Studies On Mechanical Behavior Of Surface And Interface Of Film/Substrate Structure

With the rapid development of modern science and technology,devices are required to be highly integrated and multifunctional.The film/substrate structure has been widely used in flexible electronics,flexible energy harvesting,optoelectronic devices and other fields due to its advantages in both mechanical properties and functionality.The mechanics at the interface plays an important role in applications.For example,flexible electronics with high stretchability/compressibility can be achieved by surface wrinkling and delamination,which release large amount of membrane strain.And the strain transfer between layers through interface can be used to tune photoelectric properties.However,the highly nonlinear and coupled deformation mechanism of thin film,substrate and interlayer is still not clear and need to be further studied.Therefore,it is of great significance to study the mechanics at the interface of film/substrate structure for understanding the deformation mechanism and then guiding the engineering application.This paper started by surface wrinkling behaviors of patterned film with periodic stiffness distribution on a compliant substrate.The trapezoidal,articulated and sinetrapezoid hybrid wrinkling modes were determined based on the experimental and finite element observations,and then the total strain energy of the structure under each wrinkling mode in one period was established.The critical wrinkling strain of each wrinkling mode was derived with the help of the principle of minimum potential energy.By comparing the critical strain,the condition for articulated wrinkling and the transformation condition from articulated wrinkling to trapezoid or to sinetrapezoid hybrid surface wrinkling mode were analyzed,and the phase diagram for articulated wrinkling about structure and material parameters was obtained.Furthermore,based on the deformation characteristics of articulated wrinkling,a piezoelectric energy harvester with tunable piezoelectric potential and tension/compression performance was designed.The working range of the harvester and the effect of the structure and material parameters on the piezoelectric potential and stretchability/compressibility of the harvester were systematically discussed.The buckling delamination behavior of film/substrate structure under compression were analyzed.The wrinkling induced delamination of film/substrate structure was modeled mechanically under finite deformation assumption,and the mechanical behaviors of wrinkling initiation,wrinkling evolution,wrinkling induced delamination and delamination evolution were analyzed.The compressibility effect of the substrate on surface wrinkling characteristics and the limitation of interfacial stress criteria for buckling delamination are discussed,and from the energy point of view,the formula for equivalent interlayer strength under the coexistence of surface wrinkling and buckling delamination is derived.The relation between the surface wrinkling,buckling delamination and compressive strain are discussed.The peel and sliding behaviors of graphene nanoribbons(GNRs)atop a graphene substrate were studied.A periodic potential energy function is used to simulate the van der Waals interactions,and numerical simulations,which is performed with the help of UINTER subroutine,revealed remarkably rich dynamics for peeling and sliding of GNRs.The results shown that the peeling behavior depends on the coupling effect of normal stress and nanoribbon bending deformation,and the sliding behavior depends on the coupling effect of tangential stress and nanoribbon tension deformation.Two cases with coupled peeling and sliding of GNRs were considered,peeling with a fixed end and sliding with a lifted end.Both illustrate the mixed-mode interactions with coupled adhesion and friction.A simple analysis is proposed,relating the measurable quantities in potential experiments to the adhesion and friction properties of GNRs.Finally,the deformation behavior of twisting graphene film relative to graphene substrate were studied.The finite element method was used to simulate and analyze the deformation characteristics of graphene film during twisting.Due to the strong coupling of normal and tangential van der Waals interaction at the interface,both inplane and out-of-plane deformations were observed during the twisting.According to the scaling law of the interlayer potential energy density and unit cell size during rigid twisting and the deformation characteristics of graphene film when rigid constraints are released,the strain potential energy function of deformed graphene film was established,and the evolution of in-plane and out-of-plane deformation of the film were analyzed based on the principle of potential energy.