Durability studies for aerospace applications using peel and wedge tests

• Published in: International journal of adhesion and adhesives Vol. 25; no. 3; pp. 247 - 256
• Main Author: Sargent, J.P.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.06.2005; Elsevier
• Subjects: Aging; Aircraft industry. Spacecraft; Aluminium and alloys; Application fields; Applications; Applied sciences; Engineering techniques in metallurgy. Applications. Other aspects; Epoxy/epoxides; Exact sciences and technology; Metals. Metallurgy; Polymer industry, paints, wood; Stress distribution; Technology of polymers; Aging; Aluminium and alloys; Stress distribution; Epoxy/epoxides; Adhesivity; Epoxy resin; Durability; Aluminium alloy; Experimental study; Modeling; Interface properties; Peel strength; Aqueous medium; Adhesive joint; Artificial ageing; Water absorption; Elasticity theory; Measurement method; Adhesive
• ISSN: 0143-7496; 1879-0127
• DOI: 10.1016/j.ijadhadh.2004.07.005

Measurements of peel strength are reported for some small, 2mm wide, unstressed aluminium adherend peel specimens based on aerospace adhesives AF163-2K06 and Redux 775 immersed in distilled water at 35C for over 7 years. Predictions of water distribution across the specimen width were made as a function of time using a measured diffusion coefficient and assuming Fickian diffusion. In the absence of primary corrosion, specimens after 7 years immersion showed no significant change in peel strength relative to strengths obtained in their initial dry state. This was after almost complete saturation of the adhesive. A brief review of the literature is given on the use of the Boeing wedge and DCB type tests for assessing the environmental durability of adhesive joints. Some of the assumptions used in the analysis of the wedge test have also been examined. An optical image correlation method is presented which permits accurate measurement of the adherend displacement. So long as sufficiently stable features can be identified on the adherend edge, then the position where the adherend displacement is zero may be used to give a well-defined effective crack length, and therefore fracture energy, even in the presence of extensive damage zones typical of those associated with tough structural adhesives. A beam on elastic foundation model is also given which demonstrates that apparent crack growth in the wedge test, associated with movement of the zero adherend displacement position, may be explained by relaxation of the adhesive.