This thesis examines the lethality of laser-directed energy weapons in causing structural failure to mechanically loaded laminated composites in helicopters. The analysis is based on a three-dimensional numerical finite element model of a rectangular, incipient, orthotropic compression panel with its edges rotationally restrained. The panel is made of 24"x6" graphite/epoxy laminated composite where the laminate consists of fourteen laminas of different ply orientation angles and two different thicknesses. The data for the degradation of the material properties with increasing temperature, as well as temperature dependence thermal response data, were provided by the Naval Research Laboratory, Washington, D.C. Laser irradiation beam strikes the center lines of the panel with a radius of 3" and applied power load of 1 kilowatt per square centimeter causing an intense localized heating to the already mechanically loaded panel. Failure of laminated composites is controversial, even under ambient temperature. However, a successful attempt has been conducted here to predict the mechanical and thermal buckling and post-buckling behavior of the heated panel. This is further complicated by the anisotropic behavior of the composite material and the thermal effect. Even without buckling, the problem is thermally and structurally non-linear. This work can be considered as an above preliminary numerical analysis. It provides insight (to be verified by experimentation) into using existing codes to obtain approximate solutions good enough for the engineering design, with speed and low cost. Should this expertise and knowledge be available, the designer of directed energy laser weapon can optimize designs of future weapons, or make efficient use of existing ones. Likewise, the helicopter structural designer can optimize the design of future panels and structures, or make efficient use of existing ones. In addition, the designer can tailor a composite material to meet a particular structural requirement with little waste of material capability. The ability to tailor a composite material to its job is the biggest advantage that composites have over metallic or plastic structures. The complete prediction gives the values of static and thermal loads, stresses, strains, and various other heat transfer parameters throughout the domain of interest. Finite element method superiority to other numerical analysis techniques is evident and numerical results of this work compare favorably with experimental results.

ADB 157706 Approved for public release; Distribution is unlimited. The opinions and conclusions expressed herein are those of the student-authors and do not necessarily represent the views of the U.S. Army Command and General Staff College or any other governmental agency. (References to these studies should include the foregoing statement.)