Construction of the theory of variation applicable to shape optimization problems and fracture, whose application to problems in engineering.

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The results of research are the following. (1) In theory of generalized J-integral (GJ-integral), there is the result called Main Theorem, that is, the variation of energies with respect to the perturbation of the singular points is expressed as GJ-integral. In this research, it is proved that Main Theorem hold in wide nonlinear problems with Professor Kimura. (2) Combining GJ-integral and H1-gradient method proposed by Professor Azegami, we could show that the shape optimization problems with singularities are solved theoretically and numerically. (3) It was shown that FreeFem++ developed by Professor F.Hecht at the Laboratory Jacques-Louis Lions in Paris VI University is the finite element solver for boundary value problems by mathematical thinking and programming.