Adhesive joints are widely used due to their higher strengths, lower weights, lesser expenses and ease of fabrication than other methods of joining. Hence, they are used extensively in aerospace and automobile industries. High quality bonds require the use of fixtures which are essential to ensure proper curing and to attain uniform thickness. Improper adhesive application and method of fixturing can cause irregularities in the distribution of the adhesive along the overlap which could affect the joint strength. This is especially critical for aerospace components as the replacement of parts can be costly and time consuming. This paper presents a nondestructive test (NDT) methodology to quantify the bonded joints where the adhesive does not completely cover the overlap area. Single lap adhesive joints with carbon fiber adherents were fabricated using a two-part epoxy based adhesive. The adhesive region was fabricated to have various shapes including elliptical and circular of different sizes and a joint with full coverage for comparison. Polytetrafluoroethylene (PTFE) cutouts were used to mask regions of adhesive to achieve the desired coverage pattern. After fabrication all samples were ultrasonically scanned with a 10 MHz spherically focused immersion transducer using pulse-echo ultrasonics to determine the actual as tested adhesive distribution shape. The scans were able to resolve the shape of adhesive distribution across the overlap region of 25.4 × 25.4 mm and were correlated with the actual adhesive distribution at the interface after lap shear tests. Lap shear tests were then performed on the samples fabricated and the samples were loaded to failure. It was found that the shape and the orientation of the adhesive shape relative to the loading direction had an effect on failure strength.

中文翻译：

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胶粘剂分布对粘结接头强度影响的实验研究

由于与其他连接方法相比，胶粘接头具有更高的强度，更轻的重量，更少的费用以及更易于制造，因此被广泛使用。因此，它们被广泛用于航空航天和汽车工业。高质量的粘接需要使用固定装置，这些固定装置对于确保适当的固化并获得均匀的厚度至关重要。不正确的粘合剂应用和固定方法会导致粘合剂沿搭接部分的分布不规则，从而影响连接强度。这对于航空航天零部件尤其重要，因为零件的更换可能既昂贵又耗时。本文提出了一种非破坏性测试（NDT）方法，以量化粘合剂未完全覆盖重叠区域的粘合接头。使用两部分的基于环氧树脂的粘合剂制造了具有碳纤维粘合剂的单搭接粘合剂接头。粘合区域被制造成具有各种形状，包括不同大小的椭圆形和圆形，以及具有完全覆盖范围的用于比较的接头。聚四氟乙烯（PTFE）切口用于遮盖粘合剂区域，以实现所需的覆盖图案。制造完成后，所有样品均使用脉冲回波超声仪通过10 MHz球形聚焦浸没式换能器进行超声扫描，以确定实际的测试粘合剂分布形状。扫描能够分辨25.4×25.4 mm重叠区域上胶粘剂分布的形状，并且与搭接剪切试验后界面上的实际胶粘剂分布相关。然后对制成的样品进行搭接剪切测试，并将样品加载至失效。发现粘合剂形状的形状和相对于加载方向的取向对破坏强度有影响。