Optimum Design Method Of Mechanical Reliability & Maintainability And Its Application To Construction Machinery

Reliability and maintainability of products are inherency property. They determine availability together. Reliability and maintainability of products are decided in design stage and guaranteed by manufacture, usage and maintenance. Study of reliability and maintainability design method focus on war industry, electrical and electronic equipment, and power plant, et al. Along with the ever increasing significance in national economy, the requirements on reliability and maintainability of construction machinery are becoming higher and higher. However, the development level of domestic construction machinery is much lower than foreign products, even falls behind other categories of domestic products. Aimed at this situation of lower reliability and maintainability of domestic construction machinery, reliability and maintainability design method of products was the most important studied. At the same time, the result of research used in construction machinery was also researched.Through the research on the relationship between Life Cycle Cost (LCC) and reliability and maintainability of products, a reliability-maintainability-oriented synthetically optimized design methodology has been proposed, which crosses the entire life cycle of products. Based on the analysis of all factors from the whole life cycle that have impacts on reliability and relevant extent, it is known that design is the decisive factor, while the reliability and maintainability are inherent attributes of products which are given during product design and guaranteed during use and maintenance.A study on the specific allocation methodology between reliability and maintainability during different design phases suited to construction machinery has been also implemented which provides theoretical support for the establishment of design objectives in terms of reliability and maintainability.The allocation between reliability and maintainability is a critical process in product development, aimed at converting the optimized general index of system between reliability and maintainability into that of each subsystem to direct the development of subsystems.A fuzzy-hierarchy analytical methodology, which is an effective way to do fuzzy decision-making combining fuzzy mathematics and hierarchical analysis to analyze fuzzy decision-making problems, has been proposed to allocate reliability. Because of relative high fuzziness in allocation of reliability, it is the first time to integrate fuzzy triangle number into expert judgment of allocation of reliability which can reflect the fuzziness of expert judgment, establish hierarchy-architecture model, and construct fuzzy judgment matrix. Probability methodology is adopted to calculate relevant weighing. Finally a case study of reliability allocation on the bridge of loader machine is carried out which turns out to satisfy the requirements. This allocation methodology mainly reflecting the design objective of experts is suitable for innovative design of products. Proportional combination to implement reliability allocation suits redesign of products, mainly aimed at improving reliability of old products. Based on the two methodologies aforementioned, a composite methodology has been proposed to handle allocation of reliability which can combine the above two methodologies together according to weighting, thus possess their advantages and are oriented towards the whole life cycle of products.A study has been conducted on allocation methodology for reliability as well as that for weighting factors suitable to product innovative design, moreover, a model of allocation methodology for weighting factors suitable to construction machinery has been proposed, which can identify the composition and weighting of factors. The higher the weighting factor is, the worse the maintainability will be. From Life Cycle Cost (LCC) perspective, a maintainability allocation methodology, which can minimize the maintenance cost, has been proposed. By means of investigating the relationship between maintenance cost and unit maintainability, an optimized allocation model has been established and an objective function and constraints are provided. Adopting foreign penalty function, a new penalty function has been constructed based on constraints and objective function, thus the constrained optimization problem has been transformed to unconstrained optimization to be solved.A life calculation model for components of construction machinery of fatigue failure and wear failure has been established, through which it is convenient to evaluate life-span.Through analyzing the main failure forms of construction machinery and studying their failure mechanism, main failure forms of main device components have been confirmed with an example of loader machine. The main fatigue forms are fatigue failure and wear failure.Aimed at fatigue failure, a model for calculating fatigue life has been developed. By means of multi-body dynamics software ADAMS, a virtual prototyping model of loader machine working device has been built to calculate loads, in order to identify the magnitude and orientation. The stress imposed on components with time variation is derived by finite element analysis putting given load on finite element model. This result illustrates that this stochastic stress is not standard distribution and not in accordance with traditional fatigue theory. Therefore, an equivalent accumulated fatigue theory has been set up to evaluate fatigue life span of components.Aimed at wear failure, a calculation model of wear life span based on wear degree has been established. Wear displacement and maximum force on pin is calculated by ADAMS software based on wear model of pin, and then calculation model of contact pressure has been built, based on which the strength of wear can be identified. Therefore, wear-oriented utilization life span can be evaluated based on the calculation model of wear life.An evaluation model of maintainability in terms of construction machinery has been put forward. The constituent factors affecting maintainability of construction machinery has been analyzed and influential weightings on maintainability from all factors fixed based on national military and American military standards. Focus has been concentrated on assessment of disassemblability of units to be maintained and generation model of disassembly sequences, thus disassembly sequences of components are derived as well as disassembly time and efficiency. Ultimately, the measurement of component maintainability is gained based on influential factors and relevant weightings.Through research on definitions of reliability and maintainability, a calculation model of reliability and maintainability has been proposed, by which the reliability and maintainability of products can be precisely calculated.A data flow network of construction machinery has been established, through which complete data on products reliability and maintainability can be collected. Based on these complete data, the foundation for calculation of reliability and maintainability has been laid to identify data distribution adopting methodologies of goodness of fitting and likelihood of comparative law. According to different distribution, corresponding calculation model of reliability based on the definition of reliability has been provided. It is the first time that the calculation model of maintainability with malfunction subject to Weibull distribution and normal distribution based on all probability definition of maintainability is studied. The conclusion has been drawn that the maintainability with these two malfunction distribution forms is not only related to maintenance time but also working hours.In order to guarantee the achievement of design objective in reliability, a partitioning model of demarcation points of each failure period in terms of products profit has been set up based on recovery strategy of construction machinery. From this model, demarcation points of each period can be precisely derived, therefore, the optimum model of maintenance period in preventive maintenance strategy has been proposed to provide theoretical basis for identification of idealized preventive maintenance period.A research on general framework of synthetically optimized design system in terms of reliability and maintainability of construction machinery has been carried out to set up design structure of system, constituent module and module function realization. A synthetically optimized module, whereby to figure out optimization problem of reliability and maintainability, has been developed based on synthetically optimized allocation theory and methodology of reliability and maintainability.Aimed at life span evaluation theory and methodology of typical components of construction machinery, an analytical module of reliability and maintainability based on components structural measurement has been developed to forecast reliability and maintainability of products or components.The foundation has been laid for subsequent practical measurement of reliability and maintainability by means of analytical module of reliability and maintainability based on statistics and analytical algorithm of data distribution. Based on statistics of real reliability and maintainability of products, estimation module of reliability and maintainability has been developed to estimate both fatigue and wear life span of components, results of which denote the real level of reliability and maintainability. An information management module has been developed to accomplish synthetically management of design system information due to multiple and complex information and data of the whole design system. This work is supported by corporate postdoctoral station project (LGP200401) "Several key technologies of life cycle design of construction machinery".