrasive wear resistance, were determined. These properties were compared with those obtained for the studied steels after a typical heat treatment.
 Results. It is shown that the proposed combined treatment technologies, including the production of an increased amount of metastable austenite in the structure of the studied steels and subsequent hardening, which retains the possibility of DDMT and the implementation of the effect SHL, increase the mechanical properties or wear resistance in comparison with their level after the commonly used treatment.
 Scientific novelty. To improve the mechanical properties or wear resistance of alloys an innovative principle was proposed, which consists in obtaining in them an increased amount of metastable austenite before strengthening treatments, preserving after them a part of it that can undergo DDMT and, accordingly, realize the effect SHL when testing properties and operation.
 Practical value. For the studied steels, rational modes of combined processing technologies have been determined, including obtaining an increased amount of metastable austenite in their structure and subsequent hardening, which have shown their effectiveness in increasing mechanical properties or wear resistance in comparison with commonly used treatments.

Электроискровое упрочнение дереворежущего инструмента

Choosing effective methods and devices for surface hardening of wood-cutting tools is problematic due to the variety of their designs and operating conditions. In this regard, the development of such devices becomes an urgent task. According to the literature, one of the effective methods for increasing the service life of machine parts and tools is electrospark hardening or electrospark alloying. Industrial electrospark installations such as “EFI” (electrophysical measurements) and “Elitron” with manual vibrators are used for electrospark hardening. However, using manual vibrators significantly increases the labour intensity and hardening time. Moreover, the surface quality after hardening with manual vibrators is often unsatisfactory. Various mechanized installations have been developed in order to reduce the labour intensity of electrospark hardening. Nevertheless, these installations are designed to harden specific parts and do not allow hardening tools of various designs, including woodcutting tools. The surface quality after hardening in mechanized installations does not always satisfy the customer. Further surface plastic deformation treatments, such as rolling and unrolling with rollers and balls, as well as diamond burnishing, are often used to improve the surface quality after electrospark hardening. The surface quality after additional processing by these methods boosts, although the labour intensity and cost of the hardening process increase. To increase the wear resistance of machine parts and tools, it is reasonable to reduce the height parameters of roughness, increase microhardness, and form the residual compressive stresses, which is ensured by the methods of surface plastic deformation. In this regard, it becomes necessary to use electrospark hardening simultaneously with surface plastic deformation. The work presents the design and features of using the device for hardening. The device was used to strengthen the thicknesser machine knives, which made it possible to almost double their durability. Applying this device, in comparison with using the electrospark hardening with a manual vibrator, reduces the roughness of the hardened surface and improves the surface quality of the processed workpieces. The modes of hardening have been installed, making it possible to effectively harden wood-cutting tools. For citation: Buglaev A.M. Device for Wood-Cutting Tool Hardening. Lesnoy Zhurnal [Russian Forestry Journal], 2021, no. 5, pp. 134–141. DOI: 10.37482/0536-1036-2021-5-134-141

Increasing of the steels properties by an ecological method of isothermal and step quenching

The relevance. Improving the mechanical properties of steels makes it possible to increase the service life of machine parts, which is an important task in materials science. One of the promising directions in its solution is to obtain in steel a multiphase structure, one of the main components of which is metastable austenite, which undergoes a dynamic deformation martensitic transformation (DDMT) - self-hardening effect under loading (SHL). Methods providing the required structure are isothermal and step quenching. However, at present, when they are carried out for cooling from the austenitizing temperature and holding at the constant temperature used non-environmentally friendly substances: heated oil, molten salts or alkalis. In this regard the actual problem is the exclusion of them from the technological process. The possibility of solving this problem on several steels has shown.
 Purpose is to show the possibility of increasing the mechanical properties of the studied steels 30ХГСА, 38ХС, 45Г, 40ХН, 10Г12, 60Х18 by using rational modes of an environmentally friendly method of steels quenching (isothermal - for low-alloyed and step - for high-alloyed) due to obtaining in their structure along with other components of metastable residual austenite and the implementation of the SHL effect.
 Research methods. Samples of the investigated steels after austenitization (in some cases with holding in IСIT) were cooled in water to the temperature of lower bainite formation (isothermal quenching) or stabilization of supercooled austenite to martensitic transformation upon cooling (step quenching), after which they were kept in a furnace and cooled in air to room temperature. Durometric, metallographic and X-ray research methods were used. The tensile properties and impact strength were determined. These properties were compared with those obtained for the studied steels after a typical heat treatment, including quenching in oil and tempering.
 Results. It is shown that isothermal and step quenching of the investigated steels without the use of non-environmentally friendly substances, carried out according to rational modes, makes it possible to increase the mechanical properties in comparison with their level after the commonly used quenching in oil (fire hazard, the vapors are cancerogenic) and tempering. This is achieved by obtaining a multiphase structure with metastable austenite.
 Scientific novelty. It is proposed to obtain a multiphase structure with metastable austenite in them to improve the mechanical properties of the studied steels by conducting isothermal and step quenching in an environmentally friendly way without using heated oil, molten salts or alkalis.
 Practical value. For the studied steels the modes of isothermal and step quenching are determined in an environmentally friendly way, which make it possible to increase the mechanical properties in comparison with the level achieved by quenching and tempering. Wherein in contrast to a similar typical quenching method are excluded the costs of purchasing salts or alkalis, their disposal and washing of products from them. Compared to quenching and tempering, the new method does not require the use of oil and tempering. The latter improves ecology and reduces energy consumption during heat treatment.

Calculation formula for determining the residual resource of agricultural equipment details

When calculating the residual life of machine parts, it is advisable to use the relative value of the residual life, since the calculation of the relative value allows you to obtain a dimensionless value, to obtain a relative generalized estimate of the residual life of the main components and assemblies of complex machines, as well as groups of parts of the same name.

Probabilistic Analysis of the Reliability and Fatigue Life of Machine Parts by Fatigue Failure

The problem of calculating the reliability and fatigue life of machine parts by the fatigue failure under random changes in the actual and limit stresses is considered. According to the corrected theory of the linear summation of damage, a transcendental equation has been obtained that relates the number of cycles until failure to the random loading parameters and the ultimate strength. From this equation, the ultimate strength threshold is determined, which corresponds to the destructive number of cycles over the service lifetime. The fatigue reliability equals the probability of exceedance of this value by the ultimate strength. Analytical dependences have been obtained for determination of the probabilistic characteristics of the fatigue life under a simultaneous random change in the normal and tangential stresses.

Optimization of Surface Roughness in the Turning Process of AISI 4340 Tempering Steel

Surface roughness significantly affects the work efficiency and life of machine parts that interact with each other. There are many parameters that affect surface roughness, such as the material be...

Development of a multiaxial fatigue damage parameter and life prediction methodology for non-proportional loading

Most of the prior studies on the prediction of fatigue lives have been limited to uniaxial loading cases, whereas real world loading scenarios are often multiaxial, and the prediction of fatigue life based upon uniaxial fatigue properties may lead to inaccurate results. A detailed exploration of multiaxial fatigue under constant amplitude loading scenarios for a range of metal alloys has been performed in this study, and a new methodology for the accurate prediction of fatigue damage is proposed. A wide variety of uniaxial, torsional, proportional and non-proportional load-paths has been used to simulate complex, real-world loading scenarios. Test data have been analyzed and a critical-plane based fatigue damage parameter has been developed. This fatigue damage parameter contains stress and strain terms, as well as a term consisting of the maximum value of the product of normal and shear stresses on the critical plane. The shear-dominant crack initiation phenomenon and the combined effect of shear and tensile stresses on micro-crack propagation have been modeled in this work. The proposed formulation eliminates many of the shortcomings of the earlier developed critical-plane fatigue damage models. It is mathematically simple with substantially fewer material dependent constants, and provides design engineers with a tool to predict the fatigue life of machine parts with minimal computational effort. This life prediction methodology is intended for a wide variety of LCF and HCF loadings on machine parts made of metals including advanced alloys. KEYWORDS. Multiaxial; Fatigue Damage Parameter; Non-proportional loading.

Study of Scale Effect in a Starved Elastohydrodynamically Lubricated Contact

The article describes an experimental investigation of scale effect in a starved elastohydrodynamically lubricated contact on lubricant film thickness. Lubricant film thickness and its distribution is one of the most important parameters determining the performance and life of machine parts. Current experimental and numerical studies are mostly connected with oil lubrication. However, greases are used in more than 80 % of all rolling bearings where the starvation phenomenon occurs most frequently. The aim of this work is to compare two approaches to measuring film thickness of different greases. The use of multiple contacts optical test rig based on thin film colorimetric interferometry for film thickness measurement has enables to obtain film thickness of starved contact and the film distribution. The experimental observation of full-scale model of bearing will help to understand better the behavior of real bearing. The evaluation of the experiment was made by chromatic interferometry. This method is used to measure thin lubrication films.

Reliability Estimation of Fatigue Life for Machine Parts under Uniaxial Constant Amplitude Load

Two methods acquiring p-S-N curve for machine parts are given, namely directly searching out the p-S-N curve of the material from material database and using the idealized p-S-N curve. Reliability estimation methods of fatigue life of machine parts are derived under uniaxial constant amplitude load. Two kinds of circumstances (fixed stress and probabilistic stress) and two kinds of stress cycles (reversed cycle and unsymmetric reversed cycle) are considered. An iteration method is presented and the corresponding computer program is developed for estimating reliable life of machine parts. The engineering application results show that the calculated results are closer to experimental results. The suggested method can be convenient to fatigue reliability design of machine parts. It has good stimulative effect on popularization and application of existing anti-fatigue design method for machine parts, and high value of engineering application.

The Iterative Method for Reliability Estimation of Fatigue Life

The expression of reliability estimation method for fatigue life of machine parts was derived, and two kinds of stress cycles (reversed cycle and un-symmetric reversed cycle) were considered. An iteration method is presented and the corresponding computer program named STRENGTH-2 is developed for estimating reliable life of machine parts. The engineering application results show that the calculated results are close to experimental results. The proposed method can be convenient to carry out the fatigue reliability design for machine parts under the action of uni-axial and multi-axial loadings, and promote the popularization and application of existing anti-fatigue design method. It has the high value of engineering application.

Random load processes in fatigue strength calculations

Random load processes in machine parts are assessed by schematization. The equivalent-cycle method and a method of calculating the life of machine parts from their fatigue strength are developed.

Improving machine reliability and efficiency by increasing the fatigue life of the components

Analytical determination of the γ life of machine parts in terms of parameters of a set of finite size is considered. The γ strength values of various steels obtained by the proposed method and by the Dubey method are compared.

Influence of ultrasound hardening on surface quality

In industry, premature failure of machine parts and tools as a result of cyclic loads leads to considerable losses. The most important factor determining the life of machine parts is their surface quality. The surface quality of contacting machine parts has a great influence on the friction and wear, the durability, the noise, and the efficiency of the mechanisms in which they appear. At present, the most promising method of improving the surface quality of machine parts is pulsed ultrasonic hardening. Ultrasonic hardening is based on the energy of mechanical vibrations of an indentor at a frequency of 20 kHz, with an amplitude of 0.5‐50.0 µ m. The energy in the treatment zone is transmitted to the surface of the part by the static force acting from the tool. The equipment for ultrasound treatment includes a power source, a system regulating the treatment process, a mechanical oscillatory system, and a pressure drive.

Estimation of the life of machine parts in block loading

The life of machine parts is checked with a probabilistic analysis in the case of random external loading approximated by block loading taking into account various models of material damage. The effect of the loading background and a number of physicomechanical characteristics on damage accumulation are investigated. Accumulation of fatigue damage of the material is noted to have a significant influence on reduction of the endurance limit. The results can be useful for prediction of reliability and durability of machine parts exposed to random external loading.

Modern State of Experimentation and Modeling in Contact Fatigue Phenomenon: Part II—Analysis of the Existing Statistical Mathematical Models of Bearing and Gear Fatigue Life. New Statistical Model of Contact Fatigue

The paper presents a critical analysis of some existing statistical mathematical models of fatigue life applicable to bearings and gears, i.e. the assumptions, advantages, disadvantages and several contradicting aspects of these models. Some conclusions that adequately reflect the experimental and theoretical data discussed in Part I are drawn regarding the necessary features of a successful mathematical model of contact fatigue. Furthermore, such a new statistical model that will allow to predict fatigue life of machine parts is proposed in this paper. It is based on the first five parameters from the list compiled by Kudish and Burris (2000a) that are known to strongly affect contact fatigue. The other parameters from this list can be subsequently incorporated into the model. The paper also presents a theoretical analysis of the new model and some numerical results for contact fatigue life based on this model. Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in Orlando, Florida, October 11–13, 1999

Measurement of the fatigue limit of ferromagnetic materials by a nondestructive method

The reliability and life of machine parts and elements of structures operating under repeated loads is related to the quality of metals, particularly their~mechanical properties. To evaluate the fatigue properties of metals various tests imitating service conditions to various degrees are used. The majority of the methods are long tests of specimens to failure. Accelerated methods of determination of the fatigue limit are very approximate and also involve failure of the test specimen. The fact is that traditional methods of fatigue tests do not meet the requirements of recent years either in the area of the theory of the fatigue failure of metals [i] or in investigation of the physical nature of the micromechanisms of plastic deformation and fracture [2-4]. New criteria have been revealed which may serve as the basis for development of accelerated nondestructive methods of evaluation of the fatigue properties of materials and parts. Indirect methods of studying fatigue, including eddy current [5], have not been accepted. In our opinion the basis of them is not physical concepts common to the fatigue process.

Prediction of the residual life of machine parts

Prediction of the residual life of machine parts

Polymer composite coatings as a means of increasing the life of machine parts

Recently, polymeror metal-~pol~er-composite-base coatings have found ever wider use in various branches of the national economy [1-6]. The processes occurring on the contacting surfaces in rubbing with the participation of metal-polymer systems have been far from completely studied. Rubbing significantly changes the structure of the contacting surface layers and their strength, deformation, adhesion, friction, and other characteristics [2, 7, 8].

Increasing the service life of machine parts and tools by intensification of cooling of them in quenching

1. With intensification of cooling in the martensite transformation temperature range “superhardening” of metals is observed (10–20% increase in the strength of the material with a simultaneous increase in its plasticity in comparison with normal quenching), which is caused by strain hardening of the supercooled austenite (change in specific volume of the phases). 2. With an increase in the Biot number the axial and circumferential residual stresses on the surface of cylindrical parts first increase, reaching a maximum with Bi=3.6, and then decrease and become negative (compressive) with Bi≥18. 3. Quenching of machine parts and tools under conditions of high intensity heat exchange with Bi≥18 may significantly increase their operating life as the result of the increase in their mechanical properties and the creation of high compressive stresses on the surfaces of the parts. 4. It is desirable to first quench parts of complex configuration in aqueous polymer solutions and then upon reaching the temperature of the start of martensite transformations to quench under conditions of high intensity heat exchange.

Low-carbon manganese carburizing steels

High-manganese low-carbon steels may be a new and promising class of carburizing steels. They do not contain expensive elements or those in short supply, are simple in production, and possess high strength properties and sufficient plasticity of the core. The obtaining in the case of metastable austenite which becomes harder during service opens new possibilities for increasing the life of machine parts.