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Impact Damage Characterization and Damage Tolerance of Composite Sandwich Airframe Structures - Phase II

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Final rept.

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The impact responses and the damage states in flat composite sandwich panels with thin face sheets were investigated in Phase I and were found to be dependent on the diameter of the spherical steel impactor. The residual strength of impact-damaged sandwich panels under static in-plane compressive loads was reported to be dependent on the nature of the damage state. The impact damage due to blunt impactors is difficult to detect in service and depending on the size of the damage, can degrade the residual strength more than a punctured skin. The detectability of impact damage states using different field inspection techniques was experimentally investigated for different facesheet and core combinations. The impact damage in honeycomb core sandwich panels was better detected using instruments that exploit the local vibrational characteristics of the sandwich structure, while the damage in foam core panels was more amenable to acoustic-based techniques. The effect of facesheet stiffness on the sensitivity of the field inspection techniques was investigated and the results are reported. The behavior of the sandwich panels with impact damage and subjected to the in-plane static compressive loads was investigated in detail. The impact damage behaved in a characteristic sequence of events leading to contrasting final failure modes. The sequence of events was found to be dependent on the facesheet stiffness and the transverse compressive properties of the core material. The effects of panel curvature on the impact damage resistance of sandwich panels were experimentally investigated for limited sandwich configurations. The effects of the radius of cylindrical panels, boundary conditions, facesheet type, and core type were also examined. The decreasing radius of curvature increased the global bending stiffness but decreased the local contact stiffness due to the radial compressive properties of the honeycomb core.

Subject Categories:

  • Aircraft
  • Structural Engineering and Building Technology

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