ارزيابي غيرمخرب كيفيت اتصالات چسبي در ورق‌ها به‌كمك امواج ورقي

NONDESTRUCTIVE EVALUATION OF ADHESIVE JOINTS IN PLATES BY LAMB WAVES

در اين نوشتار با بهره‌گيري از امواج ورقي ، كه به آنها امواج لمب نيز گفته مي‏شود، به ارزيابي و تعيين كيفيت اتصالات چسبي مي‌پردازيم. بدين‌منظور، ابتدا اولين مد متقارن امواج ورقي، يعني S0? به‌عنوان مد مناسب براي انجام بازرسي انتخاب شد. سپس نمونه‌هايي از اتصالات چسبي سالم و معيوب با استفاده از ورق هاي آلومينيوم ساخته و با استفاده از دو پروب فراصوتي زاويه‌ي متغير، كه به‌عنوان فرستنده و گيرنده عمل مي ‌كردند، كيفيت اين اتصالات مورد بررسي قرار گرفت. نتايج حاصله حاكي از آن است كه امواج ورقي به‌خوبي قادرند عيوب موجود در اتصالات چسبي را تشخيص داده و اندازه آن ها را معين ‌كنند.

In this paper, Lamb waves (also called plate waves) are used for inspection of two plates which are joined by an adhesive bond. The most attractive feature of Lamb waves is that they can travel long distances with little attenuation. However, the dispersive and multi-modal nature of Lamb waves makes their usage in nondestructive testing of materials difficult. Lamb waves can propagate in either symmetric or asymmetric modes designated as and , respectively, with .The most suitable Lamb wave mode for inspection of adhesively bonded plates was found to be the first symmetric mode, S0. A number of good and defective specimens were prepared from aluminum plates bonded together by epoxy resin adhesive. Using two variable-angle-beam ultrasonic transducers in pitch-catch configuration, the desired plate wave mode was generated in specimens. The incidence angle required for generating a specific mode was obtained by examining the dispersion curves of the plate. Dispersion curves show the dependence of the wave velocity on the frequency for each mode. A number of defective samples were prepared with different defect sizes. The defects were in the form of disbonds implanted in the joint by placing a piece of paper between the adhesive and adherent (see the following figure). Figure 1: Configuration of the experiments. The ultrasonic signals transmitted through the adhesive bond of each sample were analyzed and compared. The results indicate that Lamb waves can efficiently detect anomalies in the bonded joints and provide quantitative measures of defect size.