| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1994: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1993: ¥1,300,000 (Direct Cost: ¥1,300,000)
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| Research Abstract |
A new mechanics for strength of materials was devised in a microscopic view approaching from a macroscopic one, and a stress analysis system in such a field was newly constructed. In this study, a boundary condition for equilibrium of force was rebuilt by considering a surface stress derived from surface energy through Herring's relationship. The formulation involves free energy of surface or interface, it is a nonlinear equation containing curvature of surface, and cannot solve exactly except numerically. Although, we supposed that an influence of surface stresses upon the distribution of stress and displacement for nano-scaled structures could be approximately estimated even if the nonlinear equation was linearized. Thus, a stress analysis was performed by using the linearized boundary condition. Here, nano indentation test that an elastic indenter is pressed to an elastic half space coated a nano-thickness amorphous film was calculated. In the analysis, a relevant dimensionless para
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meter consisted of surface stresses, a representative length of model for analysis and elastic modulus was denfined. We can make coincidence of a stress distribution for a structure with that for another one by agreed the parameters for both structures. Furthermore, when the value of parameter decreases, the influence of surface stresses also reduces, and the distribution of bulk stresses agrees with that for ordinal boundary condition. When the value of parameter increases, the displacement and bulk stresses increase owing to the surface stresses.
A stress analysis system for nano-scaled structure was developed on the basic of the boundary element method taking into consideration surface stresses. As an demonstration for analysis using the system, mechanical properties of composite materials dispersed nano-scaled particle and the stress distribution in the particle were investigated. As a result for analysis, it was found that apparent composite modulus is significantly different from a prediction using conventional composite modulus rule below 10nm of the size of particle. Furthermore, stress state in the particle is compressive due to surface stresses even if tensile load is applied to the composite materials. We can say that any defect such as dislocation is hard to occur in the nano-scaled particles and global deformation of materials proceeds by a slip as the interface. Less
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