ABSTRACT

The Inner Fixed Structure (IFS) bond panel is a honeycomb sandwich panel with CFRP facesheet and a heat shield on one side, and a perforated CFRP facesheet on the other side, of a jet engine nacelle. It is subjected to extreme temperature on both sides which damages the inner epoxy adhesive bond between the facesheet and the honeycomb core. Accessibility to this layer for non-destructive evaluation is extremely challenging using conventional methods. This work proposes active thermography techniques such as flash thermography and induction thermography for accessing the inner layer. The infrared camera utilises the perforations in the facesheet of the IFS bond panel, which is used for attenuating the engine noise, for imaging the defects. However, flash thermography requires the removal of the thermal insulation layer for the inspection, whereas induction thermography can be performed without any modifications to the structure. The minimum detectable dis-bond size using these techniques is restricted to the spacing between the perforations on the facesheet. A numerical model has developed for induction thermography to optimise the excitation frequency that can produce reasonable thermal contrast at the inner facesheet and minimum temperature rise on the intermediate stainless-steel thin sheet that covers the thermal insulation layer.

摘要

内部固定结构 (IFS) 粘合板是一种蜂窝夹层板，一侧带有 CFRP 面板和隔热罩，另一侧带有穿孔 CFRP 面板，用于喷气发动机机舱。它的两侧都受到极端温度的影响，这会破坏面板和蜂窝芯之间的内部环氧树脂粘合剂。使用传统方法对这一层进行非破坏性评估是极具挑战性的。这项工作提出了用于访问内层的主动热成像技术，例如闪光热成像和感应热成像。红外热像仪利用 IFS 粘合面板面板上的穿孔（用于衰减发动机噪音）对缺陷进行成像。但是，闪光热成像需要去除隔热层进行检查，而感应热成像可以在不对结构进行任何修改的情况下进行。使用这些技术的最小可检测脱胶尺寸受限于面板上穿孔之间的间距。为感应热成像开发了一个数值模型，以优化激发频率，以在内部面板产生合理的热对比，并在覆盖隔热层的中间不锈钢薄板上产生最小的温升。