Research On The Failure And Failure Mechanism Of Mechanical Meta-actions

The frequent mechanical failure is the main reason for the low reliability of various kinds of equipment.Major accidents caused by mechanical failures are common at home and abroad,which brings huge economic losses to users and a bad impact on society.To improve the reliability of mechanical systems and reduce the probability of mechanical failure,this dissertation makes an in-depth and systematic study on failure modes,failure causes tracing,and failure mechanisms of mechanical Meta-actions.Based on the concept that the function of mechanical products is realized by the relative motion between parts,the failure mode of Meta-action is studied.All possible failure modes are obtained in theory.An analytical method for Meta-action failure is studied according to the internal relationship between failures and causes.Combined with the characteristics of Meta-action failure,a failure tracing method for the Meta-action unit is developed.In terms of the typical structure composition and operation conditions of the rotational Meta-action unit and the translational Meta-action unit,the main excitations of the two kinds of units during operation are analyzed and modeled.Finally,the relationship(i.e.failure mechanism)between various faults of Meta-action units and Meta-action failure mode is analyzed by the numerical simulation method.The specific contents of this research mainly include the following four aspects:(1)Modeling and analysis of Meta-action failure mode.Firstly,the concepts and definitions of Meta-actions and Meta-action units are introduced.Based on the "function-motion-action" decomposition approach,a mechanical product is decomposed to multiple Meta-action units.And then,the standard structure models of rotational Meta-action units and translational Meta-action units are established respectively by the "integrated parts method" in group technology.Based on these models,the elements of the Meta-action unit are analyzed.Secondly,in terms of the classical definition of reliability and the characteristics of Meta-action,the failure,failure modes,and failure causes of Meta-actions are defined.Moreover,from the standpoint that to meet the function and performance requirements of mechanical products,the motion parameters of Meta-action are analyzed.And then,the parameters for evaluating the reliability of Meta-action are obtained.Combined with the structure of the Meta-action unit,the kinematics model of Meta-action unit output is established.All potential failure modes of rotational Meta-action and translational Meta-action are given respectively,based on the definition of Meta-action failure and the permutation method.Finally,the rationality and practicability of the Meta-action failure mode are verified by an engineering example.(2)Cause analysis and tracing method of Meta-action failure.Firstly,based on the dynamic model of the Meta-action unit,the mapping matrix between Meta-action failure and the basic parameters of the Meta-action unit is established by the causal order method.According to the necessary and sufficient conditions for normal Meta-action,the full causes of Meta-action failure are analyzed.Secondly,given the characteristics of Meta-action that "failure depends on basic parameters which depend on causes",a “Failure-Parameter-Cause”(FPC)method is proposed.Based on the FPC model,a Meta-action failure tracing approach combined Best Worst Method with Dempster-Shafer Theory is proposed,since it is difficult to get accurate failure data and the failure information is multi-source.Finally,a practical application case in engineering is adopted to verify the effectiveness of the proposed method.(3)Failure mechanism modeling and analysis of rotational Meta-action.The eccentricity mass of moving parts is the main factor inducing the failure of rotational Meta-actions.Based on the classification of the elements in rotational Meta-action units and the analysis of the working load,the main fault modes of the elements(i.e.the cause of the Meta-action failure)and the excitations of the unit are obtained firstly.Secondly,the excitation models of the intermediate part with crack,defect,or wear are established respectively by the Hertz contact theory,dynamics theory,etc.According to the distinct effects of fasteners at different parts on rotational Meta-action,the excitations caused by various fastener loosenesses are established respectively.Thirdly,the responses of the rotational Meta-action unit under various fault excitations are analyzed via a numerical simulation method.By comparing the responses of the normal unit with that of the unit with excitations,the relationships between the failure modes of rotational Meta-actions and the various fault modes of different elements of the rotational Meta-action unit are finally obtained based on the failure mode criteria.(4)Failure mechanism modeling and analysis of translational Meta-action.The wear of the intermediate part is the main cause of translational Meta-action failure.Based on the classification of the elements in translational Meta-action units and the analysis of the working load,the main fault modes of the elements and the excitations of the unit are obtained firstly.Secondly,because of the random wear area of translational Meta-action units,the excitation model of intermeditate part wear is established by integrating the knowledge of probability distribution with geometric modeling.Combined with the distribution characteristics of the fasteners in translational Meta-action units,the excitation representation of the fasteners looseness is built.Thirdly,the responses of the translational Meta-action unit under various fault excitations are analyzed through a numerical simulation method.By comparing the responses of the normal unit with that of the unit with excitations,the relationships between the failure modes of translational Meta-actions and the intermediate part wear and fastener looseness of the translational Meta-action unit are finally obtained based on the failure mode criteria.