Kuo-Shong Wang

Optimizing preventive maintenance for mechanical components using genetic algorithms

Abstract This paper presents periodic preventive maintenance (PM) of a system with deteriorated components. Two activities, simple preventive maintenance and preventive replacement, are simultaneously considered to arrange the PM schedule of a system. A simple PM is to recover the degraded component to some level of the original condition according to an improvement factor which is determined by a quantitative assessment process. A preventive replacement is to restore the aged component by a new one. The degraded behavior of components is modeled by a dynamic reliability equation, and the effect of PM activities to reliability and failure rate of components is formulated based on age reduction model. While scheduling the PM policy, the PM components within a system are first identified. The maintenance cost and the extended life of the system under any activities-combination, which represents what kind of activities taken for these chosen components, are analyzed for evaluating the unit-cost life of the system. The optimal activities-combination at each PM stage is decided by using genetic algorithm in maximizing the system unit-cost life. Repeatedly, the PM scheduling is progressed to the next stage until the systems unit-cost life is less than its discarded life. Appropriately a mechatronic system is used as an example to demonstrate the proposed algorithm.

A study of availability-centered preventive maintenance for multi-component systems

Abstract This paper studies preventive maintenance (PM) in simultaneously considering three actions, mechanical service, repair and replacement for a multi-components system based on availability. Mechanical service denotes the activities including lubricating, cleaning, checking and adjusting, etc. which is set to alleviate strength degradation. Repair is defined on that not only slow down the degraded velocity but also restore the degraded strength partly. Replacement is settled to recover a component to its original condition. According to the definitions, the degradation of components is analyzed from its failure mechanisms and the improvements of various actions to it in reliability were measured by using two improved factors. Following the proposed model of reliability, the mean-up and mean-down times of each component are also investigated and the replacement intervals of components are determined based on availability maximization. Here, the minimum one among the intervals is chosen as the PM interval of system for programming the periodical PM policy. The selection of action for the components on every PM stage is decided by maximizing system benefit in maintenance. Repeatedly, the scheduling is progressed step by step and is terminated until the system extended life reaching to its expected life. The complete schedule provides the information, the actions adopted for the components, the availability and the total cost of system on each stage. Validly, a multi-components system is used as an example to describe the proposed algorithm.

The development of modular-based design in considering technology complexity

Abstract Applying modularity in the designing of products has been extensively researched recently to reduce the delay of product development. This paper presents a methodology of modular-based design in the conceptual stage of systems to support concurrent engineering (CE). First, the functions (Fs) are classified into different types of modules according to the correlation in design by using fuzzy cluster identification. Second, the optimal module type is selected based on the considerations of the manufacture and assembly complexities of the system for progressive parallel design. Third, the design priority of Fs within a module is scheduled by measuring the information content of Fs. As a result, the traditional design process is arranged as a series-parallel action to reduce the design time of products. Finally, an automated guided vehicle (AGV) system is used as an example to describe this method.

Modeling the bathtub shape hazard rate function in terms of reliability

Abstract In this paper, a general form of bathtub shape hazard rate function is proposed in terms of reliability. The degradation of system reliability comes from different failure mechanisms, in particular those related to (1) random failures, (2) cumulative damage, (3) man–machine interference, and (4) adaptation. The first item is referred to the modeling of unpredictable failures in a Poisson process, i.e. it is shown by a constant. Cumulative damage emphasizes the failures owing to strength deterioration and therefore the possibility of system sustaining the normal operation load decreases with time. It depends on the failure probability, 1−R. This representation denotes the memory characteristics of the second failure cause. Man–machine interference may lead to a positive effect in the failure rate due to learning and correction, or negative from the consequence of human inappropriate habit in system operations, etc. It is suggested that this item is correlated to the reliability, R, as well as the failure probability. Adaptation concerns with continuous adjusting between the mating subsystems. When a new system is set on duty, some hidden defects are explored and disappeared eventually. Therefore, the reliability decays combined with decreasing failure rate, which is expressed as a power of reliability. Each of these phenomena brings about the failures independently and is described by an additive term in the hazard rate function h(R), thus the overall failure behavior governed by a number of parameters is found by fitting the evidence data. The proposed model is meaningful in capturing the physical phenomena occurring during the system lifetime and provides for simpler and more effective parameter fitting than the usually adopted ‘bathtub’ procedures. Five examples of different type of failure mechanisms are taken in the validation of the proposed model. Satisfactory results are found from the comparisons.

The reuse of municipal solid waste incinerator fly ash slag as a cement substitute

The results of the treatment of fly ash from a municipal solid waste incinerator (MSWI) by melting are described, and the safety and the effectiveness of using the slag produced by this melting treatment are studied. The properties of the MSWI fly ash slag were analyzed, to evaluate the feasibility of its reuse as a substitute for part of the cement required in mortar preparation. This MSWI fly ash slag was found to be comprised mainly of SiO2 and CaO, which can be substituted for up to 20% of the cement content in mortar, without sacrificing the quality of the resultant concrete. In fact, the concrete thus produced has greater compressive strength, 10% higher than that without the substitution. The setting time of the fresh mortar becomes lengthens as increasing amounts of cement are replaced; while the spread flow value increases with the increasing percentage of cement substitution. X-ray diffraction analysis reveals that when the W /C/0.38 and the curing age/28 days, the crystal patterns in the mortar samples, prepared with different amounts of cement having been replaced by MSWI fly ash slag are similar. According to the results of the toxic characteristic leaching procedure analysis, MSWI fly ash slag should be classified as general non-hazardous industrial waste, that meets the effluent standard. Therefore, the reuse of MSWI fly ash slag is feasible, and will not result in pollution due to the leaching of heavy metals. # 2003 Elsevier Science B.V. All rights reserved.

A study of modularity operation of systems based on maintenance consideration

A module is a set of some disassembly and/or non-disassembly components or parts. It usually is used not only in supporting or carrying out the same function, but also in decreasing the complexity of a system in maintenance. Traditionally, the module form of a system is created according to either the function requirements or the manufacturing considerations. It is determined mainly depending on the individual condition of systems in designing, and has no concrete and scientific approach to progress system modularity. To overcome the faults in traditional modularity, the present paper presents a method of modularity based on the consideration of system maintenance policy for constructing the system modules. First, the correlations in designing the functions/components within a system are analysed according to four input/output parameters--geometry constraint, mechanical strength, energy flow and signal flow--to build the hierarchy structure of system in combination. Second, the parameters of reliability and cost of these functions/components are then investigated to describe the degradation in usage and to calculate the maintenance cost of each possible module. Third, the aged-maintenance model is used to evaluate the ideal maintenance intervals and the total maintenance costs of these modules so that the optimal module type of the system can be established. Finally, a hydraulic system used in squeezing machinery is adopted to depict the process of system modularity. Ideally, the result in modularity may feedback to designers to modify the design and to ensure the achievement in designing for maintainability.

The hydration characteristics and utilization of slag obtained by the vitrification of MSWI fly ash.

This study investigated the effects of slag composition on the hydration characteristics of slag blended cement (SBC) pastes. Synthetic slag samples were prepared by melting CaO-modified and Al(2)O(3)-modified municipal solid waste incinerator (MSWI) fly ash. MSWI fly ash was mixed with 5% CaO and 5% Al(2)O(3) (by weight), respectively, resulting in two fly ash mixtures. These mixtures were then melted at 1400 degrees C for 30 min to produce two types of slag with different contents, designated at C-slag and A-slag. Both the C-slag and A-slag samples exhibited a pozzolanic activity index higher than the unmodified slag sample. The results show that the synthetic slags all met the Taiwan EPAs current regulatory thresholds. These synthetic slags were then blended with ordinary Portland cement (OPC) at various weight ratios ranging from 10 to 40%. The 28-day strength of the C1 paste was higher than that developed by the OPC paste, suggesting that the C-slag contributed to the earlier strength of the SBC pastes. At curing times beyond 28 days, the strength of the A1 paste samples approached that of the OPC paste samples. It can be seen from this that increasing the amount of calcium and aluminum oxide increases the early strength of SBC. The C-slag blended cement paste samples showed an increase in the number of fine pores with the curing time, showing that the C-slag enhanced the pozzolanic reactions, filling the pores. Also, the incorporation of a 10% addition of C-slag also tended to enhance the degree of hydration of the SBC pastes during the early ages (3-28 days). However, at later ages, no significant difference in degree of hydration between the OPC pastes and the SBC pastes was observed with the 10% C-slag addition. However, the incorporation of A-slag did decreased the degree of hydration. A slag blend ratio of 40% significantly decreased the hydration degree.

Dynamic reliability behavior for sliding wear of carburized steel

Abstract In this paper two types of the dynamic reliability model are proposed and compared with the Weibull distribution of sliding wear. These models are concerned with the relationship between the hazard function and the dynamic reliability. One considers a differential equation form, called the DE model, the other takes an algebraic dependence, AE model. The physical problem used in the simulation deals with the sliding of multiple ring-disk system. The disk is carburized, and the ring is assumed to be much harder than the disk. The dynamic reliability and failure rate variation of the disk can be estimated by the critical wear depth during sliding. The results show that the predictions followed DE model and Weibull distribution are a little conservative. Some physical interpretations of the models are presented. Both models are recommended due to their acceptable RMS error, physical

The hydration characteristics when C2S is present in MSWI fly ash slag

Abstract This paper reports on an investigation of the hydration characteristics when C2S is present in municipal solid waste incinerator (MSWI) slag. The results can be summarized as follows: thermogravimetric analysis (TGA) observations show lower amounts of CSH and Ca(OH)2 in samples where C2S is incorporated into MSWI slag, possibly due to the partial replacement (20–40%) of the mineral constituents by less active slag. In general, the incorporation of C2S into slag, decreases the initial hydration reaction, whereas it increases the pozzolanic reactions at a later stage, by consuming Ca(OH)2. The X-ray diffraction results are in good agreement with the TGA results. Moreover, the hydration degree of the C2S–slag pastes, as determined by nuclear magnetic resonance techniques, also indicates that the C2S–slag pastes show lower hydration degree values, at all ages (1–90 days) of hydration. This may be due to the inactive behavior of an acidic film on the grains of slag, which in term retards the hydration that occurs as the Ca(OH)2 breaks down the silica framework.

A preliminary investigation of new mechanical product development based on reliability theory

Abstract This paper presents a preliminary study on the feasibility of developing a new mechanical product based on an existing well-known product. It is carried out following a modified dynamic reliability theory. In this approach it proposes a relationship between hazard rate function and reliability of the system. The importance of several parameters, such as the relative capacities of design, manufacture and prototype problem-solving, are discussed based on the complexity and maturity of the mechanical product we are investigated in. These parameters are estimated through fuzzy-set operations about intrinsic and extrinsic scaling of the technology adopted in the new product development.