Indentation Test And Characterization Of Mechanical Properties Of Particles-filled Soft Matrix Composites

Nanoindentation technique is a kind of experimental methods testing micro-nano mechanical properties of various materials. Based on the traditional contact theory and test method of macro-hardness, this method, which combines with modern processing technology of ultra-sophisticated devices, can obtain the mechanical characteristic parameters of the samples including hardness, elastic modulus, creep and relaxation and so on. The properties can be obtained by recording the relationship between the load and depth during the indentation for a material. This method is widely used in many engineering fields due to its many advantages including easy operation and material preparing requirements.In recent years, for biomaterials, polymers, composites and other complex materials, there are still lots of problems to be solved with testing microscale mechanical properties of them, although the nanoindentation technique has been significantly improved and enhanced in experimental methods, experimental principle, resolution of instrument and other aspects.Firstly, this thesis has carried out the research on quasi-static and dynamic mechanical properties of particles-filled soft matrix composites by means of indentation method. Secondly, the influence, which includes the particle size distribution, indenter geometry and particle/matrix modulus, on the mechanical properties of the material has been analyzed by simulating the nanoindentation experiment of the material using finite element method. Specific work is as follows:1). Different particle volume fraction of particles-filled soft matrix composites have been tested by quasi-static nanoindentation, then the elastic modulus, load-displacement curve and other mechanical properties of the materials have been obtained. In addition, a viscoelasticity impact on quasi-static mechanical properties of the samples has been obtained by changing the test loading/holding time as well as different experiment schemes. The results show that the phenomenon of negative stiffness is discovered in the load-depth curve when the experimental indentation depth reaches a maximum.2). Based on the continuous stiffness measurement method, the dynamic nanoindentation of particles-filled soft matrix composites has been conducted, and the composite modulus (storage modulus, loss modulus or loss factor) of the samples has been obtained. Some influences, which include particle volume fraction, indentation depth, test frequency and amplitude, on the dynamic mechanical properties of the sample have been analyzed.3). Using ABAQUS finite element analysis software, a nanoindentation contact model of particles-filled soft matrix composites has been established and performed, the influences and rules, which include geometry (such as particle size distribution and the indenter geometry), physical parameters (such as grain, modulus of elasticity of the matrix), on the indentation mechanical properties of the composites have been obtained.