Wedge tests environmental testing

A number of ASTM tests and practices involve durability, but one of the most important is the Wedge Test, ASTM D3762-03. In this method, a wedge is forced into the bond line of a flat-bonded aluminum specimen, thereby creating a tensile stress in the region of the resultant crack tip. The stressed specimen is exposed to an aqueous environment at an elevated temperature, or to any other desired environment. The resultant crack growth with time and failure modes is then evaluated. The test is primarily qualitative, but it is discriminatory in determining variations in adherend surface preparation parameters and adhesive environmental durability. 

Certain tests are specifically designed to assess the effects of environmental exposure upon adhesive joints. Such a test would be the Wedge test in which an adhesive joint is formed out of two strips of metal bonded together, face to face. A wedge is then driven into the end of the joint to force the bonded surfaces apart and the joint is then inunersed in water. The energy stored within the two strips provides a driving force for the adhesive to fail. The rate of failure of the joint will indicate the effectiveness of an adhesive and surface pre-treatment. 

Fig. 13. The Boeing wedge-test for assessing joint durability. Typical exposure to the hot/wet environment is I h, or longer, at 50° or 60°C, and 100% relative humidity. The environmental crack growth, Aa, is then determined, which is a measure of joint durability.

Nabholz JV, Clements RG, Zeeman MG, Osborn KC, Wedge R. 1993. Validation of structure activity relationships used by the USEPA s Office of Pollution Prevention and Toxics for the environmental hazard assessment of industrial chemicals. In Gorsuch JW, Dwyer FJ, Ingersoll CG, LaPoint TW, editors. Environmental toxicology and risk assessment. Volume 2. Philadelphia (PA) American Society for Testing and Materials, p 571-591. 

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