Study On Surface Wrinkling Behavious Of Film/Substrate Structure

Thin film/substrate structures exhibit different surface instability due to the mechanical interaction between thin film and substrate under compressive loads.While the instability is traditionally to be seen as a failure mechanism,it has been used to achieve a multi-functional surface with special acousto-optoelectronic-magnetothermal properties.The research on surface instability behavior of thin film/substrate structure has lasted for a long time.With the rise of microelectronics industry and thin film technology,thin film/substrate structures are widely used in engineering and technology fields,and have broad application prospects in flexible electronics,thin film measurement,micro-nanofabrication and three-dimensional self-assembly.The interface defect,geometric form and load action form of the structure have a direct impact on the buckling instability of the film/substrate structues.It is of great theoretical significance to study the surface instability behavior of the film/substrate structure under different conditions.Firstly,the wrinkle instability behavior of hard film/soft substrate structure with ideal interface is studied.A uniaxial compression model of thin film substrates is established.The thin film is described by von Karman's nonlinear elastic p late theory,and the substrate is described by Winkler's foundation model considering only tension and compression.The critical buckling load and critical wrinkle parameters are further obtained by establishing the characteristic equation of buckling usin g the method of linear stability analysis.The total energy expression of the film/substrate structure is established,and the evolution equation of wrinkle amplitude is obtained by minimizing the energy.The theoretical predictions of critical conditions and amplitude evolution are numerically validated and parameterized by simulation analysis.A more accurate theoretical prediction formula of critical parameters is proposed for the case of smaller Poisson's ratio,and the numerical verification is carried out.Secondly,the delamination characteristics of thin film/substrate structures with pre-existing delamination are studied.Through linear buckling simulation analysis,it is found that the interface crack size has significant influence on critical buck ling load and initial buckling mode.Three typical buckling modes are distinguished,namely,periodic wrinkling mode,local buckling-delamination mode and mixed mode.By changing the film thickness and modulus ratio,parametric simulation was carried out and phase diagrams were established to distinguish three instability modes.For buckling-delamination mode,the influence of structural material parameters such as modulus ratio and film thickness on the evolution of delamination amplitude is investigated without considering delamination expansion.For the mixed instability model,the coupling characteristics of wrinkle and delamination are explored without considering the layered expansion.It is found that the existence of pre-existing delamination will increase the critical load of wrinkling,and the occurrence of wrinkle will lead to the secondary bifurcation of the evolution path of delamination.For wrinkle instability mode,considering the increase of delamination,the mechanism of wrinkle evolution is explored.The critical buckling point of the structure and the critical point at which the delamination begins to expand divide the whole evolution process into three stages.Then,the surface instability characteristics of thin film substrates considerin g the interface microstructures are analyzed.The effect of column width on surface instability morphology was investigated by using micro-column array.Within a certain range of column width,the instability behavior of the structure is buckling-delamination of buckled thin films,and the instability morphology is sinusoidal-like.When the column width exceeds this range,the instability morphology of the film does not have periodicity.For sinusoidal instability-like mode,the concept of elastic rotational restraint beam to describe buckled thin films is proposed and its feasibility is verified.The interaction between thin films and microstructural substrates is described by rotational restraint stiffness,and the prediction method of rotational restraint stiffness is discussed.Finally,the instability behavior of thin film/substrate structures under low velocity impact loading is analyzed.According to the causes and characteristics of wrinkle,a method for judging the critical conditions of dynamic instability is proposed,and its feasibility is verified in the range of 10-100s^-1 strain rate.The critical parameters of dynamic instability are strain rate,critical impact time and critical stress.Compared with static loading,dynamic loading increases the critical buckling stress of the films.The influence of strain rate on the critical instability condition is investigated in the range of low velocity impact load,and empirical formulas are proposed and verified by data fitting.The relationship between the amplitude of stress wave and strain rate caused by low-speed impact loading structure is investigated.Based on the propagation of stress wave and the characteristics of film stress varying with time,the evolution process and mechanism of folds under low-speed impact loading are studied.The difference of initial instability mode,the transition of buckling mode and the migration of wrinkles are the remarkable characteristics of dynamic instability which are different from static instability.