Strain energy release rate method

In the strain energy release rate method, the parameter considered to determine failure is the strain energy release rate, which is the energy released per unit area of crack growth, commonly identified as G. For a uniformly loaded joint, the strain energy release rate, is derived from energy balance considerations as ... 

Although K and G can be related, the stress-intensity method is less useful for adhesives because K values are more difficult to calculate and also because this method is limited to linear-elastic behavior only. With the strain energy release rate method, the nonlinear effects of viscoelasticity and plasticity can be more readily accounted for in the analysis. 

The compliance methods are all based on the equation for the critical strain energy release rate, Gic, based on Gurney and Hunt (1967)... 

Once the performance of the interface bond was established by the previous delamination (durability) tests, contoured double cantilever beam (CDCB) specimens were designed to conduct mode-I fracture tests. In this study, bilayer CDCB specimens (see Fig. 6) were designed by the Rayleigh-Ritz method [8] and used for fracture toughness tests on bonded FRP wood interfaces under both dry and wet conditions. The critical strain energy release rate, G/c, which is a measure of the fracture toughness, is given as ... 

In Eq. (7), X is a material constant that defines the relative importance of the contribution of the minimum strain energy release rate Gmin and strain energy release rate range AG to the crack growth rate. The constant X is obtained by a trial and error method to best fit the data points. The final log-log plot is shown in Fig. 24, for k = 0.13, B = 1 x 10 , and m = 5.34 [7]. 

Standard test methods for plane-strain fracture toughness and strain energy release rate of plastic materials... 

D5025-94 Standard Specification for a Laboratory Burner Used for Small-Scale Burning Tests on Plastics Materials D5045-96 Standard Test Methods for Plane-Strain Fracture Toughness and Strain Energy Release Rate of Plastic Materials... 

Other optical methods include the shadow-optical method of caustics based on the deflection of light by the elastic-stress fleld around the crack tip. It gives direct information on the stress-intensity factor or the strain-energy release rate (21). 

Two quantities can be measured to describe a material s resistance to crack propagation fracture toughness, IQ, and strain energy release rate, G. Different stress states can be applied, with the most common being the opening mode (Mode I). Materials can also be tested in inplane shear (Mode n) and in torsional shear (Mode III). Testing in these modes typically involves strain rates much lower than those associated with impact teste such as the Charpy and Izod methods. Other methods... 

Another commonly used method to determine fracture toughness of coatings is through the use of compliance fracture specimens, whereby the change in compliance of the specimen is measured or calculated as the crack propagates, and related to the mode I critical strain energy release rate, G c- Elementary fracture mechanics gives the required relationship [38] ... 

Starting with rather simple geometric shapes and loading conditions facilitate the measurement of the fracture energy. The following methods represent some of the more common techniques for measuring the crack speed versus strain energy release rate. 

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