Reliability Of Mechanical Systems Research Articles

Novel and Ruggedized Power Electronics for Off-Highway Vehicles

This article covers the challenges in implementing power electronics and drive systems in emerging vehicle applications. The application of power electronics becomes important for higher energy density, decreased fuel consumption, performance and productivity enhancements, and desired protection, diagnostic, and safety features. A sustained effort is needed on power electronics and electric drive system design to achieve the desired level of performance. There can be numerous machines/drives of various types and power levels in a system. In numerous applications, the driving torque varies considerably over a given work cycle, including the occurrence of the stall condition. Therefore, the drive system should have a reliable ride-through capability. To achieve the desired torque/speed profile and dynamic response, a systematic design, development, and deployment of the power electronics-based electric drive system is needed. The application conditions make it difficult to match/exceed mechanical system reliability and costs. Therefore, this article covers the unique challenges of developing and implementing power electronics and drives in harsh vehicle applications. Field examples are described in detail to demonstrate the successful implementation of vehicle electrification programs for heavy-duty off-highway vehicles. The importance of new-generation wide-bandgap (WBG) technologies is also described to highlight the emergence of high-temperature power electronics for heavy-duty, off-highway vehicle applications.

Research on Data Modeling for Management System of Alignment Information

Due to lack of considering the non-geometric process parameters during assembly process planning, it is difficult to control the production cycle, cost, quality, reliability, stability and consistency of high-performance mechanical systems. To change this situation, a prototype software is developed by taking into account the non-geometric process parameters. Based on the alignment information, this paper concentrates on the data modeling of the system. With the system, the manufacturing process can achieve the assembly materials management, assembly process planning, alignment process monitoring, alignment data collection and statistical analysis. After analyzing the process data, design parameters will be refined and assembly performance will be optimized.

Thread Measurement Algorithm Research and Software Development

The quality of thread will directly affect the reliability of mechanical system, and the accuracy grade of geometric parameters is the judgment standard to thread quality. Thus, its particularly important to detect the geometric parameters of thread. Its a pretty mature and widely used method to measure thread parameters with universal tool-measuring microscope, but it has many shortcomings, such as tedious operation, low efficiency and the reading error. In view of the above shortcomings, the paper does some simple refits to the existing 19JA universal tool-measuring microscope. In order to improve reading speed and accuracy, the grating rulers are installed on the operating platform in two directions. CCD camera is used to get external thread image instead of human eyes and the eyepiece, which is a non-contact measurement method. A software that based on MFC of VC + + 6.0 is written, which can deal with the thread image and get the thread parameters. The experimental results show that the method can not only effectively improve the measurement efficiency but also guarantee the accuracy of measurement.

A Repairable Mechanical System Reliability Assessment Methodology Applied in a Steelmaking Context

An analysis method for reliability assessment of repairable mechanical systems is presented in the context of the hot strip mill section of large steelworks. The reliability analysis process is defined and operated using a three‐level modelling procedure, each of which functions within a different time base, thus enabling the timely identification of potential deviations in reliability performance. The main modelling approach deployed is based upon the Power Law Process, which is embedded within an automated analysis tool. The efficacy of each of the deployed modelling process is determined by the application of appropriate statistical tests. The results from this process are used to enable an in‐depth analysis of why the reliability performance of the system under review has changed. A practical application is presented with reference to two strip coilers that operate within the hot strip mill. The approach is, however, generic and would be applicable to any large‐scale mechanical repairable system. Copyright © 2013 John Wiley & Sons, Ltd.

Experimental Vibration Analysis of Railcar for Spent Nuclear Fuel Transportation

Safe operation of technical and technological equipments is necessary for preventing undesirable and dangerous states. The questions of lifetime and reliability of mechanical systems are solved very often in this context in practice. Particularly high demands are placed on safety of equipments that can operate only on the basis of special permissions. Transport containers for transportation of used nuclear fuel cassettes belong to this group of devices. On the basis of operator’s order, complex methodology of type tests of transport container including its means of transport was elaborated. Described methodology includes analysis of vibration of transport complex during its movement.

Real-Time Cutting Force/Torque Prediction During Turning

The automation of machining processes requires highly accurate process monitoring. However, the use of additional sensors leads to a significant increase in the cost and reduces the stiffness and reliability of mechanical systems. Hence, we propose a system called the cutting force observer, which uses a sensor-less and real-time cutting force estimation methodology based on the disturbance observer theory. Monitoring methods using the cutting force observer may enhance the productivity during turning. One of the parameters that significantly affect the cutting process is the shear angle. The determination of the shear angle is very important as it can be used for identifying the machining conditions. In this study, an external sensor-less monitoring system of the shear angle during turning is developed, and its performance is evaluated.

Study on Reliability of Mechanical Systems Based on Petri Nets and Failure Dependence

Mechanical systems is vulnerable to be influenced of its structure and human factors for its subsystems, components and the complex relationship between each unit, causing the mechanical systems to be failed, which severely affects the reliability of the mechanical systems. based on Petri nets models of mechanical systems analysis, from safety, intermediate and failure three aspects, 3-level working model of “safety-intermediate-failure” is introduced to reflect the reliability (functioning fully) of mechanical systems, intermediary transition between reliable and failure, failure (can not work). Through using the union and intersection operation of stochastic event, and considering the different values of the related failure parameters among basic events which impacts on the reliability of mechanical system, eventually the calculation of mechanical system reliability vector with the intermediate state is established.

RELIABILITY AND AVAILABILITY ANALYSIS OF MECHANICAL SYSTEMS USING STOCHASTIC PETRI NET MODELING BASED ON DECOMPOSITION APPROACH

Reliability and availability assessment of a complex system in a single model, considering binary states of individual components, using Markov technique is difficult due to state space explosion problem. Inclusion of various types of dependencies in the model further aggravates it. To overcome this, Stochastic Petri net (SPN) modeling based on decomposition is proposed for reliability and availability assessment of mechanical systems. The decomposition is based on three aspects of the system: Hierarchical level, basic structure and dependency. The model is demonstrated at three hierarchical levels. Individual component (level '3') SPN model is developed assuming Weibull failure distribution, while the individual subsystem (level '2') SPN model is developed considering the arrangement of components within the subsystem. The individual model at level '2' is reduced to an equivalent single net model and its equivalent transition rate is derived from its basic structure assuming the independence of components. This along with the dependencies (e.g. repair, standby redundancy) are included in the system model (level '1'). The repair distribution in this model is assumed exponential. Reachable markings are generated for the system model to obtain the reduced state space of Semi-Markov model for assessment of reliability and availability of the system. The steps of the proposed methodology are suggested and these are illustrated for a pumping system, with two pumps; one in standby.

Stress-gradient induced fatigue at ultra high frequencies in sub micron thin metal films

Abstract Mechanical fatigue at frequencies in the GHz regime in submicron metal thin films is governed by size and frequency effects. The cyclic load can lead to damage formation also known as acoustomigration and determines the reliability of micro electro mechanical systems and surface acoustic wave devices. The size and frequency effects dramatically change the fatigue behavior compared to bulk material. The resulting damage structure is similar to electromigration experiments where void and extrusion formation lead to failure. Here, a dislocation based mechanism is presented which explains the damage formation. This mechanism is induced by gradients in cyclic shear stress which is induced by the short acoustic wave length at frequencies in the GHz regime. Discrete dislocation dynamic simulations are presented that reflect the dislocation behavior at these ultra high frequencies.

Study on MEMS board-level package reliability under high-G impact

Under high-G (104 g or above) impact load conditions, the reliability of micro electro mechanical systems (MEMS) board-level package and interconnection are critical concerned that influence the mission success of total projectile. This paper conducts a research on this problem to analyze package reliability using finite element modelling (FEM) and simulation method. Theoretical analysis and mathematical model for failure mechanism of MEMS package under high-G impact are conducted and established. A FEM dynamic analysis is conducted on a typical MEMS board-level leadless chip carrier (LCC) package. Results show that the solder joints are one of the key weakness points that influence the reliability of MEMS package. The maximum effective stress in the structure occurs at the outer corner in the outermost solder point, and the alloy cover and printed circuit board (PCB) have a greater deformation.

Damage assessment in multilayered MEMS structures under thermal fatigue

This paper reports on the application of a Physics of Failure (PoF) methodology to assessing the reliability of a micro electro mechanical system (MEMS). Numerical simulations, based on the finite element method (FEM) using a sub-domain approach was used to examine the damage onset due to temperature variations (e.g. yielding of metals which may lead to thermal fatigue). In this work remeshing techniques were employed in order to develop a damage tolerance approach based on the assumption that initial flaws exist in the multi-layered.

Simulation on Life Distribution and Reliability of Long Life Mechanical and Electrical Hybrid System

Simulation on Life Distribution and Reliability of Long Life Mechanical and Electrical Hybrid System

Applying the finite-element method for evaluating the reliability of mechanical systems

Methods of improving the strength reliability of large joints with guaranteed tension are presented, as well as methods for improving assembly fault prevention, while considering assembly technology development. The higher strength reliability of the joints in question will make mechanical systems safer.

Study on Reliability Tests to a Few Samples of Mechanical System

The reliability tests play more and more important role in mechanical systems. A new method named a few samples and combined the probability and the fuzzy mathematics has been set up to explore the unknown system of a few samples with the help of the life samples of the known probabilistic distribution. The method reduced the traditional reliability test samples by some auxiliary information. It converted lots of reliability test into a few samples. This paper introduced two engineering examples to verify the method as an effective way to carry out the reliability tests. It provides the theory basis for the reliability of complicated mechanical systems. The loss caused by fatigue failure is as high as 3%~4% of Gross National Product. Fatigue fracture owned to the cycle load accounts for 95% of the total number of mechanical structure failure. Unfortunately no evidence of failure is observed when fatigue failure reaches its life. This causes human casualties and great economic loss. So the reliability research on complicated mechanical systems has to realize from reliability assessment to the active reliability design. One of the key problems of the active reliability design for complicated mechanical system is to reduce the great waste of the resources used in the probability reliability test. For example, dozens of the high precision gears made of certain material may be run out in the fatigue test which would be running day and night for several months. It has been described many methods about system reliability design in the former research [1-3]. But for many high technological products and important mechanical devices, it is impossible to get the test sample to carry out probability analysis. To exert the advantages of the active reliability design and to realize the green reliability design [4], the only way is to study small samples in the reliability tests and to develop new technique. It is named as a few samples reliability tests method of the complicated mechanical systems.

Tribological advancements for reliable wind turbine performance

Wind turbines have had various limitations to their mechanical system reliability owing to tribological problems over the past few decades. While several studies show that turbines are becoming more reliable, it is still not at an overall acceptable level to the operators based on their current business models. Data show that the electrical components are the most problematic; however, the parts are small, thus easy and inexpensive to replace in the nacelle, on top of the tower. It is the tribological issues that receive the most attention as they have higher costs associated with repair or replacement. These include the blade pitch systems, nacelle yaw systems, main shaft bearings, gearboxes and generator bearings, which are the focus of this review paper. The major tribological issues in wind turbines and the technological developments to understand and solve them are discussed within. The study starts with an overview of fretting corrosion, rolling contact fatigue, and frictional torque of the blade pitch and nacelle yaw bearings, and references to some of the recent design approaches applied to solve them. Also included is a brief overview into lubricant contamination issues in the gearbox and electric current discharge or arcing damage of the generator bearings. The primary focus of this review is the detailed examination of main shaft spherical roller bearing micropitting and gearbox bearing scuffing, micropitting and the newer phenomenon of white-etch area flaking. The main shaft and gearbox are integrally related and are the most commonly referred to items involving expensive repair costs and downtime. As such, the latest research and developments related to the cause of the wear and damage modes and the technologies used or proposed to solve them are presented.

Reliability Simulation and Prediction of Mechanical Equipment for Maintenance

The mechanical equipment faults result from parts failure in the period of service time, due to reassembly and maintenance, the reliability model for mechanical equipment is broken, so it is necessary to research and estimate the safety reliability of mechanical system. Based on the time-to-failure density function of parts, the mechanical system reliability model is constructed to track the change course of age structure of part population for the mechanical systems that are reassembled and maintained. By means of simulation of the system reliability model, concerned parameters with mechanical systems service life are defined, it is discussed how the time-to-failure density function have influence on the service life for mechanical systems undergoing reassembly and maintenance. It is significant to estimate reliability and failure rate of systems and to establish reasonable maintenance policies.

Reliability Modeling and Simulation of Mechanical Equipment Undergoing Maintenance

The mechanical equipment faults result from parts failure in the period of service time, due to reassembly and maintenance, the reliability model for mechanical equipment is broken, so it is necessary to research and estimate the safety reliability of mechanical system. Based on the time-to-failure density function of parts, the mechanical system reliability model is constructed to track the change course of age structure of part population for the mechanical systems that are reassembled and maintained. By means of simulation of the system reliability model, concerned parameters with mechanical systems service life are defined, it is discussed how the time-to-failure density function have influence on the service life for mechanical systems undergoing reassembly and maintenance. It is significant to estimate reliability and failure rate of systems and to establish reasonable maintenance policies.

Rolling element bearing faults diagnosis based on optimal Morlet wavelet filter and autocorrelation enhancement

The fault diagnosis of rolling element bearing is important for improving mechanical system reliability and performance. When localized fault occurs in a bearing, the periodic impulsive feature of the vibration signal appears in time domain, and the corresponding bearing characteristic frequencies (BCFs) emerge in frequency domain. However, in the early stage of bearing failures, the BCFs contain very little energy and are often overwhelmed by noise and higher-level macro-structural vibrations, an effective signal processing method would be necessary to remove such corrupting noise and interference. In this paper, a new hybrid method based on optimal Morlet wavelet filter and autocorrelation enhancement is presented. First, to eliminate the frequency associated with interferential vibrations, the vibration signal is filtered with a band-pass filter determined by a Morlet wavelet whose parameters are optimized by genetic algorithm. Then, to further reduce the residual in-band noise and highlight the periodic impulsive feature, an autocorrelation enhancement algorithm is applied to the filtered signal. In the enhanced autocorrelation envelope power spectrum, only several single spectrum lines would be left, which is very simple for operator to identify the bearing fault type. Moreover, the proposed method can be conducted in an almost automatic way. The results obtained from simulated and practical experiments prove that the proposed method is very effective for bearing faults diagnosis.

Extended Polynomial Dimensional Decomposition for Arbitrary Probability Distributions

This paper presents an extended polynomial dimensional decomposition method for solving stochastic problems subject to independent random input following an arbitrary probability distribution. The method involves Fourier-polynomial expansions of component functions by orthogonal polynomial bases, the Stieltjes procedure for generating the recursion coefficients of orthogonal polynomials and the Gauss quadrature rule for a specified probability measure, and dimension-reduction integration for calculating the expansion coefficients. The extension, which subsumes nonclassical orthogonal polynomials bases, generates a convergent sequence of lower-variate estimates of the probabilistic characteristics of a stochastic response. Numerical results indicate that the extended decomposition method provides accurate, convergent, and computationally efficient estimates of the tail probability of random mathematical functions or reliability of mechanical systems. The convergence of the extended method accelerates significantly when employing measure-consistent orthogonal polynomials.

Fifty years of reliability and maintenance: A personal view

The reliability of most mechanical and electronic systems has improved dramatically over the past 50 years and yet there are warehouses full of spare parts that will never get used because there is no demand, or because they will reach their use by a date before they are needed or because they will become obsolete. Parts are frequently replaced unnecessarily while others that are much more likely to cause system failures are left untouched. The result is that despite vast sums of money being invested in spares, system availability is still very much a problem. Operations research has the tools that could significantly improve this situation but why are they not being used?