Thermal-Mechanical Effect Analysis Of Structures Under Intensive Laser Irradiation

The coupled thermal—mechanical breakage effect of structures induced by intensivelaser irradiation is an important research topic of the laser breakage mechanism. In thisdissertation, the thermal—mechanical effects of structures irradiated by laser beam areanalyzed comprehensively in theory and methodology, and the structure integrity of SolidRocket Motor(SRM) irradiated by intensive laser beam is also evaluated. The main workand achievements are summarized as follows:The mathematic models of transient temperature field in structures irradiated by laserbeam are established. First, by translating laser irradiation into volumetric heat source, theanalytical solutions of temperature field in two-dimensional structures (such as circularthin plate, rectangular thin plate and cylindrical thin shell) irradiated by laser beam arepresented. Besides, the mobile laser beam is considered for the cylindrical thin shells.Second, by translating laser beam into face heat source, the analytical solutions oftemperature fields in three-dimensional structures (including cuboids and thick cylinder)irradiated by laser beam are obtained.Transfer Function Method is used to solve steady temperature fields of structures. Byintroducing stress and strain relation under thermal loading, TFM is applied to solvethermal-elastic problem of structures, which strengthen and perfect the function of TFM onstructural analysis. Firstly, by constructing truncated conical elements, the displacementand thermal stress in revolution shells under thermal loading are analyzed using TFM.Moreover, an analytical solution of thermal stress in cylindrical thin shells is derived.Secondly, using TFM, a semi-analytical solution of thermal stress problem of thickcylindrical shells is proposed. Thirdly, according to three-dimensional elastic theory, anclose form TFM solution of three-dimensional thermal stress analysis of rectangular thickplate with four edges simply supported is obtained. Based on the solution of rectangularplate with four edges simply supported, TFM can be adopted to exactly solve thermalstress problem of rectangular plate with non-simply-supported edges by introducing somespecial function. Finally, the static response to structures irradiated by intensive laser beam,as an example of especial thermal stress problem, is analyzed by applying TFM.The temperature field distribution in two-layered shells irradiated by intensive laserbeam is simulated numerically and the displacement and stress distributions in two-layeredshells are studied. Moreover, the effect of thermodynamic properties of the outer shell isinvestigated on the temperature rise, displacement field and stress field in the inner shell.On the basis of the derived temperature field distribution in the thin cylindrical shellirradiated by intensive laser beam, thermal vibration of the shell is researched by usingfinite element method. And the effect of initial thermal stress and thermal softening on the shell natural frequency and normal modes is discussed.The simplified analytical model of SRM is established, and the temperature field inSRM irradiated by intensive laser beam is analyzed using a new variable-separatingmethod that adapts to laminated structures. According to evaluation criterion for structuralintegrity, the structural integrity of SRM irradiated by intensive laser beam is evaluatedusing finite element method, and the influences of material softening, laser intensity andspot size on the structural integrity of SRM are discussed. In addition, the scheme ofthermal protection for the case of SRM is researched, and the effects of relative distancebetween the heat insulation shell and the case of SRM, thickness of reflecting coat and thecoefficient of thermal radiation on the temperature field in the case of SRM are studied.In conclusion, some developments have been achieved in theory, methods andapplications for the analysis of coupled thermal—mechanical effects of structuresirradiated by intensive laser and structure integrity evaluation of SRM. The methods andconclusions in this dissertation would provide scientific basis and technical support forimproving anti-laser penetration capability solid missile in service.