Relationship between Kmax and σf
Kannan et al. [23] had examined the applicability of a modified two-parameter fracture criterion MTPFC which introduced by Christopher et al. [24, 25] while assessing the fracture strength of structure components. They utilized a relation between the stress intensity factor (Kmax) and the corresponding stress at failure (σf) as (2) where σf is the hoop stress at the failure pressure of the flawed pipe. σu is the hoop stress at the failure pressure of the unflawed pipe. KF, m and p are fracture parameters.
The failure stress, σf of a pipe decreases with increasing crack size. If σf is less than the yield strength …show more content…
3, one needs to evaluate only KF and m in Eq. 2. If m is found to be less than zero due to large scatter in the fracture data, the parameter, m has to be set to zero. Therefore the parameter, KF can yield to the average of Kmax from the fracture data and the third parameter, p from Eq. 3 gives the value close to 12. When m is close to unity, the third term in Eq. 2 becomes insignificant. Whenever m is found to be greater than unity, the parameter, m has to be set to 1, by suitably modifying the parameter, KF with the fracture data. Fig. 3. The plasticity parameters as a function of parameter m
Substituting the hoop stress (σφ) by the fracture stress (σf) in Eq. 1 the maximum stress intensity factor (Kmax) for the specified crack size is obtained. Using this Kmax in Eq. 2, one can find the fracture strength equation in this form (5) where The hoop stress of flawed pipe at failure pressure, The hoop stress of the unflawed pipe at failure