Micro-tension System Design And Its Application On Mechanical Property Testing Of Film And Fibre Materials

In the field of scientific research and industrial application, the dimensions of structures and devices are becoming smaller and smaller, precise mechanical testing and analysis of micro structures and devices is very important for investigating their stability and reliability. Considering the imaging ability and view field of microscope, a uniaxial micro-tension system has been constructed for mechanical testing of materials and structures at microscopic scale. The setup consists of four main parts: the main supporting parts, bidirectional driving parts, micro force sensors and micro specimen supporting platforms. The setup employs displacement controlled loading technique, and the sequential deformation images can be recorded simultaneously. Special design is used to overcome the problems in loading, holding, alignment of micro specimens, and stability of sequential images within the view scope of microscope. During the testing process, micro force (3mN-30N and 7.8μN-0.12N respectively) and sequential deformation images are recorded simultaneously, and full-filed displacement/strain field can be calculated with these sequential images. The materials tested may be film and fibre materials and structures.Based on the testing setup, mechanical testing of two film materials and bamboo fibrils are carried out. The contents are: (1) Fabricating the micro polycrystalline aluminum specimen with mechanical polishing and electrochemistry thinning techniques. The micro-tension experiments are carried out under optical microscope, and the film polycrystalline deformation field and mechanical properties are analyzed at grain scale. The relationship between the mechanical behavior and deformation within local region is investigated. The methods of coupling the grain boundary characteristic structures and grain featured marks are employed to calculate the deformation fields. (2) Performing mechanical testing of nano porous gold films under optical microscope. Their elastic modulus, yield strength and fracture strength are obtained for the first time using micro-tension techniques. Mechanism of macroscopic brittleness at grain scale and microscopic toughness at nano scale are discussed. (3) Investigating the highly optimized hierarchical structures of bamboo structure at macroscopic and microscopic scale. Different hierarchical structures are fabricated using proper fabricating techniques, and their mechanical behaviors are tested and analyzed. Considering the factors of the hierarchical structures, componential materials, and tested elastic modulus, fracture stress at macroscopic and microscopic, the mechanical functionally graded property and naturally acclimation ability to withstand the harsh environment of the bamboo structure are discussed. Finally, mechanical properties (elastic modulus, fracture strength and strain-stress curve) of the fibril are tested using the setup.