Through the analysis of the misunderstanding existing in the project quality management and its explanation, the authors discuss some phenomena of "quality surplus" and "quality shortage" that occurred in the practice of construction project and puts forward the concepts of "project reasonable quality" with its definitions, too.

This paper analyzes the impact damage forecast for the airplane structure from the following four aspects: ballistic limit, residual velocity, residual mass, forecast of damage size in structure penetrated or not penetrated, simultaneously discusses the development tendency of damage forecast and finally points out the main direction and means in the future damage forecast research.

The approximated representations of residual mass and residual stiffness were deduced by partly ignoring the dy-hamic effects of the truncated modes.

To overcome this difficulty,the approximated expressions for the residual mass matrix and residual stiffness matrix are proposed in which the mass matrix and stiffness matrix are not needed.