The Correlation of Non-Destructive Measurements and Toughness Changes in Adhesive Joints during Environmental Attack
The Correlation of Non-Destructive Measurements and Toughness Changes in Adhesive Joints during Environmental Attack
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环境侵蚀期间无损测量与粘合接头韧性变化的相关性
DOI：
10.1080/00218460108030735
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
A. Kinloch
中科院分区：
文献类型：
--
作者：
K. Vine;P. Cawley;A. Kinloch
摘要对暴露在50°C水中长达18个月的两层和三层胶接接头试样进行了正入射超声扫描。接头由铝合金被粘物组成，其在用环氧聚合物涂覆（对于两层试样）或粘合（对于三层试样）之前经受四种不同表面预处理之一。研究了四种常用的预处理方法：喷砂、铬酸蚀刻（CAE）、铬酸阳极氧化（CAA）和磷酸阳极氧化（PAA）。已经开发了技术来测量试样在水暴露之前和之后的断裂韧性Gc，使得可以确定断裂韧性图，其中Gc的测量值可以被分配到试样内的空间离散位置。在本工作中使用的不同预处理的相对性能如下预期从文献中：铬酸阳极化（CAA）的表面预处理，使最持久的两层和三层的标本和喷砂预处理，使最不持久。在两层试样中，超声波检测检测到两种主要类型的缺陷：腐蚀驱动的边缘脱粘和微观缺陷。边缘剥离机制通常开始于未密封的齐平边缘，并且由在试样边缘上发展的腐蚀区域引发，该腐蚀区域底切环氧树脂层。边缘脱粘很容易和准确地检测超声。在远离边缘的区域中检测到微缺陷，这些小规模的孤立缺陷有几种形式。在三层接头试样的情况下，只有边缘脱粘可以检测到超声。然而，在一些三层接头的侵入水的攻击和削弱，破坏面表明，存在微缺陷。对于两层和三层试样，从超声波扫描的结果已与试样的断裂韧性的值，之前和之后的水暴露。虽然超声波扫描检测到两层试样中存在微缺陷，这似乎与水暴露时相间韧性损失的程度相关，但扫描显然未能检测到相间区域中的任何变化，这将表明三层喷砂和PAA试样中看到的相间韧性的一般损失。
Abstract Normal-incidence ultrasonic scans have been conducted on two- and three-layer adhesive-joint specimens exposed to water at 50°C for periods of up to 18 months. The joints consisted of aluminium-alloy adherends which were subjected to one of four different surface pretreatments prior to being coated (for the two-layer specimens) or bonded (for the three-layer specimens) with an epoxy polymer. The four commonly used pretreatments which were investigated were a grit-blast, a chromic-acid etch (CAE), a chromic-acid anodise (CAA) and a phosphoric-acid anodise (PAA). Techniques have been developed to measure the fracture toughness, Gc, of the specimens before and after water exposure such that fracture toughness maps could be ascertained, where the measured values of Gc may be assigned to spatially discrete positions within the specimens. The relative performance of the different pretreatments used in the present work followed that expected from the literature: the chromic-acid anodised (CAA) surface pretreatment giving the most durable two- and three-layer specimens and the grit-blasting pretreatment giving the least durable. In the two-layer specimens, the ultrasonic inspections detected two main types of defects: corrosion-driven edge-disbonds and micro-defects. The edge-disbonding mechanism usually started at an unsealed flush edge, and was initiated by a region of corrosion which developed on the edge of the specimen and which undercut the epoxy layer. Edge-disbonds were easily and accurately detected ultrasonically. Micro-defects were detected in regions remote from the edges and these small-scale, isolated defects took several forms. In the case of the three-layer joint specimens, only edge-disbonds could be detected ultrasonically. Nevertheless, in some of the three-layer joints which were attacked and weakened by ingressing water, the failure surfaces suggested that micro-defects were present. For both the two- and the three-layer specimens, the results from the ultrasonic scans have been correlated with the values of the fracture toughness of the specimens, before and after water exposure. Whilst the ultrasonic scans detected the presence of micro-defects in the two-layer specimens, which appeared to correlate with the extent of interphase toughness loss upon water exposure, the scans clearly failed to detect any changes in the interphase regions which would indicate the general loss of interphase toughness seen with the three-layer grit-blast and PAA specimens.