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Nondestructive detection and characterization of damages in honeycomb composite structures.

机译：蜂窝复合结构损伤的无损检测和表征。

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摘要

This thesis discusses many existing methods of nondestructive evaluation used on honeycomb structures ranging from ultrasonic transduction to various low frequency techniques. The focus, however, is given to a newly developed technique based on hysteresis effects in force-displacement curves. The area enclosed by the hysteresis loop represents the amount of energy absorbed by the sample during the loading and unloading phases. It is believed that the cause of the energy absorption is due to increased internal frictional loses which occur when the sample is damaged. The loop area was found to correlate well with the level of damage sustained by the structure. This technique is centered on the deduction of a force-displacement curve from an accelerometer tap, which allows the force-displacement curves to be generated from a single tap on one surface of the structure.; Traditionally a force displacement curve, the equivalent of a stress-strain curve, is produced using a mechanical testing machine. However, this is not a suitable method to be used to attain a force-displacement curve while it structure is in-service because it requires access to both front and back surfaces of the structure. The deduction of a force-displacement curve from an accelerometer tap proved to be an effect solution to this problem. The great advantage of this method is that it only requires access to one surface of the structure to generate a force-displacement curve. This method also takes much less time to generate the hysteresis loops. A mechanical testing machine could take up to 15 minutes to produce a single force-displacement curve, this method will produce the same curve in seconds. Much of this research was devoted to the testing and development of the techniques used to deduce a force-displacement curve from an accelerometer tap.; This thesis also takes a look at the benefits of two-dimensional Fourier Transforms. During the course of this research, many C-scans of honeycomb composite structures were generated using air-couple ultrasonics. These C-scans were used as baseline images to compare with the results of the newly developed mechanical hysteresis technique. The honeycomb structure can cause very distracting hexagonal patterns in ultrasonic images. The Fourier transform and the processing associated with it is able to suppress these distracting patterns while leaving the rest of the image relatively unaffected. In some cases, not only can the patterns be suppressed, but the flaws can also be drawn out. A program was written to perform and filter the two-dimensional Fourier Transforms to suppress the patterns from the C-scan images.
机译：本文讨论了许多现有的用于蜂窝结构的无损评估方法，从超声换能到各种低频技术。然而，重点是基于力-位移曲线中的磁滞效应的新开发技术。磁滞回线包围的区域表示在加载和卸载阶段样品吸收的能量。可以认为，能量吸收的原因是由于内部摩擦损失的增加，这种内部摩擦损失是在样品损坏时发生的。发现环面积与该结构承受的破坏程度很好地相关。该技术的重点是从加速度计抽头推导出力-位移曲线，该力-位移曲线允许从结构的一个表面上的单个抽头生成力-位移曲线。传统上，力位移曲线相当于应力-应变曲线，是使用机械测试机生成的。但是，这不是在结构使用中获得力-位移曲线的合适方法，因为它需要进入结构的前表面和后表面。从加速度计抽头得出的力-位移曲线证明是解决此问题的有效方法。这种方法的最大优点是它仅需要进入结构的一个表面即可生成力-位移曲线。该方法还花费更少的时间来产生磁滞回线。机械测试机最多可能需要15分钟才能生成一条力-位移曲线，该方法将在几秒钟内生成相同的曲线。这项研究的大部分致力于测试和开发用于从加速度计抽头得出力-位移曲线的技术。本文还研究了二维傅立叶变换的好处。在研究过程中，使用空气耦合超声波产生了许多蜂窝状复合结构的C​​扫描图。这些C扫描用作基线图像，以与新开发的机械滞后技术的结果进行比较。蜂窝结构会在超声图像中引起非常分散的六边形图案。傅立叶变换及其相关处理能够抑制这些分散注意力的图案，同时使其余图像相对不受影响。在某些情况下，不仅可以抑制图案，还可以找出缺陷。编写了一个程序来执行和过滤二维傅立叶变换，以抑制C扫描图像中的图案。

著录项

  • 作者

    Foreman, Cory.;

  • 作者单位

    Iowa State University.$bAerospace Engineering.;

  • 授予单位 Iowa State University.$bAerospace Engineering.;
  • 学科 Engineering Aerospace.; Engineering Mechanical.
  • 学位 M.S.
  • 年度 2008
  • 页码 110 p.
  • 总页数 110
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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