13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- Figure 1: Determination of threshold values from crack propagation data by DLR-method In the second step of the adaption the coefficients C, n, p and q are calculated by use of a search algorithm with nested intervals. Therefore, the four-dimensional search domain is divided into intervals. In every iteration loop a weighted effective error is calculated for every parameter combination. The parameter combination leading to a minimum error is used as center for the search domain of the next iteration loop. Additionally, the search domain is reduced, so that the intervals become smaller. Due to the nested intervals a convergence behavior of the algorithm is realized. Since error values of the threshold domain are much smaller compared to those of e.g. the KC-domain the error values are weighted with the inverse of the crack propagation. For the adaption a fracture toughness KC = 4.200 N/mm3/2 is used. The results of the adaption together with the crack propagation data of 42CrMo4 are shown in Figure 3. The appropriated mean fitting coefficients are listed in Table 1 and consists with a probability of survival P = 50 %. Figure 2: Experimental and analytical threshold values
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