An alternative method for determining the mode i interlaminar fracture toughness

There are many kinds of equations based on the elementary beam theory to calculate the energy release rate for the double cantilever beam. Essentially, they are the same and can be easily transferred to the interested one by using the load-displacement relation at the beam tip. However, it is found that the accuracy of these equations in calculating the energy release rate is different. The equation (11) which does not include the crack length is within 0.5% of accuracy compared to the finite element analysis result even for short crack. While, there is a remarkable error in the alternative equation in the calculation of the energy release rate, especially for short crack. Based on equation (11), a procedure for measuring the interlaminar fracture toughness is proposed. Three different thicknesses of DCBs are used to apply and verify the proposed method, very good agreements of the results from the present method and the ASTM standard methods are observed. The present method is simple to conduct compared to the ASTM standard methods, where tedious measurements of the growing crack length are required.