Blister test

Fig. 1, Schematic of commonly u.sed methods for testing the strength of adhesive joints, (a) Peel test. Note that the peel angle can be changed depending on the test requirements, (b) Double overlap shear test. In this test, the failure is predominantly mode II. (c) Single overlap shear test. In this test the failure mode is mixture of mode I and mode II. (d) Blister test.

Table I. Adhesive Fracture Energy in a Blister Test in Various Environments...

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 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. 

Fig. 31.7 In-situ measurement of a pressurized blister test experiment with the HR-SKP on a pure iron substrate coated with an epoxy adhesive (as in Fig. 31.2, about 70 p,m thick) and pressurized with 0.5 M NaCi at 500 mbar HR-SKP topography and potential line-scans after different times of exposure [28].

Cotterell, B. and Chen, Z. The blister test—Transition from plate to membrane behavior for elastic material, International Journal of Fracture 1997, 86, 191-198. 

Dynamic Fracture Mechanism of Thin Metallized Plastics via the Blister Test... 

The blister test has several advantages. It does not need any mechanical grip to the film to initiate a debonding. The uniformly distributed axisymmetric debonding angle close to the circular crack tip is smaller than with any other mechanical test. Thus the blister test minimizes the energy dissipation more effectively than any other test method. 

Fig. 1. Fabrication steps in thin film structures for the blister test...

Fig.2 A schematic diagram of the control system for the blister test.

Fig.3. Mechanism of ti e blister test for thin film structures...

While dW and dU are measurable in this blister test, dll and dT are not measurable. However, the sum of dfl and dT is measurable in this analyas. Thus equation (1) reduces to... 

Fig.4. Data profile of the loading and unloading mechanisms of the blister test for dynamic debonding process. Refer to the text for details of loading and unloading curves ffv), g(v) and duration of debonding time. t=b-a.

The volume is divided into three parts Part I. Metallization Techniques and Properties of Metal Deposits, Part II, Investigation of Interfacial Interactions," and Part III, "Plastic Surface Modification and Adhesion Aspects of Metallized Plastics. The topics covered include various metallization techniques for a variety of plastic substrates various properties of metal deposits metal diffusion during metallization of high-temperature polymers investigation of metal/polymer inlerfacial interactions using a variety of techniques, viz., ESCA, SIMS, HREELS, UV photoemission theoretical studies of metal/polymer interfaces computer simulation of dielectric relaxation at metal/insulalor interfaces surface modification of plastics by a host of techniques including wet chemical, plasma, ion bombardment and its influence on adhesion adhesion aspects of metallized plastics including the use of blister test to study dynamic fracture mechanism of thin metallized plastics. 

Adhesion is defined as the physical attraction or joining of two substances, especially the macroscopically observable attraction of dissirmlcir substances. There cire many techniques to study adhesion, namely pull-off tests, interfacial fracture tests, blister tests, mapping of interfacial properties, probe modification, and scratch tests. 

The adhesion at substrate/PU interfaces was measured by lap-shear and by constrained blister test methods [11, 12]. For lap-shear testing, adhesives were mixed with glass beads. Class 4A from Ferro Microbeads, and deposited on PVC and Xenoy substrates to yield dry films 0.35 mm thick. The adhesives were cured by exposure of 3 days at room temperature and 50% relative humidity, followed by 4 days at 50 °C, 0% relative hmnidity. The lap-shear specimen arrangement si shown in Figure 7.7a. All determinations were... 

Although lap-shear evaluations are more familiar, they do not necessarily evalnate the strength of adherent/adhesive interfaces. Cohesive failnre of the weaker component of an assembly can be a complicating factor, tearing of the PU layer being a possibility in certain of the present measurements. In principle, the detachment of the adhesive in the blister test is a pure interfacial event and one that can be quantified provided parameters... 

As already noted, the adhesion test data suggests the existence of significant contributions to bond strengths from non-dispersion forces acting at the adhesive/ substrate interface. Indeed, quantitative correlations have been confirmed between I p and either of the two sets of adhesion performance results. A demonstration is given in Figure 7.9, using the more complete blister test data. The correlation coefficient for this linear plot is 0.982. 

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. 

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