Study On Indentation Mechanical Behavior Of Coating Structure Based On Cylindrical Indenter And Conical Concave Indenter

The evaluation of mechanical properties of coating structure has always been a very important topic in the field of mechanics and materials,but the ratio of coating thickness to substrate thickness is too small,the deviation of traditional evaluation methods becomes unacceptable.Therefore,accurate analysis and calculation is particularly important.Indentation technology is an important means of coating structure analysis and measurement,the basis of standardized application and analysis of coating structure,and a classical method for accurate analysis and calculation of coating structure.In this thesis,the transversely isotropic coating structure under the action of cylindrical indenter and concave indenter is studied by contact mechanics analysis.Based on the finite element method,the comparative analysis was carried out,and the interface connection form,substrate and local delamination of the coating structure under the action of concave indenter are analyzed and studied.In this thesis,firstly,the general theory of contact mechanics of transversely isotropic elastic coating structure under cylindrical indenter contact is given.The three-dimensional exact solution of transversely isotropic elastic coating structure under cylindrical indenter contact is derived.The theories of non-friction contact and friction contact are put forward.Compared with the existing theory(obtained by order reduction in this thesis),the numerical calculation shows good convergence,high precision,high efficiency and stability.The difference between the finite element method and the theory in stress singularity analysis is explained,which reflects the effectiveness and applicability of the theory.The analytical theory plays an important role in the analysis of boundary stress singularity.The finite element comparison shows that the analytical theory plays an important role in the analysis of boundary stress singularity,which further proves the validity and applicability of the theory.In the numerical analysis,the influence of coating thickness on interface stress is given,and the distribution forms of stress and displacement are given.In this thesis,the general theory of contact mechanics of transversely isotropic elastic coating structure under conical concave indenter contact is given.The three-dimensional exact solution of stress and displacement is derived,and the solution is expressed by elementary function,so it is easy to obtain the displacement and stress of any point.The validity of the existing solution is verified by numerical calculation,finite element analysis and theoretical analysis,and the influence of the geometric shape of the head on the contact behavior is demonstrated.After analyzing the mechanical properties of the coating structure,comparing with the previous theoretical solution,and verifying the effectiveness of the finite element method,this thesis finally uses the finite element method which is more convenient for analysis and calculation.the effects of interface connection form,substrate and local delamination on the coating structure are analyzed emphatically.The results of force displacement,surface interface displacement,interface stress and stress cloud diagram are analyzed in detail,and the influence of three effects(interface connection form,substrate and local delamination)on the coating structure is explained.The significance of this study is mainly reflected in the following three aspects:(1)This thesis contains seemingly complex analytical expressions,which are actually about the expressions of elementary functions.The general solution gives the displacement and stress at any position of the coating,substrate and interface,which provides a code basis for interface failure analysis and material parameter determination in numerical analysis software.It also provides a high-precision sample basis for using deep learning to solve contact mechanics problems in the future.(2)The exact solution of the elastic stage is given,and there are stress singularities in the contact center and contact boundary.It provides a reference for the further study of the relationship between stress singularity and plastic mechanical behavior.(3)Based on the analysis of the three effects of interface connection,substrate and local delamination,the mechanical properties of the coating structure are more in-depth.In three aspects: the processing of the interface connection of the coating structure,the selection of the substrate and the detection of interface delamination,it provides some reference for mechanical engineers to design and test the coating structure.