Pressurized-blister test method

The pressurized blister test is an excellent method to combine electrochemical reactions at polymer/metal interfaces with a mechanical load. It allows the application of a mechanical stress from a homogeneously pressurized electrolyte on the adhesive/metal interface in a sample geometry that is accessible for the HR-SKP [28]. Depending on the adjusted conditions, information on the synergy of mechanical stresses, elastic or inelastic deformations of the adhesive, transport processes, and corrosive reactions could be obtained with this method. 

Recently, there have been reported several developments of the common blister test method." These include the island-blister test and the inverted-blister test developed by Fernando and Kinloch. Both of these test methods are designed to enable the adhesive fracture energy to be measured for a coating of thin adhered film where the coating or film has insufficient strength to resist the pressure needed for debonding if the standard blister test was employed. Wan and Mai have described a blister test in which the crack is driven by the expansion of a fixed mass of gas and stable growth ensues. ... 

Now assume that in the example of interest here, preliminary analysis of the motor case shows that at the most likely points of debonding. Mode I loading dominates adhesive crack behavior. Two test methods that could appropriately be used to determine Ya Mode I are the blister test and the double cantilever beam (26). If one assumes that the first is chosen, then a layer of the adhesive (the solid propellant) is cast on a plate of the material from which the motor case is made. This plate contains a hole that has been fitted with a pressure connection. This connection is used to pressurize (with air, inert gases, fluids, etc.) the region between the plate and propellant, arid thereby produces a blister. The value of Ya can be determined from measurement of the pressure at which this blister grows as a function of its diameter (26). In our case, let us assume a series of tests yields a "least value" for Ya of J/m2. 

The blister test was analyzed by the finite element method (16). To evaluate G, Andrews and Stevenson (17) have tentatively added the elastic energy computed by plate theory (far field) to that computed for an internal crack in an infinite medium (near field) for the same radius and pressure. But the closed form solution (analog to the JKR solution (3) for spheres, and the Kanninen solution (12) for DCB) is not yet known. 

A similar method is used if the load is applied using pressure as shown in Fig. 5. For this two-dimensional blister test the strip forms an arc of a circle of radius R giving ... 

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