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Ultrasonic nondestructive evaluation of adhesive bond degradation.

机译:超声胶粘剂降解的无损评估。

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摘要

In this dissertation, ultrasonic techniques to nondestructively evaluate adhesive bond degradation have been studied. The key to the present approach is the introduction of an external factor which pulls the adhesive bond in the nonlinear range, simultaneously with the application of an ultrasonic technique.; With the aid of an external static tensile loading, a superimposed longitudinal wave has been used to obtain the slopes of the stress-strain curve of an adhesive bond at a series of load levels. The critical load, at which a reduction of the slope is detected by the superimposed longitudinal wave, is an indication of the onset of nonlinear behavior of the adhesive bond, and therefore of bond degradation. This approach has been applied to the detection of adhesive bond degradation induced by cyclic fatigue loading.; Analogously to the longitudinal wave case, a superimposed shear wave has been used to obtain the effective shear modulus of an adhesive layer at different shear load levels. The onset of the nonlinear behavior of an adhesive bond under shear loading has been detected by the use of a superimposed shear wave. Experiments show that a longitudinal wave can also detect the nonlinear behavior when an adhesive bond is subjected to shear loading. An optimal combination of ultrasonic testing and mechanical loading methods for the detection of degradation related nonlinear behavior of adhesive bonds has been discussed.; An ultrasonic technique that uses a temperature increase as an alternative to static loading has also been investigated. A general strain-temperature correspondence principle that relates the initial slope of the stress-strain curve at a higher temperature to the slope at a higher strain but at a reference temperature. Explicit strain-temperature correspondence relations for both the tension and shear cases have been derived. An important parameter which quantifies the relation between the wave velocity and temperature has been defined. This parameter, which is indicative of adhesive bond nonlinearity and which can be conveniently obtained by an ultrasonic measurement, has been used as an indication of adhesive bond degradation. Experimental results have shown that the temperature increase method is a convenient and productive alternative to static loading.; A technique which uses the reflected waveform data to obtain the fundamental ultrasonic parameters (transit time, reflection coefficient and attenuation coefficient) of an adhesive bond has also been presented.
机译:本文研究了无损评价胶粘剂降解的超声技术。本方法的关键是引入外部因素,在超声波技术应用的同时,使粘合剂在非线性范围内拉动。借助于外部静态拉伸载荷,已经使用叠加的纵波来获得在一系列载荷水平下粘合剂的应力-应变曲线的斜率。临界载荷通过叠加的纵波检测到斜率减小,该临界载荷表示开始发生粘合剂粘结的非线性行为,并因此表明粘结退化。该方法已应用于检测由循环疲劳载荷引起的粘合剂粘结降解。与纵向波情况类似,已使用叠加剪切波来获得在不同剪切载荷水平下粘合剂层的有效剪切模量。通过使用叠加剪切波可以检测到在剪切载荷作用下粘合剂的非线性行为的开始。实验表明,当胶粘剂承受剪切载荷时,纵波也可以检测非线性行为。讨论了超声测试和机械加载方法的最佳组合,用于检测与胶粘剂降解相关的非线性行为。还研究了一种超声技术,该技术利用温度升高替代静态载荷。一般的应变-温度对应原理,将较高温度下的应力-应变曲线的初始斜率与较高应变但在参考温度下的斜率相关。得出了拉伸和剪切情况下的显式应变温度对应关系。已经定义了量化波速和温度之间的关系的重要参数。该参数表示粘合剂的非线性,并且可以通过超声测量方便地获得,该参数已经用作粘合剂的降解的指示。实验结果表明,温升法是代替静载的一种方便而有效的替代方法。还提出了一种利用反射波形数据获得粘合的基本超声参数(传输时间,反射系数和衰减系数)的技术。

著录项

  • 作者

    Tang, Zhenzeng.;

  • 作者单位

    Northwestern University.;

  • 授予单位 Northwestern University.;
  • 学科 Applied Mechanics.
  • 学位 Ph.D.
  • 年度 1999
  • 页码 130 p.
  • 总页数 130
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 应用力学;
  • 关键词

  • 入库时间 2022-08-17 11:48:00

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