Double cantilever beam test

Fig. 2. Illustrations of forces to which adhesive bonds are subjected, (a) A standard lap shear specimen where the black area shows the adhesive. The adherends are usually 25 mm wide and the lap area is 312.5 mm. The arrows show the direction of the normal apphcation of load, (b) A peel test where the loading configuration, shown by the arrows, is for a 180° peel test, (c) A double cantilever beam test specimen used in the evaluation of the resistance to crack propagation of an adhesive. The normal application of load is shown by the arrows. This load is appHed by a tensile testing machine or other...

Fracture mechanics (qv) tests are typically used for stmctural adhesives. Thus, tests such as the double cantilever beam test (Fig. 2c), in which two thick adherends joined by an adhesive are broken by cleavage, provide information relating to stmctural flaws. Results can be reported in a number of ways. The most typical uses a quantity known as the strain energy release rate, given in energy per unit area. 

These effects have been found by Creton et al. [79] who laminated sheets of incompatible polymers, PMMA and PPO, and studied the adhesion using a double cantilever beam test to evaluate fracture toughness Fc. For the original laminate Fc was only 2 J/m, but when interface reinforced with increasing amounts of a symmetrical P.M.M.A.-P.S. diblock copolymer of high degree of polymerisation (A > A e), the fracture toughness increased to around 170 J/m, and then fell to a steady value of 70 J/m (Fig. 9). 

Hashemi, S., Kinloch, A.J. and Williams, J.G. (1989). Corrections needed in double-cantilever beam tests for assessing the interlaminar failure of fiber-composites. J. Mater. Sci. Lett. 8, 125-129. 

Fig. 5.9. Load-displacement records of double-cantilever-beam tests on E-glass fiber-vinyl ester matrix composites, (a) 0.4 wt% epoxy silane (b) 0.01 wt% methacrylate silane (c) 0.4 wt% methacrylate silane (d) 1.0 wt% methacrylate silane. After Suzuki et al. (1993).

Static Double-Cantilever Beam—Static double-cantilever beam testing was conducted using ASTM D 3433. An Instron 4500 series test frame (Canton, MA) with a 5 kN load cell was used for this testing. All data were collected using custom software written with the National Instruments Lab VIEW software (Austin, TX). Specimens were loaded into the test frame, and a constant opening displacement rate of 1 mm/min was applied. 

These effects have been found by Creton et al. [81] who laminated sheets of incompatible polymers, poly(methyl methacrylate) (PMMA) and poly(phenylene oxide) (PPO), and studied the adhesion using a double cantilever beam test to evaluate fracture... 

Sebaey TA, Blanco N, Costa J, Lopes CS. Numerical investigation to prevent crack jumping in double cantilever beam tests of multidirectional composite laminates. Compos Sci Technol 2011 71 1587-92. http //dx.doi.org/10.1016/j.compsci-tech.2011.07.002. 

Figure 7.2. The double cantilever beam test for measuring interfacial fracture energy. Two welded polymer bars are driven apart by a razor blade of width 6 and the length of the crack ahead of the blade is measured.

The last important test for evaluating adhesive properties is a cleavage or fracture test. Figure 27.3 shows an example of such a test, the double cantilever beam test. The adherends are usually 1 in. (2.54 cm) wide and the thickness depends on the adherend modulus. Described in Standard Practice ASTM D3433 [9], the test is meant to measure fracture resistance (strain energy release rate) under conditions in which the adherends do not plastically deform. The units of fracture resistance (strain energy release rate) are joules per square meter and this quantity is given the symbol... 

PA-6/PP/PP-g-MA Melt mixing/fracture toughness measured using asymmetric double cantilever beam test/X-ray diffraction/XPS Seo and Ninh 2004... 

There are numerous examples of the application of fracture mechanics to structural adhesive systems. Most notable are those of Mostovoy and his coworkers which have already been mentioned. " Bascom and coworkers have made significant contributions to the understanding of the effect of bondline thickness on fracture toughness. Kinloch and Shaw extend the work of Bascom to include rate effects and to develop mathematical models of the fracture resistance of adhesives. Hunston et al have used these methods to study viscoelastic behavior in the fracture process of structural adhesives.Mostovoy and Ripling used these techniques to determine the flaw tolerance of several adhesives,while Bascom and Cottington have studied the effect of flaws caused by air entrapment in structural adhesives." Finally it must be mentioned that one of the most simple, most widely used tests for strucural adhesives, the peel test, is actually a version of the double cantilever beam test. 

DCB Double cantilever beam test IGSCC Intergranular stress corrosion cracking... 

FIG. 18—Change of stress-intensity with time of constant load cantilever beam compared to a contoured double-cantilever beam test specimen and a constant displacement bolt-load compact specimen [20]. 

FIG. 20—Dimensions and configurations for double-cantilever beam test specimen. Specimen contoured to 3 llf + Mh + C, where C is a constant [28]. Ali vslues given in inches. (Note 1 in. = 25.4 mm.)... 

The contoured double-cantilever beam test specimen is a modification that is used to measure crack growth rate at a constant applied stress intensity. This test simplifies the calculation of stress intensity by using a contoured specimen, as its stress intensity is proportional to the applied load and independent of the crack length. Under a constant load, the stress intensity for this specimen remains constant with crack extension. For the test geometry shown in Fig. 20, the magnitude of the stress-intensity factor K is observed to equal 20 times the load. 

Of the large number of SSC test methods that have been used to evaluate materitils for this service, five have survived uniaxial load tensile test. Shell bent beam test, C-ring test, double-cantilever-beam test, and slow strain rate test. The first four of these are incorporated in NACE Test Method for Laboratory Testing of Materials for Resistance to Sulfide Stress Cracking in HjS Environments (TM0177). Following are comments on these methods [3]. 

F. TM0177 Method D (NACE Standard Double-Cantilever-Beam Test)... 

Fracture then occurs in an elastic-plastic rather than a purely elastic strain field. For example, in the double cantilever beam test (Figure 12.4) the maximum bending stress is CT = 7>GcE where b is the width of the beam. Hence, the critical width for the transition from yielding to brittle failure is... 

To summarise, the choice of the particular fracture test determines a, and defines a critical length, for example the width of the beam in the double cantilever beam test piece or the plastic zone size at general yield of a notched bar. The fracture transition then occurs... 

Sundararaman, V. and Davidson, B.D., An unsymmetric double cantilever beam test for interfacial fracture toughness determination. Int. J. Solids Struct., 34(7), 799-817 (1997). 

DCB double cantilever beam (test specimen ) PIP pin-in-paste... 

A semiempirical model was developed for 7079 aluminum alloys to predict crack growth from double cantilever beam test results, but no attempt was made to vahdate the model with actual service data. 

Regarding the measurement of the adhesive fracture energy, Gc, under impact (or, in general, dynamic) conditions, the double cantilever beam test and the tapered double cantilever beam test (O Fig. 21.15) must be adapted to account for the effect induced by the loading rate. Indeed, in statics the base for the measurement is the formula (Williams 1984)... 

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