11 1 1 1 G P S T = = + , (6.2) where G is the Griffith's energy release rate. This means: the energy release rate is separable and can be separated into two parts. By introduction of =−∏ FW the equation (6.1) finally becomes k k F dW P da = , (6.3) where FW is the crack driving energy. The equations (6.1) and (6.3) show that the change of the crack driving energy consists of two vector quantities kP and k da , whereby k da is the crack front deformation. Thus, the vector quantity kP contains the force character and is therefore identified as the whole crack force. Since kP = Sk + Tk, Sk or Tk represents a partial crack force. The energy balance of the cracked body can be reformulated as follows: 0 da dW da dW da dU F − − = , (6.4) where U is the work done by the external force, W is the strain energy and WF is the crack driving energy. 5. Summary and Conclusion The questions that we set at the beginning of the article, are already covered in detail and answered. The important results can be summarized as follows: • We have introduced a uniform equation (3.3) and derived the previously existing fracture mechanics parameters such as the generalized Irwin's I*-integral expression of the crack closure energy and the generalized Rice's Jk-integral from it, • based on the uniform equation (3.3), we have also found two new vector quantities Sk und Tk, which indicate that the energy release rate can be separated into the new found vector quantities Sk und Tk, where Sk provides the crack front extension, and the other Tk describes the crack front distortion, • the two vector quantities Sk and Tk are formulated in an integral form and are pathindependent, • it has also given that the new quantities Sk and Tk as well as the generalized Irwin's I *- integral expression of the crack closure energy are not only valid for linear elastic material behaviour but also for elastic-plastic material behavior, • the two vector quantities Sk und Tk have the force character. So Sk is denoted as the partial crack force for crack front extension and Tk the partial force for crack front distortion. References [1] Inglis, C.E. (1913): Stresses in a plate due to the presence of cracks and sharp corners. Proc. Inst. Naval Arch. 60, pp 210-230 [2] Griffith, A.A. (1920): The phenomena of rupture on flow in solids. Phil. Trans. Roy. Soc. London, vol. A221, pp 163-198
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