Papers by Keyword: Life Time

Abstract: The paper is aimed to the methodology for estimation of service life of mechanical engineering components in the case of elastic-plastic contact of surfaces. Well-known calculation methods depending on physics, theory of probability, the analysis of friction pair’ shape and fit include a number of parameters that are difficult or even impossible to be technologically controlled in the manufacturing of mechanical engineering components. The new approach for wear rate estimation using surface texture parameters as well as physical-mechanical properties and geometric parameters of components is proposed. The theoretical part of the calculations is based on the 3D surface texture principles, the basics of material fatigue theory, the theory of elasticity and the contact mechanics of surfaces. It is possible to calculate the service time of the machine, but the process of running-in of the components is relatively short (less than 5%), therefore, the service time is mainly determined by a normal operating period, which also was used to evaluate this period. The calculated input parameters are technologically and metrologically available and new method for calculating the service time can be used in the design process of the equipment. The results of approbation of the method for estimation service time of mechanical engineering, which prove the applicability of mentioned method, are offered as well.

Abstract: This paper is devoted to the elaboration and verification of the new methodology for the life time prediction of wear parts in the mechatronic systems. The methodology is based on the using of the 3D surface texture parameters instead of 2D roughness parameters for more precise prediction of the life time of machine parts.Experimental testing of proposed methodology for the wear parts of linear motion modules of mechatronic system was done using 3D profilometry, pin-on-disc tribological testing for determination dynamic friction coefficient, slidability and static friction coefficient measurements. The new approach for life time prediction is based on using following 3D texture parameters: Sa, Sq, Str, Rsm₁ and Rsm₂. It is established, that the amplitude and spatial parameters (Sa and Str (Rsm₁) accordingly) have a most significant influence on the static and dynamic friction coefficient as well as on the sliding properties. It can be assumed, that for wear parts and for improving sliding properties the surfaces with less Sa and bigger Rsm₁ are recommended.Within the Ti-based multi-layer PVD coatings the best prognosis for the life time was achieved for the samples with multi-layer Ti-TiN-Al PVD coating. Proposed methodology is acceptable for use in practice of engineering calculation, in design etc.

Abstract: High cycle fatigue behavior of the compressor impeller is investigated. On the basis of numerical calculations of the stress-strain state of wheel the prognosis of life time is done. The results show relations between the number of cycles to failure and maximally possible stresses and displacements. Relation of cumulative fatigue damage is researched depending on the number of cycles for the different modes of vibration on resonant frequencies.

Abstract: Reliability of rotating machinery is determined to a considerable degree by the bearing units. For several applications the requirements in rotation speed, bearing load and maximal vibration level are so extreme that neither rolling-element bearings nor fluid-film bearings could provide necessary performance characteristics during all regimes of operation. Hybrid bearings, which are a combination of rolling-element and fluid-film bearings, can improve performance characteristics and reliability of the rotor-bearing systems. The aim of this work is to analyze the advantages and disadvantages of the hybrid bearings. Known real applications of hybrid bearings are discussed. Analysis shows that depending on the application different hybrid bearing types could improve dynamic characteristics and life time of the bearing unit, increase load capacity and DN limit of the rolling-element bearing.

Abstract: Prediction of disk spring failure life due to stress relaxation is necessary for users; the problem was not solved before. According to special test requirement, we modified a 100N mechanical testing machine into high temperature testing equipment which can be used for different types of disk spring. With a test for 36 days on a group of 45×22.5×3.5×2.5 mm disk springs, a result of prediction of 3.38% load loss ratio after 12 years relaxation is obtained, these disk springs are qualified. Our modified equipment has the advantages of real time, heavy loading, high sensitivity and good generality.

Abstract: Oil dampers are widely used as a popular countermeasure to mitigate the stay cables vibration. In this study, one actual oil damper designed for some long cable-stayed was experimentally investigated to evaluate the durability. 4 million cycles loading, with frequency of 4 Hz and amplitude of 1 mm, was imposed on the damper. The excitation displacement and damping force were measured and the equivalent damping was calculated from the experimental results. The stiffness effects of dampers behaved during durability tests were also analyzed quantitatively. The test results showed that the dampers were still in good condition after 4 million cycles loading and the dampers temperatures were stable at 50 degree centigrade during the test. According to the durability test results, a model for performance deterioration of damper was proposed to predict the lifetime of oil dampers.

Abstract: This paper reports experimental and simulation studies on degradation of optical power of low power LEDs due to current stress and temperature variation. The goal of this study was to study the effect of aging and ambient temperature on optical output power of light emitting diodes and to determine the effective lifespan of LED under stress condition. The LED samples were stressed at four levels of operating current 20mA, 30mA, 40mA, and 45mA with stress time up to 1000h. We find that degradation rate increases with increasing operating current. When LEDs are overstressed by driving at higher current the optical power degraded with stress time. A Mathematical model is developed to predict the behavior of LED at different operating current. Simulations are carried out with this model using MATLAB. Using degradation pattern at higher operating current the lifespan of LEDs was predicted at normal operating current.

Abstract: Research conducted to develop ultra-sensitive biophotonic devices using a layer by layer self assembly method with retinoic acid and chitosan is reported on in this paper. The devices had a photocurrent response and the response was sped-up with the introduction of Alq3 thin film.The lifetimes of these devices were measured and reported comparatively among the retinoids.

Abstract: Influence of load and rotation speed on life of PPS radial bearings under water lubricant condition was investigated. RCF tests were carried out at different loads and rotation speeds until 1.0×106 cycles. After testing, rolling contact surfaces were observed by using a laser confocal microscope. From the observation, it was concluded that the life of PPS radial bearings under water lubricant condition was dominated by cracks and flaking failures. The failure of PPS bearings was caused by the flaking failures. The cracks were observed prior to the flaking failures. The life when flaking failure occur depends on the load and the rotation speed.

Abstract: Magnetic abrasive grain is a kind of tool for magnetic abrasive finishing (MAF). The lifetime of the grains is the choke point which restricts its finishing efficiency and the surface quality processed by MAF .Therefore, a kind of magnetic abrasive grains based on Cr and Ni elements is investigated. The interrelated experimental results show: the new magnetic abrasive grains is a practical finishing tool with longer lifetime, higher finishing efficiency, better abrasive resistance compared with traditional magnetic abrasive grains. It supplies a power for promoting the development of MAF.