University of Virginia, Charles L. Brown Department of Electrical and Computer Engineering, Thornton Hall, 351 McCormick Rd, Charlottesville, VA 22904, United States.
NASA Langley Research Center, 4 Langley Blvd, Bldg. 1230, MS 231, Hampton, VA 23681, United States.
Ultrasonics. 2022 Mar;120:106641. doi: 10.1016/j.ultras.2021.106641. Epub 2021 Nov 17.
A primary mechanism of adhesive bond failure is a degradation of the adherent/adhesive interfacial stiffness from unwanted contamination or exposure to those environmental factors, which reduce adhesion quality. Substantial research has been conducted on the assessment of adhesively bonded structures and the detection of "kissing" bonds. Advanced ultrasonic assessment methods to interrogate bonded joints and measure interfacial stiffness using a distributed spring interface model have been developed. Amplitude-based ultrasonic methods have traditionally been used in adhesive bond quality assessment, but recent advancements in ultrasonic phase measurements allow for high measurement resolution with low-uncertainty. In this work, an ultrasonic phase technique for the monitoring of adhesively-bonded interfaces is demonstrated. Constant frequency measurements are obtained from the ultrasonic phase of the reflection coefficient from the adhesive bond with a glass adherent, where the degree of cure is controlled by exposure to ultraviolet light. A peak in the phase of the reflection coefficient, as predicted by the interfacial spring model, is measured experimentally. It is shown that the peak phase predicts the interfacial stiffness when some frequency dependent threshold value is crossed. With knowledge of the acoustic impedances of both materials at the interface, the interfacial stiffness is determined by an inverse algorithm involving measurements of ultrasonic phase shifts of bonded joint reflections. By monitoring the interface of bonded structures and coatings, this method permits a nondestructive inspection of bond strength from structural construction through its service life.
黏合失效的一个主要机制是由于不需要的污染或暴露于降低黏附质量的环境因素，导致黏附/黏合剂界面的刚度退化。人们对黏合结构的评估以及“亲吻”黏合的检测进行了大量研究。已经开发出了先进的超声波评估方法，以使用分布式弹簧界面模型来探测黏合接头并测量界面刚度。基于幅度的超声波方法传统上用于黏合质量评估，但最近在超声波相位测量方面的进展允许具有低不确定性的高测量分辨率。在这项工作中，展示了一种用于监测黏合界面的超声相位技术。通过从玻璃黏附体的黏合反射系数的超声波相位获得恒定频率的测量值，其中通过暴露于紫外光来控制固化程度。根据界面弹簧模型预测，测量到反射系数的相位出现峰值。实验表明，当超过某个频率相关的阈值时，峰值相位预测界面刚度。通过了解界面处两种材料的声阻抗，通过涉及测量黏合接头反射的超声波相移的逆算法来确定界面刚度。通过监测黏合结构和涂层的界面，该方法允许从结构施工到其使用寿命期间对黏合强度进行无损检查。
