Damage The Board Aircraft Structural Dynamic Characteristics Of Impact Studies

Corrosion, fatigue and cracks are very common reason for structure failure among ships and other ocean structures due to the special working condition and natural environment. In some fields, the corrosion, fatigue and crack can be modeled as local reduction of material stiffness. The overall mechanics behavior can be changed due to these local damages, and finally lead to structure failure.This thesis discusses the static and dynamic behavior of a panel structure with localized damage based on finite element (FE) analysis, and deduces the FE equations of both undamaged and damage elements. For different damage conditions, three kinds of damage including localized loss of plate thickness, isotropic damage, and orthotropic damage are studied. For isotropic damage condition, first a numerical model is meshed by FE grid, for the damage zones, a new parameter called damage index is introduced to represent the reduction of element stiffness, and no new trick for intact zones. For orthotropic damage condition, two new parameter kx and ky are introduced two represent the stiffness reduction of x and y direction of damaged FE element respectively. This can be done according to some basic theory of damage mechanics.The influences of damage parameters such as damage position, damage size, damage extension have been discussed to study their influence to structural static and dynamic characteristics. A numerical panel model has been designed and analyzed and found that the damage location is a major parameter to the natural modes and stress distribution. For minor damage conditions, there is no obviously variation of stress distribution and natural modes except damage zones and the zones are very close to them, the first few order of frequencies of structure has little variation too when under minor damage.This method can easily be used in damaged finite element analysis of engineering structures.